The fundamental principle behind the functioning of a flat panel solar collector is fairly straightforward. The collector is designed with a transparent cover which allows the sun's rays to penetrate and fall on the heat absorber that is coated with an absorbing layer. The majority of the solar radiation energy gets absorbed by the absorber and it is converted into heat energy. This heat energy is then transferred to the working fluid that is flowing through the fluid channel.
The working fluid that is at room temperature enters the bottom of the collector and gets heated gradually as it travels through the channel. The solar energy heats the working fluid, thus raising its temperature. At the top of the flat panel solar collector, the heated working fluid is exported with useful heat energy and stored in a standby water tank, where it can be used later.
As the temperature of the heat absorbing body increases, some heat is lost to the environment through the transparent cover and the shell. This leads to several heat losses in the flat solar collector. However, the stored useful energy gain is beneficial for various purposes. Overall, this simple process enables the conversion of solar energy into useful heat energy.