Solar panels performance in the winter vs summer (with examples)
Contrary to popular belief, it is possible for solar panels to generate a lot of electricity in the winter.
I live in Buffalo, New York. It snows a lot here. Some years, it seems like winter lasts for nine months. And yet, I have a solar panel system that still provides some electricity in the dark winter months.
While there is definitely less production in the winter months, I still come out on top financially with home solar. To illustrate what this looks like from summer to winter, I’ll share some graphs from my system below. But first, here’s a table that shows my average total production in three different months over 5 years:
|December average||March average||July average|
|122 kWh||430 kWh||717 kWh|
As you can see, the summer is when my system generates the most electricity, with an average total generation of 717 kilowatt-hours in the month of July. December produces only 122 kWh, which is just 17% as much as July. March is a lot better at 430 kWh, but still only 60% of July’s average.
So summer is the best overall for me, but you might be surprised that there are days even in the middle of winter when you can generate a lot of electricity. Depending on your climate, you might even do really well. More about that below.
What’s the best time of year for solar energy production?
It turns out that you might get your best solar energy output in the spring, and not the summer as you might think. This is because that solar panels produce less electricity when it’s hot.
This is a well-known phenomenon, and you will see it listed in the specifications on your solar panel datasheet. It is called the power temperature coefficient, and it will be listed as a percentage of power output loss per degree Celsius (%/°C).
For example, if your solar panel lists a power temperature coefficient of -0.30%, this means that it produces 0.30% less power for every one Celsius degree increase in temperature.
So far this year, the day on which I had the highest production was a perfectly clear day in May:
The high temperature in Buffalo that day, according to Weather Underground, was a cool 56°F and it was clear all day. (See that smooth production curve?) My 18 panel system generated a total of over 33 kilowatt-hours.
I still generate more electricity in the summer months, but that’s because here in the spring, we still get a lot of rainy and cloudy days. But if you live somewhere like the southwest where it rains less frequently, you might find that spring months are when you have the best overall production.
How much electricity do solar panels generate in winter?
Winter here is a different story. It snows a lot, and snow can cover my entire system for a week or more.
A light dusting of snow will get blown away, but after about an inch of snow accumulates on the panels, electricity production is stopped completely. Here’s what that looks like:
You can see that the day’s production wasn’t measured in kilowatt-hours but 441 watt-hours - less than a single kWh! The graph is basically flat all day. It doesn’t matter if it’s sunny - when my panels are covered in an inch or two of snow, production stops completely.
My panels aren’t easy to reach. I would need a high ladder to do that, and bringing an extension pole up to my roof in the middle of a Buffalo winter just isn’t worth a possible trip to the hospital. So leave the snow and wait for it to slide off, which usually happens the next time its sunny and warms up a little bit. Even if its still below freezing, the warmth of the sun is usually enough to warm up the roof and cause the snow to slide off.
But you can still generate a surprising amount of electricity in the winter, partly because of the power temperature coefficient effect mentioned above. When the temperature drops, your panels gain efficiency. That means if you live in a place where you get a lot of sunny winter days, you might generate a lot of solar electricity.
Here’s one sunny day with my system in Buffalo:
That’s about half as much as a best day in spring, which is pretty good considering how low the sun is in the sky and how short the days are.
If you live in a sunny and cold winter, you might generate enough solar electricity to fully power an electric heat pump system - a great option if you want to heat your home without fossil fuels.
An average day of solar generation in winter
Here in Buffalo, an average day in winter is just grey. It doesn’t snow every day, and most days my solar panels are clean. The sun rises at 8 am and sets at 4 pm. This is what that looks like:
If every day was like this, I’d get 120 kWh for the month, which is pretty exactly what my 5 year average was. That’s about enough power for my lights and electronics, but not much else.
Solar electricity generation on a sunny summer day
Summer here means a lot of sunny days, and because of that the summer months are the best overall for my electricity generation. But it’s also hot, which means that my solar panels run at a lower efficiency. This clearly shows up in the production reported by my Enphase system. Here’s one peak day in July:
You can see a nice smooth production curve, showing that it was a clear sky all day long. And yet, with a total production of 28 kWh for the day, that’s noticeably less than the day on May 8 where the system produced 33 kWh, even though this day in July was almost a full hour longer.
How much solar generation can you expect in the winter?
Depending on where you live, your solar generation will probably look a lot different from mine. For example, if you live in the southwest, you will see a lot more sunny days in December and January that I do here in Buffalo.
However, if you live in the northwest, your weather will be probably be grey and rainy for much of the winter - definitely less favorable for solar. You can use a weather service like Accuweather to find out what the historical averages for your city are.
Selecting a solar panel that will perform better in hot weather
If you live in a really hot climate, you might think about choosing a panel that will maintain high performance even when it’s really hot.
To do that, look at the data sheet and select one with a higher value for temperature coefficient. Remember that the coefficient is always listed as a negative number, which means that a number that is closer to zero means better performance. If the coefficient is closer to zero, it means that the panel loses less efficiency compared to one that has a larger negative number listed.
Does it matter if I produce less electricity in the winter?
This is where net metering makes a difference. If you have net metering, it means that the excess electricity you generate in the summer will be banked as credits that you can “spend” in the winter.
But if you have net billing or a feed-in-tariff scheme, you might not get full credit for the excess electricity that you send into the grid. This means that you’ll be paying the retail rate for more grid electricity in the winter when your panels don’t generate as much, but get paid a lower rate for excess power that you send into the grid in the winter.
Fortunately, most states have net netering available. But if you live in place that doesn’t offer this, there are things you can do to get maximum benefit from solar, even under net billing. Read my guide on net metering to learn more about this.
How do I calculate solar production by month?
If you’re thinking of going solar, you can use The Solar Nerd calculator to estimate how much electricity you might generate in the winter versus the summer. The calculator quickly generates an power production estimate based on your location, roof conditions, and climate.
After you run the calculator, you will see a graph like this toward the bottom of the report:
This estimate is for my home. The absolute numbers aren’t quite correct, but the relative numbers (that is, the relative difference between summer and winter) are pretty close. Keep in mind that your actual numbers could vary a lot from one year to the next, but these estimates, which are based on historical climate averages, should be quite accurate over the long run.