Developing a BIPVT

Abstract

Photovoltaic Technologies in recent years have gained immense attention owing to reduced costs and increasing efficiencies. While decades of research in Photovoltaic Thermal (PVT) technologies, producing thermal and electrical energy simultaneously have brought these costs further down, improving a system’s overall performance. PVT collectors consist of PV modules with a thermal absorber bonded/attached underneath them. Excessive solar radiation that is not converted into electricity by the panels is released as heat, causing their temperatures to rise. Rising PV panel temperatures have an adverse effect on their efficiency, particularly for building integrated photovoltaics, that generally lack sufficient ventilation for this heat release. Thermal absorbers for PVT systems, are designed specifically for absorbing the excess heat generated by PV modules. In practise, helping the panels perform better by effectively removing the heat present behind them, with the help of a heat transfer fluid.

This project has been a collaborative effort between the TU Delft, and Exasun BV, a solar panel manufacturer located in the Netherlands. At Exasun, the project has also benefited by being a part of a larger consortium project, the PVT inSHaPe, currently underway at the Solar Energy Application Centre (SEAC), in Eindhoven. PVT inSHaPe aims to realise zero energy buildings by integrating PVT systems with heat pumps alongside effective thermal storage. As a manufacturer, Exasun BV specialises in state of the art building integrated photovoltaic systems (BIPV). BIPV systems aim to integrate photovoltaic technologies seamlessly into building facades. In doing so, they forego essential thermal ventilation required for maintaining lower panel temperatures. Thus, a novel BIPVT design was developed in-house at Exasun, for extracting the excess heat of panels, and utilising it to match the domestic hot water and space heating demand for Dutch households.

A simple thermal model for concentrating PV-Thermal collectors, currently under development at the TU Delft was validated alongside widely used steady-state and quasi-dynamic thermal models. Individually calculated thermal efficiencies from the models were juxtaposed, with the simple thermal model recording an error of 1.65% against the steady-state model, and an error of 9.21 % against the quasi-dynamic model. Once validated, the model was used further for system characterisation and performance evaluations of the design.

Various technology concepts have been tested extensively. However, further feasibility, reliability and optimisation studies need to be performed, in order to test the novel, cost-effective, and relatively maintenance free design in mind. The performance of PVT systems rely on high irradiance levels from the sun, and module temperatures. As space heating demands are higher during winter months, even after heat pump integration, the system is not effective enough to match the entirety of the load demand, and must be coupled with an auxiliary (electrical) heater, that can be powered by the PV system. Presumptive performance analysis carried out for a simulated household, revealed an average thermal efficiency of 10 % for the design, while recording a combined efficiency of 36 %. The stand-alone system was able to match over 55 % of the domestic hot water demand. When combined with a heat pump, the system is able to meet roughly 80 % of the hot water demand, while it is able to match almost 40 % of the complete thermal demand for a household.