Do you know what a flat plate air collector is? Or which of the three collector types are utilized for passive solar systems? What about a drain-back system? If you don't know, worry not, for help is here. I recently interviewed Paul Shippee of Crestone Solar School. Check out Part 1 of our interview, when he answered some of the most commonly asked questions regarding solar thermal power.
Solar collectors are essential for heating water or space via solar thermal power. There are three types, which Paul discusses in detail below. Paul Shippee is a Crestone community advocate for local food growing, food sustainability, and self reliance. He is a solar consultant on active and passive solar design and planning, and he teaches Solar Design and Natural Building at the Crestone Solar School. Here's his take on solar thermal collectors.
"The flat plate solar collector is the most common type used in active solar (i.e., pumped) systems. It commonly consists of an insulated metal box with a single layer of tempered glass on the top side. Inside the box, for a water system, there is usually a flat plate made of copper riser tubes and copper fins which are bonded to the riser tubes/pipes. Larger header piping distributes the incoming pumped water to the riser piping and the array of these flat plate collectors are connected to each other in parallel configuration.
"These liquid systems require, in most climates, some type of freeze-proofing during winter nights. Anti-freeze solutions are often used for this purpose. However, to avoid toxic liquids in and around the home environment, and to decrease maintenance, many systems utilize plain water to collect the sun's heat. Then, when solar heat is not available and the pump shuts off, the plain water drains back inside the warm parts of the home. This is called, as you might guess, a drain-back system, and it is my personal preference.
"Another type of flat plate solar collector in use is the air collector. The box is similar and air is blown through the boxes to collect solar heat and then blown through the home or a rock bed to store heat for night time use. It is worth noting that either air or water solar collector systems may be operated by thermo-siphoning. This is where instead of pumping the fluid around, the sun heats the fluid, which rises through the system naturally, transferring heat to a cold sink. Here's a fact: tests show that flat plate collectors perform more efficiently when operated at lower temperatures.
"Concentrating collectors are round cylinders of glass, like a thermos bottle - a vacuum tube, with thin pipes running up and down inside and a curved reflector, also inside, to direct more sun onto the thin pipes. These types of collector are typically used when higher temperatures are required or wanted. People sometimes have the impression that concentrating collectors are more efficient. However, independent testing has shown that there are no significant efficiency differences during normal operating ranges.
"Both these active system types usually require some thermal storage media, like a large tank of water or a concrete floor or wall, to store the sun's heat collected during the day for release and distribution to the building interior on cold winter nights.
"Integral storage refers to passive solar heating systems which are popular and cheaper. This system utilizes the building itself, when designed properly, to both collect solar heat when the sun shines via large south-facing windows, and simultaneously to store the excess heat in massive earth or concrete walls and floors, or in containers of water placed in the living spaces."
-- Stay tuned for Part 3 of my interview with Paul!