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Solar Irradiance of a Photovoltaic Panelís Rear Face: Models Applicable to Snow Removal and Bifacial Technologies

Michael M.D. Ross
CANMET Energy Diversification Research Laboratory

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Note on Authorship:

This article was authored by the principal of RER Renewable Energy Research when he was an employee of the CEDRL (now known as CETC-Varennes).

Acknowledgements:

Funding for this project was provided by CETC-Varennes through the Panel on Energy Research and Development (PERD), Canada's Green Plan, and the Science Institute of the Northwest Territories (SINT) as part of the joint NRCan/SINT "PV for the North" programme.

Citation:

Ross, Michael. ďSolar Irradiance of a Photovoltaic Panelís Rear Face: Models Applicable to Snow Removal and Bifacial TechnologiesĒ. Proceedings of the 22nd Annual Conference of the Solar Energy Society of Canada, Orillia, Ontario, June 1996.

Abstract:

There exist several technologies, such as bifacial photovoltaic panels and the TN Conseil passive snow melting system, which utilize solar radiation incident on the rear face of a photovoltaic panel. In order to assess and predict the performance of such technologies, it is necessary to mathematically model the solar radiation striking the rear face of the panel.

Radiation incident on the rear face can be broken into beam, diffuse, and ground-reflected components. For the beam and diffuse components, the mathematical models for the front face apply equally well to the rear face. The front face, ground-reflected radiation model assumes that the ground is a uniformly illuminated diffuse reflector; while this is a reasonable assumption for the front face, it may not be a good assumption for the rear face, due to the portion of the ground "seen" by the panel that is in the array's shadow. Nevertheless, the model for the front face is often applied to the rear face, since accounting for the shadow requires complicated ray-tracing techniques.

In this paper, equations describing the ground-reflected solar radiation incident on the rear face of an array are developed. While these equations must be solved numerically, they are conceptually simpler than ray-tracing methods and can be implemented using standard numerical methods. This model that accounts for the shadow and the model for the front face are compared. The models are also compared with experimental data. It is determined that the shadow of the array significantly affects the radiation incident on the rear face of the panel when the array is large, relatively close to the ground, and mounted well off the vertical, and especially when the sun is relatively high in the sky.

This paper draws upon the results of a study that was carried out as part of PV for the North, a five year photovoltaic research, development, and technology transfer program supported by the Canada Centre for Mineral and Energy Technology (CANMET) and the Nunavut and Aurora Research Institutes.