Every solar thermal heating system begins with a thermal collector. These collectors draw in solar energy in the form of heat, which is trapped long enough to pass its radiation onto fluid or air encased in tubes. Those tubes then carry the solar-heated substance back to the system in the house proper.
In closed loop systems, that "heat exchanger" delivers its heat to the indoors before heading back to the collector to repeat its unending cycle. In an open loop (air-based) system, the indoor air itself passes through the thermal collector and then directly back to warm the house.
Flat-plate collectors are by far the most common thermal heating collector on the market. They are either air or liquid collectors. Evacuated tube collectors are more efficient and can reach much higher temperatures than their flat-plate counterparts, but are also much more expensive and in many areas, unnecessary. The following Solar Library articles will work to divulge the ins and outs of thermal heating collectors, including how they work, where they work, and what they can do for you.
Flat-plate collectors are actually quite simple. They consist of an insulated metal box covered with a glass or plastic cover called glazing. Within the box, is a dark-colored absorber plate that is made out of a metal heat conductor and painted black to… Read more »
Flat-plate air collectors are simpler than liquid collectors and are used for space heating. Heat evaporates from air faster than liquid, making air collectors less efficient than the liquid models. Air collectors work fine for smaller applications, but p… Read more »