Methane for the Midsized Scaled-down digester produces gas and power from 160-cow herd

November 9, 2008 06:00 PM

Jerry Jennissen's 33,000-gallon digester processes manure in four to five days. A screw press squeezes moisture from the solids, which are reused for freestall bedding.

For anyone who grew up in the 1970s, the sound coming from the back of Linda and Jerry Jennissen's freestall barn is oddly familiar.

A Chevy 350 V8 engine hums along at constant speed, powering not a Corvette but a 37-kwh generator. The engine, the perfect size for the daily gas output of a midsized dairy herd, is the business end of an Andigen methane digester that turns manure from the Jennissens' 160 Holsteins into methane, bedding, fertilizer and carbon credits.

The Jennissens' Brooten, Minn., dairy is a pilot demonstration spearheaded by the Minnesota Project, a nonprofit that promotes renewable energy and profitability for farms.

Three years in planning, the digester went online in May. It produces $300 to $400 of 8.5¢/kwh electricity per month, with hopes of doubling that amount once it is fine-tuned. It already produces enough solids to provide bedding for the milking herd.

The economics of the project are still a bit scary, however. The cost of the tank, engine, building and all that goes with it comes to $460,000.

Luckily, with help from the Minnesota Project, the Jennissens secured $329,900 in outright grants. Of that, $211,000 came from state lottery proceeds through the Environmental and Natural Resources Trust Fund. Other money came from USDA, the Minnesota Department of Commerce, local conservation districts and Stearns Electric/Great River Energy.

The grants lower the Jennissens' outlay to $130,000, making the project marginally profitable and suggesting an 11-year payback on the investment. Jerry Jennissen is optimistic: "Digesters will explode as energy costs increase and environmental demands grow.”

Bill Lazarus, a University of Minnesota economist, suggests he could be right—particularly if electricity rates climb. That could happen, since Minnesota aims to produce 10% of its electricity from renewable sources by 2015. If rates climb to 15¢/kwh, the Jennissens' profit could jump from $1,586 to $10,000 per year. But the grant money is crucial. With no grants and a $460,000 investment, Lazarus calculates a net loss of $11,000 per year, even with 20¢/kwh electricity.

Profitability is not totally contingent on electric rates. Carbon credits were trading at $5.75/metric ton in June. If that jumps to $33/ton in 10 years, as some analysts pro-ject it will under a mandatory cap-and-trade system, the Jennissens could see another $2,500 in annual income.

Currently, the biggest economic benefit is in bedding. The recycled solids, topdressed in stalls several times a week, are saving $1,000 per month in sand bedding costs.

The Jennissens believe the economics will work themselves out. One thing is certain: They won't have to worry about finding parts for that Chevy 350 V8. There were some 90 million of them built.

Jerry Jennissen

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