Cows to generate electricity

GALT
July 29, 2008 12:01am

A dairy equipped with a manure digester will use if to make biogas to fuel a generator to supply electricity to the Sacramento Municipal Utility District.

Unlike similar operations planned for the area governed by the San Joaquin Valley Air Pollution Control District, which questions the efficacy of biogas power system to deal with NOx emissions, the SMUD project involves a dairy in Galt just north of the San Joaquin district’s boundaries.

(For an earlier story on the issue, please click on the link below.)

The Cal-Denier Dairy in southern Sacramento County will be the source of the methane derived from manure.

In addition to providing renewable energy, the new digester captures methane emissions – a greenhouse gas which contributes to global warming and is 22 times more potent than CO2, SMUD says.

Milk cows produce about 120 pounds of combined manure and urine each day. Cal-Denier uses a flush manure management method to clean the stalls. The flushed manure is then stored in a holding pond or lagoon.

Cal-Denier’s new digester is an ambient temperature covered lagoon digester designed by RCM Digesters. The flushed manure is retained in the digester for approximately 40 days. As the manure decomposes, biogas is produced and accumulates under the cover.

The gas is then collected and sent to a 65kW baseload engine generator made by I Power Energy Systems.

The digester lagoon is 389 feet by 162 feet and 24 feet deep. It is lined with high density polyethylene (HDPE) plastic. A cover of the same material hermetically seals the lagoon. A secondary pond, also lined, is built to the same dimensions and functions as a storage pond for the stabilized digester effluent, which is then used for crop irrigation and fertilization.

“Dairy manure digesters have many benefits for both the community and the dairy,” says SMUD. “Everyone benefits from the reduction of greenhouse gas emissions and the additional renewable energy,” it says.

SMUD’s dairy digester incentive program provided 13 percent capital cost incentive to match the 25 percent USDA Rural Development grant, set up net metering crediting of the farm’s meters at retail rates (about 10 cents/kilowatt hour), provided a power purchase agreement for surplus electricity, provided 50 percent of the USDA grant application cost and helped with permitting, interconnection and additional grants. Approximate capital cost of the digester system is $700,000.

Additional funding for the digester project was provided by the U.S. Department of Agriculture Rural Development Program, U.S. Department of Agriculture Natural Resources Conservation Service and the California Energy Commission, through the Western United Resource Development fund administration.