by Jonathan Cole
This article is good insofar as it goes, but it leaves a couple of important points out. The life of batteries can be extended by reducing the cycle discharge depth. So for example a battery that would last 5-7 years with regular 80% depth of discharge, may last 10-12 years with shallower depth of discharge. In the end it is easiest if you calculate your monthly costs since that is what people are used to. By never letting my 4 L-16 batteries to cycle below 12.10 volts and most of the time operating above a voltage of 12.40, I expect to get 10-12 years out my Surrette 530S, 400 amp hour batteries. Connected in series-parallel to yield two 12 volt banks I get a total of 800 amp hours (9600 wattHrs) at the 20 hour rate, but I use less than half that capacity. When I purchased them (5 years ago), they cost about $1200 for the four. If I get 10 years out of them, they will have cost me $120 per year or $10 per month, a very reasonable cost. They key is to balance your solar generating capacity with your battery bank. And you have to size your solar to provide sufficient energy for your basic needs even on dark cloudy days. I run 1720 watts (nominal) of Kyocera panels and rarely require backup power from my generator. I am only a two person household and run efficient equipment and I don’t waste energy. But I am actually in surplus 80% of the time, so I am constantly adding electrical tools like food dehydrators, electric chain saw, and power tools of every sort. I have all the amenities, washer, dryer, electric fridge, large flat screen TVs, computers, stereos, etc. The battery’s life is best extended by allowing for enough storage to meet three nights worth of use and to provide sufficient generating capacity so that your batteries are never chronically undercharged.
For more information, I have a book and a web log at LightOnTheEarth.blogspot.com