Farm waste anaerobic digestion

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.

June 17, 2010 - hay is for horses

Yesterday, I looked at the U.S.'s historic energy usage.  In 1900, according to the U.S. Census, there were 76,094,000Americans, who consumed an estimated 9.587 quad of energy.  This works out to 125 million Btu per capita -- about 38% of today's U.S. per capita energy intensity.  As noted yesterday, I suspect this figure does not include the substantial energy that was used to feed draft livestock in 1900.  We don't usually think of livestock fodder as containing solar energy, but in a very real way, photosynthesis has been a major energy base for millennia.

To that end, I found an interesting note in the Thirty-Fifth Annual Report of the Secretary of the Maine Board of Agriculture, from 1892:

OUR HAY CROP.
By W. B. Kendall, Delivered at Clinton.

IMPORTANCE.

' On July 4th of each year our State of Maine celebrates its agricultural independence, by presenting its farmers with a constant, and never-failing million ton crop of grasses, the great basis of our agricultural life and wealth, in this northern clime.

So constantly do we gather this king of all crops into our barns, that, while almost every year, some of our cultivated crops, through drought, flood, insect blight or "season" are failures, the great hay crop, because ever present, is not given the gravity of consideration it demands. The hay crop of Maine has averaged, for the past ten years, one and one quarter million tons. At 87 per ton in the field $8,750,000 and at 810 per ton in the barn, $12,250,000,or more than the value of all others combined. We hear much of Maine's great lumber crop, and industry, but even this does not, in primal value, nor in the capital invested in its manufacture, nor in value after it is manufactured, amount to as much as the value of the hay crop in the field, the labor, machinery and barns for its storage and the cash value of the same delivered in Boston market, or consumed on the farm.

Our hay crop, the basis of our dairy industry, supports through our northern winters 1,100,000 head of cattle, horses and sheep.

In fact, a total failure of our hay crop for three years would practically depopulate our State, farm, town and city.

The agricultural report focuses on Maine's export of hay to southern New England, both to feed livestock used for food production (like the dairy farms) and to feed draft animals.  When you drive around the Maine countryside today, and see the hay fields that remain scattered here and there, it's easy to forget that all that hay is a vehicle for storing and consuming solar energy -- and that Maine has a long history of exporting that energy southward.