The latest winter weather event left us with 8-12″ of fresh snow, the largest deposit of the season. We have been blessed with many smaller snowfalls though, enough to remind us why we advocate for solar photovoltaic (PV) panels to be installed on ground-mounted racks where snow is likely. Yesterday was a fine example of the energy that could be harvested, even during a day of snow and eventual thinning clouds. We started the morning with the Tri-Metric Meter (our electrical system’s fuel gauge) indicating that our system was at 95%. We have this meter programmed to read the top 50% of our lead acid gel battery bank’s capacity. So when the meter gets down to 0%, there is actually still 50% left in the batteries. Never using more than 50% of the capacity greatly extends the lifetime of a lead-acid battery. So a 95% reading meant that we had used 5% of the top 50% the night before, or 2.5% of the total battery capacity. Since it was snowing quite hard, it seemed like a good time to get some office work accomplished indoors, and an hour of computer and satellite modem use drew the system down another 1%.
Around 9:00 a.m. we swept snow from the PV panels, and there was enough light filtering through the clouds and snow to charge at a 4 amp rate (our system has the ability to bring in up to 140 amps at noon on a sunny day). Even at that low rate, we would gain nearly 1% per hour, but the snow continued to fall and was covering the panels. At 10:00 a.m. we swept the panels again, this time gaining at a rate of 11.2 amps, or over 2% per hour. The snow continued to fall heavily, so by 11:30 a.m. the charge had dropped to 8.8 amps and we swept the panels for a third time. This resulted in a 21 amp charge coming in.
The system was now at 97% and we decided to cook lunch on the AC electric hotplate. Lunch was done by 11:50 and the batteries were down again to 96%, after which there were 40 amps coming in. The television (12V-DC LCD) was turned on to catch the noon weather report. At 12:15 p.m., we were still gaining 27 amps, the batteries soon filled to 100% capacity, the TV was off, and the “diversion loads” (water heating and small refrigerator) switched in. Despite the continued snow and clouds for the rest of the day, we also did about an additional hour each of working in the office, updating the web site and doing some research. We went into the evening with the batteries filled to capacity, the contents of the refrigerator icy cold, and some hot water in the tank, although the evening’s wood fire also contributed to the hot water. All in all, not a bad day for our solar system considering the sun wasn’t even shining, although there was a brief, hazy gold spot through a thin area in the clouds late in the afternoon. Just goes to show that even in cloudy weather, there is some energy to be harvested if the PV panels are not covered in snow. A broom makes quick work of the task of snow removal as long as the panels are easily accessible. If our panels were roof-mounted, even with a “catwalk” or some other way of safely getting a broom to them, it would have been more likely that we would have left the snow to accumulate all day and the potential energy harvest would have been lost. Sweeping the solar panels for us is just a way of ensuring that our investment continues to repay us with the maximum dividends.