Q: I'm considering putting in a few photovoltaic panels to augment the power produced by the 200-watt windplant on my remote homestead. Can I use the same batteries for the two systems since the output of both the solar and ·wind generators will be 12v? Also, I’m currently using recycled golf cart batteries with my wind generator. Are they a good choice, and would they be compatible with both power sources?
A: The combination of solar and wind power generators works well, since, in most areas, the wind blows strongest during the winter (when photovoltaic production is, of course, reduced significantly by the season's typically more frequent cloud cover and shorter daylight hours).
For cost and ease of maintenance, recycled golf cart batteries are hard to beat. Used batteries can often be purchased at salvage prices (for around 18¢ per pound), while new golf cart, deep-cycle battery sets (consisting of two 6V 200-ampere-hour batteries) can still be had for under $200.
The most important thing to remember when using recycled batteries is that each cell should have the same specific gravity and the same characteristics. Don't mix battery types or batteries with different ampere-hours or ages. If you do so, the weakest cell in the system will drag the others down. Therefore, your most important battery tool is a good hydrometer (under $10) to use for monitoring battery condition.
You’ll need to connect your PV array in parallel with the windplant, using a blocking diode to isolate the two systems. In addition, notice that the windplant has a shut-off switch and a fuse or circuit breaker. The PV array should have the same protection, as well as whatever meters are necessary for monitoring it. If you keep your recycled deep-cycle batteries clean and avoid discharging them by more than 40% of their rated capacity, they'll give you years of service.
Solar technology consultant Joel Davidson puts out the PV Network News.