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This article was co-authored by Michael M.D. Ross, principal of RER Renewable Energy Research, while he was an employee of the CANMET Energy Diversification Research Laboratory (now known as CETC-Varennes); his co-author was Dave Egles of Soltek Solar Energy, which has become SPS Energy Solutions, a subsidiary of Carmanah Technologies Corporation.
The background work for this study was conducted under PV for the North, a five year photovoltaic research, development and technology transfer program supported by Natural Resources Canada and the Nunavut and Aurora Research Institutes. The authors would like to acknowledge the contribution of François Leblanc, formerly of the CEDRL, for his early work on insulated battery enclosures with PCM.
Michael M.D. Ross and Dave Egles. "Valuing the Benefits of Insulated Battery Enclosures for Stand-Alone Photovoltaic Systems in Cold Climates". Proceedings of the 23rd Annual Conference of the Solar Energy Society of Canada, Vancouver, B.C., Canada: June, 1997.
In most Canadian remote-area power supplies, lead-acid batteries are used to store the energy generated by photovoltaic arrays, wind turbines, and gensets. Unless the batteries are installed in an insulated and/or heated enclosure, the temperature of the batteries at a given point in time will be roughly equal to the average ambient temperature over the previous day or several days. As a result, at most Canadian sites the batteries will be very cold during winter; this significantly affects the battery's performance, and reduces its useable capacity.
This paper examines the various effects of cold temperatures on lead-acid batteries and outlines several options for protecting the batteries from extreme cold, including insulated enclosures, phase change materials and resistive heating by photovoltaic panels.
A qualitative assessment of the importance of variables associated with the choice of battery, the site, and the design of a system is followed by a quantitative case study, in which various insulated battery enclosures are compared. Thermal protection permits smaller battery banks to offer the same reliability as large, uninsulated battery banks. It is shown that for all but the warmest Canadian sites, a 15 cm envelope of insulation is cost-effective for battery banks larger than about 1.5kWh of minimum useable capacity. This is conservative, since it does not account for the heat generated by the batteries themselves on charge and discharge; it is demonstrated that this significantly affects minimum battery temperatures, especially for large battery banks. Enclosures using phase change material (PCM), which can guarantee a minimum year-round battery temperature, and enclosures using PCM and heating provided by power from the array when the battery is fully charged are even more cost-effective than insulated enclosures when batteries are relatively expensive and voluminous or the site is relatively cold, e.g., in Northern Alberta. In addition, it is demonstrated that the deeper cycling caused by reducing the battery bank size will not shorten battery lifetime in typical Canadian PV systems.
Created 2007/03/08 Updated 2007/03/08 ©2007 RER Renewable Energy Research