Potential of Polygeneration With Solar Thermal and Photovoltaic Systems

Abstract

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.

Diffusion-emission theory of photon enhanced thermionic emission solar energy harvesters

“…For the material parameters of the anode we use the same values as Schwede et al 2 , φ A = 0.9 V and A * A = 120 A/cm 2 /K 2 . T A was set at 573.15 K in order the heat engine potentially coupled to the anode to have a reasonably high efficiency 10,11 . We also assume R F S = 0 and R BS = 1 for simplicity.…”

Limit of efficiency for photon-enhanced thermionic emission vs. photovoltaic and thermal conversion

“…This contribution can be significant since the anode temperature can be kept relatively high without affecting too much the performance of the thermionic part. Exploiting waste heat is also possible for photovoltaic converters, in particular concentrating photovoltaic (CPV) systems, but the heat is available at fairly low temperature since elevating the temperature will deteriorate the efficiency of the cells [9]. Therefore a secondary thermal stage to generate additional electricity is not very attractive.…”

Solar energy conversion with photon-enhanced thermionic emission

“…Similar arrangements were proposed to exploit waste heat from CPV systems. The waste heat can drive a lower-temperature power generation converter such as an organic Rankine cycle or Stirling heat engine [62,63]. Another power generation option without a mechanical engine is a thermoelectric converter, which usually offers lower efficiency but offers wide scalability and simple and robust operation [27].…”