From: David A Gabel, ENN
Published October 17, 2011 10:25 AM

Vermont Experiments in Cow Power

A recent case study in the State of Vermont suggests that deriving electricity from cow manure may be economically feasible. This small and largely agrarian state has no shortage of cows and dairy farms. It is conceivable that with the proper commitment from farmers, utilities, and government agencies, cow power could be a central part of the Vermont electric grid. The seven-year study was conducted by six dairy farms, and produced 12 million kilowatt hours of electricity per year.


The six dairy farms participated in the Central Vermont Public Service (CVPS) Corporation's Cow Power program. Energy consumers can choose to purchase their power from the participating farms, making it feasible for farmers to create their electricity. The farms operate generators that run on methane from cow manure, a renewable energy source and a beneficial use of an otherwise hazardous waste.

The process of producing power from manure is relatively simple and straight forward. The average cow is capable of producing over 30 gallons of manure every day. For a large farm with say 1,000 cows, that means 30,000 gallons of manure per day, quite a hefty load! The manure is fed into an anaerobic digester where it stays for 21 days at 100 degrees F. Bacteria convert the waste into methane gas. As the gas builds within the digester, the pressure rises, and the gas is exhausted through piping to the modified natural gas engine. The engine powers the generator, producing electricity. Excess heat from the engine is used to keep the digester warm.

One cow's waste per day is sufficient to power 2 100-watt light bulbs per day. The energy is added to the grid and purchased from the CVPS electric system. For the study, 4,600 customers purchased this power, paying an additional $0.04 per kilowatt hour, or roughly $470,000 annually.

Then there is the leftover manure that comes out of the digester. It is processed through a mechanical separator, and the resulting product is an odorless solid waste. It can be used as bedding for the animals or even sold to the public as fertilizer.

The Cow Power program is an excellent step in Vermont's quest to move towards renewable alternative energy. It can produce real profits for farmers, many of which may need extra help in a tough economy. However, the study concludes that the program's success will depend on a number of factors. To be truly economically feasible, the base electricity price may have to go up. Financial support from the government may be necessary for the initial investments, and additional revenue from the sale of manure byproducts may be necessary.

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