Why Solar Panels Produce Less in Winter

Why Solar Panels Produce Less in Winter

(And Why You Shouldn’t Panic)

If you’ve recently installed a solar system in Washington, your first winter with panels can feel a little unsettling. You open your monitoring app, see your panels aren’t producing as much, and suddenly, you start thinking: Are my panels working? Was solar a bad investment?

Deep breath! What you’re seeing is normal and expected. Solar energy is seasonal by nature, and the Pacific Northwest’s climate means your system was always designed to do its heavy lifting in summer, not winter. Understanding how and why this works will help you to build trust in your system’s ability to keep you powered all year long.

Let’s walk through what’s happening on your roof, in the sky, and behind the scenes of your utility bill.

 

How the sun’s angle affects solar panel production

The angle of the sun drastically affects how much power your panels produce. In summer, the sun sits higher in the sky, days are long, and sunlight hits panels more directly (66º at peak in June). In winter, the sun travels a lower path across the horizon and daylight hours shrink (19º at peak in December). Less direct sunlight means less energy available for your system to convert into electricity.

In fact, depending on cloud cover, panel type, and roof orientation, winter production in Washington can drop to roughly 10-25% of a bright summer day’s output. That number sounds drastic until you remember that our solar systems are sized with this seasonal swing (and net metering) in mind. It is your annual production–not any single month–that determines the value of your system.

 

Clouds matter for solar production, but they’re far from the whole story

Western Washington is famous for its long, rainy winters. Cloud cover diffuses sunlight, which reduces how much direct solar energy reaches your panels. That said, solar panels don’t need perfectly clear skies to work. They’ll still produce power on overcast days, just less compared to clear, sunny days.

The combination of shorter days and frequent clouds is why winter production is the slow season. It’s also why your system’s performance should always be evaluated over the course of a full year, not a single month.

 

Cooler temperatures actually help solar panel performance 

Contrary to what you might think, solar panels are more efficient in cooler weather. High heat slightly reduces panel performance, while mild or cold temperatures allow electrons to move more efficiently. This is why spring and fall often surprise homeowners with strong production numbers, even though daylight hours are shorter than summer.

 

The Pacific Northwest’s secret solar superpower: long summer days

At first glance, Washington doesn’t look like an obvious solar powerhouse. But geography tells a different story.

Western Washington sits north of the 45th parallel. That means summer daylight hours stretch astonishingly long: nearly 5 am to 10 pm in many areas. Summers here are also relatively cool compared to sunnier southern states, which helps panels stay efficient.

This results in long, clear, mild summer days that generate large amounts of electricity. This is when your system produces the bulk of its annual energy, which is often more than your home uses during that time.

Those summer surpluses are not wasted. They’re the key to how solar works financially in Washington.

 

Enter net metering: the policy that makes seasonal solar work 

If winter production were the whole story, solar wouldn’t make sense in Washington. But there’s an important policy that changes everything: Net Metering.

Here’s how it works.

During summer months, your solar system often produces more electricity than your home or business is consuming. That excess energy flows back into the utility grid, where it’s used immediately by neighboring properties. As it passes through your electric meter, your meter essentially runs backward, creating energy credits on your account.

Then, in winter, when your panels produce less and your home uses more, you draw energy from the grid as usual. Instead of paying full price for that electricity, you tap into the credits you earned during Washington’s sunnier months.

Think of the grid as a seasonal energy bank:

• Summer = You deposit energy
• Winter = You withdraw energy

This is why your system is designed around annual production, not winter output alone.

 

Why your winter bill will be higher (and why that’s okay)

Some homeowners are surprised to see a higher utility bill in winter after going solar. That doesn’t mean the system is underperforming.

Winter is when:

• Solar production is lowest
• Home energy use is often higher (more lighting, heating, longer evenings)
• Net metering credits may be drawn down

Your summer credits carry you as far as possible, but depending on your energy use, you may still pull some paid power from the grid in winter. This is normal, and already factored into our system design and savings calculations.

The goal isn’t zero bills every month. The goal is dramatically lower annual energy costs that even out over the course of each month of the year. 

 

How to know if your solar system is working properly

If you want reassurance that your solar system is functioning optimally, here’s what to check:

• Your monitoring app shows production in real time, even if it’s low
• No error messages or system alerts
• Monthly production rising again in March and April

If you ever have concerns about your solar system, please give us a call at (206)-462-1103 or email us at [email protected] and we can confirm performance remotely. But a winter dip alone is not a red flag, it’s just the seasonal rhythm of solar.

 

The big picture: solar is a long-term investment

Solar isn’t about winning every month. It’s about winning over years.

Your system was designed to:

• Capture abundant summer energy
• Store value through net metering credits
• Offset winter energy needs
• Protect you from rising electricity prices
• Reduce carbon emissions year after year

Lower winter output doesn’t mean your system isn’t performing. It means it’s doing exactly what it was designed to do in a region with seasonal sunlight patterns.

Spring will bring longer days. Summer will bring surplus production. Credits will accumulate again. And year after year, your system will keep delivering clean energy and predictable savings.

So if you catch yourself worrying while watching those winter graphs, just remember that the sun is just taking a seasonal break—and our investment is still working for you.

 

 

 

Author Bio:

Macie Mancini joined Solterra Solar as a Solar Design Consultant in 2025. She holds a Master of Science in Engineering Design Innovation with a focus on sustainable systems and products from Northwestern University. She brings deep, cross-disciplinary knowledge that enhances her solar designs—from circular economy principles to user-product interactions and green energy electromechanics. Macie excels at helping clients build custom solar solutions for their homes and communities. From designing arrays to ensuring clients understand their system, she delivers a highly personalized customer experience every step of the way.