Simulation and experimental evaluation of a hybrid flat-plate vacuum insulated photovoltaic and thermal power module.
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Date
2014
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Abstract
Current Photovoltaic (PV) technologies are characterised by low conversion efficiencies due to the inability to fully absorb solar radiation within the spectral range. This results in the generation of residual heat and raised cell temperatures. The high temperatures are undesirable for efficient operation of the PV and must be controlled hence the development of hybrid Photovoltaic and Thermal (PV/T) systems. Whereas electrical energy generation is prioritized in PV/T systems, the thermal component has often been overlooked and only used as an action to enhance electrical efficiency. They operate at low thermal efficiencies compared to conventional solar thermal systems since they are meant to reduce the PV cell temperatures. In this dissertation, a flat-plate Vacuum Insulated Photovoltaic and Thermal (VIPV/T) system has been thermodynamically simulated and experimentally evaluated in order to assess the thermal and electrical performance as well as conversion efficiencies.
A simulation model of a hybrid PV/T system made of specified components was developed to accurately predict the performance. To assess the influence of the vacuum insulation on the system’s electrical and thermal performance, a numerical energy balance equation for the VIPV/T system was formulated and implemented in TRNSYS environment using temperatures, current, voltage and power flows over medium-term duration (daily cycle) under local climatic conditions. Parametric and sensitivity studies conducted on the VIPV/T collector to determine the optimum inclination angle realised a value of 35°. The effect of changes in the PV/T system configuration e.g. with and without PV glass encapsulation has also been studied. The application of vacuum insulation allowed for the removal of PV cell glass encapsulation. This option was found to increase the optical performance by 8 %.
The experimentation was carried out under steady-state conditions in accordance to ISO 9806-1:1994 standard, at the University of Kwazulu-Natal, Durban, Kwazulu-Natal province, −29°97’N, 30°95’E, South Africa. The experimental results of the system operating temperatures and energy gains were compared with the simulation results obtained in TRNSYS based on the actual daily weather data and were found to be within the allowable margin of variation of 5 %. The VIPV/T has shown an improved overall efficiency of 9.5 % and thermal efficiency of 16.8 %, while electrical efficiency marginally reduced by 0.02 % compared to the conventional PV/T. This is due to increased heat retention capabilities resulting in raised PV module temperatures. The temperatures require high degree of controls and were regulated by controlling the water flow rates.
The simulated annual performance results for VIPV/T gave thermal, electrical and overall efficiencies of 18 %, 11 % and 29 % respectively. The solar fraction, overall exergy and primary energy saving efficiencies were 39 %, 29 % and 27 % respectively.
Description
M. Sc. Eng. University of KwaZulu-Natal, Durban 2014.
Keywords
Photovoltaic power generation., Solar energy., Theses--Mechanical engineering., Vacuum insulation., Hybrid., Thermal power module.