Potential of polygeneration with solar thermal and photovoltaic systems

The efficiency of both solar thermal and photovoltaic (PV) systems for power generation is usually in the range of 10-30%, meaning that more than two-thirds of the collected radiation energy is lost. Cogeneration, or more generally polygeneration, means capturing and using some of the wasted energy and therefore increasing the overall efficiency of the solar conversion. Several paths of solar polygeneration are investigated: both thermal and photovoltaic receivers, with use of the waste heat to generate additional electricity by a heat engine, a direct use as heat, and use of the waste heat to operate a thermal process (absorption cooling). Appropriate optical and thermal energy losses are taken into account in all cases. The receiver temperature and the sunlight concentration level serve as free parameters. It is shown that concentrating the solar radiation is essential to effective polygeneration, and that there is an optimal operating temperature for each system. Polygeneration leads to increased conversion efficiency in all cases, and the scenarios based on PV show better results than those based on thermal converters. Scenarios showing electricity replacement up to 43% (normalized to the incident radiation) are presented.