Posted by: Contributing Columnist, Mississippi Business Journal Feature, News, Energy, October 8, 2015:
While I am on the topic of energy and how we produce and use it in Mississippi, I would like to share another technology that gets very little mention in the mainstream media, but has tremendous potential. My guess is that if I say the words “solar energy” right now, you will be confused, but will also be thinking about the ubiquitous rectangular panels which produce electricity. What I am talking about though is still a rectangular panel, but instead of producing DC current, these panels produce hot water. These panels capture the heat in the sun’s rays which hit the Earth’s surface and transfer that heat into water, hence the name solar thermal energy. If this sounds elementary, it pretty much is! The intricacies come in the design of the solar thermal panels and how they are constructed to capture this radiant energy. The most common design is a flat plate collector, which were originally developed in the 1950s.
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.