Читать книгу Solar Water Heating--Revised & Expanded Edition - Bob Ramlow - Страница 21

Absorber plates are necessary to conduct the solar radiation to solar fluid. How the absorber has been coated will directly affect the efficiency of this process. Absorber coatings are rated along two parameters: absorptance and emittance. The former refers to the percentage of solar radiation that can be absorbed, and the latter is the percentage of heat that is emitted back from the absorber plate. To get the net heat gain, you need to subtract what is emitted from what is absorbed. Most coatings will have similar absorptance ratings in the range of 90 to 98 percent, but will vary in their levels of emittance. Traditional flat or selective black paints will emit anywhere from 15 to 30 percent of their heat, and the modern high-tech methods, such as sputtering, physical vapor deposition (PVD), black chrome or black crystal, can reduce the emittance levels to 5 to 10 percent.