Thermal Aspects ofPhotovoltaic/Thermal Solar

Collectors

Tim Anderson

Deparment of Engineering

University of Waikato

Solar Energy and NZSolar Energy and NZ

New Zealand land mass conservatively collects 1.4x1021 J per year

An average house rooftop of 150m2

collects 2.2x108 Wh per year ie. 20 to 30 times the house’s total requirements.

Hamilton receives ~5000 MJ/m2/year

Existing Solar Technologies

Solar Thermal Photovoltaics

Source: www.solahart.com.au Source: www.bpsolar.com

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 heatingProvides 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 BIPVTUnglazed BIPVT Glazed BIPVTGlazed BIPVT Standard roofing profileStandard roofing profile Standard roofing materialsStandard roofing materials

BIPVT Unglazed

BIPVT Unglazed

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4m/s

8m/s

BIPVT Cooling Passage Width

BIPVT Cooling Passage Width

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20mm wide

50mm wide

100mm wide

150mm wide

BIPVT Flowrate

BIPVT Flowrate

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6L/s

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BIPVT Material

BIPVT Material

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Steel

Aluminium

Copper

Stainless Steel

BIPVT Packing Factor

BIPVT Packing Factor

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BIPVT Cell to Absorber HTC

BIPVT Cell to Absorber HTC

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135

180

BIPVT Transmittance-Absorptance Product

BIPVT Transmittance-Absorptance Product

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0.86

0.82

0.78

0.74

BIPVT Insulation Thickness

BIPVT Insulation Thickness

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100mm of static air

100mm

70mm

40mm

10mm

What does it all mean?

TMY can be used for long term simulation TMY can be used for long term simulation of solar energy devices such as PVTof solar energy devices such as PVT

PVT modelling used for design PVT modelling used for design modifications – empirical validation in modifications – empirical validation in progressprogress

Modelling shows that to improve the Modelling shows that to improve the BIPVT collector we could: use less PV BIPVT collector we could: use less PV cells, try to improve PV cell optical cells, try to improve PV cell optical efficiency, reduce insulationefficiency, reduce insulation

Where to from here?

Long term modelling of BIPVTLong term modelling of BIPVT Empirical validation of design modelEmpirical validation of design model Develop correlation to predict heat loss Develop correlation to predict heat loss

from BIPVT due to natural convection in from BIPVT due to natural convection in attic space behind collector (Experimental attic space behind collector (Experimental and CFD)and CFD)