The main parts of a collector are shown above. The selective surface is designed so it easily absorbs radiation, but does not reflect or re-radiate energy back out of the collector. Special black or dark-green coatings are used. The coating converts the radiation to heat by absorbing it. The working fluid flows through the tubes and collects the heat.
Copper tubes transfer the collected heat to the working fluid more effectively than aluminum tubes.
The cover, or glazing, reduces convection and radiation losses to the surrounding air. The cover is transparent to short-wave solar radiation, but not to infrared radiation from the selective surface. The back and side insulation, typically R-value 12, reduces conduction losses. Flat plate collectors do not concentrate solar radiation. Flat-plate collectors are usually fixed to an orientation optimized according to location and time of year.