We are moving to rural France in a year or so, and in order to keep costs down (we will be "nearly pensioners") I want to design a system which will incorporate the benefits of a compost heating system (sited in a greenhouse) with a solar water heater.We anticipate having an acre or two of land for growing vegetables and especially grass cuttings for the compost heap.
My idea is to use an old hot water cylinder with a secondary heating coil (copper) inside. The water in the cylinder would be heated by the compost, and the water in the secondary system (to heat old/2nd hand radiators) by a solar heater. A small pump (solar/battery powered?) in each circuit would ensure even heat distribution and enough pressure for a shower or bath.The secondary water system would need to be "treated" to prevent scaling.I would also put in an immersion heater connected to the mains for really cold weather.
The compost heater would need to be wide enough and deep enough to heat the water, but in any case the solar water heater circuit should help boost overall temperature.
I read about a system like this many years ago in an early US alternative energy magazine.I have read recently of others using coils of plastic pipe 1 1/2" diameter in a compost heap with excellent results, but I think if you can get hold of a HWC it makes connections easier and more manageable. Using different metals could cause other problems!
I would be grateful for comments,suggestions, potential problems etc.
You can post on the blog or directly to me at johnwinlow@talktalk.net
Thanks