Optical modelling and optimisation of Spheral Solar™ Cells

Bisconti, Raffaella (1997) Optical modelling and optimisation of Spheral Solar™ Cells. Doctoral thesis, University of Northumbria at Newcastle.

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Abstract

Spheral Solar™ Cells are new technology photovoltaic devices originally developed and patented by Texas Instruments Inc. in the USA and since the beginning of 1996 owned by Ontario Hydro Technologies (Canada). Despite the extensive work at Texas Instruments on the production technology, only very little effort has been devoted to studying the optical characteristics of the cells and to optimising the light gathering by specific reflectance-reducing cover structures. Therefore, this was the main aim of this research project.
The approach to this study was based first on the acquisition of a complete understanding of the optical behaviour of the cells by carrying out a set of performance measurements followed by an optical characterisation, and then on the development of tools to be employed for the optimisation process. The innovation and relevance of the project is mainly related to the unique geometry of these devices. In fact, the optical modelling of Spheral Solar™ Cells required the development of a dedicated simulation programme, based on a spherical co-ordinate system as well as on Monte Carlo ray-tracing techniques, which could reproduce the optics of the devices and allow the cover modelling and optimisation.
In order to validate the optical modelling, two experimental facilities were designed and set up as a part of this project: a spectrophotometer and a multi-laser scanner. These facilities are working to the desired specifications and are now available also for other applications. The results obtained indicated the presence of indirect trapping mechanisms and also defined the active areas of the single spheres. On the basis of this information specific reflectance-reducing cover structures have been analysed. The proposed cover structures could improve the cell efficiency by about 25% with an AR-coating layer and by about 15% without it.
The results of this work could be applied to design an optimised cover for the commercial product, but this will depend on the conclusion of satisfactory agreements with the manufacturers.

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