Sunlight passes through the glazing (glass or polycarbonate encasing) and strikes the coated metal absorber plate (typically copper or aluminum), which heats up, changing solar energy into heat energy. Depending on the system, the heat is transferred to an anti-freeze type liquid passing through pipes attached to the absorber plates or heats up the actual liquid that needs to be used for the end purpose. Absorber plates are commonly painted with “selective coatings,” which absorb and retain heat better than ordinary black paint.
The main use of this technology is in residential buildings where the demand for hot water has a large impact on energy bills. This generally means a situation with a large family, or a situation in which the hot water demand is excessive due to frequent laundry washing. In my last column I shared information about the home in Gulfport which was the demonstration site for the Mississippi Alternative Energy Enterprise. The solar thermal system was the reason this family continued to have hot water after Hurricane Katrina hit that region. A small pump, driven by a single conventional photovoltaic solar panel circulated the water through this system. In another demo system installed in Madison County, the home owner’s backup gas water heater had not kicked on in several years, because the couple’s demand for household hot water was adequately met by the solar thermal system.
Commercial applications for solar thermal systems include laundromats, car washes, military laundry facilities and eating establishments. This technology can also be used for radiant space heating if the building is located off-grid or if utility power is subject to frequent outages. The economics for solar water heating systems are more attractive for facilities with water heating systems that are expensive to operate, or with operations such as laundries or kitchens that require large quantities of hot water, but generally they can pay for themselves in fewer than 10 years even without any external grants or incentives.
Solar thermal systems are commonly used to heat water for swimming pools but can also be applied to large scale water pre-heating. These systems are not going to convert your swimming pool into a hot tub, but they will extend the swimming season for uncovered pools by two to three months. Because these collectors need not withstand high temperatures, they can use less expensive materials such as plastic or rubber and utilize unglazed collectors which must be drained fully to avoid freeze damage when air temperatures drop below 44F on clear nights.
With 32 large flat plate collectors, one of the largest solar thermal installations on a farm in the Southeast is right here in Prentiss. I worked with John Logan, owner of Brinson Farms to apply for a grant through the U.S. Department of Agriculture that would partially fund a solar thermal system to heat water for his anaerobic digester system. The computer-controlled AD unit located on-site actually consumes the broiler litter from his 12-house farm. The specifically cultured bacteria present in the large insulated metal tank, known as the digester, break down the litter into biogas and an organic solid and liquid fertilizer. This patented process takes several days to produce the gas from the time new litter is introduced into the system. The main components of the biogas are methane and carbon dioxide and it is burned in an engine to produce electricity for the farm and in specially designed heaters to heat the poultry houses. The solar thermal system supplements the heat required to bring the system temperature to the desired specifications in excess of a 100 degrees Fahrenheit. Waste heat from the engine is also removed with a heat exchanger to heat the water and some of the biogas and waste wood from the farm is burned in a boiler to make up the rest of the hot water needed for optimal operation. When we first started working in this project more than 10 years ago, John stated that his goal was to be as environmentally sustainable on his farm as possible, but being an entrepreneur and a successful businessman, profitability was also equally important to him! He has now built similar systems for poultry farmers in Kentucky and Arkansas and has had serious inquiries from several foreign countries on four continents.
The examples of innovative uses of solar thermal energy I share in this column will hopefully get you to think of solar beyond the PV panels and consider solar thermal as a practical solution when evaluating the need for hot water, whether it is in a commercial or residential setting. Mississippi innovators like John Logan are “thinking outside the barn” and taking the concept of “reduce, reuse and recycle” to a whole another level. To learn more about various renewable energy innovations taking place in Mississippi, come join us the Mississippi Biomass & Renewable Energy Council’s 14th Annual Energy Awareness Symposium on Oct. 14th at Mississippi Farm Bureau Federation Building located on 6311 Ridgewood Road, Jackson. Regular registration is $35 and full time students get in free. The highlight for this event is a panel discussion with the two candidates, Brent Bailey, a Republican and Cecil Brown, a Democrat, running for the Public Service Commissioner in the Central District. Visit http://conta.cc/1hllHXG for more details.
» Dr. Sumesh Arora is Vice President at Innovate Mississippi, a non-profit organization with a mission to drive innovative business growth in Mississippi. His doctoral research was focused on how new ideas spread and its applications to business, economic and policy development. Follow him on Twitter @DrSumeshArora or contact via email at firstname.lastname@example.org with questions about developing innovation strategy for your company or organization.