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SmallPower! Biomass Boilers - an eco friendly start to renewable energy
by Myc Riggulsford firstname.lastname@example.org
First published January 2009 & February 2009 Country Smallholding
I started Country Smallholding's look over 2009 at renewable energy technologies with one of the best established, simple to use and most appropriate for smallholders - biomass boilers. The new generation of log, wood chip and pellet boilers can typically replace or improve an existing oil or gas central heating and hot water system and use much cheaper fuel in the future. They have been popular in Scandinavia, Eastern Europe and Austria for years, now it's Britain's turn.
The drawback (and there's always at least one major drawback) is that even though wood fuelled boilers are incredibly efficient and cheap to run once installed, they are quite expensive to buy, quite expensive to install and work best if they burn continuously, even if it is very slowly. This means you also need to have a large heat store such as a very big hot water tank to keep the heat as it is generated.
Case Study 1: In our smallholding's five bedroom, three bathroom farmhouse in North Devon we had an old and too small oil fired boiler system in an outhouse. It was costing us about £2,000 a year to run in 2006, even before oil costs rocketed, plus an annual service at about £50, just for heating the bathrooms and upstairs bedrooms, and supplying all our hot water. We used log stoves downstairs (and an Aga in the kitchen).
When we heard about the new Vigas log boilers (I thought they were Swedish but it turns out they are Slovakian - I'm a bit deaf and didn't read the manual properly) we decided to install one even though they then cost around £3,500. Our old oil boiler was on it's last legs, we thought it would be good for the environment, and we would have a secure and cheap supply of logs from our own 4 acres of coppice and hedgelaying. By the time we had finished installing the log boiler it had cost closer to £10,000 once we had relaid a flat floor in the boilerhouse (old piggeries), and our local plumber had put in larger bore piping from the boiler to the hot water tank.
A typical domestic central heating and hot water system may have a 100 litre hot water tank, as we did. For a wood fuelled boiler you're going to need 250 litres or larger to cope with the continuous heat output, at the current price of copper, that's quite expensive. We put in a new, well insulated, 250 litre hot water tank with a coil at the bottom to take the output from roof mounted solar hot water panels, a coil in the middle to take the output from the log boiler and an immersion heater in the top in case of emergencies. So that's extra plumbing and electrical costs as well, plus you need extra space.
If you go for a heat store or buffer system of 1000-2,000 litres or larger with a massively insulated tank - which helps your system to work much more efficiently - you're looking at major space implications to site the thing, and extra capital costs of over £1,000 for a 1,000 litre tank and around £2,000 for a 2,000 litre tank.
The whole system also needs a complicated set of return valves which regulate the water flow from the boiler to the domestic heating and hot water, which make sure that the water returning to the boiler is an even temperature. This apparently makes the whole system much more efficient, prevents the build up of tar during burning, and prolongs the boiler's life. These valves are also expensive, costing around £300. And you'll need safety valves and extra plumbing to flood the system and shut it down in case it overheats and to stop the boiler exploding (I'm told this never happens, but then aeroplanes don't crash either).
Finally you need some way of losing heat continuously- in our case we had a couple of radiators in bathrooms plumbed directly into the system before the main tank so that when the boiler's on, so are these radiators, continuously losing a little bit of heat. You'll remember from December 2008's article that in energy terms one kilowatt (1kW) is one bar of an electric fire's worth of power or heat. With our 25kW boiler system, even when it's slumbering during the night and the central heating is off on a time switch, it needs to lose 5kW of heat - like having five bars of an electric fire on. So we have two toasty warm bathrooms all the time, and more plumbing costs. But that's it. 25kW log boiler, special twin coil hot water tank, valves, heat loss radiators, lots of minor plumbing. It's simple and brilliant, and it works. All you need now is fuel. And all you need to start is somewhere to put the boiler.
We realised early on that opening the log boiler door to feed it could be smoky. We were used to periodic smoke from our log stoves anyway, but this could be a major problem and we were looking forward to having a clean house without a constant layer of fine ash once we converted to using the central heating instead of log stoves downstairs.
The solution for us was to put the 25kW Vigas log boiler supplied by Clifford Frost of Dunster Wood Fuels into the old piggery, replacing our previous oil boiler. Some people keep the old system in parallel in case the logs run out, but we didn't. Our scullery has an access door through into the piggeries. Jenny said that when I'm away she wasn't prepared to go outside at night to either stoke the boiler last thing or fetch logs, so we needed an integral log store as well.
Our pigsties are about 6 foot 6 inches wide and 40 foot long, so we built a partition wall dividing off the 14 feet nearest the scullery and insulated the roof. This became the boiler house and a drying room for horse rugs, dog towels, wet gloves and Barbours, and it works brilliantly. It has a door outside to stand buckets of hot ash to cool and an internal door through to the rest of the piggery which has now become our main log store (years previously it housed turkeys - and rats).
We get a lot of electrical supply failures as we're at the end of a line, which could be a problem for the central heating pump to circulate the hot water if the power fails. So our local plumber Alan Pidner put the new 250 litre hot water tank in the airing cupboard of our guest bathroom. This is almost directly above the scullery, separated by just the outside wall's thickness (it's cob, it's a lot) from the boilerhouse pigsty. It was then simple for Alan to fit the Laddomat return valve on top of the boiler, run the large bore piping through the wall, and in a continuous vertical rise along the inside house walls through the scullery and back hall up to the hot water tank, taking off spurs to the two bathroom radiators on the way to act as heat loss radiators. We decided to risk it and not go for a buffer tank as well. Alan put an old 6 foot radiator we had spare in the new boilerhouse which can come on in an emergency to lose more heat.
We decided to use our local plumber Alan, who is properly qualified and Corgi registered, even though he isn't a registered biomass boiler installer - which means we couldn't get the Low Carbon Buildings grant for any of the work he did - because the nearest recommended installers were 40 miles away and quoted around £4,000 to just install and connect the log boiler, never mind the extra internal plumbing changes we needed. Alan's price was about half this, including the other work, and he's local so if we have any problems he's immediately on hand, so he was still cheaper than getting the full grant. We therefore got just £900 as a grant, where the maximum for domestic biomass installations is £1500 or 30% of costs. Our log boiler was Alan's first, but he's now put in four or five similar systems for other smallholdings locally.
For our new boilerhouse and drying room I built Jenny some racks from old broken wooden ladders for her horse rugs. You wouldn't want to use the room, which gets lovely and warm just from the heat loss from the boiler and pipes, for drying domestic laundry as it does get quite smoky, but the outside door means we can quickly clear it of smoke if we're choking. It has plenty of room for a basket of logs, which does one refill of the boiler. It needs refilling twice a day (three times in very cold weather and when we've got lots of family staying). The Vigas boilers themselves are sturdy, robust and simple, looking a bit like a large industrial brushed metal Aga or Rayburn. You fill the top chamber through a door just like an Aga oven, laying in your split logs, up to really quite large pieces, maximum length about 15 inches. You then seal the door with a screw lever a bit like the ones on a submarine bulkhead, which makes it airtight.
The logs burn downwards, controlled with restricted air intake by a computer operated fan. This causes the logs to gasify, not burn with a yellow flame as in an open fire, but generating gases which burn far more efficiently, and almost all of the wood is consumed. You must use dry wood with a moisture content of only about 25%. The hot air passes down under the firing chamber and back up through six one- inch wide pipes surrounded by a water jacket at the back of the machine, which is the boiler. Then the exhaust emissions go up a chimney flue to the outside.
Once a week you need to empty the firebrick lined ash chamber through the bottom door of the boiler. I'm always sceptical of manufacturer's claims, but you really do only get one small metal bucket of ash a week from the thing, though you need to rake the firing chamber properly every day to make sure the ash falls through and that nails and other metal bits from waste wood aren't blocking the air flow. Then once a month you take a simple top cover off the water jacket pipes and clean them with a special tool like a long poker with a 2p piece welded to the end, a bit like cleaning a chimney. This gets rid of any soot build up in the water jacket pipes, which would insulate them and stop the boiler water heating up properly. Once a year you have the main flue chimney swept to get rid of soot, and that's all the maintenance.
We are really very pleased with the system, though we do get a strange whistle from the valves (probably air). The whole house is warm and we are only using about twice as many logs as we used to use to heat just one room, but we are getting all our hot water as well - tons of it, so saving about £2,000-£3,000 a year in oil.
On an outlay of around £9,000 after the grant was repaid (and we needed a new oil boiler anyway) that's pretty good, though we did quickly realise that we needed solar hot water panels for the summer months if we weren't going to expire from the heat if we kept the boiler on all summer. I'll cover this in a future month, but it is worth choosing your site for the boiler and your hot water tank or heat store, (and choosing a twin coil version) so that you can retro-fit solar hot water panels.
Case Study 2 Log Boiler: Furniture maker David Rutter and his partner Ayesha McNeill and their four small children moved from Chelmsford to North Devon into an unmodernised smallholding with no central heating system (or mains water or sewerage) a couple of years ago. Their house was the original home farm for a local manor, so they have a huge amount of barns and outbuildings and a good sized but not enormous house which all need a lot of work done.
David used to live in Switzerland where a friend's father owned a tractor factory which also made log boilers, so he already knew about them. It was an obvious choice for him to install renewable energy for their new central heating and hot water system He didn't want to use oil, and with a local sawmill just down the hill for scrap offcuts, his own furniture making activities and the easy availability of hardwood treetrunks and logs from local farms, wind damage and tree surgery, he worked out that a cheap supply of fuel would not be a problem. In the future they may plant trees on much of their land to become mainly self sufficient.
David looked into different types of boilers and decided that logs would suit him best for cost and ease of handling, as he has plenty of barn storage space, and chose a 40kW Vigas as a cheap, simple and robust log boiler system. The quote for the boiler was about £3,700 from UK suppliers, which was acceptable. After an initial delivery problem in the UK, which left him facing a further 5 week wait due to the current massive demand, he set about sourcing the thing himself.
He got a quote of £3,000 from German contacts, and then reduced it to around £2,000 by sourcing a 40kW Vigas from Poland (the Euro exchange rate was better then). This involved a network of interpreters to arrange delivery from the Slovakian builders through Bristol as an import port, and delivery by lorry down to North Devon. He had to pay the full cost in advance, trust to luck, organise plumbers, and wait. The Vigas failed to turn up on time.
Eventually after huge negotiations down the interpreter chain, David discovered that the delivery lorry from Bristol had broken down and the boiler was still at the docks. It finally turned up. Doing it this way meant that he was unable to get a UK grant, but the cost savings (if he doesn't include his own time) made up for this.
Being new to the area and not knowing about his near neighbour Alan Pidner, our own plumber, who had just installed our Vigas, David got registered installers from the other side of Devon to plumb the boiler in. He found this very frustrating as they spent so long travelling that they didn't turn up until 9.30am every day and left again just after 3pm. On the plus side it meant that the whole installation was priced at 5% instead of 17.5%, taking advantage of the renewable energy tariff.
Although David will need his full heat supply in the future, when the house is extended and the nearest barn converted into his workshops and office, at present the 40kW output is more than enough. So much so that he later fitted an Akvaterm 1000 litre buffer tank in an adjacent open fronted lean-to next to their boiler house, which is itself an old woodshed a few feet from the main house.
In retrospect he would have installed the boiler in the lean-to and the heat store tank in the woodshed which could then act as a drying room, as well as providing easier log-filing access and log storage for the boiler. The retrofitting has left him with some hugely inconvenient plumbing across the passageway by the boiler at ankle height.
David sources all sorts of different local timber, processes it in a Dutch barn at the top of his yard with a chainsaw and fills dumpy bags which he then moves down near to the boiler house on his tractor's front forks. He reckons the cost of his wood fuel is £4 a day in winter and £2 a day in summer. To keep the cost of his wood feedstock down he spends a tremendous amount of time himself processing and handling the firewood. But then, David Rutter is a man on a mission, passionate about using oak wood offcuts to make superb art-gallery quality furniture, and dedicated to pursuing a green lifestyle with his young family.
Case Study 3 Wood Chip: Bob Boothby and his partner Kate live in an old water mill complex including 35 acres with 3 large lakes, woodland walks and manicured lawns just outside High Bickington a few miles from our own farm. Millbrook Cottages already had an established but underexploited holiday business with letting properties converted from the old mill building and other stone outbuildings on the site.
Kate and Bob have taken the whole property upmarket, offering high quality self catering holidays set in their beautiful secluded valley and winning top tourism awards including Gold for Green for their renewable energy installations - for which Bob has become a complete carbon neutral convert. Their main five bedroom, three bathroom house with its huge sitting room of attached converted barn, and immediate yard with a small one bed staff cottage, boiler house and converted pigsties (now used as the site offices) is built on quite a steep slope separated from the main letting cottages by an access drive.
As the cost of oil soared Bob realised that he had to find an alternative but reliable fuel which wouldn't need daily attention, since his other business interests frequently take him abroad. They decided to convert their private areas of the property to run on woodchips for heating and hot water. They have also installed a water turbine, a bank of solar photovoltaic panels, and solar hot water panels around the site, and have a test wind turbine in operation on their adjacent hill.
Bob's choice of boiler was a 30kW REFO, which is claimed to be over 90% efficient, supplied directly from the importers in Reddich. It can use a variety of fuels, including dried horse dung, but he is running it on wood chips. It will happily handle irregular sized large wood chips rather than the finely chopped and graded chips needed by many more expensive biomass boilers. During the year, to heat their own spacious house and the staff cottage and offices, Bob reckons it's using 20 tonnes of chips sourced at £30 a tonne for the dry waste wood offcuts from a local sawmill.
The bundles of offcuts are first delivered to one of his fields. Bob found a specialist 16 inch chipper with operator at a cost of £500 a day. It took half a day to process the wood into chips, and Bob's local agricultural contractor brought in tractors and silage trailers to transport the chips onto the main site and dump them directly into their chip store which is out of sight from the visitor areas, tucked in next to the groundsman's equipment and compost heaps. Once a week a mini trailer of wood chips is loaded up and driven over to the fuel feed hopper and dumped in vertically. The 4 cubic metre capacity round silo then feeds the chips up an auger which passes through the boilerhouse wall into the boiler in a completely automatic process. Because of the slope the silo is half buried in the ground at the back of the staff cottage and boilerhouse. Bob would have liked to simply line the hole and make it bigger, with a sweep arm built into the base to stop the chips sticking, so that they could just dump the chips directly into it from trailers without having to handle them twice from their store shed, but this would have raised the costs by another £4,000.
So Bob and Kate's fuel for a year is now about £1,000 in all, compared with £2,000-£3,000 for oil, when they had a cold home. It's now so hot that they are thinking of running a radiator to each of the holiday cottages as well to lose some heat and save on the cottages' gas boiler costs.
The REFO boiler needs a small bucket sized amount of ash cleaning out from it once a week, which can be used as fertiliser for the gardens. Overall their wood chip boiler system, including silo, auger and a new 250 litre twin coil hot water tank as heat store cost them £12,000 after a grant from Renewable Energy 4 Devon, which gives bigger business support grants than the national Low Carbon Buildings scheme (but sadly RE4D ran out of capital funds in December 2008).
Wood Pellet Boilers: Because of the standardised fuel made from compressed sawdust (usually waste), wood pellet boilers are much more consistent and cleaner than logs or wood chip, and Nick Backhouse of Eco-Exmoor, who has years of experience as an installer, reckons that they are a huge growth area.
"Pellet boilers like the Ökofen ones we supply are low maintenance. You get 1% ash content, and they are self cleaning. You only need to check the ash every 8 weeks, and sometimes it's several months before you need to empty it. Apart from that it is a once a year service!" says Nick Backhouse.
Pellet boilers have low running costs at 25% -35% cheaper than oil to run and the boilers should last at least 20 years. The main benefits include superb control system for underfloor heating or radiators or domestic hot water and the systems can regulate hot water from solar roof panels as well.
"You can have several buildings supplied from one boiler which makes it even more cost effective. We are pricing Housing Associations for one boiler for 9 housing units, which is a system that would work just as well for a smallholding with holiday cottages", says Nick Backhouse. "Because of their consistency, cleanliness, and low maintenance the pellet boilers are much more suited to the domestic or small office market than log or wood chip boilers".
A typical 4 bed farmhouse could expect to use about 5-7 tonnes of wood pellets every year - they have a higher calorific value than logs or wood chips, so you need less - at a cost of around £1,000-£1,400 to run central heating and all the domestic hot water. The boiler can be vacuum fed from a hopper up to 20 metres away, or fed directly by an auger if the hopper can be sited next to the boiler. If space is limited a ‘day'hopper holding just one to three day's supply, or a mini hopper holding 450kg can be refilled easily using bagged pellets, which is cheaper to install but more expensive to run in the long term.
Because of the greater control a typical 25kW wood pellet boiler system may not need an accumulator tank, so with the boiler, hopper, auger, plumbing valves and smart control systems you could expect to pay a total installation cost of £12,000-£14,000 plus VAT. The systems supplied by registered installers can qualify for domestic grants of £1,500.
If you do install an accumulator tank as a heat store, which helps to even out the performance of a log or chip fuelled boiler, as supplied by Clifford Frost at Dunster Wood Fuels, you are probably looking at extra costs of £1,500-£4,000, but obviously will save money on replacing your domestic hot water tank with the 250 litre twin coil one we installed. However you will need plenty of space, and my advice would be to put your accumulator tank indoors not in an outbuilding so that any heat lost from it heats the house. Two smaller tanks are just as good as one big one, but lose more heat due to the larger surface area to volume ratio.
Our conclusions: There are so many systems out there that it is increasingly difficult to make a decision about what sort of boiler to buy, especially if you start with a random internet search. We have not been able to test or view all of the boilers we found, and there are certainly many more systems around which we have not found details for yet. The prices seem to be fairly consistent within a reasonable range, so we cannot recommend a ‘best buy' on the limited research we have been able to do. I wouldn't rely on manufacturers claims of ‘95% efficiency' - except for pellets, the quality of your fuel will make a huge difference to performance. There are cheaper, robust log boilers which are best suited to people with their own woodland, or a waste wood supply, and lots of spare outbuildings for storage and siting the boiler. Or there are some sleek, modern (and slightly more expensive) pellet models which would not look out of place in an art gallery or sitting room. It looks as though you get what you pay for.
However, you do need to consider that the cost of a boiler alone is going to be roughly one third of your overall outlay, the valves, tanks and other accessories will make up another third of the costs, and the plumbing and installation will make up a final third (which inevitably means that the government's tax take through VAT will make up a further substantial chunk). The best system to suit you will depend on the systems favoured by your local suppliers, and your local installers, and your free space to site the system and ease of access, storage and handling for the biomass fuel - more on this next month. If you do some of the work yourself or use local plumbers you may find it very much cheaper, but you will not be eligible for some or all of the grants - so you need to do your sums carefully. You'll also want an expert to turn to for advice when it goes wrong.
In March 2009 we'll look at other biomass systems, the advantages and potential problems of different fuel sources including logs, chips and pellets, and the costs and environmental impacts of biomass. We'll also check out some cheaper heating options such as back boiler systems and high efficiency ceramic stoves.
Renewable Energy: Biomass Part 3 by Myc Riggulsford
Over the first two months writing about renewables I looked at the popular log, wood chip and pellet boilers which are sweeping Britain, and several of you wrote in with questions and comments. March was our last looking at wood and biomass as fuels before moving on to wind turbines in April on our year’s quest for renewable and sustainable energy.
Grass, straw, willow and other quick growing crops fix carbon dioxide from the air to produce carbon rich solid materials or biomass. These release the same carbon back into the air as carbon dioxide when they are burned, so on balance they don’t cause climate change by increasing greenhouse gases. But once you start using slow growing wood like oak, beech or other mature forest trees then the carbon they locked up from the air may have been taken out over 100 years ago, effectively before greenhouse gases became a problem. Burning ancient oak now may be almost as bad as burning fossil fuels like oil, coal or gas.
According to Dr Patricia Thornley from Manchester University, “In many cases biomass used as a renewable fuel is actually derived from wood by-products. For example sawdust is a co-product from sawmills processing timber and can be used directly in industrial installations or used to make wood pellets. This is sustainable where there are no competing uses for the material”.
Agricultural ‘waste’residues, such as straw, are produced anyway on farms and so are renewable sources of energy. If these aren’t used they can end up on muck heaps, left to rot, or even dumped in landfill. This generates not only carbon dioxide, but also methane, a greenhouse gas 21 times more powerful than carbon dioxide, so clearly using these ‘wastes’ for energy avoids a greenhouse gas impact, which makes them more attractive as renewable fuels.
“Levels of pollutants are also much lower than would be the case for traditional coal: there is essentially no sulphur dioxide or hydrogen chloride produced, as these are not significant chemical constituents in the fuel. Nitrogen oxide emissions are lower because combustion temperature is lower and particulates, heavy metals and volatile organic compounds are also much lower” says Patricia Thornley.
Nitrogen oxides, or NOx, are a group of highly reactive gases containing nitrogen and oxygen many of which are are colorless and odorless, but the common pollutant nitrogen dioxide (NO2) often shows up as a reddish-brown layer hanging over cities.
In the case of energy crops such as the African elephant grass miscanthus, or coppiced willow and hazel, the actual carbon cost involved in making the fuel usable includes diesel for tractors in planting and harvesting. For straw there is the energy cost of gathering and baling the straw and for wood pellets the cost of actually producing the pellets, which takes steam and high pressure.
“In most cases there is about a 10% offset so that switching from a fossil fuel to a carbon fuel saves 90% of greenhouse gases” says Patricia Thornley. “There is actually a carbon cost attached to all renewable fuels such as the energy needed to make solar panels, but with biomass it tends to be more visible and variable”.
What are the costs?
If you’re fitting one of the biomass boilers that can use almost any agricultural waste then your fuel costs could be very low, perhaps only £10/tonne or even just the transport costs for poultry litter, but virgin wood chip from energy crops costs more at around £50 a tonne delivered. Basic prices for the equivalent heating value from biomass can be similar to the cost of domestic heating oil when crude oil is around $50 a barrel, but are half the costs of oil when it was $100 a barrel or higher last year.
The more handling that your fuel needs will be reflected in the costs. Logs are bulky and quite cheap, especially if you have your own woodland. Chips from forestry thinnings have been processed and are more easily handled in tipper trailers, but watch that you’re getting good quality not mainly bark. Pellets flow even more easily and can be delivered in sacks or blown in bulk into your hopper or stores. South West Wood Fuels of Dulverton in Devon suggest that if you spend £500 per year on oil you should consider a log boiler, if more than £1,000 then get a wood chip system.
How much heat do you get?
A litre of heating oil produces about 8kWh of heat energy, so at around 50p per litre this gives heat at 6p/kWh.
One kilogramme of clean dry wood chip with a low bark content produces just over 3kWh of heat energy, and so about 2.5 kg of woodchip replaces 1 litre of heating oil, which at £50 a tonne with 20-25% moisture content means that woodchip gives heat at under 2p/kWh.
Grain such as barley or wheat with 15% moisture produces a bit more heat energy per kilogramme than wood chip in some boilers, and if you can get sub-standard grain cheaply from local farms for £100 a tonne or less, it gives cheaper heat than oil.
One kilogramme of wood pellets with 8% moisture content produces about 4kWh of heat energy, so 2kg of pellets replace one litre of heating oil, and costs about £3 for a 20kg bag or £150 a tonne for bulk deliveries, which means that pellets give heat at just under 5p/kWh.
Back boiler stoves are much less efficient and even log boilers are usually less efficient than wood chip or pellet versions. Following the huge sales of log stoves and boilers last year, prompted by high oil prices, logs are now costing from £40-£80 a tonne in rural areas, which means that bought logs (preferably well seasoned and under 25% moisture) will probably only produce about 1-2kWh of heat energy per kilogramme, giving heat at about 4p/kWh, but I’ve heard wide variations on this figure, and if you have your own woodland logs should always be the cheapest option.
Use dry fuel
Dry logs are lighter to move around than wet ones, and water still doesn’t burn so your boiler will be more efficient if your logs are at least two years old. The main problem with wood chips that we have identified is getting dry enough material. At a moisture content of over 30% the wood chips will compost, at lower moisture they can still stick together, so you’re going to need an angled floor in your store with an auger running along the bottom, or a slowly rotating sweep arm which will stop the fuel from forming a solid mass.
But according to some experts if the fuel is too dried out then you get problems with higher blade wear on the machinery, more energy needed to shift the fuel to feed the boiler and more dust. Ideally your logs will be less than 20% moisture, chips about 20% and pellets should be under 10%. Wet fuel doesn’t burn well, but too dry fuel burns very quickly.
Some of the new generation of boilers such as ones made by the Polish state-owned company Hamech incorporate a pre-furnace technology which lets them burn relatively damp or green waste wood with up to 50% moisture content. British company Farm 2000 makes boilers which run on straw at 16% moisture. If you are burning corn in a suitable boiler such as a REFO then be warned that wheat produces more slag that barley, which means the ash needs cleaning out more often.
How much space?
So far in this series we’ve had a couple of queries from readers about the space you need for fuel and how you calculate the weight of a pile of logs. As a rule of thumb you will probably need half the kilowatt output of your biomass boiler as tons of wood every year to run domestic hot water and central heating in winter. So if you’ve installed a 25kW Vigas log boiler, as we have in our 5 bed farmhouse, then you can expect to need about 12-15 tonnes of dry wood a year. In practice, on the last two years, we’ve found this about right.
A neat stack of mixed woods such as ash, oak, hazel, alder and willow making a 4 foot cube - 4ft x 4ft x 4ft – is about a ton. If you think in new money then a tonne is about 2 cubic metres – 1 metre x 1 metre x 2 metres, so 500kg of logs fit in a cubic metre.
For wood chips then 4 cubic metres is about a tonne, or 220kg of chips take up a cubic metre.
Wood pellets are more dense, so you can store about 670kg of pellets in a cubic metre, but you will need a hopper to store them and keep them dry.
For comparison, wheat and barley is even denser and 800kg will fit in a cubic metre.
There are several pellet suppliers in the UK and some companies can supply nationwide. Renewable Fuels Ltd is owned by the Lantmännen Group, a Swedish farmer’s co-operative, and provides processed energy crops, heat logs and pellets. Its raw materials are sawmill waste, forestry offcuts, olive oil residue and willow coppices. Their Agrol pellets are pure sawdust from 100% virgin timber with no additives, using the natural lignin of the wood as a binder. They sell domestic bags by the full pallet, half or quarter pallet, or 650kg bulk bags, and bulk pellets by the tonne. As sample prices we found offers of 52 x 16kg bags (total 832kg) of 8mm pellets at £280.05 and 66 x 15kg bags of 6mm pellets (total 990kg) at £320.23. There are about 200 stockists for their pellets, but the main trouble is that their list is by name of stockist, rather than by the town they are in, so you have to look through it all. But it ranges from Scotland to Cornwall and East Anglia to Wales.
What happens in practice?
In January we looked at the case history of furniture maker David Rutter’s 40kW Vigas log boiler in Burrington, North Devon. He doesn’t own any woodland so has been sourcing timber from a variety of suppliers and currently has a 30 ton stack of treetrunks in his field next to the road for which he paid £20 a ton. He also found a local tree surgeon who provided excellent hardwood at £10 a ton, but the supply was too unreliable to have it as his only source.
David is now having bundles of softwood sawmill offcuts delivered from the local mill at Portsmouth Arms for £10 a bundle, weighing about half a ton each which he stores under a Dutch barn until dry. He then chainsaws up the offcuts, puts them in a dumpy bag and moves them with his tractor to the boilerhouse, which is quite a lot of handling. The pine softwood creates masses of resin and tar as it burns, but the Vigas boiler seems to burn it off and his system is running better than it did on hardwood.
In February our case history looked at Bob Boothby’s house, office and holiday cottage complex at Millhouse Cottages in High Bickington, where he installed a 30kW REFO wood chip boiler. He also tried a variety of fuel supplies, the cheapest of which were crushed pallets at £10 a ton. However he quickly found that the ash needed cleaning out of the boiler twice a day instead of once a month, as the cement dust which was impregnated into the wood fibres of the pallets doesn’t burn very well.
So Bob is now also sourcing sawmill offcuts, drying them over the summer and then bringing in an industrial scale chipper operator and agricultural contractors with forage trailers to dump the processed chips directly into his main store. From here his groundsmen take a small quad bike trailer full of chips every week to refill the boiler hopper.
Case Study 4: Plaistow Mills Trout Farm, Muddiford, Devon. Log burning stove with back boiler, cost £3,000.
Smallholders Dieter and Jann Wirtz, who sell superb smoked and fresh trout from their old watermill house at Plaistow near Muddiford in North Devon, already had hot water and central heating running off their oil fired converted Rayburn in the kitchen. The site was listed as a settlement in 1400 and the present buildings date from 1666, with a later elegant Georgian front added to the main house, which has superbly proportioned rooms, but 11ft high ceilings which are difficult to heat.
When oil prices hit their high last summer Dieter realised that he had to find a cheaper source of heating. He already had a 12kW woodburning stove in the sitting room, which was far too hot for the room and burned inefficiently as they kept it damped down. So Dieter’s economical solution was to install a new Arrow TF30 woodburner with back boiler, which was on offer at £600 from Mole Valley Farmers, our local co-operative. The woodburner provides 2kW of heat to the room and 7.5kW to their central heating from the boiler jacket.
The key element of Dieter’s new hot water is a Dunsley Baker circuit neutraliser system, which is a squat barrel shaped tank (166mm high x 450mm diameter) that sits underneath their existing 250 litre hot water tank. The neutraliser can take input from up to 4 different sources such as their new woodburner, their existing oil Rayburn boiler, and it could take heat from solar hot water panels too. They have an electric immersion heater in the top of their tank for the summer, when the woodburner and Rayburn are turned off, to provide domestic hot water.
The Dunsley Baker system also need special valves which monitor and control the temperature of the water and smart electrics which fire up the Rayburn to boost the system if the water temperature from the woodburner isn’t hot enough to power the central heating or if it runs out of fuel. Dieter still has to clean out the woodburner and relight it every morning, but it’s a cheap and elegant solution which he calculates is now saving over £1,000 a year in oil costs.
Renewable Energy: Wind Turbines by Myc Riggulsford Part IV of the SmallPower Series
Awake, O north wind; and come, thou south; blow upon my garden, that the spices thereof may flow out. Song of Solomon
Our near neighbour Bob Boothby and his partner Kate run a successful holiday cottage business based around an old water mill, and they have already put in a wood chip boiler for heating, a water turbine and solar panels. Now they are trying to erect a domestic wind turbine as well. When they put in the planning application they got an immediate reply from the planners wondering whether Bob knew that he was proposing to site the turbine on top of a hill. And asking if perhaps he could put it down in the valley next to his holiday cottages where it would be less visible.
Since ancient times people have been harnessing the wind for work - to separate wheat from chaff, to power sailing boats and drive windmills. Wind turbines work by intercepting a flow of air and turning the sideways force of the wind into rotational energy, which is converted to electricity by a generator, usually using a system of gears to step up the speed.
Some of the sun’s energy falling on earth is absorbed in the atmosphere, causing different parts of the world to heat up at different rates. When air is heated it expands, causing different pressure around the world, which become winds when the air moves, adding to the winds caused by the earth spinning. This gives us our global wind pattern and on top of this are local wind patterns, such as sea breezes and mountain or valley winds.
The end result is that the UK has the most wind in Europe – the Energy Saving Trust claims that we have 40% of Europe’s wind resource - but it varies across the country and many of the best sites are in high mountain areas. Onsite monitoring will help you assess whether it’s worth investing in a wind turbine at your smallholding. However recent results of an extensive wind turbine trial by renewables consultancy Encraft have shown that the same turbine can generate 20 times more electricity in one site than another, and that urban sites are probably not worth it.
Bigger wind turbines are more efficient since wind speeds increase hugely with distance off the ground – so most commercial wind farms monitor at 25 metres height. The government expects that offshore wind will be the most significant renewable energy source for the UK in the long term, though in spite of all Britain’s claims of climate leadership and our complaints about other irresponsible countries, the USA has now installed the most commercial windpower in the world, with China a close second.
In the UK we have around 14,000 freestanding domestic turbines and 14,000 building mounted turbines installed, although following Encraft’s survey results released in January this year, the DIY chain B&Q has announced that it will no longer stock the £1,900 Windsave turbines that went on sale in 2006 which were claimed to generate 1kW of electricity when wired directly into a house ring main.
Most of the modern wind turbines in the UK are horizontal axis with two or three blades, rather than the four paddles of a traditional Dutch windmill, but newer designs include vertical axis turbines. The vertical axis turbines have some advantages since the gearbox and generator can be sited directly on the ground and so the mounting pole or tower does not need to support their weight.
But all turbines are affected badly by turbulence, and this is usually much greater at ground level, around buildings, in urban areas and near trees, which is why the usual horizontal axis turbines are mostly mounted on tall poles or towers, held in place by guy wires, and ideally at least twice the height of any nearby obstructions. Domestic wind turbines range in size from 1kW to over 2MW (2000 kW).
An average wind speed for a site could be made up from mostly calm weather with occasional gale force winds – neither of which will allow you to generate power. Manufacturers ratings are calculated at winds of about 10-12 metres per second, but 4-5 metres per second is more realistic. Imagine the turbine is cutting out a cylinder from the air as wide as the blades and as long as the wind speed per second. The power depends on the mass of that cylinder of air.
“The kinetic energy intercepted every second (the power) is proportional to the cube of wind velocity. Hence power rises very rapidly with wind speed”, says Dr Patricia Thornley from Manchester University’s Tyndall Centre for Climate Change. “Every wind turbine has a wind speed-power curve; which shows how power output varies with wind speed. Generally there is a cut-in speed below which the machine will not generate, and then rising up to the rated power. Further increases in wind speed do not achieve any higher power output and in very high winds the machine will automatically shut down”.
Shut downs for plant maintenance are usually only one or two days each year, and with 40% of Europe’s wind our supply cannot be that intermittent, so I’ve been trying to get to the bottom of the rumours that most wind turbines fail to live up to manufacturers claims and have much longer payback periods than you expect.
Why don’t wind turbines generate the power you expect?
I asked renewables supplier Andrew Moore of British Eco why turbines produce so little power. After all if you have a 6kW turbine, and the wind blows half the time, that should generate 6kW x 12 hours x 365 days = 26,000 kWh or 26MW of electricity, which at current prices of 10-15p per electricity unit should pay you at least £3,000 per year. This would make the payback on a typical 6kW wind turbine costing £15,000 only about 5 years, and the reality seems to be twice or three times longer.
“There are a number of reasons why the outputs of wind turbines fluctuate; but the main factor is wind speed”, says Andrew Moore. “The usual misconception is that a 12kW turbine is twice as powerful, or will generally produce twice the amount of energy as a 6kW turbine. This is not necessarily true”.
“It is very unlikely that a wind turbine, even in an ideal situation, will constantly experience its optimum working conditions and therefore will not continually produce the maximum amount of energy that it is capable of, as outlined in the manufacturer’s guidelines”, says Andrew Moore. “Realistically speaking, no small turbine - less than 12kW - is more than 30 per cent efficient. This is based on the models that are currently available in the marketplace which operate at full capacity at 10-12 metres per second in high winds - approximately 27mph winds. With a good site match and assuming good maintenance, we can estimate an average 30 per cent or more mean output over five years”.
Based on Andrew’s assessment that would mean cutting my calculation by a third, but that would still give you a theoretical annual income of £2,000 per year from a 6kW turbine, if the electricity companies paid retail rates for the power you generate, though some only pay the wholesale rate of about 5p/1kW unit .
Andrew’s figure of winds speeds of 10-12 metres per second seems a bit high too – the British Wind Energy Association reckons that speeds of 4-5 metres per second should make installing a turbine worthwhile, and claims that a 5kW machine will produce 13,000kW per year on average, nearly three times the electricity used by an average household.
Paul Baker of Devon Association of Renewable Energy explained to me that the rated output of a wind turbine can be thought of a bit like a car. So just because the top speed is 120mph and the manufacturer claims that it will do 35 miles to the gallon doesn’t mean that we can realistically expect to hurtle round the country using minimal fuel the whole time.
“As a rule of thumb, if you installed the turbine in a decently windy site, you can expect to generate 25-30% of the manufacturer’s rated output”, says Paul Baker. “Commercial wind farms, with much bigger scales, reckon on a load factor of 28%”.
That would drop my calculation for a 6kW turbine to an electricity income equivalent of around £1,000 per year, which sounds much closer to reported levels. Paul also tells me that the smaller turbines are much more badly affected by any turbulence, cutting their efficiency still further, so turbines in towns are particularly affected.
However the good news is that from this April domestic energy producers will qualify for double Renewable Obligation Certificates – previously worth about 4.5p/1kW unit of electricity generated, which from this month will now be worth 9p per unit.
“If you use as much of the electricity as you can yourself, and get paid by the electricity companies for your ROCs you can multiply the value. Up to 50kW domestic installations should now be able to get deals from their electricity supply companies”, says Paul Baker of Devon Association of Renewable Energy. “Up to April this year, for under 5kW turbines, EDF were offering 5p/kWh for everything you produced while Scottish & Southern were offering 18p/kWh for electricity exported to the grid”.
In February rumours said the government will introduce a feed-in tariff, which would replace the complicated ROC system, and provide even better incentives for microgeneration using wind turbines. If we adopt the German system (which I want) this could mean payments of up to four times the retail price of electricity for any power you generate – so instead of paying 10p per unit you could receive 40p per unit or more for each 1kW you generate, but personally, I’ll wait to see what the government actually offers before investing.
So far most British action has been just talk, and in the current downturn many of the most polluting companies in the UK are now cashing in the free carbon credits they were given, generating cash windfalls at taxpayers expense. Personally I also cannot see any reason why a hedge fund should be allowed to own any carbon credits at all, or cream off profits for overpaid vulture bankers.
The Encraft survey looked at several different models and manufacturers of wind turbines ranging in cost from £1,900- £5,400:
Zephyr Air Dolphin Z1000 1000W
Ampair 600 600W
Eclectic StealthGen D400 400W
Windsave WS1000 1000W
Iskra AT5-1 5000W
Proven 2.5 2500W
Proven 6 6000W
Encraft found that many of the turbines performed at less than one tenth of the manufacturers’ predicted energy output, and some only generated one twentieth or 5% of the expected electricity. In fact, one performance was so bad that the electronics of the turbine equipment used more power than it generated. Average energy generation was 628Wh of electricity per day when the turbines were switched on, dropping to 214Wh of electricity per day if every day of the year was included, while energy consumption of the turbines averaged 80Wh per day.
As well as the turbine itself you are probably going to need some smart electronics to monitor, start and shut down the equipment, and an inverter to connect your direct current output to the grid, so that you can simply use or export any surplus electricity you generate to the grid. Otherwise you will need a massive, expensive and short lived bank of batteries to store your electricity, and you’ll have to equip your farm with yacht technology designed to run on 12vDC current.
Installation is relatively easy as most turbines come ready assembled from the manufacturers, you often just need small digger and delivery van access to the site. Pole and tower mounted turbines need a solid concrete block about 3 metres by 3 metres by 1 metre to support the pole, and another smaller block about 1 metre cube nearby for a winch anchor, which will also allow the turbine to be raised and lowered for annual maintenance.
Your biggest headache by far is likely to be getting permission for a sufficiently high pole past the local planning department. All turbines vibrate, especially in turbulent air, so building mounted kit could shake older houses to pieces, and buildings create their own turbulence. You’re also going to get noise concerns from the neighbours, usually unfounded.
Millbrook Holiday Cottages, High Bickington, Devon, award winning green tourism holidays at www.millbrookcottages.co.uk on a 30 acre smallholding based around a former water mill. Planning application for wind turbine under consideration, supported by parish council. Budget: £18,000-£22,000.
Equipment: Proven 6kW wind turbine on a 15m mast, sited centrally in a high and open field, largely shielded from the view of a nearby hamlet by a very large neighbouring farm building. Annual mean wind speed at site 5.76m/s. Manufacturers’ estimate it should produce 9,000Wh of electricity annually valued at £875-£1250. Baseplate 10m3 concrete plus winch anchor point within 12m. Turbine blades 5.57m diameter, maximum height of tip of blade to bottom of tower 17.78m.
Dr Claire Devereux who now works with the publicly funded Science & Technology Facilities Council near Oxford showed in a scientific paper published in the 2008 Journal of Applied Ecology that wind turbines have a minimal effect on farmland birds. Previously critics have suggested that wind turbines kill birds that collide with them, constructing the towers and infrastructure causes habitat loss, and the turbines cause birds to change their behaviour, displacing them to less favourable feeding and breeding sites.
The scientists studied two windfarms in East Anglia, each containing arrays of eight 2MW turbines, with each turbine 100m high at the top of the blade and with a 20m gap at the bottom. The turbines had little effect on grain-eating farmland birds such as yellowhammers, corn buntings, tree sparrows and reed buntings during the vulnerable winter months. Skylarks and partridges were also unaffected by the turbines, and crows and corvids seemed if anything to increase their use of areas around the turbines. The only recorded birds which kept away from the turbines on the sites were pheasants, which are non-native and a larger less manoeverable bird than the other species studied, although very tasty.
Wind Turbines & Suppliers: Small scale wind power – microwind.
Approved products and installers of wind turbines can be found through the Energy Saving Trust website: www.energysavingtrust.org.uk which links to the government Department for Business Enterprise and Regulatory Reform (BERR) funded Low Carbon Buildings Programme, which links to a website called Green Book Live at www.greenbooklive.com which lists over 70 types of wind turbines, all eligible for government grants.
The manufacturers include Ampair, Southwest Windpower inc, Proven Energy Ltd, Gazelle Wind Turbines, Iskra Wind Turbine Ltd, Vergnet S.A. (PSF), RopatecAG-SPA, Juan y David Bornay S.L., Atlantic Orient Canada Inc, eoltec SAS, Fortis, Bergey Windpower Co, Wind Turbine Industries Corp, African Windpower, Renewable Devices Swift Turbines Ltd, Wind Energy Solutions, Windsave Ltd, Westwind, Zephyr Corp, Advanced Alternative Power Ltd, Quietrevolution, YangZhou ShenZhou Wind-Driven Generator, Gaia-Wind, Entegrity Wind Systems (Perpetual Energy Ltd), SMA Regelsysteme GmbH, Xantrex (Wind & Sun Ltd), Studer, Outback Power Systems (Genasys Power Systems), Magnatek SPA, SPS (Energy Equipment Testing Services Ltd), Ouyad Electronic Co.
If you click on the BERR website link www.lowcarbonbuildings.org.uk for approved installers it gives you a long list for each region – the one in the South West lists 67 certified installers, and work by them will be eligible for government grants.
The British Wind Energy Association also has a helpful website at www.bwea.com which lists their small systems members giving telephone numbers, websites and email addresses for 51 organisations – however not all of these are manufacturers and suppliers of wind turbines (though many are) – five are universities and one is a Research Council.
Renewable Energy: Water Power Part V of the SmallPower Series by Myc Riggulsford
Water, I can feel it in my water.
Since the middle ages huge areas of Britain have been powered by water – almost every village grew up on a stream or river which supplied drinking water, washing facilities and water as a raw material for industrial activity. Water wheels quickly followed with paddles turned by the natural flow of the river, and many settlements grew up around mills.
These early simple wheels lowered into the water were mainly replaced by the nineteenth century by more efficient mill races, and overshot wheels in places where there is a good vertical height difference. The water is diverted along a channel until it flows over the top of the wheel, filling buckets or compartments of the wheel. This forces the wheel to turn, gaining energy from gravity from the weight of the water in the buckets and also the flow of the race.
The actual power source driving all of this technology is of course the sun. Solar radiation causes water in the sea, rivers and lakes to heat up and evaporate, and it falls again as rain or snow over mountains, from where it flows back down to the sea. The stored or potential energy from the height difference is converted to the kinetic or movement energy in the river flow. The energy which we can trap and use depends on both the height difference or ‘head’ of the river and the volume of water or rate of the river’s flow.
Water turbines today, including recent technological advances such as Archimedes screw based generators, Pelton wheels, self cleaning Banki or crossflow turbines, and propeller turbines which are suited to different flow and head conditions, give a clean and much more reliable source of power than most other renewable energy sources. River flow is more predictable and constant than wind, and with turbines at 80% efficiency is more energy efficient than converting direct sunshine to electrical power. This makes it one of the cheapest forms of renewable energy per unit, according to the British Hydropower Association.
The first practical water turbine was designed by Frenchman Benoît Fourneyron in 1827 when he was 25 years old. His 6 horsepower (4.5 kW) machine sat in the water and the wheel was horizontal, rotating about a vertical axis, using two sets of turbine blades which were curved in opposite directions to extract as much power as possible from the river flow. Over the next ten years he built more powerful turbines, slowly improving his design, and developing a compact 60 horsepower (45 kW) turbine by 1837. This model was 80% efficient and weighed only 40 pounds with a wheel just one foot across.
The discovery of electricity by Faraday led to the first full scale hydroelectric power station in Godalming in 1881. In 1895 the United States installed Fourneyron turbines at the Niagara Falls to generate hydroelectric power and in 1935 the first major hydroelectric power station was built at Galloway in Scotland, generating 110MW. Hydroelectricity now supplies around 1% of the UK’s total electricity demand.
The most suitable sites for hydroelectric power generation, where the water turns a modern efficient turbine, all have good vertical height drop, and most of the best sites for generating industrial scale power in the UK have already been used up. Rivers which simply have a strong flow but not much vertical drop or head usually need massive engineering works to dam the river and create a reservoir upstream – often flooding large areas of the countryside, destroying wildlife habitats such as marshes, and occasionally submerging whole villages.
Many smallholders thinking of installing a water turbine will already live in an old mill house, with an existing race which could be restored for a sufficient water flow to generate electricity. The Energy Saving Trust calculates that costs for small scale hydroelectric with a low head, but where you already have an existing pond or weir, are likely to be around £4,000 per kW for schemes up to 10kW, with costs dropping for larger schemes.
But if you’re thinking of starting from scratch you really need a good head of water, even if it’s a relatively small flow, as Country Smallholding writer John Butterworth discovered when he looked into hydropower in July last year after an inspiring visit to Gibson Mill in Yorkshire. If you’re very high in mountains or moors the flow is often much smaller anyway, but this means the turbine can be quite small too. The biggest expense is often the cost of the long length of channel or pipe down which the water drops to drive the turbine, which must be able to stand up to fairly high pressures. You usually won’t be allowed to divert the whole stream, you must let it go on flowing all year.
If you’re thinking of damming a river to create sufficient pressure to drive a turbine you’ll need Environment Agency permission and sufficient space to make a small reservoir. Usually the turbine house can be sited on the dam itself, which will want to be at a place where the river narrows naturally to keep costs down. You will need to make a thorough environmental assessment report as part of your planning application for any engineering works and to get environmental licences. The major concern is likely to be any impact on angling and valuable fish.
If your river has migratory fish, or is a tributary and spawning ground for salmon or trout then you will come under the Salmon and Freshwater Fisheries Act. Your filters and turbine mesh will need to be fine enough to stop fish being sucked into the blades and you will have to build a bypass channel allowing fish to migrate upstream and downstream. This may mean the extra costs of building a fish ladder, a small series of overflowing pools which allow the fish to jump up.
For medium head schemes the costs are likely to be capital investment of £10,000 plus £2,500 per kW up to about 10kW, so a typical domestic installation of 5kW should cost around £20,000-£25,000 according to the Energy Saving Trust. The fuel of course is free. However water turbines these days are very reliable, so once you have got over the initial shock of the capital costs, annual maintenance should be quite cheap. The major maintenance effort will be spending a day clearing weeds, removing any sediment build up and any obstructions such as fallen tree branches which have caught against coarse filters and gratings.
Box 1: Water Turbines & Suppliers
Small scale water power – hydro-turbines.
Approved products and installers of water turbines can be found through the Energy Saving Trust website: www.energysavingtrust.org.uk which links to the government Department for Business Enterprise and Regulatory Reform (BERR) funded Low Carbon Buildings Programme, which links to a website called Green Book Live at www.greenbooklive.com which lists over 40 types of water turbines, all eligible for government grants.
Water turbine manufacturers include Valley Hydro, Nautilus Water Turbine Inc, Ossberger GmbH & Co, Derwent, NHT Engineering Ltd, Ritz-Atro, Wasserkraft Volk AG, Hydro Generation Ltd, Energy Systems and Design Ltd, Hydrowatt GmbH, Asian Phoenix Resources, TEPERSAC, Ampair (Boost Energy Systems), Pedley Water Wheel Ltd, Greenearth Energy.
If you click on the BERR website link www.lowcarbonbuildings.org.uk for approved installers it gives you a list for each region – the one for the South West contains just 5 certified installers, but apart from Boost Energy Systems in Berkshire and Segen in Hampshire the others are in Ayrshire, Midlothian, and Cumbria, which hardly makes them local, although their work is eligible for government grants. The lists for the South East and the Midlands are oddly identical to the South West. When I chaired the Devon Association of Small Holders symposium a couple of years ago the hydropower expert was Chris Elliott from Western Renewable Energy, based in Ponsworthy, Newton Abbott, Devon whose own site generates 90kW of power from a water turbine near Widdecombe.
The British Hydropower Association also has a helpful website at www.british-hydro.co.uk/download.pdf and a tremendously useful downloadable manual ‘A Guide to UK Mini-Hydro Developments’. Contact them at British Hydropower Association 12 Riverside Park, Station Road, Wimborne, Dorset, BH12 1QU. Tel: 01202 880333
Box 2: How much power?
Power = Flow rate x Head x 6
Power per kW = cubic metres of water per second x metres height x 6
Head: Vertical distance between the surface of the water as high as you can access it, such as on the leat above your water wheel where it drops down to drive it, to the lowest point you can release it, such as at the bottom of the existing wheel pit. Typically old mills have 2 to 10 metres head. You need at least one metre head, turbines driven by just the flow of the river are simply uneconomic according to Western Renewable Energy.
Flow rate: Method 1: For small flows such as out of a pipe, catch all the water into a known volume container, timing how long it takes to fill. One cubic metre is 1000 litres per second.
Method 2: For bigger flows such as in your mill leat, time how long it takes a marker in the middle of the stream to travel 10 metres down a square sided straight length of your channel, where you know the depth and width (which gives you the cross sectional area). Multiply the speed of the water flow in metres per second by the cross sectional area in metres squared and multiply by a correctional figure of 0.7, which will give you a rough estimate. Small streams may have a flow rate of around 10 litres per second, larger streams 100 litres per second.
Method 3: For irregular channels, larger streams, or a more accurate reading, employ a firm of experienced hydro engineers like Western Renewable Energy to do a site survey and feasibility study – they will work it out for you. Small rivers may have a flow rate of 1000 litres per second (one cubic metre), a larger river 10,000 litres per second (10 cubic metres).
Step 2: Now you need to work out the average annual flow rate by taking readings at different times of year.
Box 3: Case Study
Projected costs (including some for restoration): £25,000-£30,000. Costs so far for materials, plant hire and labour £17,000 including grants from Defra.
Chris Brown and Catriona Roberts farm near Swimbridge, North Devon on 50 acres with house, water mill and barns, orchard, walled garden, fields and woodland, formerly the centre of a 357 acre tenanted property in the Duke of Bedford’s Estate.
Chris Brown is a successful businessman who has brought his professional management and planning skills to his own and partner Catriona’s personal mission. They are restoring the farm, land, waterways and buildings of their 50 acre smallholding to be as near as possible to the architect designed and planned farm they were built as between 1853 and 1857. This has involved major engineering works to restore the water flow to their mill building, which formed the central power house of their estate model farm, marking a crucial turning point in the industrial and agricultural revolutions.
So far they are about halfway through the project, after restoring the Victorian dam, excavating the holding pond, restoring the spillway and leats, installing silt traps, weirs and a new spillway with flow management, excavating and restoring the millpond and repairing and restoring the storm drains.
“I would say the planning was about 2-3 months which included discussions with the builder, a water system expert and a local handyman-cum-land contractor”, says Chris Brown. “The actual works took another 2-3 months. The more planning you do the more likely you are to save money. Unbeknown to me at the start this was in fact a small civil engineering project which requires management of resources and contractors. Fortunately I had a good team. Having a Critical Path Plan to manage out the hiring of equipment and vehicles and deployment of your team at the right stages is highly desirable”.
Part of the funding for the works came through their Countryside Stewardship Scheme (now Entry Level Stewardship) which they entered in 2004, under the scheme’s objectives to restore traditional farm buildings and conserve areas which demonstrate the history and development of the landscape.
Their farm is important not because of the age of the farmhouse and working buildings but because their design, layout and construction as a model farm is very special and possibly unique in North Devon. The original 357 acre holding was amalgamated out of three small farms plus some extra land, and a new range of buildings and mill to power them constructed by the estate managers to the very latest efficiency and design standards for modern farming in the 1850’s.
The main barn contains a 40ft well shaft and a water turbine for which the drive shaft and gearing are still intact but not operational. The turbine was built of cast and wrought iron and drives a system of shafts and bevel gears which transfer power onto a horizontal layshaft. Water was supplied by a leat running from the holding pond north of the house, and exits via a culvert from the main barn leading to a goyle (for non Devon residents, that’s a wet ditch, from the same root as the word gargoyle, the carved stone waterspouts which empty gutters on church roofs).
The machinery barn housed various fixed machines driven by the water turbine including a winnowing machine, linseed mill, chaff cutter, root slicer, cake breaker, bruiser and kibbler. The threshing machine was operated by a drive belt taken from the layshaft, which originally ran 21 metres from west to east.
Chris and Catriona have even managed to research estate papers which include a 1853 letter from the estate’s agent, Mr John Benson, to His Grace the Duke of Bedford which says “The buildings include a water driven threshing machine and a covered dung pit and power from the water wheel is applicable for chaff cutting or any other similar machinery. These advantages this farm certainly possesses beyond most others”.
The next stage of their project is looking at the various types of water turbines (they do not intend to reconnect the water wheel), and comparing their costs and outputs against wind turbines as a source of green power. The best turbine deals they found are from abroad, though this may raise servicing issues.
“The turbines I was looking at in New Zealand and Canada worked out in the region of £3,000-£4,000 including all running gear but not delivery, installation, housing, civil works or batteries. It all depends on scale but I was budgeting a further £5,000-£8,000 for this”, says Chris Brown. “I do not intend to get involved in batteries as my limited understanding is that this could be a nightmare. I have not got figures on an inverter and connecting to the grid”.
“Our house is expected to use in the region of 6,500kW per year, or about 18kW per day. At present from the power generation data I have collected on our flow rates to date we are averaging about 30-35kW per day over a year. This would in theory allow us to sell to the grid at times, but we would also need to draw from the grid in periods of drought. We started the data collection in September 2008, so we are only halfway through the exercise and we still have summer to come, although in North Devon that might make little difference!” says Chris Brown.
Renewable Energy: Solar Thermal – reverse radiators on your roof
Part VI of the SmallPower Series by Myc Riggulsford
If we could trap all the sunlight falling on the earth’s surface we wouldn’t be worrying about the impending fossil fuel shortages, we’d be awash with energy. One of the ways we can tap into this free potential from the sun is to use solar thermal panels to convert sunlight into heat for domestic hot water. Unfortunately, we can’t yet efficiently use these panels for central heating as here in the northern hemisphere we get most of our direct sunshine in the summer months, around 70% of it, and not enough in winter to provide sufficient heat for our homes.
Most solar hot water panels will ideally be facing south to work properly, though modern evacuated tube systems will work at 90% efficiency even if facing south-west. If you have an east-west pitched roof, then don’t bother putting in an expensive frame and complicated elevated platforms to make the hot water panels face south. These days it’s probably cheaper and simpler to put a second solar panel on the east pitch to trap early morning sunlight and rig it in parallel with your main west-facing one, straddling your roof.
It’s possible to make a solar hot water panel by simply taking an old radiator, painting it black, and sticking it under a cold frame or glass case on your roof. It’s not very efficient and you run the risk of it freezing and bursting in winter, so you are probably better to choose one of the hundreds of commercial systems on the market, but basically their principle is still the same.
To qualify for the government’s Low Carbon Buildings Programme grants of £400 for a domestic installation you will need to meet the preconditions such as having a suitably well insulated loft, and use only approved equipment and certified installers. Somerset residents can get an extra £500 local authority grant as well, according to Scott Burrows of suppliers Eco-Exmoor of Parracombe.
Flat Plate v Evacuated Tube
Flat plate solar collectors are the simplest system. The sunlight passes through a glass cover and hits a black absorber panel which warms up. Connected to this black panel are pipes containing water or other heat transfer liquid which in turn transfer the sun’s energy into your household hot water supply. This makes an important carbon neutral contribution to your domestic energy needs, as hot water is usually about 40% of your overall heating budget.
Some modern heat stores can also partly warm your central heating. Unfortunately our central heating or space heating requirements in the UK are at the time of year – winter - that is the period of lowest solar radiation in the northern hemisphere. So you really need a boiler, backed up by solar hot water panels in the summer when you don’t want the central heating on, which is what we’ve done on our smallholding.
The alternative to the cheapest flat plate solar collectors are evacuated tube collectors. These also come in two types. The cheaper are arrays of twin walled tubes like giant double glazed test tubes with a copper or other metal core and reflectors inserted into the air-filled middle. The core transfers heat by conduction to a manifold fixed to the ends of the tubes. The most efficient sort, single skinned vacuum tubes, have the copper core already sealed into the system. This type is more expensive to manufacture and more difficult to repair if damaged.
Obviously all three types of solar panel and their associated plumbing, valves and pumps release carbon emissions in their manufacture and fitting, which has environmental impacts, but the systems are so efficient these days that the carbon payback is quite quick, perhaps 2 years. The panels are now also much thinner – usually about 10cm or 4 inches – so the visual intrusion is less, with most sitting below the roofline and acceptable to planning departments.
New planning rules mean that you don’t even need planning permission (with its extra costs) for most solar panels – they now come under what is called permitted development. The exceptions will be if you are in a conservation area, when you should check with your local planning authority, or if your building is listed so it is illegal to install solar panels without first getting permission.
You will still find some crusty old listed building officers who automatically tell you that permission will be refused due to the visual changes solar panels will make to the building, as ours did in Torridge District Council. But if you are persistent and insist on a site visit you can usually find an acceptable compromise.
Most small farmhouses need a standard 2m2 panel costing around £1000, but installing it with a complete solar hot water heating system will be about £3,500-£4,500, according to Scott Burrows of Eco-Exmoor. Payback time is typically 5-10 years depending on how much hot water you use and the costs of your alternative fuel.
Case study 1:
Myc & Jenny Riggulsford, High Bickington, Devon: 20 acre culm smallholding with 5 bed listed farmhouse built around 1650, main house faces east with two rear wings facing south/north and rear west facing flat roof over former courtyard forming 1960s kitchen. Total costs for solar hot water £3,560.53 including 5% VAT and less £400 LCBP grant, making net costs £3,160.53 (excluding cost of twin coil hot water tank).
We replaced our oil fired central heating in February 2007 with a 25 kW log boiler which does all our domestic hot water and central heating from October until Easter. However, this system needs to lose at least 5kW of heat all the time just to keep ticking over, so we have radiators in two bathrooms which are permanently switched on while the boiler is working.
By Easter this means that anyone going to the lavatory or having a bath gets a sauna style experience and comes out several pounds lighter. However from April our two solar panels are heating our hot water to 40oC, so we can have baths by running just the hot water taps, and do the washing up, allowing us to switch off the log boiler.
Before we fitted the solar panels in September 2007 (we had to wait for planning permission for our listed farmhouse) we ran the hot water for one summer - with lots of visitors - using just the immersion heater, and our electricity bills skyrocketed.
The log boiler needed a large hot water tank to act as a heat store – at least 250 litres compared with the 100 litre domestic one we had previously. While we were paying for the plumber to install this we figured that it would make economic sense to have one with twin coils, so that we could retro-fit solar panels when we could afford them, if we eventually got planning permission. We knew listed buildings consent would be a fight with our terminally obstructive listed buildings officer as we had unsuccessfully tried for two years to be allowed hand made oak double glazing to replace our rotted out Victorian pitch pine single glazed windows.
As expected the planners initially turned down our request flat, claiming that solar panels would destroy the look of our 17th Century farmhouse, marring the view for neighbours and passers-by. We eventually persuaded a charming planning officer to make a site visit, who realised that our house and courtyard is completely hidden from view, up a quarter of a mile of inaccessible track and that our nearest neighbours are half a mile away.
We wanted to put the solar panels on a hidden south facing rear wing roof, already marred by gutters, drainpipes, water tank overflows, the range and boiler chimneys but easily accessible from the flat roof of our kitchen without scaffolding. This whole aspect of the house is hidden in the hillside and shielded by an 8ft beech hedge. Once she had tripped round to the muddy back of our house in her high heels the planning officer quickly agreed with our application, so for a cost of £135 fees we were allowed solar panels. The government has now removed this planning requirement, so you should get permission free, even if your house is listed.
I’m not a competent plumber, so we had Nick Backhouse’s team from Eco-Exmoor who came and surveyed the site, calculated our needs and quoted for the job. On the appointed days two experienced fitters came and installed 2 Roth solar collectors, electric pump, pressure tank, valves, smart controls and insulated piping to connect the solar collectors through our loft to the bottom coil of the hot water tank in the airing cupboard almost directly below.
The fitters’ job was slightly complicated by the government’s stupid requirement to fit 10 inches of highly allergic rockwool loft insulation before you start any of this other renewable energy work, if you are going to be eligible for any Low Carbon Buildings programme grants (rather than afterwards, which would make sense).
Our long-suffering plumber, Alan Pidner had already braved rashes and itching from the rockwool in our loft when fitting the feeder tank and re-routing the wider bore plumbing for our log boiler system. The professionally laid 10 inch thick insulation rolls had to be ripped up and pushed to one side so that Alan, and later the solar panel fitters, didn’t fall though the ceilings, since once the insulation is in place you can no longer see the rafters and beams to walk on. One day I’ll get round to climbing back up into the loft and laying it all properly in place again. But that’s what you get if you allow civil servants, not practical tradesmen, to set the rules.
It took the two solar panel fitters one and a half days and 10 cups of tea to finish our job, and they cleared up very professionally, leaving a neat and superbly successful solution to our summer hot water needs. For just over £3,000 net it has been a bargain – the extra charges over DIY costs are the site visit for estimating, 4 man-days for the fitters, and a proportion of the £1,800 per technology that the government charges firms to register for LCB grant eligibility.
Our solar panels now supply all our hot water for 6 months of the year, and pre-heat the whole 250 litre central heating tank from about 5oC to 17oC in winter, saving fuel for the log boiler. The manufacturers estimate that the system should provide 3,627kW of heat output per year, which would be about £400 worth of electricity, giving a 7-8 year payback, which sounds a bit high compared with our experience.
Case study 2:
Ian Ripper & Maggie Watson, Wheatland Farm, Hollocombe, Devon: 21 acre smallholding with farmhouse, stone barn holiday cottage, 3 wooden lodges and a culm grassland Site of Special Scientific Interest, Popehouse Moor. Costs for solar hot water £1,500 per holiday lodge, no grants. www.wheatlandfarm.co.uk
Ian Ripper has 20 years experience of sustainable tourism, much of it working in Africa, and Maggie Watson is a professional ecologist and science editor, so Wheatland Farm’s mixture of an SSSI and eco-holiday business potential sold it to them in 2006. They have restored ponds, care for the important local wildlife and expanded their holiday cottage business to help fund their conservation activities, winning gold level in the Green Tourism Business Scheme, and another gold award from the Devon Wildlife Trust.
Ian has installed solar hot water systems in all three holiday lodges (backed up by immersion heaters), which with their green electricity supplier and good insulation makes taking an eco-holiday with them very cosy as well as satisfying.
Ian is very practical and they are trying to keep costs to a minimum to make their lodges as affordable as possible (they even let you bring your dogs), so he quickly realised that he would have to install the solar hot water panels himself.
Navitron Ltd, based in Oakham, Rutland, sells complete solar kits and Wheatland Farm bought the £1,300 version for their lodges, which includes a 20 tube solar panel with manifold taking the 47mm twin-skinned vacuum tubes; roof mounting kit; double insulated twin coil 172 litre hot water cylinder; circulation pump; isolation and anti-syphon valves; smart electronics to control the system; 10 metres of insulated pipe; 5 litres of antifreeze; and a pressurised system kit which Ian describes as basically an adapted weed sprayer, plus full instructions.
“The self assembly option at about £1,500 was so much cheaper than any of the registered installers that we easily saved more then the 15% grants on offer. The cheapest fitter was quoting over £2,500 plus VAT”, says Ian Ripper. “I originally thought that we would be lucky to get a financial payback within 3 years, assuming they work from May to September, but now that’s looking realistic, the systems are stunningly effective. In the last 12 days of March the lodge occupants didn’t need the immersion back-up for the hot water at all, even with plenty of showers”.
“The hardest thing was fitting the thermal stores into the tight airing cupboard space – there wasn’t much spare room and I had to keep sliding the tank in and out to check that all the fittings were in the right place”, says Ian Ripper. “The systems are very flexible, you can get longer tubes or fatter ones if you want to up the power, or just add another unit”.
Their Navitron systems have been set to kick in at 10oC temperature difference, and switch off at 3oC difference, so you don’t pump heat out onto the roof, but these settings are variable. On the east/west facing holiday lodge it was cheaper to simply fit two panels with two pumps, one on each roof pitch, than try to build a ramp or platform to make the panel face south.
“The other big advantage for a commercial site is that we don’t have to heat the water to 60oC to clear legionnaires disease every couple of weeks since we’re not storing any hot water”, says Ian Ripper. “The pipe from the panels passes through the thermal store, heating that up. Then our hot water output is simply a cold water feed which also loops through the thermal store where it heats up in one more thermal exchange, so the hot water is at mains pressure. This also means that no matter how hot the tank is the thermostatic mixer makes sure that the water doesn’t come out of the tap scalding”.
Fitting the first solar panels was a steep learning curve, but Ian reckons that it would now take him about 5 days to fit one of the complete systems, plus refurbishing the bathroom. The evacuated tube system means that the manifold can be plumbed in, filled with water and antifreeze and pressurised before the copper cores from the tubes are plugged in and the system heats up.
Box 3: Solar thermal equipment and installers
As with other types of renewables, approved products and installers can be found through the Energy Saving Trust website: www.energysavingtrust.org.uk which links to the Green Book Live website at www.greenbooklive.com which lists over 130 types of solar thermal equipment, all eligible for government grants. I trawled the first dozen websites before I lost the will to live; the worst were unhelpful and didn’t give prices or performance, the best gave panel sizes and stockists. I can recommend Navitron’s website at www.navitron.org.uk which in 3 clicks gives you the chance to purchase self assembly kits with full contents list and costs. This will at least give you a baseline price to negotiate with plumbers and installers.
The BERR website link www.lowcarbonbuildings.org.uk lists grant approved installers for each region, the South West one includes 157 companies including such well-known westcountry names as AD Heating from Aberdeen, AW Matthews from Hereford and Absolute Solar from Dunbartonshire which are all nicely local to us here in North Devon.
The Solar Trade Association has a helpful website at www.solar-trade.org.uk which also gives you a regional list of installers, and their South West list included over 40 names, more than 30 of which were actually local to our area
Renewable Energy: Photovoltaics – turning sunlight into power
Part VII of the SmallPower Series by Myc Riggulsford
If you are particularly unromantic you can think of sunlight as simply a stream of photons, each bringing some of the sun’s immense power to earth. The energy trapped in different colours or wavelengths of light varies, with ultraviolet having the highest frequency and highest energy, but in infrared light the photons carry less energy.
Solar photovoltaic or PV materials, usually made from a combination of two types of semiconducting silicon, use this energy from the sun to create electricity. The stronger the intensity of the light, the greater the flow of electricity.
Modern PV panels just need daylight, they do not have to be in direct sunlight, so you can still generate electricity on a cloudy day, though in the UK they should face south, southwest or southeast.
You can now get a wide variety of different types of PV fittings ranging from the familiar shiny panels which look a bit like rooflight windows, to solar tiles that can be used instead of slates for roofs, and special glass for conservatories and windows that reduce glare while generating electricity. Solar panels are quite heavy, so you need to check that your roof is strong enough if you’re putting in a sizeable PV array.
The sustainability, or embedded carbon, of solar PV cells is surprisingly good, even with quite energy intensive manufacturing costs. Dr Patricia Thornley from the Tyndall Centre for Climate Change tells me that solar PV panels save 85% of the carbon dioxide emissions of grid electricity over the lifetime of the cells. A typical domestic system could save over a tonne of carbon dioxide every year, and should run for about 25 years.
However, according to the European Commission Joint Research Centre, solar PV is most viable south west of a line drawn across from North Wales to Norfolk – so PV panels fitted in Scotland may never generate enough electricity to pay back their embedded carbon, although solar panels in Somerset probably should.
“PV costs have fallen rapidly over the last few years, but it remains one of the most expensive ways to generate electricity – costs can work out at 30p/kWh” says Patricia Thornley. If photovoltaic panels are built into the fabric of new buildings they can replace other materials such as roof slates, which reduces their extra costs. However most smallholders would be fitting them onto existing farmhouses or barns, so solar PV is not as economically attractive as many other forms of electricity generation such as wind or water turbines.
According to the Low Carbon Buildings Programme, costs for photovoltaics should be around £5,000-£7,500 per kW of generating capacity, and a domestic system will usually be from 1.5-3kW. They reckon that a 2.5kW array will provide enough electricity to meet around half a typical household’s needs, saving around £250 a year. Panels that sit on top of an existing roof are cheaper than ones fitted in as part of the roof surface. Solar tiles and slates cost more than conventional panels.
If you are going to join the PV system to your normal electricity connection, which allows you to export any surplus electricity to the grid, you will need an inverter. Otherwise, for a stand alone system such as on a remote barn, you’re going to need an expensive array of batteries to store your power, and these will need checking and testing regularly and replacing every few years.
Solar slates and tiles provide a simple alternative to conventional slates or roofing tiles and can be laid in patches or as a complete roof. Solar Century’s C21e solar slates (600mm x 300mm or 500mm x 250mm) and tiles each replace four conventional tiles or slates and are attached straight to the roof battens, generating 52W per tile or about 1kW per 8m2.
Solar Century has a network of approved installers but is also training ordinary roofers who can purchase and fit the slates and tiles through builders merchants. Installation and commissioning should be £300-£600, with costs for a 24 tile or slate solar electric 1.25kW system generating 1,036kWh per year of £8,510 and a 36 slate or tile 1.86kW system costing £12,060 (see www.solarcentury.com).
Photovoltaic glass is being developed by several companies around the world. Some types have crystals in the glass which divert part of the light at right angles to the edges of the pane where it is harvested by solar PV cells in the frame space between the double glazing panels. Another glass, made by Romag in Consett, County Durham, called PowerGlaz, has groups of 5” or 6” square PV wafers incorporated into each single or double glazed panel, providing shade control and electrical power. This type of glass has been used on the new education building ‘The Core’ at the Eden Project in Cornwall, producing 80W per panel. Romag is currently working on a PV glass car parking canopy which could recharge an electric vehicle.
“If you’re building a conservatory, and your budget stretches to it, and you want a high concept product then choose solar glass,” says Hugo House of renewable energy electricity supplier Good Energy. I also asked him about thin film and PV membranes. “At the moment they are more military applications than commercialised products - the US army has tents which can generate electricity, so their troops can operate off-grid”, says Hugo House. “These new types of PV materials are one of the products with the widest possible application today, and could be used by smallholders since you can stick it on properties in places where you cannot fit other renewable technologies. With greater efficiency and lower costs they have the potential to boom in the future”.
Case Study 1
Bob Boothby and Kate Jones, Millbrook Cottages, High Bickington, Devon. 32 acre smallholding based around mill house, old water mill, cottages and outbuildings now forming a holiday complex. Renewable energy on site includes wood chip boiler, solar hot water panels, water turbine, solar PV panels, planning permission for wind turbine, and they are considering an air source heat pump. PV system cost £6,000. Website: www.millbrookcottages.co.uk
In September 2008 Bob and Kate had an array of a dozen 85W Kyocera solar panels installed on their south facing garage roof by Chris Verney of Barum Solarheat from Barnstaple, Devon. The array cost £6,000 including installation and should generate 1.1kW of electricity at maximum output. The system is connected to the grid through an inverter, which has 2kW capacity so they can add to the system later.
The Kyocera panels are made from silicon based cells protected by a tempered glass cover and the whole module is laminated in an anodized aluminium frame for strength and easy installation. The manufacturers claim that their newest versions are 16% efficient, one of the highest energy conversion rates on the domestic PV module market.
Planning guidelines say that you can now fit PV panels in England without planning permission so long as they don’t protrude more than 20cm (8 inches) above the roof. But Bob’s roof mounted panels need 2 inches of air circulation underneath them to avoid overheating, so it was touch and go.
The panels sit very neatly on their garage, blending in well with the slates, and indoors the control panel looks very similar in size and appearance to a modern electricity fuse board, so you don’t need much space. Even at 8.30am on an overcast late April morning the system was generating 145W of power. The previous day it had generated 2,578Wh and the previous sunny Sunday 4,862Wh.
Bob showed me their monthly figures:
October 2008 35.3 kW
November 2008 21.6 kW
December 2008 16.7 kW
January 2009 21.8 kW
February 2009 31.6 kW
March 2009 105.0 kW
April 2009 (3 weeks) 83.2 kW
I asked Bob if he was pleased with the results, and what the cost benefit was.
“Like all these things it’s a bit of fun, you can’t justify the cost”, he said. If you consider that since April 2009 when they have received double the normal Renewables Obligation Certificates for all the PV power they generate at Millbrook Cottages, that’s still only 15p per unit. If you add to that the 15p per unit cost of buying electricity from a green source, each kW they generate is worth 30p to them. If you take March as a typical month when they generated 105kWh of electricity, that’s still only £30 worth. That would make an estimated income for the year of £360 pounds or thereabouts from a £6,000 array generating 1200kWh.
Chris Verney of Barum Solar says that a 1kW PV silicon cell array which takes up 8m2 of roof space should generate at least 800kW a year in the UK, mainly between May and September. Like Bob, he thinks grid connection through an inverter is a better option than batteries, which only last about 8 years. Chris also recommends buying an import-export meter as well since the electricity companies are now paying much more for renewably generated electricity. With his own system, and with Scottish and Southern as his supplier, Chris is currently paying 13p per unit for any electricity he uses, but being paid 28p for every unit he generates from his own 2.5kW array.
If you don’t want the PV panels to protrude above the roof surface you can opt for solar slates or they can inset the panels. Insetting is a colossal amount of extra work (and therefore extra cost) according to Chris. You have to take off all the slates or roof tiles, install a waterproof tray – which is like a rigid plastic sheet – then put in mounting rails which give the two inch air cooling gap under the panels, then install the PV array on top, making the whole system appear flush with the roof from outside.
Case Study 2
Tim and Fiona Start in Herefordshire installed a 3kW solar array on their south-facing roof in May 2006 at a cost of £16,300 and received a grant of £7,500. The panels produce three-quarters of the electricity they need, around 2,400kWh. Because their electricity supplier Good Energy pays 15p/kWh for all the electricity you generate, even if you use it on your own site, they also receive an annual payment of £103. Good Energy sources all its electricity from renewables (no nuclear) and you don’t need an import-export meter. They charge around £40 a year more than conventional suppliers if you just use electricity from them (www.goodenergy.co.uk).
Box 1: Photovoltaic grants, equipment and installers
Rumours that the government’s solar PV grants have run out are untrue – the Energy Saving Trust assures me that private householders are still eligible for up to £2,500 towards the costs of accredited PV panels fitted by approved installers, see their website: www.energysavingtrust.org.uk .
The BERR website www.lowcarbonbuildings.org.uk lists grant approved installers for each region, and as usual the South West one names 88 approved companies in the Westcountry - from Norfolk to Aberdeenshire. It also lists a whole range of approved PV products from 52 different manufacturers, some with a dozen different types of module.
The British Photovoltaic Association is housed in the National Energy Centre, Milton Keynes, which is also the base for last month’s solar thermal trade body, the Solar Trade Association. Their website at www.solar-trade.org.uk has weblinks to the British Photovoltaic Association which unfortunately don’t currently work, and neither does the European Commission’s link at www.pv-uk.org.uk, which bounces you to the National Energy Foundation.
Box 2: Planning permission
Changes to permitted development rights for domestic microgeneration technologies introduced on 6th April 2008 in England, and 12 March 2009 in Scotland mean that you now don’t need planning permission for most solar PV equipment, unless you have a listed building. Wales and Northern Ireland don’t require planning permission either according to the Energy Saving Trust. However you will still need to check that you comply with building regulations.
PV panels fixed to a building are now permitted development so long as they don’t protrude above the roofline or more than 200mm (8 inches) from the surface. In a conservation area they must not be on the main elevation facing a road or visible from one. In Scotland you also cannot put them on any part of the external walls of a building containing a flat, or within 1 metre of the edge of a roof or have them protruding more than 1 metre above the plane of a roof, or let them project above the highest point of the roof, without getting planning permission.
Stand alone PV panels must be less than 4m high, more than 5m from any boundary, in a maximum array smaller than 9m2, not visible from a highway in a conservation area. In Scotland, not within the grounds of a listed building at all, or nearer to the boundary than the height of the array, and you can only have one free standing solar array or you will still need planning permission.
Box 3: How PV materials work
Solar photovoltaic materials were discovered in 1839 by Edmund Becquerel. The sun’s light energy is harnessed by joining a semiconductor, such as modified silicon crystals, which has lots of free electrons to a semiconductor with lots of electrons missing (think of it as a set of holes ready to be filled by electrons). The spare electrons would like to move from one semiconductor material to the other, but they need energy to do it. Electrons only exist in definite energy states according to quantum mechanics, so if exactly the right wavelength (or frequency or energy state) photon comes along it can help to nudge an electron from one side to the other where it fills a hole. The moving electron creates an electric current if a circuit is completed.
Photovoltaic panels are made from materials where visible light will provide the right energy nudge, and provide the most electricity as an electric current. Solar PV cells are usually made from a combination of two types of silicon – one with extra electrons, one needing some.
Box 4: Solar Towers
The Co-operative Insurance Solar Tower in Manchester is Europe’s largest commercial solar facade and was installed by Solar Century in 2006, costing £5.5 million. The 400ft high tower was covered in 7,244 solar panels, replacing the 40 year old mosaic tiles on the listed building, which should generate 180,000kW or enough energy to power 55 homes for a year, see www.solarcentury.com.
Solar reflectors: Although not strictly solar photovoltaic, more a specialised version of solar hot water, the world’s first commercial solar tower plant was built in March 2007 in Sanlucar la Mayor in Andalusia, not far from Seville in Spain. It produces 23 gigawatt hours a year, replacing 16,000 tonnes worth of CO2 from fossil fuels every year, according to Devon Association for Renewable Energy. The solar plant has 624 reflectors each measuring 124m2 which focus the sun’s rays onto a 115m tall tower which absorbs the energy into sealed water filled panels that heat under pressure to 250oC, converting the water into steam which powers a turbine. This Spanish power plant is planned to have nine towers by 2013, producing enough energy to power 180,000 homes, or all of Seville. Similar towers built in North African deserts could theoretically power most of Europe in the future according to our politicians and policy wonks (or indeed, Africa)
Renewable Energy: Heat Pumps – tapping into thin air
Part VIII of the SmallPower Series by Myc Riggulsford
Heat pumps sound like voodoo technology – you can somehow multiply the energy from the electricity that you put in by about three times to get much more heat out than you would simply by switching on your sitting room fire, fan heater or immersion.
Air source heat pumps work on the same principle as refrigerators by using a cycle of expanding and condensing a low boiling point liquid to extract heat from the air and transfer it elsewhere. Air source heat pumps can still work even when the outside temperatures has fallen to –15oC.
Air to air pumps work best if you are running an agricultural or industrial process which generates waste heat somewhere in your building that you want removed. Air to water pumps can warm your radiators or underfloor heating.
Manufacturers measure heat pumps’ efficiency by the co-efficient of performance or CoP which compares the amount of heat produced with the power needed to run the system. The Energy Saving Trust says air source heat pumps have a typical CoP of 2.5 which means that for every unit of electricity put in, you get two to three units worth of heat energy out.
Some air source pumps claim to have a CoP of 5, which sounds possible in laboratory conditions but unlikely in our 17th Century farmhouse. For a CoP of 3, about two units of the energy output are delivered from the renewable source such as heat from the air and one comes from the power input by recovering the waste heat generated by the pump itself.
Costs for a domestic system of 8-12kW will be £7,000-£10,000 including installation, with running costs for room heating alone around £450 per year. Obviously the better insulated your home is, the more efficient the heat pump will be.
Heat pumps are modified air conditioners, so most can work backwards in summer, cooling your house. If you didn’t have air conditioning before, you could use more electricity over the whole year than you did previously.
According to the Heat Pumps Association, air to air pumps range in power from 3kW to 100kW see www.heatpumps.org.uk . Further information from the UK Heat Pump Network www.heatpumpnet.org.uk and www.heatpumpcentre.org
Box 1: Heat pumps: grants, equipment and installers
Domestic grants from the Low Carbon Buildings Programmme for air source heat pumps are £900 maximum or 30% of the eligible costs whichever is lower, using registered suppliers, installers and equipment and meeting the other requirements such as loft insulation and double glazing.
The BERR website www.lowcarbonbuildings.org.uk lists over 80 grant approved installers for each region, but actually they are from all over the UK, in alphabetic order, which is frustrating. It gives you exactly the same list for air source heat pump installers as ground source, which seems unlikely. Complicated weblinks and search clicks from there eventually track down the web address: http://www.microgenerationcertification.org/Home+and+Business+Owners/Microgeneration+Products which lists certified products from five different air source heat pump makers.
Box 2: Types of heat pump
Air to Air pumps are wall, roof or attic space mounted units, often for air conditioning, providing both heating and cooling.
Air to Water pumps can heat swimming pools and provide domestic hot water as well as space heating for homes.
Water to Air pumps use wells, boreholes, rivers and lakes as the heat source.
Ground to Air pumps use the constant temperature underground to deliver warm air indoors. Ground to Water pumps transfer the heat from underground into underfloor heating systems or low temperature radiators.
Box 3: How do heat pumps work?
A typical heat pump has four main parts: one heat exchanger called the evaporator which takes in the heat from the outside air; a compressor that pressurises the working fluid in the pump, which causes it to warm up to the temperature needed for your heating system; a second heat exchanger called the condenser which gives up the heat to your home; and an expansion valve which allows the working fluid to expand and cool before returning to the evaporator.
Case Study 1
Air Source Heat Pump: Graham Phillips and his wife live in Scotland between Inverness and John O’Groats with a hectare of organically run land overlooking Loch Fleet nature reserve. They built a 4 bedroom timber framed house in vernacular Sutherland style three years ago. Heat pump budget £8,000
Graham Phillips originally wanted a heat pump for their self built house in the far north of Scotland, but the nearest suppliers were in Orkney or England, so they installed underfloor heating and suitable upstairs radiators anyway and settled for an oil fired condensing boiler. All 4 bedrooms are en-suite and fitted to 5 star B&B quality to keep their business options open, so their future space heating and hot water needs could be considerable. With the rise in oil prices last year they revisited the energy question and want to invest capital now to cut energy costs later when they are relying on their pensions, if the government leaves them any.
The Phillips considered ground source heat pumps, but their soil is almost pure sand which is quick to heat and quick to cool. This makes sandy ground hot in summer and cold in winter, delivering only 8-10W per square metre of trench, doubling the normal ground loop costs. They are well above the water table, which is a shame because wet sand delivers 40W/m2.
Air source heat pumps are established technology in Japan and Europe, but will they work in furthest Scotland? Graham found the Energy Saving Trust suppliers list so long, and manufacturer’s case studies so generalised that they were useless. They decided on household name companies with a decent support structure in their area, which restricted their options.
They narrowed the choice to the German owned company Dimplex whose new quiet system uses water for heat transfer, and Daiken a leading Japanese air conditioning manufacturer, whose pump uses refrigerant travelling quickly through the system, minimising heat loss. They are awaiting final written quotes but expect costs of around £8,000 before grants.
Graham designed the house to fit a heat pump, so their underfloor heating manifold and main electricity panel are both in a big store room downstairs and the hot water cylinder is directly overhead upstairs. If they choose the Dimplex, the heat pump will be installed outside, on the external wall directly next to the underfloor heat manifold. They will need a secondary hot water tank and control unit inside, losing some store space, but balanced by recovered space in their utility room when they remove and sell their oil boiler (and outside oil tank).
If oil prices remain low their capital payback should be less than 10 years, if oil prices return to their 2008 highs, payback will be 4-5 years. Heat pumps may work in icy Scandinavia and northern countries, but their electricity costs may be much less than ours. The lower the outside temperature the higher the energy cost of extracting heat from the air, with performance dropping way off at –5oC which may require an immersion heater boost.
Graham says air source heat pumps have the reputation for being as noisy as the refrigeration unit on a lorry, which they and neighbours might not tolerate, so recommends that you listen to the type you are thinking of buying actually in use before you choose, since it could be running all night, especially on an Economy 10 tariff.
Case Study 2
Air Source Heat Pump: Peter Moffett, Morchard Bishop, Devon, 7kW Worcester Greensource air to water heat pump cost £7,700 including VAT and electrical tests.
Former smallholder Peter Moffett moved from a Rayburn heated farmhouse into a typical 1960s suburban house in Morchard Bishop, Devon in November 2007 and decided to replace the oil fired central heating which was using 1,600 litres of oil a year costing about £1,000 with a heat pump system. Peter would have preferred a ground source heat pump but didn’t have access for a digger into their garden or room for a sufficient ground loop.
He chose the first British installed 7kW Worcester Greensource heat pump. Their existing radiators were adequate, so in July 2008 it was coupled into their plumbing system where it runs the central heating and domestic hot water. The air to water pump cost £6,800 plus £900 for an electrician to check the connections and all their wiring, and as they didn’t apply for a grant until afterwards this was refused.
The heat pump itself is about one metre cube in size and sits outside on the hardstanding that previously held their oil tank. It is quiet, although they do have some radiator hum, and Peter estimates that it cost around £550 in electricity to run last year after a particularly cold winter. More information at www.worcester-bosch.co.uk
Renewable Energy: Ground energy – hot rocks rock!
Part IX of the SmallPower Series by Myc Riggulsford
We smallholders have fields, paddocks, or largish gardens, making some alternative energy technologies like ground source heat pumps cost effective for us. As a disadvantage many of us live in old or listed buildings, and digging up your sitting room and kitchen floor to put in underfloor heating pipes may not be practical.
This month I’m taking another look at the voodoo technology of heat pumps which multiply the electricity power that you put in by about three times to get much more heat out than you would normally expect by simply switching on an electric fire.
Just like the air source version, ground source heat pumps work on the same principle as refrigerators and air conditioning units by tapping into the warmth of the earth deep beneath the surface. The ground two metres down stays at a constant temperature even in winter, around 10-12oC, and this heat can be used to warm your radiators or underfloor heating. A ground source heat pump can also pre-heat the cold water feed into your central heating boiler.
Ground source pumps need pipes buried in your field or garden, or down a borehole if you don’t have enough free land space or you cannot get at it with a tractor or digger. Combining this installation with other building work cuts costs, so ground source heat pumps are most economical when you’re building a new property or adding an extension.
A typical loop system needs around half an acre of paddock space with pipes buried two metres or six feet down which circulate a mixture of water and antifreeze (usually propylene glycol), absorbing energy from underground and circulating it back into your house.
The pipes can be installed flat in a straight trench, or if you have less ground space, as a spiral coil or slinky in a slightly deeper trench about 10 metres long for each 1kW of system. According to the UK Heat Pump Network the buried parts of ground source collectors now have an expected operating life of over 40 years.
The efficiency of a heat pump is measured by the co-efficient of performance or CoP which compares the heat produced with the amount of energy needed to run the system. A typical CoP for a ground source heat pump is 3-4 which means that for every unit of electricity put in, you get between three and four units worth of heat energy out. This makes them typically cheaper to run and more efficient than air source heat pumps which have CoPs of around 2.5.
A domestic system will usually be about 8-12kW and the best performances are from pumps running underfloor heating which works at around 30oC-35oC, a lower temperature than radiator based central heating.
According to the Energy Saving Trust costs for installing a farmhouse sized system will range from £6,000 to £12,000 plus your own plumber’s charges to connect it to your central heating. Running costs should be about £500-£600 a year after that for all your background room heating and half your domestic hot water costs, depending upon how big and well insulated your house is.
The electricity you put in powers a compressor and a circulation pump to push the water around the underground pipe loop. The heat pump uses a heat exchanger to take the heat supplied from the water in the ground loop, the compressor pressurises the working fluid in the pump which heats it up further, passes this heat to your central heating system through another heat exchanger, and then a valve lets the working fluid expand again which cools it down before it goes round the circuit once more.
The final part of the system is of course your own central heating circuit, which can be underfloor heating or conventional radiators, and possibly a bottom coil in your hot water tank to pre-heat the water before your boiler brings it up to washing and bathing temperature. For a CoP of 3, one third of the heat comes from the power you put in by recovering the waste heat generated by the pump itself, and two thirds come from the renewable source such as underground heat.
However, depending upon your electricity supplier, your system will not be completely renewable energy unless you install solar photovoltaic panels, or a wind or water turbine to power the system. Or you use a renewable energy supplier like Good Energy. Many of the main electricity companies’ so-called green tariffs, which avoid coal or oil fired power and charge you a premium for the privilege, do it by sourcing their electricity from nuclear stations instead, which they count as ‘renewable’ or low carbon in spite of the huge amounts of concrete and radioactive waste involved.
Another major advantage, or concern for environmentalists, is that like air source heat pumps or air conditioning units, a reverse cycle ground source heat pump can be made to work backwards in summer, cooling your house down and storing the heat back underground. If you didn’t have air conditioning before you installed the pump, in a hot year you could end up using more electricity over the whole year than you did before.
If for some reason you don’t have access space for a digger to make trenches, your land is all covered with buildings and permanent crops, or it’s simply at a distance from your house, then you can dig straight down instead. Boreholes usually need to go down about 100 metres to achieve the same effect as the trench based systems, and drilling is more expensive than digging trenches.
However you can often bore two shallower holes rather than one deep one, especially if your house is sitting on particularly difficult rock strata. Drilling rock sounds expensive, but remember, sand, clay, chalk and shale are all rock types even though they are fairly soft. The holes can even be drilled at an angle to hit the easiest and most heat efficient rocks. If you are undertaking a new build or extension the borehole can be directly under your property, leaving no visible traces on the surface, and with the borehole manifold feeding straight into your heating systems, minimising heat loss.
You will need a proper survey by an experienced company as some rocks can also contain pockets of dangerous or poisonous gases. Unfortunately this technology has generated so many time-consuming domestic enquiries that several established survey companies now only deal with commercial buildings or larger groups of dwellings in housing association developments.
On a more commercial scale, even more energy can be recovered from some types of hot rocks such as granite deep beneath the earth’s surface. A seminar at The Geological Society in April this year heard that 10% of the UK’s electricity needs could be met from geothermal power from suitable heat bearing rock formations found in Cumbria, Derbyshire, Cornwall and County Durham.
A 3MW geothermal power station costing £18 million, which brings up water through a 3000m deep borehole at 160oC, generates electricity, then supplies much of the remaining energy as district heating and hot water to hundreds of local houses and university buildings has been running since November 2007 in the Rhineland area of Germany at Landau. A similar power plant has just been announced for the Eden Project in Cornwall, tapping into the underlying hot granite.
The Eden Project is based in an old clay quarry at Bodelva, near St Austell, but under the surface vast quantities of geothermal energy are stored in the rocks beneath the site. The developers plan to generate enough electricity to power the whole Eden project and sell any excess to the grid. The plant will produce heated water as well which will serve the tourist attraction, heat local homes and provide commercial opportunities for agricultural and farming businesses (or possibly even a shrimp farm).
The power plant at Eden will have two boreholes - one injection well and one production well, both around 3000-4000m deep. Water will be circulated between the bottoms of the two wells, where it will be heated by the hot rocks before returning to the surface at approximately 150ºC. There it will drive a turbine to create 3MW of electricity. The partnership expects the boreholes to be drilled and the plant to produce power by 2012.
Tim Smit, Eden Project chief executive, says "Powering the Eden Project site from a renewable source of energy is clearly a priority for us and we are very pleased to have the opportunity to bring our unique vision and environmental skills to the project alongside EGS Energy's experience and skills in engineering geothermal systems”.
Further information from the UK Heat Pump Network at the National Energy Centre, Davy Avenue, Knowhill, Milton Keynes MK5 8NG, tel: 01908 354545 at www.gshp.org.uk or the BRE Sustainable Energy Centre (BRESEC), Garston, Watford, WD25 9XX, tel: 01923 664500, www.heatpumpnet.org.uk or the International Energy Agency at www.heatpumpcentre.org
Box 1: Heat pumps: grants, equipment and installers
Domestic grants from the Low Carbon Buildings Programme for ground source heat pumps are £1,200 maximum or 30% of the eligible costs whichever is lower, provided you use registered suppliers, installers and equipment and your property meets the other renewables requirements such as loft insulation and double glazing.
The BERR website www.lowcarbonbuildings.org.uk lists over 80 grant approved installers for each region, but actually they are from all over the UK, which is frustrating. So for instance for the East Midlands it lists installers from the Shetlands and from Kent. It seems to give you exactly the same list as it did for air source heat pump installers, which is hardly confidence inspiring. Complicated weblinks and search clicks from there eventually track down the web address: http://www.microgenerationcertification.org/Home+and+Business+Owners/Microgeneration+Products which lets you find hundreds of certified models from over 40 ground source heat pump manufacturers.
Case Study 1
Ground Source Heat Pump: Smallholders Bea Hearne and Anthony Barnett have 30 acres with Devon Closewool sheep, Dartmoor ponies and 5 bed farmhouse at Cadleigh, Devon. A 5kW wind turbine and 9kW ground source heat pump runs their heating and hot water. Renewables costs: over £35,000.
Bea Hearne and Anthony Barnett completely renovated their 1920s built derelict farmhouse near Cadleigh, Devon, rebuilding it as a 5 bedroom, 4 bathroom home. It took them over 18 months, doing much of the backbreaking labour themselves and relying on their local legend, Bill Butt, a man with a digger, for the rest.
They installed a 5kW Iskra wind turbine on a 15 metre tower at a cost of £26,000 including groundworks, less a £2,500 grant. This should produce around 8,000-10,000 kWh every year, fed into the grid, providing them with a payback of 15p per unit (even if they use it themselves) from their electricity supplier Good Energy. Annual maintenance checks cost £300 and the turbine should last 25 years.
The wind turbine output runs their 9kW ground source heat pump from manufacturers Ice Energy which cost £7,000 less a £1,500 grant, plus their £2,000 DIY groundworks, materials and sand costs. The heat pump installed in their garage runs their £4,000 Nu-Heat underfloor heating system and 300 litre domestic hot water tank.
The ground loop part of the system was laid in June 2008 as 250 metres of coiled pipe, called a slinky, in two 60 metre long one metre deep and one metre wide trenches under a south facing field. The trenches were cut by Bill’s digger and lined with 10cm of sand, then the slinky pipe. Then Bea and Anthony raked by hand a further 50 tons of sand on top of the pipe from piles dumped into the trench by Bill, covering it evenly to a further 10cm, which Bea modestly describes as “one week of hard work”. The heat pump was added in one day in September 2008, and was operational the next day.
Their heat pump runs for an average of 5 hours a day in winter using 2.5kW electricity for underfloor heating, and needs no annual maintenance. The system will eventually have a reverse unit which could cool the house by 2-3 degrees in summer.
The heat pump and wind turbine combined should give them zero annual energy needs, and some income if their wind turbine output exceeds 8,000 kWh. The house also has a wood burning Rayburn used for some cooking, heating towel rails and supplementary hot water.
Renewable Energy: Where there’s muck, there’s brass: harnessing energy from waste
Part X in the SmallPower series by Myc Riggulsford (this is the longer first draft version of this article and may contain errors subsequently checked and corrected in the magazine at the proofreading stage)
Two million households in India use gas made from manure for cooking, and one million people in Nepal, about 4% of the population, rely on biogas made from animal, plant and human waste for their cooking and some lighting according to the Ashden Awards for sustainable energy.
A German town just north of Dortmund called Lünen is planning to one-third power itself from cow and horse manure and other farm waste through a biogas network which will generate 6.8MW of sustainable electricity for the 90,000 inhabitants. Manchester is going to convert the output from the UK’s second biggest sewage works to power 500 homes by 2011 and eventually up to 5,000 houses in a £4.3 million biogas scheme funded by the government and backed by United Utilities and National Grid.
Even some larger British farms are getting in on the act – the South West Regional Development Agency has already approved funding for six biogas producers or anaerobic digesters for farms which have tapped into the £119 million fund available before 2013, which is allocated regionally for livestock projects and top sliced, usually just for the big farmers, from our Single Farm Payments. So why is domestic biogas, a widely used smallholder technology around the world, hardly known in Britain?
The first recorded commercial use of biogas was in Exeter in 1895 where gas from a septic tank was used to run street lighting. Today’s biogas is usually a mixture of methane and carbon dioxide produced by the breakdown of living materials such as plants, sewerage and animal wastes by bacteria in the absence of oxygen.
The composition of biogas will vary depending upon how it is produced, what waste is decomposing, and the precise wet conditions that the bacteria are living in. Biogas is roughly a mixture of 60% methane, 39% carbon dioxide; nitrogen, ammonia, hydrogen, hydrogen sulphide and oxygen, with some water vapour, which will vary with the temperature, and since water still doesn’t burn, needs to be trapped.
In Britain biogas produced in wet conditions in sealed pressurised containers called anaerobic digesters by bacteria is almost the same composition as the natural gas fed through the gas mains system to households in towns and villages. It can run ordinary natural gas appliances such as central heating boilers or gas cookers. Some of the more polluting, dangerous or equipment-rotting gases such as the hydrogen sulphide need to be removed or absorbed before burning the biogas, but effective and fairly cheap filters will do this.
There are two different groups of micro-organisms that produce the methane in biogas. One group of bacteria works best at temperatures of 35-40°C, and a second group related to the extremophile archaea which live deep beneath the oceans near hot vents called black smokers work best at higher temperatures of 55-60°C. This gives us two different operational temperatures for biogas digesters. But basically either group of bugs could run your biodigester, you just need to keep the temperature fairly constant, which means filling the pit you put the tanks in with gravel and making sure it stays well drained as waterlogged ground will leak too much heat away.
The higher temperature systems break down the waste matter quicker – around two weeks at 50°C , where it would take two months at 15°C, so the hot systems produce gas faster. The higher temperature also sterilises any material which you take out for fertiliser, but you may need to heat the whole system to keep it operating efficiently in cold weather. However there are more types of bacteria which can operate at the lower temperature range, so these systems are probably more stable and tolerant of variations in the outside temperature, and since they will eventually produce almost the same amount of biogas from a given weight of waste input, the energy efficiency or energy balance may be better, you just have to be patient.
One kilogramme of biodegradeable material will produce around 4000 litres of biogas or 0.4m3. Gas lights need 100 litres per hour and two gas rings use around 1-2m3 every couple of hours. I’ve been calculating energy in kilowatt hours in my articles, so you can expect an energy output of 750kWh-1300kWh from each dry tonne of food waste and manure that you put into the digester, so you need about 5 tonnes every year per household.
To put it another way, we each produce about 90kg of faeces every year, and most urban people could add about three times that in wasted food, but if you have a few cows, pigs or horses you should be able to run a domestic sized system on the output from your farmhouse’s sewerage system, plus a wheelbarrow full of manure, grass cuttings, food waste and weeds every day.
After viewing one smallholder installation I’m convinced that this technology could be used much more widely. You could set up a system to burn the gas to heat water to drive a turbine to generate electricity, though there is quite a lot of energy efficiency loss in that sequence of conversions. Or you could run a domestic gas boiler for your heating and hot water. Or you could just run an ordinary gas cooker to burn the biogas directly.
The system I saw, which was just being commissioned, did leave me with some questions. If you have two tanks side by side: one sealed and currently producing gas, and one that you’re filling every day, what stops methane emissions from escaping into the atmosphere every time you open the loading tank while you’re filling the thing? Since methane is a greenhouse gas twenty times as powerful in effect as carbon dioxide, local authorities worry about the biogas emissions which leak from deep inside landfill sites and waste dumps all over our country, and we shouldn’t be making matters worse, though methane does break down fairly quickly in the atmosphere, unlike carbon dioxide. Also, what happens if you make more gas than your central heating system or cooker can burn? Likewise, what happens to your Sunday roast if the gas runs out - is it possible to have a backup?
Lastly, over my whole renewable energy series so far one inescapable fact has become apparent: most of these technologies, such as wind turbines or wood chip boilers, work better and more economically the bigger they are. So instead of us as smallholders all putting in our own biogas digesters, would we be better off subscribing to a district collection scheme for manure, farm and food waste and livestock slurries, so that enormous amounts of biogas can be safely and continuously produced by some sort of local authority and piped back to all our homes through the gas network?
My gut feeling in no, otherwise we’d have central control, central planning and politicians suggesting that we should build more spectacularly expensive and dangerous nuclear power stations instead, when we don’t know what to do with the nuclear waste we’ve already got (even if they do provide would-be despots with a constant supply of weapons grade nuclear warhead material as an accidental by-product). And we’re not on the gas network.
Case Study 1
Biogas: Engineering company finance director Graham Thompson and his wife Cheryle live in a barn conversion in Wembworthy, Devon, with 20 acres of pasture, 2 horses and 2 ponies. Their anaerobic digester system cost £12,000 including installation, plus an ordinary 2.6kW domestic gas boiler. They also have a Rayburn which can’t be converted to gas, and a propane gas cooker, which has the wrong type of burner for biogas.
Graham saw a biogas demonstration last year at the Devon County Show, and as their barn conversion was heated by oil decided to do something about their rising costs – last year they spent over £2,000 on heating oil alone for their underfloor heating and radiators (helped by a wood burning stove in the sitting room).
Their new waste digester sits in a large hole in the ground and is just being commissioned. Basically it’s a stomach. The two 4000 litre submarine shaped chambers are both plumbed in so that when one is digesting and making gas the other is being filled. Pressure in the chamber pushes the waste down and transfers any excess water to the other chamber. It’s a similar principle to old fashioned gasometers, with a static head pipe, and works at a pressure of 0.5 Bar or 14 PSI.
The digesters are dug into a pit some distance (about 20 metres from memory) from the house which minimises any smells as they are loaded daily from the compost and manure heap beside the chambers. Output from the house lavatories and sewage system, previously going to a sealed treatment plant buried in the garden, are now pumped up into the digesters as the system requires lots of water.
Graham and Cheryle fill one digester and then shut the valves to build up gas pressure. They then fill the other tank. Methane (CH4) is given off from the anaerobic bacteria process. The digester can take horse manure, grass clippings (up to 25%), and fully loaded each tank takes 10% dry matter or 400 litres of food waste, plants and manure. Any woody waste such as willow (they planted a willow screen around the digester and compost heap site) needs to be chewed up by macerator pumps in each chamber as the larger surface area then lets the bacteria do their digestion work quicker.
The system runs at 55oC as an exothermic reaction, and the heat kills any pathogens. A heat exchanger increases the efficiency of the gas made from 8% to 33%. The bacteria will eventually break down the waste to nothing, though some sludge could be taken off as fertiliser. Heavy metals sink to the bottom of the tanks, and eventually this waste may need to be removed.
The methane gas produced, which is exactly the same as natural gas, goes to feed the house boiler (which because it’s the same as natural gas can be any standard domestic house model). The gases given off are mainly pure methane; with some water, which is trapped, as water still doesn’t burn well; a little hydrogen sulphide (H2S) which would corrode the boiler so it is scrubbed from the system using an iron filings cartridge housed in a section of drainpipe; and carbon monoxide and carbon dioxide which is scrubbed using a slaked lime cartridge. The cartridges will need changing every 6-12 months.
The groundworks needed were a hole in the ground, excavated with a digger, 1.5m deep x 6m long to take the 4m long chambers, plus other parts such as the dosing chamber which drains off excess rainwater from the pit (which otherwise would lose chamber heat), sending it back into the chambers and any excess to a soakaway. When it rains the second tank fills from the bottom and a sump bails it out from the top to stop it overflowing (like a bilge pump). Convection currents inside the tanks circulate the material and liquid. All these pumps take a very small electric load – working for less than 5 hours in 7 days.
The system has practically no working parts to go wrong, so there are no annual maintenance costs for the anaerobic digester compared with the sewage system it replaced which needed constant electricity and servicing and maintenance. Graham plans to install a generator to turn excess gas into electricity which will be fed back into the grid.
Further information from Peter Webb at Solwind Energy 07933 55660 or 01271 883569 www.solwindenergy.co when he builds his website.
Case study 2
Fraddon Biopower: In a historic final judgement by Cornwall District Council before it was disbanded this year, farmers Ernie & Nick Dymond of Penare Farm in Fraddon, Cornwall got planning permission to build the UK’s first pig manure power station. Budget: £4 million.
The biogas power plant at Penare Farm in Higher Fraddon near Newquay will run on slurry and effluent waste from the farm’s 600 pigs, generating 844kW of electricity. This could power 1500 homes, and if affordable local houses are built later, a district heating scheme could heat up to 300 more homes using hot water generated as a by-product. The methane producing digesters will be fuelled by the farm’s pig farrowing and finishing unit’s effluent, mixed with 100 tons of food waste from local restaurants and food companies.
“The work should start on site in November 2009, but it has been a paperwork nightmare to raise the bank finances and comply with Environment Agency regulations”, says Russell Dodge of Business Location Services in Truro, the project’s planning consultants. “The environmental impact assessment and planning application have cost the farm £200,000 so far, and it was a great leap of faith for Ernie and Nick Dymond to invest this much in the hope of a successful bid”.
“The main problem facing pig farmers is new legislation for disposing of pig slurry, especially since this farm is right on the edge of the village but it cannot go into the mains sewerage. These increasing costs could have killed the farm within a couple of years anyway. All pig farmers are operating on very tight margins and low profitability as it is. This project will save the farm. But before we can raise the finances from banks and regeneration grants we must have minimum 5 year contracts with food waste producers, so that we have a guaranteed stream of waste to dilute the pig effluent, which is otherwise too wet to work the digesters” says Russell Dodge.
In Germany, where biogas power plants are established technology, farmers grow maize as feedstock for electricity generation, but this simply isn’t practical in Cornwall. The economics of the power plant rely on charging a fee of about £40 a tonne for disposing of the food waste – which currently costs the restaurants far more in landfill taxes.
Grants: although the Low Carbon Buildings programme seems to recognise the existence of biogas it doesn’t offer any grants or installer and product lists through its websites. Your best bet may be to talk to Defra or BERR directly. July’s renewables feed-in tariff proposals from the Department of Energy and Climate Change (now consulting) may offer incentives.
Renewable Energy: Biofuels: From Deep Fat Fryer to Biodiesel
Part XI in the SmallPower series by Myc Riggulsford
Ordinary vegetable oils such as used chip pan fat can run domestic boilers for heating or be converted to diesel for tractors, Landrovers and other vehicles. But using vegetable oils in their raw state is usually a mistake as they are much stickier than fossil fuels, particularly at low temperatures, and have impurities which could corrode your engine.
Oils and fats can be upgraded using a simple chemical process called transesterification. This typically means treating the fat with methanol over a strong alkaline such as caustic soda (sodium hydroxide) as a catalyst, making biodiesel and glycerol as a by-product. The biodiesel can be used directly in diesel engines or mixed with traditional fossil diesel as a blend.
In the same way bioethanol can be blended with petrol to run an ordinary car or quad bike. Bioethanol is usually made by fermenting a high sugar plants such as sugar beet or sugar cane, or starchy grains such as maize and wheat. Currently about half of Brazil’s sugar cane goes into making bioethanol, which is a high energy fuel, and very much better environmentally than making biodiesel from soy. Growing GM-free soya beans is causing most of the recent increase in destruction of the Amazon rainforest, overtaking cattle ranching and logging, which is embarrassing for vegans who drink soy milk.
In environmental terms the greenhouse gas balance is quite poor for some biofuels, according to Dr Patricia Thornley from the Tyndall Centre for Climate Change in Manchester, who says “Saving only 50% of the normal carbon output of fossil fuels is not uncommon and some fuels may not result in any net carbon savings at all”.
This is because the sugar beet and cereals still need ploughing, planting, harvesting, transporting and processing. Most farmers use fossil based fuels such as red diesel to run their tractors, and there are enormous greenhouse gas costs in producing and spreading the fertilisers typically applied to commodity crops like wheat and maize.
Making biofuels from grains that are also food means that people from rich countries will buy up corn to feed their cars, while prices of bread, tortillas and pasta are pushed up for poor peoples. Land will go from food to fuel production, increasing world hunger. On the other hand, waste materials such as used cooking oil and animal fats like tallow could be turned into biodiesel, avoiding rubbish disposal or landfill.
Making bioethanol and biodiesel currently costs more than drilling for fossil oil, though tax advantages and carbon credits could encourage biorefineries. In the short term farmers can usefully convert surplus or poor quality oil seed rape and similar crops into biodiesel. But on a commercial scale most of the feedstock will need to be imported, with little benefit for British farmers, and because of the capital costs, smallholders cannot economically make their own fuel from home grown oil or grain.
Until recently biodiesel was priced at 20p per litre duty below conventional diesel, so even small producers still had to keep records and voluntarily send a cheque for the rest of the duty to the Treasury. Home made biodiesel was just cheaper than petrol station bought fuel, but more expensive than red diesel. It was uneconomic for large refiners to import feedstock for conversion.
But since 1 July 2007, according to HM Revenue & Customs, producers of less than 2,500 litres of biodiesel a year have not had to register their premises, make returns or pay excise duty on their fuel. So if you’ve got a cheap or free source of oil, such as used chip fat from your local pub, it’s now much cheaper but quite time consuming to make domestic quantities of biodiesel. Tax queries should be directed to the National Advice Service on 0845 010 9000, quoting Revenue & Customs Brief 37/07.
Next month: Combined Heat & Power or going Nuclear. To comment on Country Smallholding’s renewable energy series contact Myc Riggulsford at email@example.com.
Case Study: Chip Fat Fuel
Robin & Ann Hampshire, West Brushford, Devon. Three bedroom farmhouse with granny flat and 15 acres, 12 black rock chickens and Ann’s agility competition dogs. Renewables: biodiesel conversion plant cost £1500.
When Robin Hampshire was chairman of Devon Association of Small Holders, he and I hatched a plot to find out about alternative energy. We organised two seminars and each day I interviewed eight different technology suppliers in front of an 80 strong audience, backed up with a mini trade fair.
I replaced our oil heating with a log boiler and solar panels; Robin bought a prototype kit from Greenfuels to convert batches of 40 litres of used chip fat into biodiesel for £950. For this Robin got a recipe, a basic conversion plant of a pump, some processing tanks and a heater.
Step1: Strain your 40 litres of used chip oil into a drum to settle for 24 hours. Drain off water and solids through a valve at the bottom.
Step2: Pump the vegetable oil into the heating tank where it is stirred and warmed to 55oC, which takes about 4 hours in winter, 2 hours in summer. The 3kW heater runs off a normal 13amp plug and uses about 6 units of electricity, cost 80p.
Step 3: The oil is next pumped to a mixing tank for 30 minutes where 200g caustic soda and 4 litres of methanol are added. Robin substitutes potassium hydroxide for caustic soda as it is more environmentally friendly. Leave the mixture to settle for the rest of the day. Costs: 20p for 200g, (25kg potassium hydroxide is £25); methanol is £50 for 200 litres plus delivery charge of £20, so methanol cost per batch is £1.40.
Step 4: Glycerine by-product settles out of the tank and is bled off through a pipe at the bottom. Each batch makes about 4 litres of glycerine or 10% by volume. Because Robin is using potassium hydroxide not sodium hydroxide the waste glycerine can safely be spread on weeds in the vegetable patch or onto their compost heap and left to biodegrade. If you use caustic soda, and the temperature drops in winter, the oil quickly solidifies and gunges up the outlet pipe. Robin uses an infrared thermometer, costing about £40 from Screwfix, which he can just point at the tanks.
Step 5: The biofuel is now washed with a fine water spray from above while air is bubbled through from underneath using a standard pond aerator. The biofuel is clean when it stops being opaque and turns clear. Depending upon the quality of the original oil, this stage takes around 4 hours at 40 minutes per wash, repeated several times. Robin then leaves the air pump running for a couple of hours to encourage the last emulsified water droplets to separate out of the fuel.
Step 6: Since Robin doesn’t always want to fill his Landrover when he makes biodiesel he pumps the finished batch up into a holding tank outside his workshop, which fills his vehicle by gravity when needed. The whole process has taken about 2 hours of his time during a 48 hour period, and costs about £2.40 per batch of 40 litres or 6p a litre, plus his time and any costs for collecting the chip fat.
“To get the full value of making your own fuel you need to keep below 2,500 litres a year, so that you pay no duty whatsoever”, says Robin Hampshire. “If you make 2,501 litres you pay fuel duty on the whole lot. Since June 2007, although I still have to keep records for Revenue & Customs, I don’t have to send them anywhere”.
Robin recommends that you find your free oil before you commit yourself to investing in a biodiesel conversion kit. “Chip fat oil is now becoming difficult to find, so make sure that you have got a good, reliable, regular supply” he says. “The oil must not be too tired out or used for weeks and then left outside in the air before you collect it”.
Oil that has had a lot of frozen food fried in it also contains a lot of emulsified water, which is difficult to clean up, according to Robin Hampshire. Pre-prepared chips which are then deep fried are fine, as this water separates out in the settling stage. But the more water that is emulsified into the oil, the more chemicals and time it will take to clean it up.
“I am very, very pleased with my system”, says Robin, “But I have recently been through a shortage of chip fat. I now get my oil from a large organisation in Exeter with its own kitchens, in exchange for some duck eggs, which I buy from a neighbour. It’s all part of the rural economy. On this system it means a litre of diesel oil costs me about 10p”.
Robin’s kit paid for itself very quickly after his initial outlay of £1,500 and now saves him £2,000 a year. But beware of trying to make biodiesel commercially. “If you pay for raw oil, and duty and VAT, and you have to buy the equipment, then you’ll very quickly find that the price is the same as diesel” says Robin Hampshire.