|MadSci Network: Physics|
David, You have a well thought-out thought experiment started here. Let's see if I can help some. Recall that the radiant heat is basically infrared radiation that is streaming through the window. It only turns into "usable" heat when it hits something and causes it to heat up. Those objects absorb the energy and reradiate as well as heat up the air in contact with the object's surface. Thus, the usable heat in the room DOES change when you add the solar panels because they are intercepting the radiation and converting it into electricity and clearly some heat. In the process, it blocks the radiation from hitting objects in the room. However, you also need to consider that some of the radiant energy will be reflected back from the solar panel and back out the window. Solar panels tend to be much more reflective than, say, a dark couch or carpet and are coated to absorb only the wavelengths of radiation that get turned into electricity, reflecting away the others. You could change the angle so that the incoming energy is less direct and gets reflected into the room instead of back outside, but you will also lower the efficiency of the solar panel because for greatest efficiency you want the energy hitting the panel normal (i.e., at 90 deg angle) to its surface. To figure out the equation, I would look up the information on a typical solar panel (efficiency, reflectivity at various wavelengths, etc.) then devise a simple room on paper with materials for which you know or can find the absorption coefficients. Then calculate the amount of solar load in the room both with and without the solar panel in place. By the way, there is no particular reason why a "one way" glass could not be used on the solar panel that would keep the heat inside the solar panel, except for the fact that the solar panels would probably overheat. Depending on the characteristics of the one-way coating, you might be able to ventilate the solar panels and use the heat to heat the room. Of course, it might also reduce the efficiency of the panel, as well. Good luck Todd Jamison Chief Scientist, Observera Inc.
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