Thoughts I had are similar to a cylinder except instead of internal coils have wrap around container coils. I expect the heat to be very low grade though. What is the internal temp of manure stacked in say a volume of a 40,000 litre tank for example? My estimate is that it would need a temperature of at least 60/70°. The transfer of heat from a solid? To a liquid would see a huge temperature loss?Its just finding an really good way of siting the pipework in , or under the muck ,without wrecking it all afterwards, when the mucks done its heating ?
Probably a few people have tried it