Last updated: October 28, 2026 · By Oren Tamir, Founder & CEO, NRG Clean Power
Quick answer: In California, one 400 W solar panel produces about 1.7 to 1.9 kWh a day, or 625 to 680 kWh a year. Each 1 kW of panels makes about 1,560 to 1,690 kWh a year, depending on the city. That is from NREL’s PVWatts model for a south-facing roof at a 20 degree tilt. Riverside, Los Angeles and San Diego top the list, and San Francisco comes in lowest.
Most solar output guides tell you California gets more sun than anywhere but Arizona and stop there. What they miss is that the yearly total barely changes across the state. The winter does. We ran the same 400 W panel through NREL’s PVWatts model for seven California cities. Riverside beats San Francisco by only 8% over a full year. In the darkest winter month, though, the same panel makes 41 kWh in Riverside and about 30 kWh in Fresno or Sacramento. That seasonal swing is why our quotes for a Central Valley home and a coastal Southern California home look different even when the annual numbers match. It decides how many panels you need and how much a battery is worth.
Key takeaways
- A 400 W panel in California makes about 52 to 56 kWh a month on average, 625 to 680 kWh a year.
- Annual output varies only about 8% across California’s big cities, from 1,561 kWh per kW in San Francisco to 1,694 in Riverside.
- Winter output varies far more. Coastal Southern California keeps about 60% of its summer output in its darkest month, while Fresno and Sacramento drop to about 40%.
- A west-facing roof loses about 12% versus south in Los Angeles. East loses 16% and north loses 31%.
- A home using 600 kWh a month needs about 11 panels at 400 W in most of California.
How much energy does a solar panel produce in California?
A typical 400 W residential panel in California produces 625 to 680 kWh of electricity a year. Here is what NREL’s PVWatts model shows for seven cities, for one panel and for each 1 kW of panels.
Solar panel output by California city (400 W panel, south-facing, 20 degree tilt)
| City | kWh per kW per year | kWh per 400 W panel per year | Average kWh per panel per day | Average kWh per panel per month |
|---|---|---|---|---|
| Riverside | 1,694 | 678 | 1.86 | 56 |
| Los Angeles | 1,677 | 671 | 1.84 | 56 |
| San Diego | 1,675 | 670 | 1.84 | 56 |
| Fresno | 1,639 | 656 | 1.80 | 55 |
| San Jose | 1,639 | 656 | 1.80 | 55 |
| Sacramento | 1,618 | 647 | 1.77 | 54 |
| San Francisco | 1,561 | 625 | 1.71 | 52 |
Source: our runs of NREL PVWatts version 8 (NSRDB TMY weather data), standard module, fixed roof mount, 20 degree tilt, 180 degree (south) azimuth, 14% system losses, October 2026. Your roof will differ; shade, tilt and direction all change the result.
Every major California city lands within about 8% of every other on yearly solar output.
Two things in this table surprise most homeowners. Fresno, with its hot, clear summers, does not beat Los Angeles over a year, because winter tule fog cuts its winter output hard. And San Jose matches Fresno, thanks to strong summers in the South Bay. If you are anywhere in our California service area, your yearly output per panel is within a narrow band.
How many kWh does a solar panel produce per day by California city?
On average, a 400 W panel produces 1.7 to 1.9 kWh a day in California. The real number swings with the season. In peak summer it is about 2.2 to 2.4 kWh a day, and in the darkest winter month about 1.0 to 1.4 kWh.
Daily and monthly output for one 400 W panel, best and worst month
| City | Best month (kWh) | Worst month (kWh) | Best month, kWh per day | Worst month, kWh per day | Winter as share of summer |
|---|---|---|---|---|---|
| San Diego | 67 (August) | 43 (December) | 2.2 | 1.4 | 64% |
| Riverside | 70 (July) | 41 (December) | 2.3 | 1.3 | 59% |
| Los Angeles | 69 (August) | 40 (December) | 2.2 | 1.3 | 58% |
| San Francisco | 68 (May) | 32 (December) | 2.2 | 1.0 | 47% |
| San Jose | 75 (July) | 32 (January) | 2.4 | 1.0 | 43% |
| Fresno | 71 (July) | 30 (January) | 2.3 | 1.0 | 42% |
| Sacramento | 73 (July) | 30 (December) | 2.4 | 1.0 | 41% |
Source: NREL PVWatts v8 monthly output, same inputs as the table above. Daily figures are the month’s total divided by its days.
What this means for you:
- Coastal Southern California (San Diego, Los Angeles, Orange County, the Inland Empire) has the flattest year. A system sized for annual use covers winter bills well.
- Northern California and the Central Valley (Sacramento, Fresno, San Jose) make more in July than Southern California, but their darkest month falls to less than half of their summer peak. Expect bigger winter bills even with solar, and expect a battery to matter more in the dark months.
- San Francisco peaks in May, not July, because summer fog cuts July and August output.
To see how much direct sun your own roof gets through the year, read our guide on how much sun your house gets.
What is the difference between watts and kWh on a solar panel?
A panel’s watt rating is its power output under lab conditions. Kilowatt-hours are the energy it actually produces over time. A 400 W panel delivering 400 watts for one hour would make 0.4 kWh. In the real world it rarely runs at full rating, so it makes about 1.8 kWh over a California day, not 400 W times daylight hours.
Three things close the gap between rating and real output:
- Sun angle and hours. Full output only happens near midday in clear weather.
- Heat. Panels lose efficiency as they get hot, which is why a cool, sunny spring day can beat a 105 degree July afternoon in the Valley.
- System losses. Wiring, inverter conversion, dust and small amounts of shade cost about 14% in PVWatts’ default model.
Most new residential panels are rated around 400 to 450 W and measure about 21 square feet. See how big solar panels are and how solar panel efficiency affects watts per square foot.
How much does roof direction change solar panel output?
In Los Angeles, a west-facing roof produces about 12% less than a south-facing roof, an east-facing roof about 16% less, and a north-facing roof about 31% less. Here is the same 1 kW of panels at a 20 degree tilt.
Solar output by roof direction, Los Angeles (per kW of panels)
| Roof direction | kWh per kW per year | Change versus south |
|---|---|---|
| South | 1,677 | Baseline |
| Flat (0 degree tilt) | 1,488 | Down 11% |
| West | 1,484 | Down 12% |
| East | 1,410 | Down 16% |
| North | 1,165 | Down 31% |
Source: NREL PVWatts v8, Los Angeles, 20 degree tilt (flat row: 0 degree tilt), 14% losses.
Under NEM 3.0, west can be worth more than the kWh numbers suggest. West-facing panels produce later in the afternoon, closer to the 4 p.m. to 9 p.m. peak, when power is most expensive and export credits are highest. On many California homes we split arrays between south and west for that reason. North-facing roofs can still work at a low pitch; see our guide to solar on a north-facing roof.
How many solar panels does a California home need?
A California home using 600 kWh a month needs about 11 panels at 400 W, or about 4.4 kW of panels on a south-facing roof. The formula is your monthly use divided by one panel’s monthly output.
Panels needed by monthly use (400 W panels, south-facing)
| Monthly use | Los Angeles | Sacramento | San Francisco |
|---|---|---|---|
| 500 kWh | 9 panels | 10 panels | 10 panels |
| 600 kWh | 11 panels | 12 panels | 12 panels |
| 800 kWh | 15 panels | 15 panels | 16 panels |
Our math: monthly use divided by average monthly output per 400 W panel from the PVWatts runs above (56, 54 and 52 kWh), rounded up. Assumes covering 100% of yearly use with no shading.
Worked example: a Sacramento home that uses 600 kWh a month uses 7,200 kWh a year. One 400 W panel in Sacramento makes 647 kWh a year, so the home needs 7,200 / 647 = 11.1, or 12 panels (4.8 kW). Under NEM 3.0 we often size slightly smaller and add a battery, because exported summer solar earns far less than the power you buy in winter evenings.
Not sure what you use? Check your last 12 bills or compare with how many kWh per month is normal and the average electric bill in California. For a full sizing walkthrough, see how to calculate solar system size.
How much does solar panel output drop over 25 years?
Most solar panels lose about 0.5% of their output each year. After 25 years, a panel typically still produces about 88% of what it did in year one. That median rate comes from NREL’s review of field degradation data. Newer panels often warranty a slower rate, so check the datasheet for the panel on your quote.
For a 400 W panel in Los Angeles, that means about 671 kWh in year one and about 595 kWh in year 25.
Calculate your own solar output
Use the calculator below with California inputs: 400 W panels and about 5.2 average daily sun hours for most of the state, which matches the PVWatts results above after typical system losses.
Solar Panel Output Calculator
Enter your panel wattage, average peak sun hours per day and number of panels to estimate production.
Frequently asked questions
In California, expect about 1,560 to 1,690 kWh a year for every 1 kW of south-facing panels. A 6 kW system should make about 9,400 to 10,200 kWh a year, or roughly 780 to 850 kWh a month on average, with more in summer and less in winter.
For many California homes, yes. A 6 kW system produces about 780 to 850 kWh a month on average, which covers a home using up to about 800 kWh a month. Homes with an EV, a pool or a heat pump often need 8 to 10 kW.
In California, a 400 W panel produces about 1.7 to 1.9 kWh a day averaged over the year. In summer that rises to about 2.2 to 2.4 kWh a day, and in the darkest winter month it drops to about 1.0 to 1.4 kWh a day depending on the city.
Most panels last 25 to 30 years or more. They lose about 0.5% of output a year, so a 25-year-old panel still makes about 88% of its original output. Inverters usually need replacing sooner.
Yes, but much less. Winter fog is the clearest example in California: in its worst winter month, a 400 W panel makes about 30 kWh in Fresno (January) versus about 40 kWh in Los Angeles (December). Our guide to whether solar panels work on cloudy days has more.
Related: do solar panels work on cloudy days.
See what your roof would produce
Every roof is different. We model your actual roof direction, tilt and shade before we quote a system, so the kWh number you see is the one you get. Get a quote in 2 minutes, or see current solar panel costs in California.