Thermal Aspects of Photovoltaic/Thermal Solar Collectors Tim Anderson Deparment of Engineering University of Waikato

Solar Energy and NZ   New Zealand land mass conservatively collects 1.4x10 21 J per year   An average house rooftop of 150m 2 collects 2.2x10 8 Wh per year ie. 20 to 30 times the house’s total requirements.   Hamilton receives ~5000 MJ/m 2 /year

Existing Solar Technologies   Solar Thermal   Photovoltaics Source:

What is a Photovoltaic/Thermal Solar Collector Solar Thermal + Photovoltaics = PVT +=

PVT Collectors   Photovoltaic and solar thermal in a single device: Cogeneration of heat and power   PV-cell efficiency decreases with increasing temperature   Efficiency of PV cells increased by active cooling   Area dedicated to solar energy devices can be reduced

PVT Air Heating   Simple   Cheap   Cavity formed behind a PV panel  Provides reasonable air heating Insulation PV Module Air

PVT Water Heating Systems   Could look very similar to a “standard” solar thermal collector   Simple   Typically better efficiencies than air heating   Suitable for heating over wide range of temperatures Cover Insulation Water Tube PV Module

Market for PVT Systems   Solar thermal collector market in Australia and New Zealand was growing at a rate of 19% per annum   Market for photovoltaic solar collectors has experienced a very high rate of growth during the last decade   PVT systems could meet the entire European PV quota while also providing 30% of the solar thermal target   Largest market is the domestic sector   Short to medium term PVT will find “niche market” applications Source: International Energy Agency (Photovoltaic Power Systems Programme), 2005, Trends in Photovoltaic Applications - Survey report of selected IEA countries between 1992 and 2004, Report IEA-PVPS T1-14:2005

University of Waikato PVT Research   University of Waikato is conducting research into Building Integrated Photovoltaic/Thermal (BIPVT) collectors   BIPVT is the use of PVT as building elements such as roofing or façade   Compromise between thermal, electrical and building needs   Thermal and electrical performance of a typical BIPVT collector has been modelled, using a modified Hottel-Whillier method (i.e. as a standard flat plate solar collector)

BIPVT Implementation  Unglazed BIPVT  Glazed BIPVT  Standard roofing profile  Standard roofing materials

BIPVT Unglazed

BIPVT Cooling Passage Width

BIPVT Flowrate

BIPVT Material

BIPVT Packing Factor

BIPVT Cell to Absorber HTC

BIPVT Transmittance-Absorptance Product

BIPVT Insulation Thickness

What does it all mean?  TMY can be used for long term simulation of solar energy devices such as PVT  PVT modelling used for design modifications – empirical validation in progress  Modelling shows that to improve the BIPVT collector we could: use less PV cells, try to improve PV cell optical efficiency, reduce insulation

Where to from here?  Long term modelling of BIPVT  Empirical validation of design model  Develop correlation to predict heat loss from BIPVT due to natural convection in attic space behind collector (Experimental and CFD)