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Many people outside the tropics would like to make biogas at home. I am one of them. Can we do it without having a farm? Making biogas outside the tropics has a problem. The bacteria are most productive at tropical temperatures. It is hard to achieve this in such countries as Britain, in the Winter - or even in the Summer. One can heat the mixture, but the purpose of making biogas is to produce useful energy. If the energy used to heat the mixture is equal to or more than the energy produced there's not much point. This is the fundamental problem when designing a system for use outside the tropics. The problem of heating is solved on the large scale farm and industrial biogas digesters easily because the proportion of insulation to volume goes down the larger the volume. But for a small scale plant for domestic use the cost of insulation and providing heat rises. The image here shows a digester operating in a tropical area - probably Australia.
A related factor is the amount to spend on the apparatus itself. Temperature affects the capital cost. The lower the operating temperature the more digestion space one needs. As I have mentioned elsewhere, if one needs a daily bucket of chicken manure to produce enough gas for cooking, lowering the temperature by 5 degrees requires doubling the digestion space to produce the same amount of daily gas. Another problem with biogas in cold climates is that the need for gas is higher than in tropical areas. The main need for energy is in the Winter for heating. It seems unlikely that an ordinary household (without a farm attached) can make enough gas for heating a house. This suggests that a radical change in housebuilding is needed if biogas is to play a part in the cooler areas. The Rocky Mountain Institute founder Amory Lovins claims (see Factor Four) that although he lives in an area with a fiercely cold winter he does not need bought-in energy at his house in Colorado - and he grows bananas. If all houses were built to these standards the amount of energy needed would become much less, and biogas might be suitable in many more geographical areas than it is at present. (Despite having cavity wall insulation and all the roof insulation required by current standards, my heating bill in southern England is still worryingly high). Building Standards For experimental use perhaps it's worth trying to put the digester in a greenhouse or a horticultural tunnel, or a conservatory attached to a house. Energy difficulties in future. Whereas small scale biogas in hot countries can become a part of everyone's lives it is less clear that biogas can be important in colder countries. One good reason why we need people to experiment with biogas is that our societies have become dependent on cheap energy from oil and gas. The simple physical reality is that these have not been unlimited, even though we behave as though there will always be more oil to fill our cars and more gas to heat our houses. There really is uncertainty about how we can heat our houses in a foreseeable future. It is quite rational to assume oil and coal will get more expensive to buy as more people in the world want to use them, and as it gets more expensive to pump oil and gas or dig coal and transport it. Will governments be able to continue to subsidise energy costs for pensioners? The period of really high prices has not yet come but it would be useful to build up a body of people with experience of what to do. In a future of expensive and scarce energy ordinary people need to reduce their needs. The less energy you need, the easier it is to supply those needs with such devices as biogas and solar collectors. The main problem that needs to be solved is keeping a biogas digester warm. If the whole house is already being kept warm by the methods used by Lovins, it becomes possible to build a digester into the house to produce enough gas for cooking. This would mean that people in cold countries could have the same advantage in using biogas for cooking as people in tropical countries. They still need to solve the problem of finding enough material to digest. Waste Food All the wasted food could be composted and could be used to produce biogas.
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