Gibbons C. J. B. Sc. M. Phil.1, Murphy D. B. Eng.1

1Energy Engineering Group, Department of Mechanical and Manufacturing Engineering, Cork Institute of Technology, Cork, Ireland. Tel 00353-21-4326224, Fax 00353-21 4326627, email cgibbons@cit. ie

Introduction

The conversion efficiency of Photovoltaic cells is influenced by a large number of diverse factors, ranging from the material properties of the semiconducting materials, the environmental conditions under which the cell is operating, and the thermal properties of the encapsulants. The work presented in this paper examined the influence of the Thermal Interface Resistance (TIR) between the layers of the composite encapsulated cell, and more specifically the interrelationships between aspects of the encapsulation process, and the operating TIR of the module.

Objectives

The main objective was to quantify the significance of the stages of the manufacturing process, and specifically the thermal curing cycle, on the TIRs which occur between each pair of composite layers of the PV Laminates. The TIR acts as additional resistance to heat flow away from the cells, and hence an increase in TIR induces a higher cell temperature. The highe r cell temperature leads to a significant reduction in the conversion efficiency of the cells, with less electrical output being produced.

The effect of the curing cycle was evaluated experimentally using a Guarded Heat Flow Meter that was designed and constructed to the required international standard. The meter allowed accurate measurement of the TIR under controlled conditions.

A Taguchi methodology (Peace, 1993) was employed to determine the sequence and production factor levels for the three parameters thought to be likely to effect the TIR. These manufacturing parameters were; the thermal cycle duration, and the temperature levels during the bonding and curing phase. The results were analysed statistically to determine the significance of each parameter and combinations of parameters.

Theoretical analysis of the behaviour of materials at interfaces was also completed, and used to try and predict TIR values for selected situations, these results compared well with experimental results and some general agreement was established. However this aspect of the research is not presented in this paper due to spatial constraints.