EXPERIMENTAL EQUIPMENT

The hybrid system consisted of a PV module, where a glass plate window (jacket) was layed over the front surface, a circulating pump and a heat exchanger. The glass plate was temporarily attached and could be removed at any time without much effort. A fluid, distilled water, was circulated between the front surface of the PV module and the jacket layed on the front surface.

The incident solar radiation first passed through the glass jacket and the layer of circulating water before reaching the module. The high transmittance of glass and water layers for the visible radiation, ensured that the silicone cells of the PV module would receive most of the visible radiation to generate electricity without much sacrifice in power. Infra-red part of the incident radiation is essentially absorbed by the glass-water and module structure combination leading to warming of the solar cells. It is this excess heat that the hybrid unit is designed to remove, by circulating water, and utilize in domestic applications. While the circulating water removes the heat and leads to cooling of the module, at the same time it provides a source of warmed water for preheating applications in a domestic use.

A standard commercial module, M, rated at 55 Watt peak, with dimensions 130x47x5 cm was used. The jacket, J, had the diamensions of 130x47x1.5 cm (Fig. 4) and was placed over the module surface with a gap, about 0.4 cm to allow flow of water. The PV module was tilted 45 degrees to horizontal and faced south for maximum solar insolation, I. Initially pure water, Q, was circulated at the rate of 36 liters per hour. An identical PV module was used as a control and measurements were performed on both the hybrid and the control modules at the same time and location.

A data acquisition card was used to record a range of data. Meteorological information published by the Statistics office[1] was used. The electrical characteristics of both modules and thermal performance of the hybrid system were measured. The data listed below were recorded at various times from 9.00-17.00 hrs. each day and the average values were plotted. The temperature of the circulated water, at input/output Tin, Tout, the ambient temperature, Tamb, and surface temperatures, Tsc, Tsh, on the control and hybrid modules respectively were recorded. All temperatures were recorded in degrees centigrade. The short-circuit currents, Iscc, Isch and open-circuit voltages, Voc, Voh of both control and hybrid modules respectively were recorded. The maximum operating power of each module is defined as P = Voc Iscc FF (1)

The fill factor, FF, was taken as 0.7, which is typical of single crystal silicone cells.

The electrical energy, Ec and Eh, of control and hybrid module respectively were calculated using numerical integration. Hence, the area under the power-time curve, was taken at various one-hour periods.

Thermal energy collected by the circulating water in one-hour period, can be defined as Qw = Q Cp AT (2)

where Q is the volune flow rate of the water in lt/hr, Cp is the specific heat at constant pressure (4187J/kg. °C), and AT is the temperature difference (Tout — Tin ).

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