Do Solar Panels Work in Winter? What Happens to Production in Cold Months

Ask most homeowners what happens to their solar panels in winter and you'll get a predictable answer: "They barely work, right? No sun, snow on the roof, done."

It's an understandable guess, but it's mostly wrong. Panels keep producing all winter, cold weather actually helps their efficiency, and snow losses turn out to be far smaller than intuition suggests. The real winter story is about geometry, not weather, and it changes how you should think about whether your home is worth going solar.

Cold weather helps your panels, not hurts them

This is the most counterintuitive part of solar: panels are more electrically efficient in the cold than in the heat. It's basic semiconductor physics, not marketing.

Panels are rated at Standard Test Conditions, which assumes a cell temperature of exactly 25°C (about 77°F). Every degree above that reduces output according to the panel's temperature coefficient, typically -0.30% to -0.44% per degree for modern silicon panels. On a hot summer afternoon when panels heat to 60-75°C, that can cut output by 14% to 22%.

The reverse is true. When the temperature drops below 25°C, panels operate above their rated efficiency. Take a panel with a -0.40%/°C coefficient running at 0°C: that's a 25-degree improvement over test conditions, or roughly a 10% efficiency gain. A 400W panel can effectively produce around 440W in full sun at freezing temperatures.

The National Renewable Energy Laboratory accounts for this cold-weather advantage explicitly in its PVWatts production model, which runs both effects at the same time: the winter irradiance drop from fewer hours and a lower sun angle, and the efficiency boost from cold. On a clear, cold winter day, your panels can produce close to their full rated output despite the freezing temperatures.

The real problem is peak sun hours, not cold

The genuine winter penalty comes from peak sun hours, the number of hours per day that equal full test-condition irradiance. The drop is dramatic, and it's driven by day length and sun angle, not by the weather.

In June, Boston gets about 5.5 peak sun hours a day. In December that falls to roughly 2.1, a 62% reduction. Day length alone drops from 15 hours 17 minutes on the June solstice to 9 hours 5 minutes on the December solstice. And the sun sits much lower: at Boston's latitude, the noon sun is only about 24.5° above the horizon in late December versus 71.5° in late June. A low sun angle means light travels through more atmosphere and hits the panel at a worse angle, both of which cut intensity.

Here's the key takeaway: the seasonal difference is mostly geometry. Cloud cover compounds it, but December in Boston averages only about 15-16 cloudy days, not dramatically different from other months. Your panels aren't failing because of snowstorms; they're producing less because the sun is lower and the day is shorter.

What that actually means for your output

NREL's PVWatts data for a standard 10kW system, south-facing at 20° tilt with 14% system losses, shows typical monthly output by city:

| City | December (kWh) | June (kWh) | Winter/Summer | Annual (kWh) | |------|--------------|-----------|---------------|-------------| | Phoenix, AZ | 1,250 | 1,680 | 74% | 17,200 | | Denver, CO | 960 | 1,680 | 57% | 15,200 | | Dallas, TX | 1,020 | 1,620 | 63% | 15,400 | | New York, NY | 680 | 1,720 | 40% | 12,800 | | Boston, MA | 670 | 1,750 | 38% | 12,600 | | Chicago, IL | 570 | 1,620 | 35% | 11,800 | | Minneapolis, MN | 490 | 1,640 | 30% | 11,400 | | Seattle, WA | 330 | 1,380 | 24% | 10,200 |

A few things jump out.

Even in the worst month of the year, Seattle still produces 330 kWh in December. At a typical local rate, that's real dollars of electricity offset even on your darkest days.

Winter output is not negligible. In Boston, the four winter months (November through February) contribute roughly 2,800 kWh to an annual total of 12,600, about 22% of the year's production. At Boston's roughly 29¢/kWh rate, that's around $810 of bills offset every winter, before you touch a summer month.

What snow actually does

A fully snow-covered panel produces close to zero, so the concern is real. But NREL research at sites across the northern U.S. found average annual production losses from snow of just 1.5% to 5.3% in most northern markets. That's much lower than most people expect, for a few reasons:

• Tilt helps. Residential panels mount at 15-35°, and snow starts sliding off before it builds up on surfaces steeper than about 10°.
• Snowstorms are short. Most last 12-36 hours. If your panels are clear before and after, the total loss per event is modest.
• Winter is already low output. Losing 3 kWh on a snowy December day hurts less than losing 3 kWh in June.

There's even a bonus. Fresh snow reflects 80-90% of the light that hits it (an albedo of 0.80-0.90), and that reflected light can add a little to what your lower panel edges pick up.

How to smooth the season for yourself

A few practical points if you're weighing solar in a cold climate:

1. Tilt angle matters. A steeper tilt of 45-55° captures more of the low winter sun at northern latitudes by facing the low sun more directly. The tradeoff is some summer output, and most residential systems are tuned for maximum annual production rather than maximum winter output.

2. Net metering carries the season. In most net metering states, your surplus credits roll forward month to month. You build up a credit balance during the high-production summer and draw it down through winter. That's how a system sized for the year keeps your bill low even in the dark months, without any battery required. (Note that the rules vary a lot by state, and some regions have shifted toward net billing, where the value of what you export to the grid is lower. Worth understanding your local policy before you commit.)

3. Cold climates can still win on ROI. Massachusetts, New Jersey, and New York consistently rank among the better U.S. states for solar returns despite cold winters, because high local electricity rates often matter more than raw sunshine.

Bottom line

Winter does not shut down your solar. Panels keep producing, the cold actually improves their efficiency, snow costs you a few percent at most, and net metering lets your summer surplus cover the winter gap. The honest number is that winter months typically deliver 24% to 74% of summer output depending on where you live, and that's enough to offset real bills year-round.

But "enough" depends entirely on your specific roof, your local climate, and your utility's rates. The average numbers above are averages, and your home is not an average.

If you want to know what your roof would actually produce, month by month, and what that means for your bill, the fastest way is to run your address through SolrScan. It scans your home from satellite imagery and builds a solar potential report: annual sunshine hours for your exact address, a recommended panel count and wattage, an estimated system size and cost, and projected savings. It takes a couple of minutes and costs $19.

Start here: https://solrscan.com