Renewable Energy
Animal Waste
According to the NC Department of Agriculture, as of 2005, North Carolina has the second largest pig population in the United States with approximately 10 million head. Turkey farms raised over 39 million turkeys and the chicken industry produced 700 million “broilers”. These animal stocks produce massive amounts of waste, all of which can be used for energy production.Swine Waste
Raising a large quantity of swine creates an overwhelming quantity of manure. In fact, 200 50-pound hogs can produce over 96,000 gallons of manure per month. A 250 pound hog will have most likely produced 1.5 tons of waste by the time it reaches its particular weight. This waste, once flushed from the swine confinement facility, is separated into solids and liquids by a solid manure separator. The solids are used for compost, mulch, and animal feed supplements. The liquids, or wastewater, can be pumped into an anaerobic digester, where anaerobic microorganisms breakdown the organic nitrogen into ammonia and ammonium and the carbon compounds into carbon dioxide and methane gas. The methane can then be used to create energy, which through interconnection, or the ability for producers of energy to connect to the grid, can help offset non-renewable energy production.
Barham Farms of Zebulon, NC was one of the first in North Carolina to capture methane from pig waste for energy production. The farm, a 4,000 head farrow-to-wean operation, originally combined an ambient temperature anaerobic digester with an engine generator to convert the methane produced into electricity. The ambient digester consists of an impermeable cover over an in-ground digester that creates and captures the methane gas used for electricity production. This methane gas was extracted and delivered to a generator, where electricity was produced for use on the farm. Heat from the generator was captured and used to produce hot water that was used by the farm in its production activities. Unfortunately, technical setbacks such as a weak interconnection standard, led to the discontinuation of energy production at Barham Farms. NCSEA is working to improve the interconnection standard, which creates regulations that utilities and small energy producers must follow. You can read more about interconnection standards in our Issues section.
In 2006, the North Carolina Utilities Commission along with the NC General Assembly commissioned a study of all renewable resources in North Carolina. This study, performed by La Capra Associaties, is the current definitive source for electricity production from hog waste. It found that:
“According to the 2004 North Carolina agriculture statistics, there are 620 hog operations in North Carolina with over 5,000 heads per site, totaling about 7.5 million. The average operation is estimated to consist of about 12,000 heads, which can produce methane in the range of about 10,000 mmbtu/year to18,000 mmbtu/year. EPA’s AgStar program conducted a study to assess the biogas opportunities for North Carolina with the assumption that farms with greater than 2,000 swine can provide methane for electricity generation. That program identified 1,179 total feasible operations with 9,358,000 heads of mature swine. The study estimated 11.5 billion cubic feet per year of methane production (1.3 mmbtu/head/year) and 766,000 MWh/year of electricity generation. This would be equivalent to about 116 MW of electric generation capacity at a 75% capacity factor."
“Taking the median of the wide range of methane production potential, we assume an annual net methane production for a 12,000 head operation to be about 14,000 mmbtu per year, which can power a 150 kilowatt (kW) internal combustion engine generator at 75% capacity factor with a heat rate of 14,000 btu/kWh. For modeling purposes, we assume a typical generator capacity of 150 kW per location, which would provide a maximum potential (at operations greater than 5,000 heads) of about 93 MW of electric power generation statewide. The actual size of generators would have to be sized appropriately for the farm size, average animal size, and anticipated methane production. Furthermore, farmers are able to reduce their own retail electricity costs by consuming the electricity generated on-site or participate in net-metering if the generators are sized below 100 kW. Owners of multiple farms may also consider aggregating sites that are in close proximity to one another to take advantage of scale economies, but transport costs would have to be taken into account.”
“Taking the median of the wide range of methane production potential, we assume an annual net methane production for a 12,000 head operation to be about 14,000 mmbtu per year, which can power a 150 kilowatt (kW) internal combustion engine generator at 75% capacity factor with a heat rate of 14,000 btu/kWh. For modeling purposes, we assume a typical generator capacity of 150 kW per location, which would provide a maximum potential (at operations greater than 5,000 heads) of about 93 MW of electric power generation statewide. The actual size of generators would have to be sized appropriately for the farm size, average animal size, and anticipated methane production. Furthermore, farmers are able to reduce their own retail electricity costs by consuming the electricity generated on-site or participate in net-metering if the generators are sized below 100 kW. Owners of multiple farms may also consider aggregating sites that are in close proximity to one another to take advantage of scale economies, but transport costs would have to be taken into account.”
Poultry Litter
With 39 million turkeys and 700 million chickens, North Carolina is also home to abundant poultry litter. Poultry litter refers to the mixture of poultry manure and spoiled bedding material such as sawdust, wood shavings or rice hulls. Currently North Carolina is exploring how to use excess poultry litter (poultry litter is used as fertilizer but in excess amounts can cause groundwater pollution due to surplus nutrients in the wash off) for energy generation. Poultry litter works as a fuel because it's relatively dry, so it's easy to burn compared with cow and hog manure. Already, Craven County Biomass is utilizing poultry litter for a small portion of its biomass fuel supply. The La Capra study estimated a total of 105 MW of electricity could be produced from poultry litter in North Carolina, finding that:
“In estimating the potential in North Carolina, we used the State’s 2004 total turkey production and broiler production and applied the average litter per thousand birds for each which results in an annual potential of over 1.4 million tons of poultry litter. We then applied a heat content of 6,200 btu/lb77 to the annual litter production to estimate a potential capacity of around 175 MW if the litter is consumed in a plant dedicated to poultry litter such as the Fibrowatt facilities. This is equal to five facilities of 35 MW capacity. Due to potential competition with farmers for use of the poultry litter as a fertilizer substitute, it is assumed that only three 35 MW facilities, or a total of 105 MW, can ultimately be built and receive cost-effective fuel supply.”
