Thermal Modeling and Life Prediction of Water-Cooled Hybrid Concentrating Photovoltaic/Thermal Collectors

Abstract

In this paper, a multiphysics, finite element computational model for a hybrid concentrating photovoltaic/thermal (CPV/T) water collector is developed. The collector consists of a solar concentrator, 18 single junction germanium cells connected in series, and a water channel cooling system with heat-recovery capability. The electrical characteristics of the entire module are obtained from an equivalent electrical model for a single solar cell. A detailed thermal and electrical model is developed to calculate the thermal and electrical characteristics of the collector at different water flow rates. These characteristics include the system temperature distribution, outlet water temperature and the thermal and electrical efficiencies. The model is used to study the effect of flow rate on the efficiencies. It is found that both efficiencies improve as the flow rate increases up to a point (0.03 m/s), and after that point remain at relatively constant levels. However, as the flow rate increases the outlet water temperature decreases, reducing the quality of the extracted thermal energy. In addition to the thermal and electrical modeling, finite element analysis is used to estimate the fatigue life of the module based on the different temperature profiles obtained from the thermal model at flow rates of 0.01 m/s and 0.03 m/s. Results show that for the higher flow rate, the outlet water temperature decreases, but the fatigue life improves. Based on the fatigue life model predictions, it is shown that the thickness of die attach layer must be increased for high outlet temperature applications of the hybrid CPV/T collector.

Concentrated photovoltaic thermal (CPVT) solar collector systems: Part I – Fundamentals, design considerations and current technologies

“…Orhan / Renewable and Sustainable Energy Reviews ∎ (∎∎∎∎) ∎∎∎-∎∎∎ 10 Naturally, the inlet temperature of the HTF strongly affects both the HTF outlet temperature and the PV cells' temperature in a direct relation [266]. Additionally, Xu et al [239] confirmed that obtaining a higher HTF outlet temperature comes at the expense of the durability of the CPVT. This implies that an increase in the thermal exergetic efficiency comes at the expense of electrical efficiency and CPVT durability, and vice versa.…”

“…In their study, Xu et al [239] concluded that increasing the mass flow rate by a factor of three (from an inlet velocity of 0.01-0.03 m s À 1 ) yields a total performance improvement of less than 1% and results in a sharp drop in the HTF's outlet temperature from 56.2 to 35.5 1C. Sharan and Kandpal [250] reached a similar conclusion where experimentally increasing the HTF's mass flow rate results in electrical efficiency as well as electrical and thermal output increases up to a certain mass flow rate where performance improvements become negligible.…”

“…The thermal expansion coefficient mismatch between the PV cell and its substrate with thermal cycling (due to concentration ratio and operation temperature variations) leads to the eventual failure of the solder layer. As such, the authors developed a fatigue life model to predict the failure modes under different operation conditions [239]. It was found that obtaining higher HTF outlet temperatures comes at the expense of the durability of the CPVT system.…”

“…Thus, a properly designed CPVT should have a similar lifetime. Xu et al [239] developed a thermomechanical finite element model to predict the fatigue life of a CPVT. The thermal expansion coefficient mismatch between the PV cell and its substrate with thermal cycling (due to concentration ratio and operation temperature variations) leads to the eventual failure of the solder layer.…”

Performance Evaluation of a New Type of Combined Photovoltaic–Thermal Solar Collector

“…It is a finite difference approach for a hybrid waterheating PV module. A multiphysics, finite element computational model for a hybrid concentrating photovoltaic/thermal water collector was developed by Xu et al [39], to calculate the thermal and electrical efficiencies of the collector at different water flow rates. Fontenault and Gutierrez-Miravete [40] developed a model of a system consisting in a rectangular aluminum box on the rear side of the PV module, where water has flown.…”