Make a Biogas Generator to Produce Your Own Natural Gas

Transform grass clippings, food waste and livestock manure into renewable biogas energy with a homemade biogas generator.

| August/September 2014

You can use many household organic “waste” materials to produce your own natural gas for cooking, lighting, and space and water heating. This gas, known as “biogas,” can also replace fossil-based natural gas to fuel an engine or an absorption cooling system, such as a gas refrigerator or chiller. Some gasoline engines are designed for or can be modified for use with natural gas, propane or biogas. Diesel engines can accept up to 80 percent biogas.

Biogas is a mixture of primarily flammable gases — mostly methane — along with carbon dioxide that forms anywhere organic material decomposes anaerobically (without oxygen), such as in water, deep in a landfill, or in the guts of animals, including you.

I prefer the term “generator” for the system, because it conveys the intention of producing something. By constructing a home biogas generator, you can make enough fuel to at least provide your cooking energy. A family with modest daily cooking needs will at a minimum require the output of a warm, well-fed, 200-gallon (27-cubic-foot) generator. This much biogas will allow for about one hour of daily stovetop cooking. Start small to develop an understanding of biogas by making a small generator from a single 55-gallon barrel. Find plans in The Homeowner’s Energy Handbook.

Home Much Homemade Biogas Energy Can You Make?

A well-managed methane digester can produce approximately its own volume of biogas each day. Anywhere from 10 to 60 percent of the solids will convert into biogas during digestion, so expect between 3 and 18 cubic feet of available biogas energy for each pound of dry material.

The exact makeup of biogas depends on what you feed to the digester. The main ingredient of biogas is methane. Methane (chemically known as CH4) is the primary component of conventional natural gas, commonly used for cooking and heating, although biogas is not as energy-dense. The methane content of biogas will probably range from 50 to 80 percent, compared with about 70 to 90 percent in utility-supplied natural gas. Natural gas contains up to 20 percent other combustible gases, such as propane, butane and ethane, while biogas does not. Biogas’ primary noncombustible components are carbon dioxide, some water vapor, nitrogen and possibly traces of hydrogen sulphide.

A good material for producing biogas in terms of both production and availability is freshly cut grass clippings, which can produce about 1-1⁄2 cubic feet of biogas per pound. At this rate, about 20 pounds of grass clippings will generate one hour of cooking fuel (grass silage is even better, requiring only about 10 pounds to produce this same amount of biogas). Food waste can yield slightly greater amounts of biogas per pound than grass, but most people will have access to grass clippings in larger quantities (see Slideshow to compare various materials). If you own a cow, fresh manure is well-suited for on-farm methane production, despite its relatively low yield per dry pound. One cow will produce about 140 pounds (18 gallons) of manure each day, which could ultimately generate, on average, 85 cubic feet of biogas, or about three hours of daily cooking fuel. (Keep in mind that manure produced during hours your cow is on pasture will be difficult to collect.)

7/25/2014 3:57:37 PM

Could one do this to his septic system, obviously with modifications?

7/22/2014 10:33:12 AM

Author's video on making a small scale digester to get started

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