Performance of a parabolic trough solar collector

The performance of a South African parabolic trough solar collector (PTSC) module has been characterised using the ASHRAE 93-1986 standard. The collector is designed for component testing and development in a solar energy research programme. Low-temperature testing was performed at Mangosuthu Technikon’s STARlab facility using water as the working fluid. Both an evacuated glassshielded receiver and an unshielded receiver were tested, with which peak thermal efficiencies of 53.8% and 55.2% were obtained respectively. The glass-shielded element offered superior performance at the maximum test temperature, desensitising the receiver to wind and reducing the overall heat loss coefficient by half. The collector time constants for both receivers indicate low thermal inertia and the measured acceptance angles exceed the tracking accuracy of the PTSC, ensuring the collector operates within 2% of its optimal efficiency at all times. Off-sun thermal loss results and the behaviour of the PTSC under increased angles of incidence are described. A description of the test system components is given