How Solar Works in Cloudy Weather
Solar Panels Don’t Need Direct Sunlight to Work
Photovoltaic cells respond to daylight, not just direct beam sunlight. On an overcast day, panels still produce power from the diffuse light scattered through cloud cover, typically somewhere between 10 and 25 percent of a clear-sky day’s output. Production drops on cloudy days. It does not stop.
- Panels produce power on every daylight hour, sunny or overcast
- Cooler temperatures actually improve panel efficiency, partially offsetting Seattle’s shorter sun-hour totals
- Seattle averages 152 sunny days and 88 partly sunny days a year
What a Typical System Produces
What Does a Solar System Actually Produce in Seattle?
With Western Washington’s roughly 3.5 to 4.2 peak sun hours per day, a typical residential system here produces about 1,000 to 1,100 kWh per installed kW every year. On a 10 kW system, a fairly common size for our service area, that works out to roughly 10,000 to 11,000 kWh of clean power annually, enough to offset a significant share of a typical Seattle-area home’s electricity use.
Compared to Sunnier Climates
How Does Seattle Compare to Sunnier States?
Seattle does get fewer peak sun hours than Phoenix or Los Angeles. But solar panels lose efficiency as they heat up, so extremely hot, sunny climates do not out-produce cooler ones by as much as the raw sun-hour numbers suggest. The gap is real, but it is smaller in practice than most homeowners expect, and Washington’s sales tax exemption on qualifying solar systems helps close it further.
An Honest Assessment
When Solar Isn’t the Right Fit
Solar is not the right answer for every roof. It usually is not worth pursuing if mature trees heavily shade your roof for most of the day, if you plan to move within the next two to three years, or if your roof needs replacing soon (in which case, replace the roof first). We would rather tell you this upfront during a site assessment than sell a system that will not perform well on your specific home.
Frequently Asked Questions
Is solar worth it in Seattle with all the rain and clouds?
For most homes, yes. Seattle still gets 152 sunny days and 88 partly sunny days a year, and solar panels produce power on every daylight hour, not just direct sun. A typical system here generates roughly 1,000 to 1,100 kWh per installed kW annually, enough to make solar pencil out for most Western Washington homeowners.
How much less power do solar panels make in Seattle vs. sunnier states?
Seattle gets fewer peak sun hours than a place like Phoenix, roughly 3.5 to 4.2 hours a day versus 6 or more. But panels lose some efficiency as they heat up, so hot climates don’t out-produce cooler ones by as much as the raw sun-hour gap suggests.
Do solar panels work at all on a cloudy or rainy day?
Yes. Photovoltaic cells respond to any daylight, not just direct beam sunlight. Production drops on overcast days, typically to somewhere between 10 and 25 percent of a clear-sky day, but it never goes to zero during daylight hours.
How long does it take solar panels to pay for themselves in Seattle?
It depends on your system size, financing, electricity usage, and which incentives apply to you. A Solphos design consultation gives you a specific payback estimate for your home rather than a generic number.
See What Solar Would Produce on Your Roof
A free, LiDAR-based production estimate for your specific home in Seattle or the Eastside.
