Today there are many ways to produce heat, among which solar collectors are released that transform thermal energy from sunny. However, the question arises of how effective these devices are?
Let’s say right away, the effectiveness of these devices is not one hundred percent, since thermal and optical losses are inevitable.
The thermal losses include part of the energy of the Sun, which was transformed into thermal, but dissipated in the air and was not used to heat the coolant. This depends on the difference in air temperature and collector, as well as on the coefficient of heat losses, which can be convection, for radiation or thermal conductivity.
The thermal losses include part of the energy of the Sun, which was transformed into thermal, but dissipated in the air and was not used to heat the coolant. This depends on the difference in air temperature and collector, as well as on the coefficient of heat losses, which can be convection, for radiation or thermal conductivity.
Optical losses are solar energy that fell on the collector, but did not transform into thermal. It is expressed by the optical efficiency η₀, which is determined by the absorption ability of the absorber (A), the transparency of the insulator (t) and the effectiveness of the absorbing panel (FR). The value η₀, calculated by the formula η₀ = a · t · FR, is considered the passport value of the collector, and the efficiency reaches the maximum at a zero temperature difference, which means zero thermal losses.
Solar collectors are constructed so that their absorption ability increases, and thermal losses decrease. The largest optical efficiency and at the same time, open collectors are distinguished by the greatest thermal losses. Vacuum collectors have the smallest heat losses, but the use of two layers of glass and intermediate heat transfer significantly reduce optical efficiency.
