do solar panels work in the winter?

Short answer: yes, during daylight hours of course!

Sunrise to sunset, faithfully.

So here’s the long answer…

Our solar arrays come with a internet-connected software that allows us to see minute-by-minute production, down to each individual panel. Yes, it’s a dream for a data-glutton like myself, especially on these cold, rainy days (yuck!).

But it quickly gets confusing. When I talk solar, most people ask me 1) “are you going off the grid?” and 2) “where’s the batteries?!” Neither of which we are currently interested in. But both have a lot to do with two important terms: energy & power.

Energy is the capacity to do work (exerting a force over a distance). Power is the instantaneous rate of producing or consuming energy.

A microwave will pull around 1 kilowatt (kW) of power. If you leave it on for an hour (which I don’t recommend), it will consume 1 kilowatt-hour (kWh) of energy. Ditto if you run two microwaves for half the time… it’s still 1 kilowatt-hour, and the utility will bill you $0.15.

When you think of your home, the power (electricity) is ultimately limited by the size of the transformer feeding your home. For homeowners, the utility charges for the energy you consume… that is, power over the course of time (a month).

Think of water in a bathtub as an analogy. Whether you fill it quickly or slowly (power), it still takes the same volume of water (energy) to get it full.

Nature stores potential energy (ability to do work) in it’s carbon bonds, powered via the slow process of photosynthesis.

So… solar panels are rated by their maximum power output. We installed 295-watt Solarworld panels. They are engineered to max out at 295-watts (power) here in Indiana just as they would in Texas. But over the course of Texas’ longer and sunnier days (sigh…), they will produce more energy down South.

Ok, did I over-explain that? Good. (No? Read more, or watch a video).

Just to complicate things further, our solar installation features single-axis tilting to maximum both power & energy (I posted the video in August). Our arrays always face south (azimuth of 180 degree), but we tilt them four times a year, between 12 degrees in summer and 45 degrees in winter.

Like this (ignore their angle values):

So… do they produce in the winter?

Yes, solar panels are actually more efficient at cooler temperatures.

So when it comes to maximum power, there are some great cool and sunny winter days.

This photo above is from December 30, when the temperature was just above freezing. Power peaked at 12:30 pm at 64,200 W, which was higher than at any point registered in July or August. (The record output so far was 66,825 W on October 16th).

It was sunny all day on Dec. 30, so the power profile shows a steady rise to midday, a plateau, then a slow decline as the sun set.

The total energy produced that day was 356 kWh, all between 8:00 AM and 5:00 PM, a scant 9 hours. That was the most of any December day.

So even though the maximum power exceeded anything from July or August, the short days of December mean less energy is produced overall. December as a whole was about 45% that of July’s production. The average day in July produced 380 kWh. July 6th had 526 kWH produced between 6:30 AM and 8:30 PM, during the full 14 hours of daylight.

Two final notes on weather: clouds, and snow.

While energy production over the course of an entire year is very predictable, day to day variation in solar irradiation can be substantial.

Here’s a snapshot of the last day of the year (I’m writing as the sun sets). It’s December 31st, and you could barely tell the sun was up. Cold and drizzly rain all day long. The maximum power was 2,500 W, a scant 4% of the maximum from the day previous! Total energy production was 7 kWh.

Because we have net metering, and aren’t concerned about going off-grid, this doesn’t concern us in the slightest, aside from the crummy feelings many of us experience on these gloomy days!

Intermittency is a reality for grid operators managing renewable energy resources. But grid resilience is an emergent function of the whole, not merely a sum of its parts. Suffice it to say that grid dynamics can be a little counter-intuitive, and adding in new energy sources is more than doable with the tools we have available. It’s an exciting time! (Well, if you’re a nerd).

Ok, snow time. This is a photo of the 24-panel Moontree Studios array on November 27.

Below is a snapshot of the energy production of these same panels on Nov. 27-28. Each panel is labeled with its energy production in Watt-hours. Switch back and forth between the photos… Notice that snow clinging to any particular panels does reduce production for that panel.

But generally, we don’t worry much about snow. It comes during the few months where production is already lower. The racks are tilted up at 45 degrees, so that keeps it from accumulating (to a point). The panels are dark and made of glass, so it gives a chance for snow to melt and slide off. An energetic homeowner could even take a soft broom and carefully brush the snow off in a matter of a couple minutes. I know someone who does this in Mishawaka, just as they shovel snow from their small stretch of sidewalk.

Ok… all that, and we didn’t get into DC/AC conversions, inverter sizing and efficiency, and so on. More to come. So far, so good…

3 Replies to “do solar panels work in the winter?”

  1. Linda Volk

    ZOWIE! That being said, I bet you could also add how many angels could stand on the edge of a pin lying on the fourth quadrant of the ninth panel of the solar panel by MoonTree! Just teasing, thanks for the explanation – rather fascinating and I’m sure pure poetry for some.

    Reply

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