Solar Heat Transformation Alternatives

SYNOPSIS The utilization of solar energy in wintertime corresponds with the low temperature of the produced heat, which is often too low to directly feed heating plants. Heat transformation appears to be an attractive way of increasing the temperature of solar fluids, so that in the present paper some solutions are examined with different operating mixtures, i.e. H2O-LiBr, CH3OH-LiBr, CH3OH-LiBr-ZnBr2 (2:1, 3:1). The overall efficiencies of the mentioned systems are determined, as well as the heat rates and the exergetic efficiencies. The conclusions are positive, especially with low values of the solar radiant power Wi. For values of Wi less than 700W/m2, which cover the majority of situations in temperate climates, it is remarkable that the introduction of an absorption heat transformer increases the overall efficiency; the advantage becomes very appropriate for low values of Wi, as it is usual in cold-temperate climates.