Experimental Study of a Novel Hybrid Solar Photovoltaic/Thermal and Heat Pump System

Mustapha Obalanlege, Yasser Mahmoudi, Roy Douglas, John Davidson, David Bailie

Research output: Chapter in Book/Report/Conference proceedingConference contribution


large area in which energy is utilised is in heating, which about 50% of global energy production is used for heating. In the UK central heating accounts for approximately 80% of national heat demand, which for 37% CO2 emissions in the UK in 2016. In order to meet the Paris Agreement target the UK should reduce CO2 emissions by 80% by the year 2050 in comparison to CO2 emission levels of 1990. To address this need, a movement towards the de-carbonisation of heating and cooling systems using renewable energies is taking place. In this regard, solar energy is used to generate both heat and electrical power on both large and small scales.
Solar panels are used to convert solar energy into heat and electricity. Most solar panels are designed to convert solar energy to only one of these forms, and an electrical photovoltaic (PV) panel is typically no more than 20% efficient. The rest of the absorbed sunlight rays are converted into heat. The temperature rise due to this heat reduces the performance of PVs. Hence, the energy that is not converted into electricity by the PV panels must be extracted to prevent reduction of PV efficiencies. PV panels can be actively cooled by passing a fluid through the rear of the panel. It then becomes possible to extract both heat and electrical power. This combined solar heat and electrical power system is known as a Photovoltaic/Thermal (PVT) system. The challenge here is that the heat energy recovered from the hot PV panel is does not have high temperature to cover the heating demand of a household.
One solution to this challenge is to integrate the PV panel with a heat pump. An area of research with this technology is in Indirect Expansion PVT Heat Pump (IEPVT/HP) systems. In order to test the validity of the system an experimental rig of the IEPVT/HP system has been designed and built in an indoor monitored environment in which certain parameters of the system can be controlled. In the experimental testing of the system, these parameters are controlled and varied; the solar irradiation received by the cooled solar PV panel (produced by a solar simulator); the mass flow rate through the cooling of the PV panel; the volume of the water tank supplying the cooling water to the PV panel and feeding the heated water to the heat pump. The integrated system utilises a closed water loop to cool the PV panel and transport the heat to the water-to-water heat pump. As the water is not used as the working fluid by the heat pump and only as transport media for heat, the system is called an Indirect Expansion Photovoltaic Thermal Heat Pump (IEPVT/HP) system.
Experimental results show that cooling the PVT panel using the developed integrated system, reduces significantly the panel temperature from 102oC to 50oC (for solar irradiation of 650 W/m2), demonstrating the promising function of the system in cooling the solar photovoltaic panels. Such an effective cooling of the panel, increases the on-site electrical efficiency of the PV panel by 25% compared to the un-cooled PV panel. The coefficient of performance (COP) of the heat pump found to be as high as 3.5, confirming the high performance of the developed hybrid system.
Original languageEnglish
Title of host publication5th International Congress on Energy Efficiency and Energy Related Materials
Publication statusAccepted - 26 Oct 2019
Event5th International Congress on Energy Efficiency and Energy Related Materials - Mugla, Turkey
Duration: 22 Oct 201928 Oct 2019


Conference5th International Congress on Energy Efficiency and Energy Related Materials

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