Study On Performance Of Photovoltaic-Thermochemical Complementary Solar System

As a kind of abundant-reserves,clean and pollution-free renewable energy,solar energy has a broad development prospect and is of great significance for solving the problems of energy shortage and environmental pollution.But solar energy also faces the problems of low energy conversion rate and high cost of power generation,which restrict its further development.The main reason is that the spectrum of solar radiation is wide and the full spectrum of solar energy cannot be efficiently utilized.For the full-spectrum solar radiation,only the short-wavelength photons with energy greater than the bandgap of photovoltaic cells can be absorbed and utilized by the solar photovoltaic cells,while the photons of other wavelengths cannot be utilized by photovoltaic cells and will lost in the form of heat.Therefore,it is an effective method to improve the convention rate of solar energy by using full-spectrum solar energy.A low-temperature thermochemical reaction of methanol decomposition is introduced and coupled with photovoltaic cells to propose a photovoltaic-thermochemical(PV-TC)hybrid solar system.Photovoltaic and thermochemical conversions are applied to utilize the solar spectra in different wavebands,so as to realize high-efficiency utilization of full-spectrum solar energy.Based on the full-spectrum utilization of solar energy,the design method and performance of the photovoltaic-thermochemical hybrid solar system are studied in this paper.The main contents include:1.A photovoltaic-thermochemical hybrid solar system and the design method that couples photovoltaic cells with the thermochemical reaction of methanol decomposition is proposed for the full-spectrum utilization of solar energy.A calculation model of the optical system is established based on the spectral-splitting optical structure with secondary reflection and concentration.The calculation methods for the dimensions and installation parameters of the key components,such as photovoltaic cells,thermochemical reactor,concentrator,and spectral beam splitter,are determined.By simulating the concentrating and spectral splitting of the solar radiation in the optical system through the Monte Carlo ray tracing method,the solar irradiance distribution on the surface of PV cells and thermochemical reactor are analyzed,which provides theoretical guidance for the design and construction of the PV-TC hybrid solar system.2.For the complex processes of solar spectra splitting and allocating,solar photovoltaic conversion and solar thermochemical conversion in the PV-TC hybrid system,a solar spectrum splitting and allocating model of the PV-TC system is established,and the solar photovoltaic conversion and thermochemical conversion mechanisms are described.Based on the principle of photovoltaic conversion,an energy conversion model of the PV module under concentrated and spectal-splitting solar radiation is established to calculate and analyze the photoelectric conversion performance in the PV-TC hybrid system.Based on the principle of thermochemical reaction of methanol decomposition,the heat transfer,flow,diffusion and reaction kinetic models of the thermochemical energy conversion process were established to calculate and analyze the thermochemical conversion performance in the PV-TC hybrid system.The energy outputs of the PV-TC hybrid solar system has been unified,and a system evaluation method for net solar-to-electric efficiency is established to provide a standard for the performance studying of the PV-TC hybrid solar system.3.Based on the principle and design of the PV-TC hybrid system,an experimental test platform of the hybrid system is built to experimentally verify and study the coupling performance of solar photovoltaic and thermochemical conversions.Due to the significant effects of key operating parameters such as solar irradiance and methanol flow rate on the solar photovoltaic and thermochemical conversions,the effects of solar irradiance and methanol flow rate on the performance of the hybrid system are experimentally investigated.The operating performance of the hybrid system under daily conditions with variable irradiance is studied,and an all-day operating mode with dynamic methanol flow regulation is proposed to enhance the all-day operating performance of the PV-TC hybrid system under variable irradiance conditions.4.In the PV-TC hybrid solar system,the allocation of the solar spectra determines the matching of photovoltaic and thermochemical conversions and influences the utilization of solar energy by the hybrid system.In order to realize the effective coupling of PVcells and thermochemical reaction,the influences of different spectral allocations on the performance of the PV-TC hybrid solar system are analyzed.A new spectral allocation method with multi-cutoff wavebands is proposed to optimize the solar energy distribution along the surface of the thermochemical reactor to match the energy demand of the thermochemical reaction.The loss of solar energy is reduced.The performance of the system with spectral allocation method with multi-cutoff wavebands is investigated and validated by theory and experiment.