Solar photovoltaic panels are the relatively young rock stars of the green technological movement. When most people think green, they picture rows and rows of sparkling silicone semiconductors harvesting the limitless power of the sun and converting it into clean, free electricity. What about solar thermal heating?
Solar Thermal Heating
But while solar photovoltaic panels may bask in the glory of both the sun and green building advocates, an alternative form of harvesting the sun’s energy known as solar thermal heating continues to be one of the most cost effective, and mature, on-site sources of renewable energy. The potential for solar water heating in the United States alone is mindboggling – the Texas Renewable Energy Industries Association (TREIA) estimates the potential for one quadrillion Btu of energy savings per year. 500 square feet of solar thermal collectors will displace the hot water generated by a small natural gas-fired boiler, generating 2,021 therms per year and offsetting more than 26,825 pounds of C02 per year. What these numbers boil down to is that a typical array of solar collectors would generate more than 100% of the hot water needs of a household during the summer and a considerable portion of the hot water needs during the winter.
More than just hot water, however, solar hot water systems can be utilized to heat pools in any climate, heat the interior space of the house, or, when used in conjunction with absorption chillers, even cool building interiors. The latter involves a thermal-chemical absorption process, not unlike a refrigerator, but without using electricity. When installed correctly by a professional ecobuilder, such as Native, a simple hot water collector can cut total household energy consumption by more than 10%.
Flat Plate Collectors vs. Evacuated Tube Collectors
For those interested in installing a solar hot water system, there are essentially two basic typologies on the market – flat plate collectors and evacuated tube collectors. Flat plate collectors have been around in one form or another for the past century or so. Flat plate collectors are essentially glazed metal boxes that trap heat and sunlight which in turn heat up a fluid circulating via tubes inside the collector. These cheap-and-cheery solar collectors work particularly well in hot, sunny regions such as central Texas. Flat plates typically cost between $80 and $160 per square foot. Vacuum tube collectors perform better in colder climates where the reduction in heat-loss through vacuum-sealed tubes is more significant. Installed costs tend to be the same or slightly higher than that of flat plate collectors. There is still not a general consensus on which of the two systems is better as each has its own strengths and weaknesses.
However, one thing that everyone can agree upon is the fact that solar thermal collector systems are a highly cost-effective means of supplying a home with renewable energy, reducing long-term lifecycle costs, and solid step towards green building goals.
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