Some aspects of a PV/T collector/forced circulation flat plate solar water heater with solar cells

Abstract

Solar energy is mainly utilized via two routes—thermal and electrical. Two forms of energy are generated by two separate systems. The present work is about the study of a system which combines thermal and photovoltaic systems in one unit. The system is basically a conventional forced circulation type water heater. It is converted into a combined system by pasting solar cells directly over the absorber plate. The system equations are solved by a finite difference method. The simulations are done for different solar cell areas, mass flow rates and different water masses. The differential temperature controller, i.e. pump-off and pump-on, are used. It is shown that the pump-on time is more or less independent of the total stagnant water mass in the collector unit. The pump-off time is a sensitive function of the water flow rate. At higher flow rates, the pump is switched off early in the afternoon. Since the total working time decreases, the efficiency also decreases. There is an optimum flow rate for which the collector efficiency is a maximum. The cell efficiency, which is a function of temperature, is calculated using an iterative method. The average cell efficiency turns out to be more or less independent of the solar cell area on the absorber plate. This result helps in saving calculation time because the total electrical energy available for any solar cell area can be calculated simply. A normal domestic solar water heater of about 2 m 2 generates sufficient electrical energy (after taking into account the various losses in storage, etc. and the energy required by the pump) to run 2 tube lights of 20 W each for 5 h and 1 television of 30 W for 4 h.