Investigation of the thermal performance of a Concentrating PV/Thermal Glazing Façade Technology

Developing effective solar energy technologies which can be integrated into buildings and provide heat, electricity and/or reduce energy needs, is vital to achieving set international targets for renewable energy generation and carbon emissions reduction. While a range of technologies are available at the moment for building integration most of them are simply super-imposed on the building structure rather than becoming an essential part of it. This does not allow for the full advantages of building integration to materialise as it does not reduce costs by replacing conventional building materials and components. A Concentrating PV/Thermal Glazing (CoPVTG) façade technology that combines glazing based solar concentrating elements, coupled with PV/Thermal absorbers has been developed. The technology is a modular multifunctional building component based on conventional double glazing. It is compatible with traditional façade structures and fenestration framing arrangements which allows easy integration into new and retrofit buildings. It can provide solar generated electricity and air heating through the PV/T absorbers while insulating the building thermally. Depending on the incidence angle the glazing based concentrating elements are designed allow the direct sunlight to enter the building and provide natural daylight when required whilst redirecting it onto the PV/T absorbers to generate electricity/heat when solar gains need to be minimised to reduce cooling demands. The thermal performance of a 500 mm x 500 mm CoPVTG prototype unit integrated into a conventional window frame has been investigated under controlled conditions in a solar simulator facility. Outlet air temperatures have been measured for a range of inlet temperatures at two different incidence angles of illumination. Generated Hottel-Whillier-Bliss equations show an optical efficiency of 52.6% and a 25.2 W/m2K heat loss coefficient at a 55° incidence angle. At a 20° incidence angle the measured optical efficiency is 43.8% and heat loss coefficient 27.7 W/m2K. The difference in the measured thermal performance is shown to be strongly related to total internal reflection of the light at the surface of the glazing concentrating elements. This is demonstrated by short circuit current measurements of the PVT absorbers.