Solar Panels in Winter: How Much Output Drops and Why

Solar panels work in winter, but they make much less electricity. The cause is mostly daylight, not cold: shorter days and a lower sun cut output, while cold temperatures slightly improve panel efficiency. In the two NREL estimates we reviewed, December output ranged from about 47% of June’s in Missouri down to about 14% of July’s near Seattle, before counting any snow on the panels.

That gap matters for how you judge a system. A winter bill that barely moves after you go solar is normal, and it is why your utility’s crediting rules count as much as the hardware. Our guide to net metering by state explains how summer surplus can carry a household through winter.

Why Winter Output Falls

Three things change between summer and winter:

• Fewer hours of sun. Panels only produce in daylight, and winter days are shorter.
• Lower sun angle. The sun sits lower in the sky, so light hits the panels at a steeper angle and passes through more atmosphere.
• Weather and snow. Cloudier months and snow cover cut output further. Snow is local and varies widely by region and roof (see below).

Cold is not the problem. Panel datasheets list a temperature coefficient: how much power changes for each degree away from the 25°C (77°F) cell temperature used for ratings. For the Qcells Q.MAXX-G5+ panel, that coefficient is −0.34% per °C, so power falls when cells get hotter and rises when they are colder.

Our arithmetic, using that datasheet figure: a cell at 0°C is 25 degrees below the rating temperature, which works out to about 8.5% more power than rated (25 × 0.34%), all else equal. A cell at 60°C on a hot summer roof is 35 degrees above it, about 11.9% less. Cells in sunlight run warmer than the air, so real figures will differ. The point is direction: cold, clear days are good for panels; they just don’t last long.

What the Monthly Numbers Look Like

NREL’s PVWatts calculator estimates monthly output from local weather data, system size, tilt and direction. We found two PVWatts reports in public filings and compared their best summer month with December.

Sources: NREL PVWatts reports as filed; shares are our calculation.

What this means per household. The Kirksville estimate works out to about 71.5 kWh per kW of panels in December and 151 kWh per kW in June. Scaled to a 7 kW home system, that is roughly 500 kWh in December and 1,057 kWh in June, and about 9,915 kWh a year (our arithmetic, assuming output scales with size). November through January together produce about 16% of the year’s output in that estimate; May through August produce about 41%.

The Seattle case is more extreme for two reasons: Pacific Northwest winters are cloudy, and a nearly flat array catches little of a low winter sun. In that estimate, November through January produce about 7% of the year’s total.

Two cautions. These are typical-year model estimates, not measurements, and neither represents your roof. The Kirksville system is a commercial-size, open-rack array modeled with older typical-year weather data from Columbia, Missouri; we use it only for its monthly pattern. You can run PVWatts for your own address, and a good installer quote should show a monthly production estimate. Our guide to comparing solar quotes covers what to look for.

How Much Snow Costs

Snow is a separate loss on top of shorter days. A 2017 NREL technical report by David Severin Ryberg and Janine Freeman (NREL/TP-6A20-68705) modeled snow losses across the U.S.:

• Annual losses for fixed-tilt systems ranged from 0% to about 16% in the continental U.S. One Alaska site came out at almost 40%.
• The highest continental losses were in Minnesota and Michigan. International Falls, Minnesota, came out at 15.9% and Sault Ste. Marie, Michigan, at 15.1%, both for a 20-degree tilt.
• Local terrain matters. Flagstaff, Arizona, was modeled at 3% to 5%; Phoenix had none.
• Steeper panels lose less. Systems tilted at an angle equal to the site’s latitude generally showed lower losses than 20-degree systems in the continental U.S., because snow slides off sooner.

The authors caution that the figures are a starting point for typical years and that the model should be used for annual estimates, not month by month.

What 1% is worth. For the 7 kW example above (about 9,915 kWh a year), each 1% of annual snow loss is about 99 kWh. At 18¢ per kWh, close to the U.S. average residential price EIA forecasts for 2026 (see our EIA price forecast report), that is about $18 a year. A 5% loss would be about $89; a 15.9% loss about $284. Your own rate and climate will change these numbers.

Should You Clear Snow Off Your Panels?

For most homeowners, no:

• Roof safety comes first. A snowy, icy roof is a fall hazard. The dollars at stake, from the math above, are usually small.
• Snow slides off tilted panels. NREL’s model treats sliding as the main way snow leaves panels, and steeper tilt speeds it up.
• Tools can void a warranty. Panel makers set rules for what can touch the glass. First Solar’s module cleaning guidelines, for example, say not to use prohibited tools to remove snow “as it may damage the modules” and state that “Failure to comply with the Module Cleaning Guidelines may void warranty.” Other makers’ manuals warn against sharp or pointed objects on the module. Check the manual for your own panels before using anything.

If panels on a low roof or ground mount are reachable from the ground, a soft, non-abrasive tool approved by the manufacturer is the safer route. If you’re worried about snow load on the roof itself, that’s a question for a roofer or structural professional, not a reason to climb up.

What It Means for Your Bill

Lower winter output means winter bills usually rise even with solar, especially in homes with electric heat. Three things decide how much:

1. How your utility credits exports. With monthly rollover of net metering credits, summer surplus can cover winter shortfalls. Where exports earn a lower rate or credits expire monthly, winter bills are harder to offset. The Colorado Springs Utilities changes are one recent example of rollover rules changing.
2. Fixed charges. Monthly customer charges are billed whether or not your panels produce. Our guide to fixed charges and solar explains why they weigh more in low-production months.
3. Your winter usage. A heat pump or electric resistance heat can push winter use far above summer. If you are adding one, size the system with that load in mind.

If a smoother bill matters to you, ask your utility about budget billing, which spreads costs evenly across the year.

Sources and Verification

Shares, per-kW figures, the 7 kW scaling, temperature arithmetic and dollar values are our calculations from these sources.