[[Image:biogas pump.jpg|thumb|right|300px|Biogas irrigation pump. Photo: [http://www.flickr.com/photos/djfulford/3156710354/in/set-72157612011013426 d.j. fulford.]]]
Biomass, in the form of firewood, charcoal, agricultural residues, or dried animal dung is already the main energy resource for the majority of the poorer half of humanity, over 2 000 million people. They currently use 15% or more of total world energy, entirely in the form of biomass. Certain poorer countries depend on biomass fuels at present for over 90% of their energy needs (i.e. mainly for cooking fuel). It has been estimated [69] that 53% of energy use in Africa, 17% in Asia and 8% in Latin America is currently met from biomass resources. Therefore biomass is already a huge and vital economic resource, although it is usually informally exploited mainly for cooking purposes and still remains rarely used for the production of shaft power via heat engines, and even less so for irrigation pumping.
Because biogas digesters have the capability of storing at least a 12 hour supply of gas, an engine can be used that draws gas at quite a high rate. In fact the size of engine is not critical since it is only the number of hours it will run that are governed by the digester gas capacity.
An interesting option for irrigation by biogas power is to combine the digester sludge and the irrigation water in order to perform three functions simultaneously; i.e. irrigation, the application of fertilizer and waste disposal.
==Suitable conditions==
This issue of food versus fuel is an important one, but where the fuel crop is used for irrigation pumping to produce food crops, especially in a small-scale "on-farm" process, the same objections need not apply.
The country which has made by far the most use of biogas production in agriculture is China, where, particularly in Sichuan province, there are several million working biogas units. This development took place almost entirely within the last 10-15 years. Various studies (eg. [86]) have indicated that the value of the fertilizer output usually surpasses the value of the energy produced by the process in China. The waste disposal and sanitation aspects of the process are also important justifications for its use.
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==Acknowledgements==
* [http://www.small-farm-permaculture-and-sustainable-living.com/methane_generator.html DIY Methane Generator.]
* [http://www.fao.org/docrep/010/ah810e/AH810E13.htm BIOMASS AND COAL (THE NON-PETROLEUM FUELS)] FAO.