Solar spectral beam splitting for photochemical conversion and polygeneration

Abstract

Conversion efficiency from sunlight to electricity is relatively low for both solar thermal and photovoltaic converters, where more than three quarters of the solar energy is dissipated back to the environment. Division of the solar spectrum (spectral splitting) enables better use of photon energy in each spectral band. Here we present a polygeneration approach to solar energy conversion where the main contribution is a photochemical process, while co-producing power and medium grade heat. A collector design is introduced with a linear Fresnel lens, a ‘cold mirror’ spectral filter, and photochemical, photovoltaic, and thermal converters. To illustrate a wide scope of applications, three photochemical options are investigated: photonitrozation of cyclohexane, photooxigenation of citronellol, and catalytic disinfection of wastewater. The analysis of conversion efficiency uses detailed optical modeling based on realistic (commercially available) component properties and on experimental characterization of participating compounds. Overall system efficiency is up to 50%. The amount of electricity displaced or saved vs. current lamp-driven photochemical processes can reach as high as 97% of the incident solar energy, for several combinations of photochemical and photovoltaic converters. The polygeneration approach can be implemented using low-cost components and may lead to cost-effective, highly efficient solutions with a significant contribution to displacement of conventional energy sources.