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The PVSAT-13 Conference, 5-7 April 2017at Bangor University, Wales, UK
A Conceptual Strategy to Control the Cell Temperature in a Concentrating
Photovoltaic/Thermal Roof-top System
Li W. a, Baig H.b, Paul M. C.a,*, Mallick T. K.b and Knox A. R.a
a
School of Engineering, University of Glasgow, Glasgow, G12 8QQ, UK
b
The Environment and Sustainability Institute, University of Exeter, TR10 9FE, UK
E-mail: [email protected]
Abstract
Concentrating photovoltaic/thermal (CPV/T) solar collectors have been increasingly used to
enhance the electrical and thermal performance of PV/T solar collectors. However, the PV cells in this
kind of collectors are subject to a higher temperature in comparison with that of an ordinary flat-plate
PV/T solar collector, thus resulting in a lower electrical conversion efficiency. So, controlling the cell
temperature is a key issue for CPV/T solar collectors. In this work, a CPV/T solar collector, i.e. a
roof-top system, is developed and to control its cell temperature, a conceptual strategy to control the
water flow rate through heat exchangers under variable outdoor conditions in Penryn is proposed.
At first, we develop a lumped optical and a thermal model for the concentrators, i.e. crossed
compound parabolic concentrators (CCPC) and the tube heat exchangers, respectively. A relationship
between the water flow rate and solar irradiance for a certain mean cell temperature is initially
established and it is understood that the flow rate varies with the effective solar irradiance.
Secondly, a new relationship for the water flow rate with an aim to control the overall mean
cell temperature at 25oC is developed and implemented in the model consisting of 27 CCPCs with 27
PV cells and a tube heat exchanger beneath them. A full 3D optical-thermal transient analysis on
ANSYS CFX is also performed and the system’s performance is demonstrated.
It is turned out that the linear flow rate control strategy, by which the flow rate increases from
0 L/min to 1.04L/min and then maintained, leads to the variation of the mean cell temperature of only
about 3oC. While this variation is about 10oC without any flow control, this thus proves that the
proposed method is an effective strategy to control the mean cell temperature in the concentrating
PV/T roof-top system.
Keywords: flow rate, photovoltaic/thermal solar collector, crossed compound parabolic concentrator,
optical model, thermal model, control strategy, cell temperature
Acknowledgement
The work is supported by EPSRC with grant: EP/K022156/1-Scalable Solar Thermoelectrics
and Photovoltaics (SUNTRAP).