Chapter 5 of "Short Circuit" - page 3
Unfortunately, rather than investigating how wind projects could be structured on Danish lines so that no branch manager was asked to make a single loan of more than £200,000 but made lots of smaller ones to individuals, Mercury decided to set up The Wind Fund plc in partnership with a Dutch bank, Triodos, with which it later merged, to raise £5m. to provide share capital to windfarms. "We found that share capital was even harder to obtain than bank loans" Glen Saunders, a Mercury director, told me, explaining that Mercury would be providing part of the bank loans that The Wind Fund projects required itself and that he was confident that other banks would put up the rest. The initial rate of return required by The Wind Fund is over 12.5% and projections in its prospectus show this rising to 48% within 15 years. Community projects should therefore look for finance elsewhere.
A young German, Reiner Eschwey, announced at one of the meetings that he was already measuring windspeeds at Drumlough. He joined the co-op and the data from his instruments were given to a US firm, New World Power, which agreed to give the co-op a seat on its board and 1% of the revenue from a £5m. windfarm it is to build there. The co-op has also had discussions with two companies which use of £10,000-worth of electricity a year to keep potatoes in cold storage and McWilliams is optimistic the cost-benefit figures are good enough to ensure that at least one of them will install a windturbine to cut its consumption from the mains.
Besides publishing a detailed assessment of the prospects for developing several types of renewable energy in Inishowen16 , the co-op has investigated two small hydropower sites and, in association with the county council, the prospects for growing coppiced willow and chipping it to heat a proposed community education centre. "As a result of our contacts with the county council, they are already thinking about how they can become more involved in energy self reliance and are looking at plans for an energy-efficient housing project" Williams says.Click for 2003 update
Inishowen's wind energy potential is exceptional and most places will probably find, like Hatherleigh, that biomass (plants and plant residues) is their most promising renewable energy resource. In all probability too, they will decide it makes sense for them to explore how they can turn their existing agricultural and forestry waste into useful energy before examining whether they should grow plants specially for energy as well. In Britain and Ireland, forest and sawmill residue, animal dung and cereal straw are the most common plant wastes with good energy potential while willows and poplars are the species most likely to be planted for fuel.
Straw
In a sustainable agricultural system involving mixed (i.e. arable and
pasture) farming, it is doubtful if significant quantities of straw would
ever be available for use as fuel because it would be used for feeding and
bedding animals before being composted in a biogas digester. Many organic
farms outside the main cereal-growing areas already it difficult or
expensive to get supplies. However, in the prairie-lands of the East of
England under the present unsustainable system of agriculture, every four
tonnes of grain harvested by the combine leaves two tonnes of straw in the
field with the energy equivalent of a tonne of coal. About 12 million tonnes
of straw is produced there each year and since only half of this is fed to
animals or used for their bedding, this leaves a surplus of some 6m. tonnes.
Although this contains calories equivalent to about 1% of the UK's total
energy consumption until the law was changed recently it was burned off in
the fields largely because it is unsuitable for large-scale, centralised
power producers as it is bulky even when baled and therefore expensive to
transport far. Consequently, if straw is to be burned for energy, it has to
be exploited on a local basis.
In any case, burning straw needs a special furnace because, like other types of biomass, 70% of it becomes a gas when heated, and a mixture of ash and char is left which will only burn if more oxygen is made available. This characteristic makes it suitable for combustion in the gasifiers we will be discussing later but despite this, most of the research in Britain has been into ways in which it can be used to replace coal in standard furnaces. Two approaches have been developed. One is to chop it into short lengths and blow it in on top of the burning coal. The second is to turn it into 'wafers' (pellets) so that it can be handled by conventional automatic stoking systems and replace coal entirely. This latter process may 'expand the use of straw as a fuel into the rural industrial markets and perhaps even into the domestic market' according to an official Energy Technology Support Unit report17 .
There have been several commercially successful demonstrations of the use of straw as fuel in Britain. Two hospitals in Birmingham, the Queen Elizabeth and the General, blew it into their boilers and cut their coal consumption by half. Woburn Abbey has a furnace which consumes 400 tonnes of straw bales a year to heat the main buildings. And an Ipswich company, Needham Chalks, is using 2,000 tonnes of straw a year to dry up to 45 tonnes of chalk an hour18 .
However, as in other renewable energy areas, it is the Danes who have shown what really can be done. 12,000 Danish farms have straw-burning boilers and the first straw-fired district heating system was built in 1979. Fourteen years later there were sixty throughout the country, many in places where no district heating system had existed before so that pipes had to be run to take heat to the houses. "Even plants as small as 2MJ/s, corresponding to roughly 200 single family houses are economic" Dr. Jørgen Boldt of the Danish Energy Agency told a conference in Helsinki in 1993 19. "The plants are reliable and have an efficiency of 80-90%, which is comparable with coalfired ones, and they generate less pollution. They are economically competitive too. The initial and operating costs are higher than for oil-fired plants but the fuel costs are lower, even ignoring the energy tax. (The Danish government has imposed a tax on oil to cover some of the environmental damage its combustion causes. The amount of the tax rises whenever the world price of oil falls, and falls when it rises so that the consumer pays a near-constant price.) The combined effect of the energy tax and government grants towards the capital cost of renewable energy projects was to make district heating with straw 20% cheaper than with oil, Boldt said. Nevertheless, only a fifth of the surplus straw was being burned in 1992; but when the resource is fully developed it will provide 7% of Denmark's energy. (Click for 2002 update by Caroline Whyte)
Forest Waste
About a third of the total above-ground mass of a conifer never
reaches the sawmill but is normally left to rot on the forest floor.
However, this residue can be burned as fuel, as can the early thinnings too
small for pulping or chipboard manufacture which are produced by some modern
forestry systems. In Sweden, both types of waste are normally left where
they fall to dry out naturally during the summer months before being chipped
in the forest and taken away to complete the drying process under cover.
From then on they can be treated exactly like chips produced in the
specially-grown plantations we will be discussing shortly. However, two
points need to be considered by any community considering this resource. One
is that, like straw, wood chips are bulky, and so need to be burned close to
the forest. The second is that while the trunk of a tree is very little more
than a combination of water and carbon dioxide, its leaves and small
branches contain most of the minerals it has extracted from the soil during
its life - which is why leaf mould is so good for the garden. Consequently,
if leaves and twigs are taken away, the forest will lose nutrients and,
unless these are replaced or returned, it will become less fertile. In other
words, the burning of forest waste will not be sustainable unless the ash is
returned. All forms of biomass energy share this nutrient-loss problem to a
greater or lesser extent.
Animal Dung
Surprisingly, a cow extracts only 10-15% of the energy in the
grass she eats. The rest is passed out in her dung, a fact which explains
why slurry (the mixture of dung and urine which collects in tanks or
'lagoons' near the sheds with slatted floors in which most cattle now spend
their winters) can be so damaging if it gets into streams accidentally. Its
high energy content means that a lot of oxygen is absorbed when it breaks
down and if the oxygen is taken from the water in a river, too little can be
left for the fish and they drown.
"A medium-sized cattle house produces about 33 tonnes of beef a year - and 3,000 tonnes of slurry" says Les Gornall, who has been working on ways of extracting the energy from slurry in association with the University of Ulster at Coleraine in Northern Ireland since 1978. "[That amount of slurry] contains methane of at least the value of the beef together with 300 tonnes of fibrous matter which is almost all carbon and as good as 300 tonnes of best anthracite. But at the moment, farmers concentrate on those two lorry loads of beef and throw away the 30 lorry loads of coal."
Gornall set out to develop a system which would allow slurry to decay in the absence of air to produce a methane-rich gas which could be burned as a fuel. This was scarcely new. The Italian scientist, Count Volta, had shown that methane was given off by decaying vegetation in 1776 and by the time Gornall started work, the Indian and Chinese governments already had major programmes under way building digesters - tanks in which animal, human and plant waste rotted to produce gas for cooking purposes - in tens of thousands of villages. But these were countries in which labour was cheap and higher temperatures enabled decay to proceed more rapidly. What Gornall and a number of other workers in Europe were hoping to develop were digesters which were reliable and cheap enough to be attractive to individual farmers in temperate climates with high labour costs.
His first big success came in 1984 when he won a contract to install a digester to handle the slurry from 300 cattle kept by the Cistercian monks of Bethlehem Abbey at Portglenone in Co. Antrim. The gas was piped to the abbey itself to fire the central heating system; the fibrous residue was composted and sold for horticulture and the remaining liquid was sprayed on the abbey's land. This returned most of the nutrients in the dung to the soil, eliminating the need for chemical fertilisers and allowing the monks' system of organic farming to continue. A problem waste became an asset worth £60,000 a year.
Work on farm-scale digesters was going on simultaneously in Denmark but results from the forty-odd farms on which they were installed were disappointing. This was partly because the digesters themselves were inadequate but mainly because the farmers gave attending to them very low priority: they always felt they had something more important to do. As a result, three-quarters of the prototypes fell out of use fairly quickly and the national effort shifted to developing bigger digesters which could serve several farms and thus warrant a full-time manager. These centralised digesters had the added advantage of taking less capital to build per farm served and being better able to meet steadily rising environmental standards. The first was built at Vester Hjermitslev in the extreme northwest of Jutland in 1984, and ten years later fifteen centralised digesters were in operation and another five planned or under construction. Nevertheless, Denmark was exploiting only about 3% of its biogas resource and only one of the first nine plants had achieved a break-even income. Despite this, a 1992 Danish Energy Agency report concluded that if the lessons from the existing plants was incorporated into new ones they would be profitable without state grants provided Denmark's taxes on fossil energy were maintained 20.This seems to have been borne out by a digester at Hashøj, southwest of Copenhagen, which opened in May 1994 and which had significantly lower capital costs and extracted more gas from its slurry than its predecessors. However, had such 'poor' initial results been obtained in most other countries, detractors would have had a field day and the effort would have been abandoned as a flop. Instead, the Danes learned from their experiences and, by now, have gone through five cycles of designing, building and testing.
So far, centralised co-operatively-owned digesters have not reached the British Isles but that statement will be out of date by 1998 if Mary O'Donnell's efforts bear fruit. Mary, who is married with a grown family, was one of the founders of Earthwatch, the Irish arm of Friends of the Earth. In 1991, she had left the organisation and was looking for an activity, preferably in the environmental area, which would create jobs in West Cork where she lives. She and her husband Jim, who runs a furniture manufacturing business, had been working with Jerry O'Sullivan, the manager of the West Cork Institute for Rural Development of which Jim was chairman, investigating the possibility of setting up a factory to build modular farm-scale methane digesters using technology developed by Professor Martin Newell of University College, Galway. However, during an environmental conference she had helped organise in Skibbereen, her local town, she was advised to take another direction. "It was one of those discussions which take place out on the street at three in the morning after the pubs have closed" she says. "I was with Richard Byrne from the Danish company Krüger-Bigadan A/S, one of the leading designers of biogas plants and Iain Maclean, then Cork County Council's environmental officer and now the head of Ireland's national Environmental Protection Agency. 'Forget about farm scale, Mary,' Richard said, telling me about the problems that had arisen in Denmark. 'Go for centralised digesters.'"
And so she did. She knew Kieran McGowan, the head of the Industrial Development Authority (IDA) from the time he had worked for the Crafts Council of Ireland and rang him up to arrange a meeting at which she told him about her plan to turn waste into a resource. Why aren't these digesters used already? McGowan asked, and after she had told him he promised a £15,000 grant towards a feasibility study. This sounded wonderful but IDA grants present problems because they cover a maximum of half of the cost of a study and are only disbursed against receipted invoices after the costs have been paid. Where was she to get the money she had to spend to be able to collect the grant?
The West Cork Institute formed a special company, West Cork Biogas Ltd. to carry out the feasibility study and Mary became its project director. Skibbereen's credit union and its two banks gave the new firm £2,500, the Institute provided it with office space and gave the rent back as their contribution. Other people sent office equipment. Her husband's furniture business paid her salary in a way which enabled it to be considered as part of the £15,000 needed to match the IDA grant. Three years later, as this book went to press, her feasibility study had convinced Cork County Council and a local farmers' co-operative, Drimagh, to put up a further £30,000 between them to employ consultants to take the project through to the construction stage.
"We've mapped the potential sources of waste within 10km of the proposed site" she told me. "There are sixty dairy and pig farms and we will be taking paunch contents from a slaughter house. 80% of the material going into digester will be slurry. The rest will be sorted household waste, sewage sludge - that's great for gas making - and residues from a cheese factory. The County Manager has promised to bring forward the construction of sewage treatment plants in the small towns in the area so that we can get the sludge. We've already started mapping for a similar plant in the north of the county and we'll move to the east later."
In O'Donnell's proposal, the gas from the digester will be used to generate electricity and the heat from the engine's exhaust piped to greenhouses. Some of the fibre will be composted and sold to gardeners and the rest will be mixed with wood chips and briquetted to be sold as a domestic fuel. The liquid from the digester will go back to the farmers' land, as it does at Bethlehem Abbey.
"Spraying digester liquor on the land is much better for the farmer than spreading slurry because, as it does not contain fibres, it can be sprayed over the whole farm, including growing grass," she says. Moreover, because its nitrogen content is readily absorbed by the plants, farmers have been able to cut their nitrogenous fertiliser purchases by over half.
"There's much less risk of pollution" O'Donnell says. "Farmers often have to spread slurry in wet weather because their tanks are overflowing and the streams suffer the run-off. But if there is a digester in the area, the slurry can be collected, treated, and the de-gassed liquor delivered back to them when and where they want it. The biggest advantage of the liquor, however, is that unlike slurry, it contains no weed seeds and no pathogens and there's less recycling of intestinal bugs. Studies of farms using it show their vets' bills are significantly down." Other studies have shown higher milk yields, less lameness ,increased animal fertility and a longer grazing season. Grain crops sprayed with liquor are less liable to lodging.
O'Donnell cannot praise the Danish Energy Agency and the Agricultural Economics Institute21 highly enough for the help she received. "They publish regular updates on technology in English and have spent an extraordinary amount of time answering questions on every aspect of the project," she says, adding that the West Cork digester project could easily be replicated elsewhere and that she and Les Gornall are working together on proposals for one at Castlederg in County Tyrone. These involve the construction of a 1MW biogas-fired power station which will take slurry from two large farms with 3000 cattle between them. However, O'Donnell and Gornall hope that smaller farmers will want to participate too. "I knew at the outset that this was a five-year project" O'Donnell says. "It's still just bits of paper but there's still two years to go."
Growing special energy crops
While it certainly makes sense to use waste
products like farm slurry or surplus straw to produce electricity or heat a
house, is it equally sensible to grow crops such as oilseed rape (canola) or
coppice willow as a source of power and heat? Industrial agriculture is now
so energy intensive and the price signals given to the market system are so
distorted by subsidies that it could easily be commercially attractive to
use more fossil energy to grow energy crops than can be usefully recovered
when they burn.
Just how easily is illustrated by rape oil, which although it has a very poor energy-in/energy-out ratio, has been the subject of many demonstration projects to show how successfully it can used to replace diesel fuel - for example, a treated version of it as used to run part of Reading's bus fleet recently and in Ireland it powers food delivery vans in Waterford. But according to a study prepared for the British Department of Trade and Industry's Energy Technology Support Unit (ETSU) in 1992, growing rape purely for oil to turn into biodiesel produces only 35% more energy than the farmer puts in, a return which makes the effort a nonsense 22. If the rest of the plant is used for energy too, the ratio naturally improves but the plant's performance is still very poor and a 1990 Irish study, Liquid Fuels from Conventional Agricultural Crops, found that more external energy was needed to produce a litre of rape oil than the equivalent amount of any other crop-based liquid fuel it investigated. Ethyl alcohol from sugar beet proved a much better proposition in both energy and commercial terms as the bi-products of the process were very valuable 23. A German study found that using biodiesel in a vehicle would cut its greenhouse gas emissions by only 25% and that this gain had to be set against the damage done to the soil and the environment generally by the chemicals used to grow the crop 24.
Yet in spite of rape oil's poor showing, governments have been urged by farming groups to provide subsidies to make its production and sale commercially viable. "Rape seed oil is competitive with diesel fuel provided the EC crushing subsidy is available" another Irish report said in 1991, arguing that as the subsidy was equivalent to 70% of the cost producing the rape seed and the farmer could sell the extraction residue as cattle food for another 45%, he or she would be able to sell the oil for 10p per litre, the cost of extracting it, and match the pre-tax-and-duty price of diesel fuel at the time 25.
The coppicing of fast-growing trees like poplar and willow produces a much more favourable fossil-energy in/renewable-energy out ratio. According to Caroline Foster of ETSU, this type of short-rotation can give thirty times as much energy in the form of dry woodchips as was used to produce them 26. However, a lot depends on how well the crop grows and is managed, and it is generally accepted that a more realistic ratio is one to twenty. Foster's analysis not only took in the energy used to fence and plough the land, plant the crop, protect it from weed and fungal infestation with chemicals, cut it, stack it to dry, chip it and then transport the chips to the power plant, but also that which went into building the drying shed and a share of the amount used to build the tractor and other equipment.
Unfortunately, not all the energy in the wood chips can be extracted as useful power. The most efficient way to use them is to turn them to gas in a gasifier (which burns some of the chips to heat the rest and convert their volatiles into gas) and then burn the gas itself in an engine which powers a generator. This process allows about 60% of the energy in the chips to be captured, one third as electricity, two-thirds as heat. In other words, the overall outcome of growing willow, chipping it, drying it and burning it in a gasifier has been to promote one unit of a high-grade form of energy like diesel oil to about four units of a higher grade of energy, electricity, and 8 units of relatively low-grade energy, heat suitable for warming rooms.
Coppiced woodchip production is therefore only worthwhile if all the heat can be used, a fact well known to Malcolm Dawson who has been involved in the effort to turn specially-grown willows into useful energy for longer than perhaps anyone in the British Isles. Dawson works at the Horticultural Centre at Loughgall in Northern Ireland where experiments have been carried out since 1974. Under the system which has evolved, short lengths of fast-growing willow are pushed into a ploughed and weedkiller-treated field a metre by half a metre apart. They root and sprout and after three years, the long, thin shoots are cut and bundled by a special harvester attached to the back of a tractor, and the stumps left in the field to provide another crop. The bundles of willow wands contain 50% moisture when cut and are allowed to dry for three months in the open before being taken to a covered storage area where they are chipped. Drying continues - using exhaust heat from the generator-engine in the final stages - until the moisture content falls below 15% and the chips can be satisfactorily gasified. On average, each hectare of willow coppice produces the energy equivalent of 6 tonnes of oil a year. The highest yields are obtained if several willow species are grown together as this gives better protection against pests and disease and each type has slightly different requirements from the soil.
Dawson says that Northern Ireland has 200,000 hectares of rush-ridden rough grazing which would be ideal for willow coppice and he would like to see farmers' co-operatives set up to provide both electricity and heat to colleges, hospitals and factories in the province. "Two thirds of the energy in the willow is released as heat so you've got to have a use for that to make this operation attractive. You've also got to be able to displace electricity bought at retail prices rather than just selling it wholesale to the grid" he says. He therefore sees the farmers' co-ops installing gasifiers and generators on clients' premises and running them under contract. "The farmers will only get the maximum value-added if they do the whole thing in-house. Willow needs to be grown on a collective basis because the farms around here aren't big enough to supply a gasifier alone and it makes sense to use the harvesting equipment on more than one farm."
Dawson has been running a 100kW gasifier and a generator at Loughgall for several years to heat and light an agricultural college and a number of greenhouses and feels that the technology is now advanced enough for a demonstration project in an institution to go ahead, especially as woodchips have also proved themselves as a source of heat and light in many communities in Sweden which pipe the heat from house to house. I agree. When he arranged for the gasifier to be demonstrated to me, I was surprised how quickly it began to make gas when starting from cold and how simple a device it was. Any competent welding shop ought to be able to make one.
Unfortunately, few farmers with suitable land seem to be interested in getting involved in producing wood chips because of subsidies for suckler cows and sheep. "They are getting direct EC grants worth £300/hectare. If we had that level of subsidy for short rotation forestry we'd be flying" Dawson says. As a result, if he can get a demonstration project under way as he hopes, the coppice is likely to be planted by non-farming landowners.
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