This past December killed the old battery. The system ran almost continuously for almost three years. Not bad, but why did the battery fail? First off, cloudy winters days left the battery very weak. Then you have the cold temperatures. A fully charged battery would go for about five nights. Winter can have cloudy day for ten or more in a row. During the month of December and January the light would be off for days at a time. So basically, I had a drained battery in the cold. Not a good idea. But SLA (Sealed Lead Acid) batteries don’t have a long lifespan anyway.

Now, from data in my area, a sunny winter day will give you about 80% or more power as a sunny summer day. The main reason is temperature. Cold sunny days produce more because heat degrades the solar cell output. This colder temperatures help to offset the fact that the sun is not above the horizon nearly as many hours in the winter. What kills the average solar insolation in Indiana is the clouds. If we did not have the cloud cover, we would have double the average insolation. (Maximum recorded December insolation from ’61 to ’90 was 3.7, almost a 50% increase over average)

My new battery is not a SLA. I can and will perform maintainance.  I purchased a trolling motor battery from Wal-mart. While not a true deep-cycle battery, neither was the price. The old battery was 22aH, now I have an 85aH. I should be able to go almost 20 days before the lights go out. I will need more days of full sun to recharge but I think this is a good trade-off. One sunny day yield two nights with lights. A light overcast would be about one half to one. In the summer I will over produce. But I have an inverter attached to the system so I can find ways to use that. Winter, I think I will turn the night light function down from 4 hours to two total hours. That should help with battery life too.