Numerical investigation and experimental validation of a heat pipe based PV/T system

Abstract

The global energy demand and dependency on fossil fuels continues to increase with growth of the population. This has resulted in the production of higher amounts of harmful greenhouse gas emissions, global warming and a change of the world’s habitable climate. Over the past decade, humankind has been actively looking into finding substitutes for fossil fuels to overcome the greenhouse effect by utilising sustainable renewable energy sources. A widely available source of renewable energy is solar energy which can be harnessed to produce electricity and heat using systems such as photovoltaic-thermal (PV/T) collectors. The technology offers several benefits in terms of improving the photovoltaic (PV) electricity production and simultaneously harvesting the solar thermal energy by-product. The main objective of this study is to illustrate how, by utilising a novel thermal management technique, the output performance of a PV/T system can be improved. In this research, a reliable model will be developed, which can provide output performance predictions of the PV/T system under various conditions and indicate how the energy demand of a household in the UK can be provided using realistic energy consumption. The proposed model can be used as a demonstration tool to provide indications of the functionality of the system to an end-user throughout the year during day and night. In order to achieve the above-mentioned goals, a unique PV/T collector was fabricated by integrating a PV module with a multichannel heat pipe thermal collector and experiments were performed at different angles of orientation to identify the electrical and thermal output performance of the system. In order to conduct the experiments, a test rig and a solar simulator were designed and manufactured, which allowed an examination of the behaviour of the PV/T module and the multichannel heat pipe under various solar irradiation conditions and coolant flowrates. The experiments were conducted for water flowrates between 2 L/min – 8 L/min and it was demonstrated that the amount of thermal energy recovered from the system increases with the increase of water flowrate. Two separate experiments were performed on the thermal collector using heaters and PV panels and the impact heat transfer rate on the thermal resistance of the module was demonstrated. Using the heaters, it was discovered that the average thermal resistance of the system decreased dramatically from 0.012 K/W to about 0.004 K/W as the rate of heat transfer increased to the highest amount. Using the PV modules as the heat source, the thermal resistance of the system was shown to decrease from 0.009K/W to just below 0.003K/W from the lowest heat flux to the highest heat transfer rate depending on the tilt angle of the panel. ii In addition to this, the results from the experiments indicated that the temperature of the PV module can be reduced by almost a maximum of 24°C, which resulted in an electrical power output increase of almost a fifth. The maximum electrical and thermal output efficiencies from the experiment were discovered to be about 6% and 70% respectively. By a developing a modelling tool, the water outlet temperature was also predicted and compared with the experimental data, which showed an average error of ±15%. In order to demonstrate the application of the developed PV/T module, a transient system simulation was performed to indicate how the energy demand for a household in the UK can be provided. The results from the study were validated using the experimental data and it was demonstrated that the system requires an auxiliary power unit to provide the required thermal demand. By considering the heating and cooling loads of the modelled house, the proposed system was shown to be able to maintain the temperature of the building zone at a comfort condition of about 22°C to 24°C during different seasons of the year.