Data approachEIA rates · NREL sun hours · 2026 federal policy · methodology
Yes, solar panels work in winter. Cold air does not hurt them; shorter days and a lower sun do. For a 6 kW system, NREL PVWatts-based figures put average December output at roughly 24 kWh per day in Phoenix, 11.5 kWh in Boston and 7.5 kWh in Seattle. That range surprises many homeowners who assume a system goes dormant for three months.
The real driver of winter underperformance is the amount of sunlight, usually measured in peak sun hours. Your annual energy bill is what matters for most financial calculations, and winter shortfalls are typically balanced against higher spring and summer production, subject to how your utility credits exported power. The seasonal pattern is also predictable, which makes winter output easy to model before you buy.
This guide covers what actually changes in winter, how output varies by city, how snow and clouds matter, and how to size a system so you are not surprised by a January bill.
⚡ Efficiency
Do Solar Panels Work in Cold Weather? How Temperature Affects Efficiency
Solar cells convert light, not heat, into electricity, and silicon cells become slightly more efficient as they get cooler. Panel ratings are measured at a cell temperature of 25°C (77°F). Above that, power drops by a fixed amount per degree, set by the panel’s temperature coefficient. Most modern panels fall somewhere around 0.26% to 0.40% per °C, and the exact figure is on each model’s datasheet.
That means hot weather is the bigger efficiency problem. Rooftop cells in summer sun can run 20°C or more above the air temperature, which can trim output by several percent. In winter, cells are cooler, so each hour of sunshine is converted a little more efficiently. The gain is real but modest, because panels still warm above air temperature in direct sun. It does not come close to offsetting the loss from fewer hours of light.
The practical takeaway is that peak sun hours, not temperature, determine winter output. One peak sun hour is the equivalent of one hour of sunlight at 1,000 W/m², the intensity used to rate panels. A simple estimate of daily production is:
Daily kWh ≈ system size (kW) × peak sun hours × 0.83
The 0.83 factor is the default system derate in NREL’s PVWatts v8, which bundles inverter, wiring, soiling and other losses. Using roughly 2.3 peak sun hours for Boston in December, a 6 kW system works out to about 11.5 kWh per day, which matches the figure in the next section.
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📊 Real Data
How Much Do Solar Panels Produce in Winter? Output by US City
The United States has a very wide range of winter solar resource. The table and chart below compare average daily output for a 6 kW system in three cities, using PVWatts v8 results for a fixed-tilt array.
City
December (kWh/day)
June (kWh/day)
December as % of June
Phoenix, AZ
23.7
40.7
58%
Boston, MA
11.5
30.4
38%
Seattle, WA
7.5
29.3
26%
Data visualization
December output is far more location-dependent than summer output. A 6 kW system averages 23.7 kWh per day in Phoenix in December but only 7.5 kWh in Seattle. Source: NREL PVWatts v8 results, fixed tilt, default losses.
Chart summary: Summer output is in the same general range in all three cities, but winter output is not. A 6 kW system in Phoenix averages about 24 kWh per day in December, roughly three times Seattle’s 7.5 kWh and more than double Boston’s 11.5 kWh, or about 735, 357 and 233 kWh over a 31-day December. These are single-city examples from a typical meteorological year, so your own result will differ with tilt, shading and weather.
Do Snow and Clouds Stop Solar Panels From Working?
Clouds reduce output but do not stop it. Panels keep generating from diffuse light, and heavy overcast commonly cuts production to roughly 10–25% of what the same array would produce in clear sun. Because cloud cover is already part of the typical-year weather data used in tools like PVWatts, a good estimate already reflects an average amount of cloudy weather.
Snow is different. A light dusting that melts or slides off by mid-morning barely affects monthly totals. A thick layer that sits on the array for days behaves like full shading, and output stays near zero until it clears. Over a full year, snow losses are usually a few percent of production, with higher losses for low-tilt arrays in snowy regions. Steeper pitches shed snow faster, which is why installers in snowy areas sometimes favor a steeper tilt.
If you do decide to clear snow, do it from the ground with a soft roof rake designed for solar panels, and never climb onto a snowy or icy roof. Scraping can scratch the glass and may affect your warranty, so check the manufacturer’s guidance first.
📋 Key Insights
How to Size a Solar System for Winter Production Shortfalls
The standard approach is to size a system to cover your annual electricity use. That implicitly accepts a winter deficit and a summer surplus. It works best when your utility credits exported power at or near the retail rate, because spring and summer credits offset winter bills. Our net metering calculator can model how this plays out under your rate structure.
Many utilities and states have moved to net billing or other structures that pay less for exported power. If exports are credited at a low rate, oversizing for summer is less rewarding, and sizing closer to your daytime and winter load can make more sense. Check your utility’s current export rules before choosing a system size.
Sizing for December alone is usually impractical in cloudy northern climates. Using the figures above, a Boston system produces about half of its average monthly output in December, and a Seattle system about 40%. Covering a winter month’s full usage can therefore take a system roughly two to three times larger than one sized for annual offset, which most roofs cannot hold.
Data visualization
Phoenix keeps 58% of its June output in December, while Seattle keeps 26%. Each value is December kWh per day divided by June kWh per day for a 6 kW system. Source: NREL PVWatts v8 results, fixed tilt, default losses.
Chart summary: The lower a city’s December share of June output, the larger the gap a system sized for annual use has to cover in winter. Seattle’s 26% means December production is about one quarter of June, while Phoenix keeps more than half. Use your own PVWatts run to see where your address falls.
All-electric heating makes winter gaps larger, since a cold-climate heat pump can add several hundred kilowatt-hours or more to a January bill. A well-insulated home and a time-of-use plan, where you draw cheap overnight grid power and let solar cover daytime loads, is usually more cost-effective than trying to cover that load with panels alone.
Batteries add resilience during winter storm outages and can shift solar or cheap off-peak power into the evening, but they do not create extra winter generation. Whether a battery pays back depends on your rates and incentives, so model it for your situation with our battery storage calculator.
One financial note: the 30% federal Residential Clean Energy Credit (Section 25D) no longer applies to homeowner-owned systems placed in service after December 31, 2025, according to the IRS. State, local and utility incentives may still apply, so check them before comparing quotes. Our state incentives pages are a good starting point.
📋 Key Insights
Winter Solar Output in the UK and Australia
Seasonality is stronger the farther you are from the equator. In the UK, winter solar output is a small share of the annual total, with most generation coming from late spring through summer. That means UK solar economics depend on annual production, export payments under the Smart Export Guarantee and the price of grid electricity, rather than on winter output alone.
In Australia, winter runs from June to August. Output in northern and western cities such as Brisbane and Perth stays comparatively strong, while southern cities such as Melbourne see a bigger seasonal swing. In areas with a lot of rooftop solar, export limits and midday curtailment can matter as much as winter output.
In both countries, the most reliable approach is the same as in the US: ask for a month-by-month production estimate for your exact roof rather than relying on a single annual average.
📋 Key Insights
How to Check Your Winter Estimate Before You Buy
Most solar quotes lead with an annual number, such as 8,000 kWh per year. That is a useful headline, but it hides how production is spread across the year. Before signing, ask your installer for a month-by-month estimate generated with PVWatts or a comparable NREL-based tool, and compare the December and January figures to your own bills.
Check the inputs behind that estimate. Confirm the tilt and azimuth, and that shading from trees or nearby buildings is modeled, because shading matters more when the winter sun sits low. Panels facing within roughly 15–30° of true south typically lose only a few percent of annual output, so a small deviation is rarely a deal-breaker. Make sure system losses are not set unrealistically low; PVWatts defaults to about 14%.
Hardware choices can help at the margins. Module-level power electronics such as microinverters or optimizers can reduce losses when part of an array is shaded or snow-covered, which is most relevant on complicated or partly shaded roofs. Panels with a lower temperature coefficient lose less output in heat, though the difference in winter is small. Run your numbers through our solar payback calculator to see how these choices affect your break-even timeline. For state-by-state figures, our guide to Solar Panel Payback Period by State shows where solar pays off fastest.
Sources: NREL PVWatts v8 (pvwatts.nrel.gov) for monthly production estimates and the default 0.83 derate; city figures are PVWatts-based values for a 6 kW fixed-tilt system and should be re-run for your address; IRS Residential Clean Energy Credit page for the Section 25D status.
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Direct answers for US homeowners — sized for a $150/month electric bill.
Yes. Solar panels generate electricity from sunlight, not heat, so they keep producing in cold weather. In fact, panel power rises slightly as cell temperature drops. The reason winter output is lower is shorter days and a lower sun angle, which reduce the amount of sunlight reaching the panels. Depending on location, December output for a typical system is roughly a quarter to a little over half of June output.
It depends mainly on location. Based on NREL PVWatts-derived figures, a 6 kW system averages about 24 kWh per day in Phoenix, 11.5 kWh in Boston and 7.5 kWh in Seattle in December. That is roughly 58%, 38% and 26% of each city's June output. To estimate your own system, multiply system size in kW by your December peak sun hours and by about 0.83 for system losses, or run your address through NREL PVWatts.
Yes, but snow covering the panels stops production until it clears. A thin layer often slides or melts off within hours because the dark panel surface warms in sunlight, and steeper roof pitches shed snow faster. Over a full year, snow losses are usually a few percent of production, higher for low-tilt arrays in snowy regions. Avoid scraping or using tools that could scratch the glass; if you do clear snow, use a soft roof rake from the ground and never climb onto an icy roof.
Yes, at reduced output. Panels still capture diffuse light through clouds, but heavy overcast commonly cuts production to roughly 10–25% of what the same array would make in clear sun. Because cloud cover is built into NREL's typical-year weather data, a PVWatts estimate already accounts for an average amount of cloudy weather.
Often yes, because the financial case rests on annual production, not December alone. Under traditional net metering, surplus from spring and summer is credited against winter bills, but many utilities now pay less for exported power, which can reduce the value of that summer surplus. Note also that the 30% federal Residential Clean Energy Credit (Section 25D) no longer applies to homeowner-owned systems placed in service after December 31, 2025, so check state, local and utility incentives and get a quote that models your actual rates.
$150/month electric bill by state
System size and payback vary by electricity rate and sun hours — see your state.
18.19¢/kWh — US average residential price. Source: EIA Electric Power Monthly, Table 5.6.B (year-to-date through July 2026), residential average retail price (July 2026) (EIA)
Solar production
4.5 peak sun hours/day × 0.82 system derate. Approximate state-average daily solar resource (peak sun hours) based on NREL solar resource data (NSRDB); not location-specific — use NREL PVWatts for an address-level estimate. (NREL PVWatts)
Installed price
$3.00 per watt before incentives. Blended 2026 US residential installed price used by this site; EnergySage marketplace reported about $2.60/W (mid-2026); full-market medians are higher.
Federal tax credit
$0 for homeowner-owned systems installed in 2026 — the 30% §25D credit ended Dec 31, 2025 (IRS)
Net metering
National blend — solar assumed to offset 75% of the bill (87% in full-retail net-metering states, 55–70% elsewhere).
Estimates only — not tax, legal or financial advice. Get at least three installer quotes and confirm incentives with your utility and a tax professional.