Farm waste anaerobic digestion

Friday, June 8, 2012

Yesterday I attended a celebration at Stonyvale Farm in Exeter, Maine, where an innovative anaerobic digester system is now producing renewable electricity from cow manure and other organic waste.  The project demonstrates both a promising technology and an opportunity for farms to produce and market new products.

Two anaerobic digesters at Stonyvale Farm in Exeter, Maine.

Stonyvale Farm is a fifth-generation family dairy farm.  Today the farm is home to 1,000 milk cows and 800 calves.  Several years ago, the family decided to explore the development of an anaerobic digestion system to convert manure and other farm waste to usable biogas.  This led to the creation of Exeter Agri-Energy, a renewable energy company that built and operates a 1-megawatt generator fueled by methane produced through anaerobic digestion at Stonyvale Farm.

Exeter Agri-Energy's digester and generator came online in late 2011.  Today the project converts cow manure and off-farm organic waste from a variety of sources into biogas.  EAE is permitted to accept a variety of food-based and organic wastes from off-farm for conversion into biogas.

The biogas is burned in a combustion engine to produce electricity (enough for about 800 homes) and heat.  I helped the company qualify the project for incentives under Maine's community-based renewable energy pilot program, which gives Exeter Agri-Energy a long-term contract to sell the facility’s output to its local transmission and distribution utility for up to 20 years at average prices up to $100 per MWh (equivalent to 10¢ per kWh).  This works much like a feed-in tariff for qualified projects, giving them a guaranteed buyer and price for the project's output.

Fuel production on the farm: dairy cows at Stonyvale Farm.

This on-farm energy project also enables the creation of additional products and revenue streams, as well as cutting the farm's costs.  Byproducts of the digestion process become organic fertilizer, organic soil additives, and animal bedding used on the farm, creating a variety of products with minimal waste.

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