Washington’s Solar Fantasy Meets Cold Reality

When you hear some policymakers or salespeople talk about solar power, it can sound like an easy fix: Just put up more rooftop panels and Washington simply won't need hydropower or natural gas.

The idea is that our state can run on sunshine.

But there's a glaring problem with that story. It ignores the reality of where we live.

Solar works differently in Spokane and Seattle than it does in Phoenix or Los Angeles. The difference isn't just "cloudy here, sunny there." The real reason comes down to solar insolation, the measure of how much usable sunlight strikes a square meter of solar panel. And that's driven by two big factors: the angle of the sun and seasonal variation.

Sun Angle: Washington's Northern Latitude

Washington sits between 45° and 49° north latitude, far above Arizona (32-37°) and California (32-42° north). That difference in latitude means the sun is positioned lower in the sky here, even on clear days.

• In the summer, we enjoy long daylight hours in Washington, but the sun never rises as high overhead as it does in the Southwest.
• In the winter, the sun stays low on the horizon, and solar panels receive weaker, more diffuse light.

Seasonal Swings & Washington's 'Dunkelflauten'

Regions at similar latitudes—places like southern Canada and central Europe—face the same challenge. In fact, the Germans coined a word for it: dunkelflauten, which literally means "dark lulls," when the sun hides and the wind doesn't blow.

Washington has its own dunkelflauten. Here it stretches from about mid-November through early February.

During our long June days, solar panels perform reasonably well due to more than 15 hours of daylight. But by December, output collapses. We see barely eight hours of weak sun, low angles and clouds that can hang for days or weeks.

That's the cruel irony of solar in Washington. It peaks in summer, when rivers are full of snowmelt and hydropower is abundant, and fades in winter, when demand for heat and grid stress are highest.

The Numbers: Washington vs. California & Arizona

Here's how Washington's solar availability compares to Arizona and California, using "peak sun hours per day" (a common measure of usable solar energy).

• Arizona: ~6.5 peak sun hours year-round, relatively steady even in winter.
• California: ~5.4 average, but with winter dips.
• Washington: only ~3.6 average, dropping to ~2.6 in winter.

That gap is why a rooftop solar system that powers most of a home in Arizona would supply far less power in Washington, particularly during our cold months.

In practice, the same 5 kW system might generate:

• About 33 kWh per day in Arizona
• 27 kWh per day in California
• Roughly 18 kWh per day in Washington

So, that system in Washington produces only about half as much electricity as the same system in Arizona, due mainly to lower insolation.

Even Across Washington, There Are Big Differences

Not all of Washington is equal, in terms of peak sun hours. Southeastern and Eastern Washington typically receive more sun than the West side of the state.

• Seattle: ~3.5 peak sun hours, with very weak winters.
• Spokane: ~4.0 peak sun hours.
• Tri-Cities: ~4.3, with sunnier summers.

Still, none of these Washington cities comes close to Arizona's consistency.

The Reality of Battery Backup

Many solar companies promise that pairing panels with a home battery (like a Tesla Powerwall) means you can "go off-grid" or keep your home fully powered through an outage. In practice, the story is more complicated, especially when it's 13 degrees outside and electric heat is running nonstop.

• A typical home battery stores around 13–15 kilowatt-hours (kWh) of energy.
• An electric furnace or even multiple space heaters can easily draw 15–20 kWh in a single day during extreme cold.
• That means one fully charged battery might not even last 24 hours, especially if you’re also running lights, a refrigerator and electronics.
• And in December, Washington solar panels may only generate 2–3 kWh/day in Spokane, far too little to recharge the battery.

Pairing solar panels with a home battery in winter sounds reassuring, until you run the numbers. It's as if your battery is doing the energy equivalent of holding an umbrella in a hurricane.

In plain terms, the battery might keep your lights on, but not your heat. In a three-day outage during a cold snap, you'd still be out of luck without a generator or reliable grid power.

Why This Matters for Energy Policy

There is certainly a place for solar in Washington. Solar panels can reduce demand on the grid and add diversity to Washington's energy supply. But solar is supplemental power, not baseload power.

Supplemental (or intermittent) power is electricity that helps when conditions are right, like sunshine during the day. It adds to the mix but isn't always available. Think of it as a side dish at dinner: nice to have, but not the main course.

Baseload power, by contrast, is electricity that runs all the time, regardless of weather or time of day. It's the main course of the energy system. Hydropower, nuclear and natural gas plants provide this steady, around-the-clock supply.

That distinction matters. The idea that solar can substitute for hydropower, natural gas or nuclear as Washington's dependable energy supply isn't visionary. It's physics denied.

Solar only produces when the sun shines, and in Washington's winters it produces far less. Batteries can help for a few hours, but they cannot cover days of cold, dark weather.

To keep the grid stable during cold snaps, heat waves and periods when the wind isn’t blowing, Washington relies on firm, dispatchable power—sources like hydropower, nuclear and natural gas that can be counted on 24/7.

Bottom Line: Washington Can Never Be Arizona or California

Washington is a remarkable place to call home, with mighty rivers, abundant forests and communities built around affordable hydropower. Unlike much of the country, our state also has unmatched renewable resources and even nuclear expertise that make our energy system both reliable and innovative. But it isn't the desert Southwest, and our energy choices must reflect the strengths of where we live.

Washington's geography, latitude and climate mean we will never match the solar potential of Arizona or California. The science of solar insolation makes that clear.

That doesn’t diminish the value of solar power; it simply shows its constraints. And any honest conversation about Washington’s energy future must recognize those limits.

Otherwise, we risk trading reliable baseload power for an electricity source that disappears exactly when we need it most.