This specialised "plate" collects solar radiation and turns it into useable heat energy, which is then used to efficiently heat water for bathing, cooking, laundering, or other daily uses.
Source: Wagner & Co / ESTIF
How a Flat Plate Collector Works
At first glance, a flat plate collector seems deceptively simple; it is essentially a flat metal box covered with a plastic or glass glazing on the top, insulated sides, and a dark absorption plate with a special dark coating at the bottom. Copper or aluminum pipes run underneath the absorber plate which transfer liquid used to heat a specially designed and attached water tank. Flat plate collectors are usually mounted on roof tops to get the full benefit of solar energy.
The sun's rays pass through the clear glazing and begin to heat up the absorption plate. This then heats the solar fluid in the copper tubing that will, as the design of the solar water heater allows, heat the water in the water tank. There are typically intake and outlet pipes as well, for consistent water and coolant flow.
A flat plate collector is not only a very financially sound investment, it's also much more environmentally-friendly than heating with gas or electricity alone. Because a flat plate collector uses solar power to operate, there is no need for natural gas or oil consumption to heat water, meaning fewer non-renewable resources are being used.
Cheaper than evacuated tube collectors
The plate collector is cheaper than the evacuated tube collector. But a flat plate collector also loses more heat and is less efficient than its more expensive cousin, so you need more space on the roof to get a comparable amount of energy. The plate collector is suitable for solar water heating as well as space heating, though not suited to solar process heating because its operating temperatures are too low.