Yes, solar panels work on cloudy days. They generate power from daylight, not just direct sunshine, so they keep producing under clouds, fog, and rain, just at a lower level than under clear skies. Your system is designed around a full year of sunshine rather than any single day, and a battery stores what the panels make so you can use it when you need it.
That matters here. Between Marin's coastal fog, the morning marine layer that rolls into Sonoma and Napa valleys, and our rainy winters, North Bay homeowners see their share of gray skies. Here's what those days mean for your solar.
How panels make power when the sun is hidden
Sunlight reaches the ground in two ways. Direct light comes straight from the sun. Diffuse light is scattered by clouds, fog, and the atmosphere, which is why it can still be bright outside on an overcast day. Solar panels use both.
When clouds move in, the direct light drops, but the diffuse light keeps reaching your panels, and they keep turning it into electricity. How much they make depends on the clouds. A thin, high overcast lets plenty of light through. A thick, dark storm system lets through much less. Either way, the panels don't switch off. They produce a fraction of their clear-day output and pick right back up as soon as the sky brightens.
What North Bay fog really means for your system
Coastal fog is part of life in much of Marin and along the Sonoma coast, and it worries some people considering solar. In practice, our fog is easier on a system than it looks.
Much of it follows a pattern. The marine layer often settles in overnight and through the early morning, then burns off as the day warms. That leaves the strongest hours of sun, from late morning through the afternoon, clear for many homes. Your panels make most of their power in the middle of the day anyway, so a foggy morning often costs less production than people expect.
Fog also varies a lot over short distances. A home on a ridge or a little way inland can sit in sunshine while the neighborhood below is still socked in. That's why we look at your specific site rather than relying on a general assumption about your town. During design, we use your roof, its orientation, and local sun data to estimate how much your system will produce throughout the year, including foggy mornings.
Rain helps more than it hurts
A rainy day means lower production, just like heavy overcast. But rain does your panels a favor. It rinses off the dust, pollen, and grime that build up during our long dry season, and cleaner panels make more power once the sun comes back out. For most North Bay homes, the winter rains handle the cleaning on their own. Our post on whether solar panels need maintenance covers the little upkeep that remains.
Gray weather has another small upside. Solar panels run more efficiently when they're cool, and on bright days just after a storm clears, cool air and clean glass can make for some of the season's best production.
Your system is sized for the whole year
The most important thing to know about cloudy days is that we don't design your system around one of them. We design it around a full year.
Before we draw anything, we look at your home's monthly electricity use and how much sun your roof receives across all four seasons. Long, bright summer days produce far more than many homes use, while shorter, grayer days produce less. Good design accounts for all of it, so a cloudy week is expected and planned for, not a surprise.
We cover the seasonal side of this in more detail in do solar panels work in winter, since winter is when gray days are most common.
How a battery makes gray days easier
A home battery is part of every system we design, and it's especially useful in mixed weather. On a partly cloudy day, your panels might produce in bursts as clouds move in and out. The battery captures what your home doesn't use right away and saves it for later, so you can use more of your own solar in the evening instead of buying power when rates are highest.
A Savings Battery does this every day to help lower your electricity bill. A Backup Battery does the same and also keeps your chosen circuits running if the grid goes down. When a storm rolls in, many homeowners with a Backup Battery raise their backup reserve so it holds more charge for an outage, which we explain in our post on home battery settings. And because the battery recharges from your panels, even a few hours of daylight between storms helps top it up.
Your grid connection fills the gaps
Your home stays connected to the grid, so a cloudy stretch never leaves you short. When your panels and battery are covering less than usual, the grid quietly supplies the rest. When the sun returns, your system takes over again. You don't have to change anything or think about it. That partnership between your solar, your battery, and the grid is what makes gray days a non-event for most homeowners.
Reading your production on a gray day
If you check your monitoring app on a cloudy day, you'll see lower numbers than on a clear one. That's normal. It's more useful to look at your production over a week or a month than to compare a foggy Tuesday against a perfect Saturday in June.
What's worth a closer look is a drop that the weather doesn't explain, like low output on a string of bright, clear days. If you see that, give us a call, and our service team can check it out. Our post on tracking your solar production shows what to look for.
Solar that works with North Bay weather
Places with plenty of cloudy weather run solar successfully every day, and the North Bay's mix of fog, rain, and long dry summers is a good place for it. A design built around your home and your year, paired with a battery, makes the most of the sun we get.
We've designed systems for foggy hillsides, sunny valleys, and everything in between since 1984. We're 100% employee-owned, we've installed more than 9,000 systems across Marin, Sonoma, and Napa, and we're licensed as a General Contractor (B) and Electrical Contractor (C-10). We were also one of the first companies in California to earn the state's C-46 solar license.
Want to know how solar and a battery would do at your home? Contact SolarCraft or call Sonoma/Napa 707.778.0568 or Marin 415.382.7717.
