Washington solar guide
DIY solar in Washington: incentives, sizing, and the off-grid angle
Washington has the lowest peak sun hours in the contiguous US — 3.7 hours/day averaged across the state, and parts of the Olympic Peninsula drop to 3.0. That sounds disqualifying for solar, but it isn't: full retail net metering, sales tax exemption on equipment, and cooperative utilities (PSE, Seattle City Light, Snohomish PUD) make the economics work as long as you oversize the array.
No state income tax means no state tax credit to claim, but also a lower all-in cost basis since you're not absorbing sales tax on a $15K+ system. The federal 26% credit applies the same as everywhere else.
Incentive snapshot
As of mid-2026. Verify on your state's energy website before relying on the dollar figures.
- Federal Residential Clean Energy Credit
- 26%
- State tax credit
- —
- Sales tax exemption on solar equipment
- Yes
- Property tax exemption
- No
- Net metering
- Full retail (1:1)
- SREC market
- None
- Average peak sun hours
- 3.7 hrs/day
- DIY-permit friendly
- Yes
Phases down: 30% through 2025 → 26% in 2026 → 22% in 2027 → 0% under current law. Dwellings only — vehicle/RV systems don't qualify.
Your panels, batteries, and controllers ship sales-tax-free.
PV may add to your property tax assessment.
Full retail net metering. PSE and Seattle City Light both compliant.
No SREC revenue available in this state.
Used to size your array — more sun hours = fewer panels needed for the same output.
Lowest peak sun hours in the Lower 48 — bigger arrays needed for the same output. Off-grid systems work fine if sized accordingly.
DIY install angle in Washington
Washington is generally DIY-permit friendly. Pierce, King, and Snohomish counties all allow homeowner electrical permits for own-occupancy installs. Seattle requires a licensed electrician to do the final grid-tie connection but otherwise allows DIY work up to that point.
The orientation game matters more in WA than anywhere else. A south-facing roof at the right tilt squeezes 15–20% more out of limited sun than a poorly-oriented array. East-west splits often outperform pure south in WA because you catch morning and afternoon sun through cloud breaks.
Off-grid setups are doable but expensive in WA — you need roughly 30–40% more panel and battery capacity than the same load would require in Colorado or Arizona. Plan accordingly.
Sizing for Washington sun
Average 3.7 peak sun hours/day, but heavily seasonal: December gets ~1.5 hours, July gets ~6.0. Net metering buffers this for grid-tied builders (summer surplus carries to winter), but off-grid systems must size for the December reality.
For an off-grid build powering a typical 5 kWh/day load in Western WA, plan on roughly 1.8–2.2 kW of panels and 12+ kWh of LFP battery with 3 days of autonomy. Eastern WA (Spokane, Yakima, Tri-Cities) gets meaningfully more sun and can size like Colorado.
The good news about cool weather: WA panels run closer to nameplate output more of the year. Hot-state systems lose 10–15% to summer heat derating; WA systems lose almost nothing to temperature.
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