EXPERIMENTAL-STUDY ON A HYBRID PHOTOVOLTAIC THERMAL SOLAR WATER-HEATER AND ITS PERFORMANCE PREDICTIONS

The combined photovoltaic thermal system is a new kind of solar system which, so far, has not seen intense research and developmental activities as other systems have seen. The most attractive feature of such a system is that it could produce both electrical and thermal energies from the same panel. These systems could play an important role in popularizing solar energy. In order to understand and evaluate solar hybrid systems, an experimental study was undertaken. The system chosen is a thermosyphon water heater with solar cells. The cells are pasted directly over the absorber plate. The solar insolation falling on the aperture area of the collector is concentrated on the solar cells using a simple parabolic reflection. The temperatures at several points in the system (or the absorber at several points, of the solar cells, of the water in the tank at several positions, of the inlet and outlet water from the collector) are measured by using thermocouples. The solar cells are arranged in three groups. Among a group, the solar cells are connected in series. The three groups can be connected either in parallel or series. The electrical characteristics of the cells, i.e., the I-V characteristics of various combinations with several different load resistances are measured. The experiment was performed for several days with thermosyphon flow and without it. The heat transfer coefficients, heat loss coefficient of the tank and overall heat loss coefficient of the collector are determined from experimental data. An attempt is made to fit the various experimental observations, like water temperature in the tank, inlet and outlet water temperatures of the collector, with the well known model of thermosyphon solar water heaters. The model equations are modified to include the presence of the solar cells and the reflectors. The agreement between the experimental and theoretical predictions, within the experimental errors, is excellent.