Efficiency of solar conversion in flat plate and vacuum tube solar collectors

The paper presents results of efficiency of solar radiation conversion in flat plate and vacuum tube collectors. The research was carried out for uniform forced conditions and varied temperature in a hot water tank. Conversion efficiency, determined as a relation of the utility heat from collectors to the total solar radiation energy, was calculated for the varied water temperature in a hot water tank. Results of efficiency were presented as the reduced temperature function presenting a relation as a difference between the average temperature of the transfer fluid and the ambient temperature in relation to the solar radiation intensity. For the measured sizes, values of parameters were determined, based on which we may calculate the conversion efficiency according to the standard of investigation of collectors. Based on the obtained results, a model form which enables determination of the average temperature of the transfer fluid as a function of the ambient temperature and solar radiation intensity was found.