The green energy opportunities of farm waste have been interesting farmers for some years. Modern agriculture produces considerable quantities of slurry which has been stored and spread on the land as required, where of course it has continued to play its part in the cycle of production – saving costs and contributing to efficiency.
Alistair Fell of H&H Renewables
Now, thanks to pioneering work by engineers, a breakthrough in the production of biogas using small scale slurry digesters has been achieved, reports Alistair Fell of H&H Renewables, in Carlisle.
Slurry has always held a latent fascination as a potential source of fuel and has been used as such in sewage treatment works in Britain for years, however farm manure has been impractical to recover in any usable way – until, that is, the Feed-in-Tariff was introduced making it financially viable to produce biogas on farms.
Enthusiasm for anaerobic digesters [AD] was quick to bubble forth – especially as energy costs rose, and controversy began to engulf the previously untarnished image of that other form of wind energy!
In an AD plant feedstock (silage, food waste, slurry etc) goes in at one end, and methane gas is produced at the other. The use of AD on farms has been practiced in Europe for over 20 years and it is a well proven technology. The key problem is the cost of developing large scale AD, often in the range of £1-2M.
But though farmers sought other diversification opportunities to produce energy, engineers continued to work on the problem making the AD plants smaller and cheaper. Alastair Fell now reports that a breakthrough has been achieved. “There is now a commercially viable digester available on a scale small enough to work on the average farm. So at a cost of between £150K and £750K, the price begins to smell sweet as well.”
“The new design has other advantages. The 1st generation of digesters required slurry mixed with silage and maize to produce methane. The latest plants will now operate using 100% slurry – and using only the bacterial action inside the digester, give a healthy supply of gas which then can be fed to a turbine that produces free electricity. When the slurry has exhausted its potential as a source of methane, it can then take its traditional place as a fertiliser on the land.”
Alistair points out the advantages to farmers: “This means that a farmer with 150 dairy cattle, or a sizeable pig or poultry unit, can recycle 100% of their slurry to produce free electricity or heat and achieve very attractive financial returns. And with a small amount of silage added, even more energy is obtained from the digester.”
“Here at H&H Land and Property we are working with digesters suitable for between 35 and 150KW schemes – which are considerably smaller than conventional plants. The lower capital costs are easier to finance. In addition, the Government is supporting AD, and, in fact, has increased the feed in tariffs for farm AD schemes, whilst they have reduced the FITs for most other technologies.”
Alistair confidently sees AD as the way forward “not only for agriculture but for community organisations and commercial operations. We are also working on larger scale schemes of between 500kW and 5MW.”
He reports interest already from famers who previously turned down the expensive large scale digester proposals. “We are ideally placed to help anyone who wishes to explore the nature and potential of an AD scheme. We start with a feasibility study which includes a full cost analysis for the business or group concerned. We look at the existing farming operation and try to design a scheme that is sustainable and not rely on a complete change in the farming set up. We can handle the whole process from initial consultation through to commissioning.
After that, he concludes, it couldn’t be easier. “Slurry and silage go in at one end, with no oxygen, and the bacteria do their work, breaking down the slurry into Methane, which is used in a gas turbine to produce your cost free electricity and heat. Your slurry ends up on the land as fertiliser, as usual, when it’s all over.”
If you are interested in the workings of a scheme for your own farm or organisation, contact Alastair at H&H Land and Property on 01228 406 260.
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