Time of Diminishing Returns From Our Solar Array

By , November 3, 2009

We received a foot of snow in the first two days of November. Yesterday morning we went out again to sweep the solar panels. This chore reminds me that we’re in the time of diminishing returns for solar power.

Our homestead’s situation is not very advantageous to solar power. Perched beneath a low ridge, facing east, we get sun in the morning, but by midafternoon we begin to lose generative sunlight as shade moves to cover the panels.

Contrary to popular belief, solar panels charge even on cloudy days. It is less than full sun, of course, but there’s still some power coming in. As winter advances and sunlight weakens, though, even the sunniest days will generate less power. The decreased daylight is mitigated somewhat by “bounce,” when sunlight reflects off the snow-covered mountains across the fjord onto our panels, extending our generation time.

We originally installed the panels in time to begin charging just after December 21st, close enough to the winter solstice to fall within the period of least daylight. We did this so that as we became used to the solar panels, we would see a slow but steady increase in available power. Now we’re experiencing the flip side of that choice: we watch as the sunlight steadily declines, and with it, our solar array’s contribution to our power supply.

Daylight lessens seasonally as the earth’s tilt in relation to the sun makes the sun appear lower in the sky each day. Currently at our latitude, we’re losing five minutes of daylight each day. The daily loss will increase until we reach the Winter Solstice minimum of six hours, six minutes. The solar array’s contribution to our power will lessen precipitously, more so on days when snow covers it. At the same time, windstorms become more common, so the wind generator contributes more power than it does in the gentler summer weather.

Last year, the Winter Solstice came amidst a long clear, cold streak. We had full sun on the Solstice. The accompanying 50-knot winds (57+ m.p.h.) prevented us from running the wind generator (our rule of thumb is to shut it down in sustained winds above 40 knots) so we relied wholly on solar power that day.

We marked the occasion by monitoring the amps coming in from the solar panels. We charged for a good hour. We got 0.8 amps at most. That dropped a tenth of an amp per minute after the first half hour, but then we got a couple of hours of “bounce” that gave us a period of 0.1 amps—very small amounts of power, but adequate for our needs. Not bad for the shortest day of the year!

Diminishing solar power is something we’re aware of, but it’s no great concern. With more panels and greater care, we could harvest more solar power throughout the year. Within our current means, solar power is seasonal, like the produce from our gardens, or fish, or moose. It will diminish, but will return again in its proper season.

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