Solar Thermal Collectors

Abstract

The solar collector is the main component of a solar system. It transforms radiant energy from the sun, in the spectral range 0. 3 – 3μm, into usable heat (Fig. 1). The density of fluxes involved is low, at a maximum of the order of 1 kW/m² (1000 times less than in the case of nuclear reactors). Heat losses depend essentially on temperature levels. A black plate, at 70^°C, put in ambience at 10^°C, will lose about 1 kW/m². The useful extracted energy will be the difference between the absorbed energy and the energy losses:

$$(\text{USEFUL ENERGY}) = (\text{ABSORBED ENERGY) - (ENERGY LOSSES)}\text{.} $$

Only carefully designed collectors which minimize the heat losses will show an acceptable efficiency for practical applications. The first part of this lecture is devoted to the description and the evaluation of the thermal processes concerned with solar collectors in order that the user may become familiar, either with the limitations, or the potential improvements which can be expected from solar systems.

From ‘Heat Transfer Processes in Solar Collectors’, M. E. Aranovitch, first published by Elsevier Sequoia.