Other Solar Thermal Collectors
There are other kinds of solar thermal collectors. For the most part, you might say that these are less attractive and older in design than the standard closed loop system, though some of them are quite effective in their own right.
Evacuated tube collectors
These are rows of parallel glass tubes with black absorbent material on the back. Sunlight shines through the water and is absorbed into the black material to heat the water. Tubes are vacuum-sealed. This allows them to achieve much higher temperatures, making them appropriate for industry and commercial systems.
In these, the water runs through a U-shaped tube. The U shape focuses the sun's rays on the liquid. These can make the water very hot in a very short time.
It's as big as a breadbox-a 40 gallon tank full of water. It's insulated, lined with glass and painted black, so that the sun heats the water inside. This is undoubtedly the simplest solar thermal system, and it is very practical for any location where there is no freezing.
Take a large aquarium, paint the glass black and insulate it, and you'll have a pretty good idea what a batch solar thermal heater is. Cold water goes in at the bottom, and hot water comes out on top. This is often called an integrated collector and storage water heater by the current professional industry, while solar old timers call it a "breadbox" water heater.
City water is heated by a collector, and once it is warm enough (detected by a controller), a "drain down" valve opens, into a sump or tank. This system has some advantages, but this type of collector has fallen out of vogue, as it is problem-plagued and complicated.
Solar Thermal Air Heating
Solar thermal also refers to heating the air. A transpired solar collector is any south facing wall painted black. Ideally, this wall is sheet metal, just like furnace venting, and it has a fan or blower to move the air throughout the house or building.
Find a dealer for solar thermal equipment.