We began producing biogas for cooking fuel at LEF in 2019. It is a well established technology in common use worldwide. Basically a liquid compost pile, archea (ancient microorganisms, even older than bacteria) digest food scraps and other organic matter in anaerobic conditions. The system produces liquid effluent which can be used for fertilizer, and biogas, which is mostly methane and with minor modifications can be used just like natural gas for cooking or heating. We have found biogas to be an excellent supplement to our solar electric cooking.
Biogas is already gaining popularity in tropical climates. This is largely because digesters must stay warm to produce significant quantities of gas: 85 – 105 degrees Fahrenheit is best. (At lower temperatures, gas is produced but at much lower quantities.) Keeping a digester warm is a significant technical challenge in our climate.
At LEF, we warm our digester the same way we warm our houses: with a solar thermal heating loop, which passes solar heated fluid (gylcol) through a heat exchanger inside the digester. Our digester (a 2,000 gallon tank) is surrounded by about 3′ of insulation (straw bales and blown cellulose), to maintain high temperatures.
We feed our digester with a combination of human waste, food scraps, grass clippings, and leaves. About 3-5 gallons of organic matter per day is enough to produce cooking gas for the community.
The Chinese Biogas Manual is a great source of information about building biogas digesters, and is available for free online.