Numerical analysis of hybrid photovoltaic-thermal systems utilizing different spectral bandpass filters

摘要

Hybrid photovoltaic-thermal (PV-T) solar technology can produce electricity and heat simultaneously. The intention of hybridizing PV and thermal systems is to maximize the utilization of solar irradiance on a PV cell. Typical silicon-based PV cells do not fully utilize the entire solar spectrum, and the unutilized solar spectrum is dissipated as waste heat. Consequently, this waste heat increases the PV temperature and thereby reduces the PV efficiency. In conventional hybrid PV-T systems, the thermal receiver is used to extract the waste heat from PV cells and convert them into useful heat. However, direct coupling between the PV cell and the thermal receiver limits the performance of PV-T systems because optimal operating conditions of temperature of the two subsystems differ. The thermal receiver can produce only less useful low-temperature energy because the PV cell temperature must be maintained as low as possible for high efficiency. Therefore, we studied spectral beam-splitting techniques to overcome the aforementioned limitations in conventional hybrid systems. Moreover, this approach not only reduces the waste heat dissipation in PV cells, but also substantially increases the fluid temperature of the hybridized thermal system in contrast to conventional systems. A wavelength-selective filter (WSF) is a significant component of the present design because it splits solar irradiance into transmission and reflection. The PV cell and thermal receiver can absorb solar irradiance separately and operate independently of each other. The transmission comprises a useful spectral band, visible and near-infrared, for the PV cell, whereas the reflection comprises the rest of the spectral band that is concentrated onto a solar thermal receiver. In this study, we developed a Monte Carlo ray-tracing (MCRT) model to determine the transmission and reflection of a WSF. In addition, we developed analytical models coupled with the MCRT results to calculate the efficiency of PV cell and thermal receiver separately. The daily performance of a hybrid PV-T system with various passband designs was then derived to analyze the passband effect and the seasonal effect, as well as to provide a few ideas regarding the application of WSF to the system. When the filter passband decreases from 700 to 400 nm, the annual electrical efficiency decreases from 12.3% to 7.4% but the annual thermal efficiency increases from 5.5% to 29.8%. (C) 2018 Elsevier Ltd. All rights reserved.