Solar · Washington
How many solar panels do I need in Washington?
For the average Washington home, which uses 956 kWh a month (EIA, 2024), about 23 × 400 W solar panels (8.88 kW) facing south at the best tilt. One kW of panels in Washington makes about 1,292 kWh a year, 5.3 kWh a day in July and 1.4 in December, the 50th sunniest of 51.
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Solar output by month in Washington
Output falls to 27% of the July level in December. Grid-tied homes are sized on the year; anything off-grid has to be sized for December.
| Month | kWh per kW | Per day | 200 W panel, Wh/day into a battery |
|---|---|---|---|
| January | 51 | 1.66 | 281 |
| February | 74 | 2.63 | 446 |
| March | 104 | 3.36 | 571 |
| April | 130 | 4.35 | 739 |
| May | 146 | 4.72 | 802 |
| June | 145 | 4.82 | 820 |
| July | 165 | 5.33 | 906 |
| August | 155 | 4.99 | 849 |
| September | 129 | 4.30 | 731 |
| October | 92 | 2.96 | 503 |
| November | 57 | 1.90 | 322 |
| December | 44 | 1.43 | 244 |
Charging a power station in Washington
A 200 W panel propped up facing south refills a 1,000 Wh power station in about 1.1 days in July and 4.1 days in December. To refill it in one day you’d need about 230 W of panels in July and 820 W in December. Check your station and panel →
A balcony or plug-in panel in Washington
A 400 W panel hanging upright on a south-facing railing makes about 351 kWh a year, worth about $51.36 at Washington’s average rate (14.63¢/kWh, August 2026), if you use the power as it’s made. Shade and the rules where you live matter more than anything here. Try your kit →
The rules in Washington: We found no state law on plug-in solar in Washington as of November 5, 2026; ask your utility. Every state we track →
Across Washington
Washington’s figure is the population-weighted average of Seattle, Spokane and Tacoma, its three largest cities; across them, a kW makes 1,270 to 1,386 kWh a year.
| City | Population (2024) | kWh per kW a year |
|---|---|---|
| Seattle | 780,995 | 1,272 |
| Spokane | 230,609 | 1,386 |
| Tacoma | 228,202 | 1,270 |
Cross-check: an estimate from NASA POWER sunshine came out at 1,150 kWh per kW, 12% below the Global Solar Atlas figure. That’s more than our 12% review threshold, so we checked it by hand: both sources agree on the sunshine itself; the gap comes from the cross-check’s simpler tilt model and its fixed losses, which understate output in cool climates. We use the Global Solar Atlas figure.
Electricity rates and appliance costs in Washington →
FAQ
How many solar panels do I need in Washington?
For the average Washington home, which uses 956 kWh a month (EIA, 2024), about 23 × 400 W solar panels (8.88 kW) facing south at the best tilt. One kW of panels in Washington makes about 1,292 kWh a year, 5.3 kWh a day in July and 1.4 in December, the 50th sunniest of 51.
How much does a solar panel produce in Washington?
A 400 W panel facing south at the best tilt makes about 517 kWh a year in Washington: about 66 kWh in July and 18 kWh in December (Global Solar Atlas).
How long does a 200 W solar panel take to charge a 1,000 Wh power station in Washington?
About 1.1 days in July and 4.1 days in December, propped up facing south, at 85% charging efficiency. Lying flat, about 7.3 days in December.
How many solar panels for the U.S. average home in Washington?
The U.S. average home uses 863 kWh a month (EIA, 2024). In Washington that takes about 8.01 kW: 21 × 400 W panels.
Is there still a federal solar tax credit?
Not under the residential credit for systems installed after 2025: the IRS says the section 25D credit will not be allowed for any expenditures made after December 31, 2025, and an expenditure counts as made when installation is completed.
Sources and assumptions
- Solar output (kWh per kW of panels, by month): Global Solar Atlas 2.0, long-term averages to 2025 (data version 2.2.68, updated 2026-04-01), for crystalline-silicon panels facing south at the best fixed tilt, after typical system losses. Data obtained from the “Global Solar Atlas 2.0, a free, web-based application is developed and operated by the company Solargis s.r.o. on behalf of the World Bank Group, utilizing Solargis data, with funding provided by the Energy Sector Management Assistance Program (ESMAP). For additional information: https://globalsolaratlas.info” Licensed CC BY 4.0; we rounded and combined it as described here. Not affiliated with or endorsed by Solargis or the World Bank Group.
- State figure: population-weighted average of the state’s three largest cities (U.S. Census Bureau Vintage 2024 population estimates; coordinates from the 2020 Census Gazetteer). Hawaii and DC use one city.
- Cross-check: NASA POWER sunshine climatology (2001–2025), tilted with a standard isotropic-sky model × 0.80. States more than 12% apart were reviewed by hand; the gaps are explained on our methodology page.
- Home use: EIA Table 5A, 2024 average monthly residential kWh by state. Rates: EIA Electric Power Monthly, August 2026.
- Tax credit: IRS FAQ on the One, Big, Beautiful Bill (FS-2025-05, Aug. 21, 2025).
- Assumptions: 85% charging efficiency into a battery, 85% from battery to appliance, panel counts rounded up, off-grid sizing for the worst month.