Analysis Of Solar Thermal Energy As A Heat Source For Bioreactors In Cold Climates: A Case Study

Two pilot-scale bioreactors were built to test the feasibility of using solar thermal heat as a means of heating in the process of anaerobic digestion. One 175-gallon bioreactor was built using an electric hot water heater as a heat source that provided a constant temperature of 95 degrees F. An identically sized bioreactor was constructed that used heat from a 4x8 solar thermal panel. In the solar heated bioreactor the process of thermosiphoning was taken advantage of to eliminate the need of electrical inputs, such as a pump. During a 25-day test performed in March 2010 in Boone, NC, the bioreactor heat loss due to feedings and ambient air temperatures was greater than heat input from the solar panel over the given experimental period. Although the two bioreactors produced similar amounts of gas during the first 10 days of the experiment, a week of cloudy weather followed and the solar-heated bioreactor fell far behind the control bioreactor in gas production. Over a period of 25 days, the solar panel heated bioreactor only produced 285 gallons of biogas, while the control bioreactor produced 1100 gallons of biogas.