Design and Operation of Solar Water Heating Panels
A solar thermal panel operates on solar energy emitted by the sun and is made up of 55% visible radiation - visible rays that we all can see. The remainder is almost all infrared radiation, except for a very small amount of ultraviolet radiation.
Modern solar thermal panels, or thermal solar collectors as they are also referred to as, operate on visible and infrared radiation utilizing most of our sun’s spectrum.
A solar panel consists of a rectangular insulated box, usually made of stainless steel and painted black to absorb heat from the sun. Inside the box are rows of glass tubes laid onto the black insulated back, and the water to be heated is pumped through the tubes. Some panels incorporate a solar PV panel in the main panel that provides electricity to run the circulating pump. The tubes may have copper fins incorporated that conduct the heat from the sun’s rays into the water.
Lastly, a glass panel is sealed onto the box above the tubes. This can be double glazed and e-coated to prevent heat loss. Most swimming pool solar water heating panels just have a hardened glass cover as the low temperatures make radiation losses negligible.
The system operates by the water pump supplying water through the filter to the solar panel from the pool. The panel heats the water as it passes through the tubes and returns it a little hotter back to the pool. As the day goes on and, as long as it stays sunny, and the solar panel remains out of the shade the pool water will heat up by around 10°F from its original temperature.
There is a by-pass valve in the system whereby at night time the water can be directed through the filter and back to the pool, bypassing the panel.
Some solar thermal panels have their own PV panel incorporated in them that runs a small circulating pump, which can be used instead of the pool main pump.