Stephen Temple, Director of JF Temple & Son Ltd, small scale, Norfolk
The 550ac mixed dairy & arable farm operates a 170kW plant. The plant takes slurry from our 100 milking cows, whey from our cheesemaking, lower quality maize silage (leaving the best for the cows), energy beet and wholecrop.
We needed to comply with NVZ restrictions on dairy slurry which were being introduced at the time, and wanted to ensure some financial return on the investment. We also had a heat requirement which AD could satisfy.
Having self-financed the plant for £750,000, capital costs certainly proved a challenge.
Environmental Agency permitting (particularly with respect to retrospective changes).
The cost & logistical complexities involved with grid connections.
Almost every part of plant has had to be modified or replaced to achieve reliable operation. As one of the pioneering on-farm AD models, we relied on professional engineering expertise on site to ensure that the plant remain efficiently operational. These initial technical niggles are, however, something which more recent systems should have ironed out.
Making AD work:
We utilise as much heat from the CHP as possible for: grain drying; dairy hot water; cheesemaking process heat; heating the farmhouse and 3 farm cottages; and warm drinking water for cows. It is fully integrated into our farming system, utilising all digestate as fertiliser. We are constrained by planning restrictions and permitting to sourcing all feedstock from our farm.
Advice to farmers considering AD:
Talk to as many operators with similar size plants, with similar feedstock, as possible before making any commitment. Talk to those who have been maintaining the proposed equipment for some time before accepting the equipment in your installation.
Ensure the plant is designed for ease of maintenance and access to all powered machinery, also ease of washdown and cleanup after maintenance activities (as simple a thing as ensuring that all
concrete areas fall to a drain where small spillages can be collected.)
Adopt a plant design which could accommodate the worst possible failure – for example, if the tank or pipework (above or below ground) fails? Could the plant manage flammable and toxic (hydrogen sulphide) gas leaks?
Finally, plan to make best use of digestate – store to ensure that it’s used at the optimal time of year. Also digestate could be pumped underground to point of use so as to reduce tractor traffic and cost. Integrate the system into the farming operation.
What would we have done differently:
We have learnt so much about physically handling the feedstock; had we understood this earlier we would have saved a lot of redesign.