۱- Introduction

۲- Description of the proposed spectral splitting concentrator

۳- Design methodology

۴- Design example

۵- Application in a typical solar hybrid system

۶- Summary and outlook

۷- Conclusions

References

Abstract

Full-spectrum solar energy utilization has drawn widespread attention for cascading solar energy utilization. The hybrid approach integrating photovoltaic generation and solar thermochemical reaction is attractive to convert full-spectrum solar energy into electricity and chemical energy. This paper proposes a concentrating solar photovoltaic/thermochemical hybrid system. Meanwhile, a spectral splitting concentrator is proposed and designed. The proposed concentrator consists of above-mirror and sub-mirror. The above-mirror enables the visible spectrum to be concentrated onto photovoltaics. The sub-mirror allows the infrared and ultraviolet spectra to be concentrated onto a solar thermochemical reactor. The design methodology based on ray tracing is described. The distribution of solar radiation on the photovoltaics and the thermochemical reactor is made analysis. The results show that solar radiation can be uniformly cast to the photovoltaic surface without using secondary optical element; the common solar flux concentration of thermochemical reactor is also mitigated. The proposed spectral splitting concentrator is introduced in the hybrid system. The total conversion efficiency of the solar energy can exceed 20%. Compared with individual photovoltaic electricity and solar thermal fuel, this hybrid system has the potential to increase the conversion efficiency of solar energy into both electricity and fuel, with greater than 5% absolute enhancement. The design of the spectral splitting concentrator provides the possibility of cascading utilization of full-spectrum solar energy.

Introduction

Solar energy as the largest renewable energy is expected to replace fossil fuel for satisfying the energy demand of humankind, which provides access to reliable and ample supplies of energy [1]. At present, full-spectrum solar energy utilization has attracted widespread attention [2]. For example, various approaches [3] and experiments [4] have been proposed and conducted to improve full-spectrum solar energy utilization; US Department of Energy has put forward a research plan of full-spectrum solar energy utilization in 2013 [5]. According to the spectral response characteristic [6], the full-spectrum solar radiation could be converted into photovoltaic electricity (using visible spectrum) and solar heat (using ultraviolet and infrared spectra). Correspondingly, the hybridization of solar photovoltaic (PV) and solar thermal processes is common considered to improve fullspectrum solar energy utilization. The waste heat recovery hybrid system and spectral splitting hybrid system are two typical hybridizing approaches. It is based on whether the ultraviolet and infrared spectra directly participate in photovoltaic heat generation. Waste heat recovery hybrid system: Full-spectrum solar radiation is first concentrated onto photovoltaics and then converted into photovoltaic electricity and waste heat of the photovoltaics. This dissipated heat of a photovoltaics can be further used in heating, cooling and other heating related applications for domestic and industrial processes. For example, Carlo Renno [7] proposed a concentrating solar photovoltaic/ thermal hybrid system (CPV/T) with waste heat recovery, it was satisfied for the thermal demand of a building space by recovering the photovoltaic heat. Similarly, Coventry et al. [8] designed and fabricated a test bench about CPV/T, the measured results show that the 58% lowtemperature waste heat from photovoltaics can be recovered to produce domestic hot water.