Do solar panels work on cloudy days, at night and in winter?
Short version: less on cloudy days, not at all at night, and noticeably less in winter. Here's how much less, city by city.
Solar panels make power from daylight, so they still produce on cloudy days, but less; they produce nothing at night. Winter output is lower too: in the cities I cover, the weakest month gives 42% (Fresno) to 66% (San Diego) of the best month's output (NREL PVWatts).
Best and worst month by city
kWh made by one kW of panels:
| City | Weakest month | Best month | Weakest as share of best | Nov–Feb share of the year |
|---|---|---|---|---|
| Phoenix, AZ | 117 (Dec) | 178 (May) | 66% | 27% |
| Tucson, AZ | 119 (Dec) | 184 (May) | 65% | 28% |
| San Antonio, TX | 96 (Feb) | 152 (Aug) | 63% | 27% |
| Austin, TX | 94 (Feb) | 154 (Aug) | 61% | 26% |
| San Diego, CA | 113 (Dec) | 170 (Jul) | 66% | 27% |
| Fresno, CA | 75 (Jan) | 180 (Jun) | 42% | 22% |
NREL PVWatts v8 monthly estimates from typical-year weather, which already include an average number of cloudy days. Month-by-month tables: solar panel production.
Cloudy days
Clouds cut the light reaching the panels, so output falls on overcast days and recovers when the sky clears. Yearly and monthly estimates like the ones above already average in typical cloudy weather for each city, so plan with them rather than with a single sunny day.
At night
No sunlight, no production. At night a grid-tied home buys power from the utility as usual. What you earned for daytime exports depends on your utility's program: net metering vs net billing. A battery can store daytime solar for the evening.
In winter
Shorter days and a lower sun reduce output. If your bill peaks in winter, check how much of your use falls in those months before sizing the system.
In a power outage
A standard grid-tied system shuts down when the grid goes down, so it doesn't send power onto lines crews are repairing. To keep power during an outage you need a battery or a system designed to run on its own.
Run your own numbers
Enter your ZIP and bill: the estimate uses NREL production for your ZIP across the whole year.
Keep reading
- How many solar panels you need — Size a system from your electric use and local sunshine, in four steps.
- How much electricity a solar panel produces — Daily, monthly and yearly output per kW and per 400 W panel, city by city.
- Net metering vs net billing — How each utility credits the power you send to the grid, and what it does to savings.
Updated 2026-09-15.