As the key component of active solar –heating systems, solar collectors gather the sun’s energy, and transform form it into heat, then transfer that heat to water, solar fluid or air. The three main types are flat-plate, evacuated-tube and integral collector-storage systems.

For solar water heating systems in home and solar space heating flat –plate collectors are the most common type of solar collector used. Flat-plate collectors are an insulated metal box with a glass or plastic cover (called the glazing), and a dark-colored absorber plates. These collectors heat liquid or air at temperatures less than 180 degree Fahrenheit.

Liquid flat-plate collectors heat liquid as it flows through tubes in or adjacent to the absorber plate. The simplest liquid systems use household water that is heated as it passes directly through the solar collector and then flows to the house. Solar pool heating uses liquid flat-plate technology but the collectors are typically unglazed.

Air Flat Plate collectors are used mainly for solar space heating. The absorber plates can be metal sheets, layers of screen, or non-metallic materials. The air lows past the absorber by suing natural convection or a fan. Since air conducts doesn’t conduct heat as easily as liquid, air collectors are typically less efficient that liquid collectors.

Evacuated-tube collectors can achieve higher temperatures (170 to 350 degrees F) than flat-plate collectors can. These higher temperatures make them more effective for commercial and industrial applications. More expensive than flat-plate solar collectors with the same unit area costing about twice that of a flat-plate collector.

Usually made of parallel rows of transparent glass tubes with each tube containing a glass out tube and metal absorber tube attaché to a fin. The finis covered with a coating that absorbs solar energy well, and inhibits radiative heat loss. Conductive heat loss is eliminated by removing air from the space between the two glass tubes, thus forming a vacuum.

Integral Collector-Storage Systems are also known as ICS or “batch” systems. Made of one or more black tanks or tubes in insulated black boxes, these systems are simple reliable solar water heaters Cold water passes through the solar collector, which preheats the water, and the continues to the conventional backup water heater.