Seattle gets about 226 cloudy days a year. And yet it’s one of the cities where I most often tell people to go solar.

That probably sounds backwards. Most of what you’ve read about solar panels implies they’re really a product for Phoenix or Miami, places where the sun is relentless and the electricity bills are punishing. You might be wondering whether panels are even worth considering if you live somewhere like Portland, Buffalo, Chicago, or the UK-adjacent corners of the Pacific Northwest. Here’s what I tell people who come to me with that exact question: solar panels don’t run on sunshine. They run on light. And that distinction matters more than most installers bother to explain.

Why Clouds Don’t Kill Solar Production

Photovoltaic cells respond to diffuse light, not just direct sunlight. When clouds scatter sunlight across the sky, panels still generate electricity, just at reduced output. On a heavily overcast day, a well-installed system might produce 10-25% of its rated capacity. On a partly cloudy day, that range climbs to 50-80%. Those aren’t my numbers; NREL’s irradiance data consistently backs this up across weather stations in the northern US.

There’s also a counterintuitive effect that I always mention: solar panels actually perform better in cooler temperatures. High heat degrades output. A panel rated at 400 watts is tested at 25°C (77°F). In Phoenix in August, when ambient temps hit 110°F and a roof surface can reach 150°F+, panels can lose 10-25% of their rated efficiency just from thermal losses. In Seattle or Portland, where summers are mild, panels often perform closer to their nameplate rating during peak production hours than their counterparts in the desert Southwest. Germany, the world’s fourth-largest solar market according to SEIA data, gets less peak sun annually than Alaska. That should settle the argument.

The Number That Actually Matters: Peak Sun Hours

Recommended Emporia Vue Gen 2 Home Energy Monitor 16 Sensors

Real-time whole-home electricity monitor with 16 circuit sensors and solar/net metering capability.

Check Price →
LocationPeak Sun Hours/DayAvg. Grid RateAnnual Production Difference vs. PhoenixClimate Notes
Phoenix6.5LowerBaselineHigh heat reduces panel efficiency
Seattle3.5-4.0~$0.12/kWh-30-40%Cooler temps improve performance
Boston4.2~$0.22-0.28/kWh-30-40%High rates improve ROI despite lower sun
Massachusetts/New York/Connecticut3.5-4.5$0.22-0.28/kWh-30-40%High electricity prices offset lower production
Juneau, Alaska2.7SubsidizedPoorestNorth-facing, tree-covered lots problematic

Helpful resource: Renogy 100W 12V Flexible Solar Panel is a top-rated option for this. (As an Amazon Associate this site earns from qualifying purchases.)

Here’s where I want to slow down, because this is the number most homeowners never see but should demand before signing anything.

Peak sun hours measure the total solar energy hitting a surface per day, expressed as the number of equivalent hours of full 1000 W/m² sunlight. It’s not the same as daylight hours. A 16-hour partly cloudy day might yield 3.5 peak sun hours. A 10-hour clear desert day might yield 6.5.

Phoenix averages about 6.5 peak sun hours daily. Seattle averages roughly 3.5-4.0. Boston is around 4.2. That gap is real, and I won’t pretend it isn’t. A 10 kW system in Phoenix will produce meaningfully more electricity annually than the same system in Seattle, probably 30-40% more. The honest question isn’t “will it work?” but “will it pencil out financially in my specific location?”

Here’s what closes the gap: electricity prices. Seattle actually has some of the cheapest grid electricity in the country, thanks to hydropower, which is exactly why solar ROI there is often mediocre despite the cloudy reputation. But in Massachusetts, New York, or Connecticut, where grid rates are among the highest in the nation (often $0.22-0.28/kWh), lower peak sun hours still translate into solid financial returns. If you’re paying $0.25/kWh for electricity you’re currently buying 700 kWh of per month, even a modest reduction in that bill changes the math considerably.

I’d recommend plugging your address into EnergySage’s solar calculator before calling a single installer. EnergySage’s market data aggregates real quotes and real production estimates from your area, which gives you a baseline before anyone tries to oversell you.

What Equipment Choices Actually Change in a Low-Sun Climate

Related video

What Type of Solar Panel Should You Buy? · The Solar Lab on YouTube

Not all panels handle diffuse light equally, and this is where I push back on the “just get the cheapest per-watt option” advice.

Standard polycrystalline panels are fine in high-sun climates where direct irradiance dominates. In persistently cloudy climates, monocrystalline panels have a meaningful edge in low-light performance, and premium lines like the Panasonic EverVolt or REC Alpha series are specifically engineered with heterojunction technology that harvests diffuse light more efficiently than standard mono cells. The premium is real, maybe $0.15-0.25/watt more installed, but in a climate where diffuse light makes up a larger share of your annual production, it’s usually worth paying.

Microinverters also matter more in cloudy climates than most people realize. String inverters are vulnerable to the “Christmas light effect”: if one panel gets shading or performs poorly (say, a cloud bank covering one side of the roof), it drags down the output of the entire string. Microinverters from Enphase, or power optimizers from SolarEdge, let each panel operate independently. In a climate where partial shading from clouds or trees is routine, this can recover 5-15% of annual production compared to a basic string setup. That’s not nothing.

If you want to monitor your system’s performance in real time and catch underperformance early, a device like the Emporia Vue energy monitor is an inexpensive way to track production and consumption at the circuit level. (The site may earn a commission on that link.) I’ve seen homeowners go months with a poorly performing panel before catching it on their utility bill. Real-time monitoring fixes that.

The Honest Case Against Solar in Certain Cloudy Climates

I’d be doing you a disservice if I just cheerleaded.

There are places where the math genuinely doesn’t work well. If you’re in a heavily tree-covered lot with a north-facing roof in Juneau, Alaska, where peak sun hours average around 2.7 and electricity is somewhat subsidized, solar is a tough sell on pure financial grounds. If you rent, or plan to move in under five years, the 7-10 year payback period common in low-sun markets means you likely won’t recoup your investment before a sale. (Though solar does add to home resale value, typically $4-15 per watt of installed capacity according to Zillow and Lawrence Berkeley National Lab research.)

The cases where I tell people to hold off: flat or low-pitch roofs that collect debris and lose production, short expected tenure in the home, or locations with very low utility rates and no meaningful net metering policy. Washington State, ironically, is on that list for some homeowners. Great climate for panels thermally. Mediocre economics due to cheap Bonneville Power grid electricity.

Know your own numbers before you’re sitting in front of a salesperson.

The honest version of this conversation is that cloudy climate solar is real and viable in many cases, and genuinely borderline in others. What it’s never is a simple yes or no. Run your specific numbers. And if an installer tells you the weather doesn’t matter at all, that’s a sign to get a second quote.

Sources

Disclosure: As an Amazon Associate, we earn a small commission from qualifying purchases at no extra cost to you. We only recommend products that genuinely support the topics covered in this article.

Disclosure: As an Amazon Associate, we earn a small commission from qualifying purchases at no extra cost to you. We only recommend products that genuinely support the topics covered in this article.