Earth Day was an appropriate day to celebrate the newest member of CVPS’s Cow Power family. The odd concrete structure framed against the distant mountains is the literal and figurative belly of the operation. Inside the digester cow manure is converted into methane biogas that in turn runs a 225-kilowatt generator to produce electricity. Photos by Richard Creaser
COVENTRY — Several hundred guests attended an event they couldn’t even see at Maxwell’s Neighborhood Farm in Coventry on Earth Day, Wednesday, April 22. While the cows earned their fair share of attention, the real stars of the show were hidden in a concrete bunker and are ordinarily so small they couldn’t be seen with the naked eye.
Not being able to see, or smell, these little heroes is the surest proof that the microorganisms in the methane digester are doing their job, said Matt Maxwell. Mr. Maxwell is the driving force behind Maxwell’s Neighborhood Energy LLC.
“We started looking at this a few years ago when milk prices were low, kind of like they are now,” he said. “We were looking for ways to diversify the farm and earn income when prices are down.”
The added income came with a hefty investment on the part of the Maxwell family. Fortunately the family was able to secure grants and aid from both the state and federal government to offset the cost. The United States Department of Agriculture (USDA) provided $360,000, a renewable energy grant provided $100,000, and the Vermont Agency of Agriculture added $250,000 of the $1.5-million project.
The Maxwells’ digester is considered to be on the small side of economically viable methane digesters with a typical digester running in the neighborhood of $2-million, Agency of Agriculture engineer Rob Achilles said. At that price it becomes essential to ensure the farm has the resources to make the investment as well as the manure to keep the digester operating.
The cows are more than willing to contribute from their end, their back-end, that is. Mr. Maxwell said the average milking cow produces approximately 40 pounds of manure a day. Heifers produce perhaps half as much, he added. All of that manure is black gold for both the farmer and the digester.
In spite of the tremendous up-front cost of the project, Mr. Maxwell expects that the digester will pay for itself within five years. The farm sells the electrical output to the Vermont Electric Co-op at a wholesale rate of 8.2-cents per kilowatt hour (kWh). In addition Central Vermont Public Service (CVPS), through whom the Cow Power program is operated, provides the farm with an additional 4-cents per kWh premium from the sale of the renewable energy credits derived from the cow power generation.
CVPS customers also have the option of buying Cow Power at a 4-cent per kilowatt premium. Though customers are paying the premium and, in turn supporting the expansion of the Cow Power program, CVPS can offer no guarantees that the electricity its customers use came directly from the farm.
“The electricity delivered under the CVPS Cow Power rider will be indistinguishable from other electricity supplied by the company
Matt Maxwell is the driving force behind Maxwell’s Neighborhood Energy LLC. The venture added a methane digester to the Maxwell’s Neighborhood Farm operation.
because it is impossible to track the flow of electricity on the regional electric power grid,” states the CVPS Cow Power brochure. “This is unavoidable because all customers are served through the same transmission and distribution system.”
The digester provides the farm with a number of benefits. The first is that it converts a waste product into three distinctly valuable end products. Through the digester, naturally occurring methane or biogas is used to power a generator that in turn produces electricity. Stripping the methane from the manure has the added benefit of eliminating one of the more obnoxious odors associated with manure. The conversion of methane into biogas does not, however, eliminate the hydrogen sulfide compound, Mr. Maxwell said.
“We are able to use the methane that would have just gone straight into the atmosphere,” Mr. Maxwell said. “Methane is one of the worst greenhouse gases, and we are not only taking it out of the atmosphere, we’re using it to generate electricity.”
The second benefit is that the digestion process eliminates 99.9 percent of the weed seeds and pathogens present in the average cow flop. After passing through the digester, the remaining solids, usually the tougher fibers from whatever the cows have eaten, remain behind. These fibers can be used as bedding for the animals.
“A few years ago a truckload of sawdust would run you about $600,” Mr. Achilles said. “Now that same truckload costs $1,800, assuming you can still get it. For some farmers the solid-liquid separator alone is worth the investment because it provides them with clean, inexpensive bedding.”
The third benefit is that the separated liquid retains 66 percent of its nutrient load, allowing the farmer to fertilize his fields with a virtually scent-free end product. A farmer could additionally truck the separated fibers for use as fertilizer using a conventional dump truck as opposed to a liquid fertilizer spreader. The lighter weight of the fertilizer could result in savings on fuel during field application.
Another benefit of the process comes from the operation of the electrical generation equipment. At present the Maxwell farm has a single 225-kilowatt generator connected to its digester unit. The farm is wired for a second generator should additional generation capacity prove desirable and economically feasible in the future, Mr. Maxwell said.
While the generator runs it creates a considerable amount of heat. Mr. Maxwell said that the heat is not being wasted at all. The heat is used to operate a boiler system that provides heat and hot water for the farm’s milking parlor. Heat from the generators is used to keep the digester at its optimal temperature of 101 degrees Fahrenheit, the temperature of a cow’s stomach.
A future consideration involves piping that hot water to greenhouses, Mr. Maxwell said. That potential was planned for when the system was designed and installed. Having a greenhouse on site would provide the farm with yet another economic opportunity while utilizing existing resources.
Methane digesters are a promising technology in the state, Mr. Achilles said. The range of benefits to farmers is considerable, but the technology could also be applied to other uses. In the spectrum of waste to energy products, manure is actually at the low end. Much of the latent energy has been consumed in the process of creating milk and beef with a relatively small amount passing undigested through the animal.
Food waste or feed crops would provide far more energy than manure, Mr. Achilles said. Indeed, one gentleman in Grand Isle is examining the possibility of methane generation minus the cow. The concept involves dropping the feedstock directly into the digester to harness all of the food energy.
A farm can boost its energy output by combining food waste with the manure, Mr. Maxwell said. Restaurant food waste or the leavings from food processing plants can be added to supplement the process. Doing so does not come without complications, he said.
In order to include off-farm supplements, the farm would need to secure the proper permits from the Agency of Natural Resources. If the digester contains less than 51 percent manure, the farm is then classified as a waste storage facility and subject to different rules and regulations. The added food waste will contribute to a different nutrient composition in the extruded liquid. This different nutritional profile could affect the farm’s nutrient management plan and potentially affect where, when and if the liquid could be applied to the farm’s fields.
In order to maximize the energy output, it would be necessary to house the food crops for a much longer period of time. The typical manure digester requires a 21- to 25-day period of digestion. In order to break down the more complex structure of food crops, specifically the lignin (a substance that binds cellulose fibers in plants), the material needs to digest for approximately 100 days. This alone requires a storage capacity that is four to five times larger than a manure digester.
In essence, a farmer could become an energy farmer raising crops for the sole purpose of generating electricity. A single acre of corn could produce one kilowatt of electricity every day for a year, Mr. Achilles said.
Another option exists that would enable multiple farms to utilize a single, centrally located digester. This approach has been used successfully in Tillamook, Oregon. Its applicability to the Vermont landscape does face some challenges, however. The proximity of farms to the facility is the major issue. If getting manure to and from the facility exhibits prohibitive transportation costs, the project could die before it hits the ground.
“If you are more than a couple of miles round trip, anything you save by generating electricity you lose in trucking,” Mr. Achilles said. “That said, there are a few locations, particularly around St. Albans Bay, where a central digester could work. It also helps that there is a dairy processing plant that could contribute commercial food waste to increase the energy output.”
Another hitch in the communal digester idea concerns the state’s regulation of farms. Co-mingling the waste from multiple farms, even farms that fall outside of the 200 dairy cows or more medium farm range or the 700 dairy cows or more for a large farm permit, could tip the scales, forcing all the farms to comply with large farm waste storage regulations. This would require the farms to build and maintain an engineer-certified manure pit.
“From the standpoint of manure management, they would be considered a large farm,” Mr. Achilles said.
That said, the potential for a central digester is not entirely unreasonable. As energy demand increases farmers may indeed turn to farming electricity, providing Vermont with the green, clean and renewable energy it needs and desires.
“We figured we got all this manure so we might as well use it,” Mr. Maxwell said. “It helps us stay viable; it generates renewable energy and helps the environment.”
News 
