Washington Solar Calculator

Enter your utility, county, and monthly bill — get system size, WA sales tax exemption savings, net metering value, property tax exemption, and 25-year savings.

Your Washington solar inputs

Monthly electric bill?

Electric utility?

System size?

County (for sales tax exemption)?

Washington solar estimate

15 × 400W panels (6 kW system)

Recommended size for your bill: 10.6 kW

Monthly usage909 kWh/mo

Annual production (WA 3.6 PSH)6,307 kWh/yr

Annual net metering savings$694/yr

Gross system cost$16,800

Sales tax exemption (10.5%)~$1,764 saved

Federal ITC (30%)-$5,040

Net cost after ITC$11,760

Property tax exemption (est.)$3,360

Payback period17.0 yrs

25-year savings$17,345

Washington's solar sales tax exemption applies to the entire installed system cost at your county rate (10.5%). This automatic exemption saves $1,764 — confirm with your installer that they apply the exemption on your invoice.

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How to Use This Calculator

Enter your bill and select your utility

Puget Sound Energy (PSE) serves most of western Washington outside Seattle — including Bellevue, Tacoma, Kirkland, Redmond, and most of the I-5 corridor. Seattle City Light serves Seattle proper. Avista serves eastern Washington including Spokane, Pullman, and the Palouse. All three utilities offer retail-rate net metering.

Washington's sales tax exemption — the biggest solar incentive

Washington's combined state (6.5%) and local sales tax ranges from 8.5% to 10.6% depending on county. Washington law (RCW 82.08.962) exempts solar energy systems from this tax. On a typical 7 kW King County installation costing ~$19,600, the 10.5% tax exemption saves $2,058 — automatically, with no application required. This is Washington's most significant solar incentive and makes the state's high sales tax work in solar customers' favor.

Select your county for accurate savings

King County (Seattle) has the highest combined rate at 10.5%, followed by Snohomish at 10.6%. Eastern Washington counties like Spokane (8.9%) and Benton/Franklin (8.8%) have lower rates but still save $1,500-2,000 on a typical system. The calculator shows your exact tax savings based on your county.

The Formula

Monthly kWh = Monthly Bill ÷ Electricity Rate Annual Production = System kW × 1000 × 3.6 PSH × 365 × 0.80 efficiency ÷ 1000 Net Metering Savings = Annual Production × Retail Rate (WA credits at retail) Gross Cost = System kW × 1000 × $2.80/W Sales Tax Savings = Gross Cost × County Tax Rate (8.5%–10.6%) ITC Credit = Gross Cost × 30% Net Cost = Gross Cost − ITC Credit Payback = Net Cost ÷ Annual Savings

Washington averages 3.6 peak sun hours (PSH) statewide — the Tri-Cities (Kennewick/Pasco/Richland) average 5.0 PSH (more sun than Los Angeles), Spokane gets 4.3, and Seattle averages 3.3. Eastern Washington's high desert climate makes it one of the Pacific Northwest's best solar locations. At $2.80/W, Washington has above-average installation costs due to high labor costs in the Seattle metro area.

Example

Michael — Spokane Avista customer

Michael lives in Spokane (Avista territory, Spokane County) paying $110/month at $0.10/kWh. He wants an 8 kW system to offset his electricity costs.

Monthly bill$110 (Avista, $0.10/kWh)

System8 kW, Spokane County (8.9% tax)

LocationSpokane, WA (4.3 PSH)

Result

Annual production~8,019 kWh/yr

Annual net metering savings~$802/yr

Gross system cost~$22,400

Sales tax exemption (8.9%)~$1,994 saved

Federal ITC (30%)-$6,720

Net cost after ITC~$15,680

Property tax exemption (est.)~$4,480 over 20 yrs

Payback period~19.6 years

25-year savings~$20,050

Michael's payback is longer than sunnier states because Avista's low 10¢/kWh rate (among the cheapest in the US from hydropower) means each kWh saved has less dollar value. However, the sales tax exemption saves nearly $2,000, and Spokane's 4.3 PSH is significantly better than Seattle's 3.3. For comparison, the same system in the Tri-Cities (5.0 PSH) with Avista would produce 16% more energy and have a faster payback.

FAQ

How does Washington's solar sales tax exemption work? ▼

Washington RCW 82.08.962 exempts solar energy systems from state and local sales tax. This applies to the entire installed system — panels, inverters, racking, wiring, and labor. Your installer applies the exemption on your invoice; you do not need to apply separately. Washington's combined state (6.5%) plus local rates range from 8.5% to 10.6%, making this exemption worth $1,500 to $3,000 on a typical 6-10 kW system. King County (10.5%) and Snohomish County (10.6%) residents save the most. Confirm with your installer that they are applying the correct tax code (exempt) on your final invoice.

Is solar worth it in Seattle with low electricity rates? ▼

Seattle's solar economics are challenging but viable for the right homeowner. The obstacles: Seattle City Light's rate is 11¢/kWh (low) and Seattle averages only 3.3 PSH (cloudy). The advantages: the 10.5% King County sales tax exemption saves $2,000+, the 30% ITC applies, net metering is at retail rate, and property values in Seattle are high (making the property tax exemption more valuable). Typical Seattle payback is 14-20 years depending on system orientation and shading. If you have a south-facing, unshaded roof and plan to stay in your home 15+ years, solar makes sense financially. If your roof faces east/west or has tree shading, the economics are marginal.

How does net metering work in Washington State? ▼

Washington's net metering law (RCW 80.60) requires PSE, Seattle City Light, Avista, and other utilities to credit solar customers at the full retail rate for exported electricity. Monthly net credits roll forward on your bill. Washington does not require cash payment for excess annual credits — unused credits roll forward indefinitely. Note: Washington's net metering rules are scheduled to change under legislation passed in 2023 — new "successor tariffs" may take effect for new installations. Check with your utility for current interconnection terms. Interconnection typically takes 4-8 weeks in PSE territory.

Is the Tri-Cities the best place for solar in Washington? ▼

Yes — the Tri-Cities (Kennewick, Pasco, Richland) in southeast Washington averages 5.0 PSH, making it one of the sunniest cities in the Pacific Northwest. This is comparable to Los Angeles (5.1 PSH) and far better than Seattle (3.3 PSH). A 10 kW system in the Tri-Cities produces ~14,600 kWh/year vs. ~9,700 kWh in Seattle — 50% more energy from the same equipment. Despite Avista's low electricity rate (~10¢/kWh), the Tri-Cities' sunshine levels make payback 4-6 years shorter than Seattle. The Tri-Cities + the 8.8% Benton/Franklin County sales tax exemption create some of Washington's best solar economics.

Does Washington have a property tax exemption for solar? ▼

Yes — Washington law (RCW 84.36.400) exempts solar energy systems from property tax assessment. Your home's assessed value for property tax purposes does not increase due to the solar installation. Washington's effective property tax rate averages about 1.0%, making the exemption worth approximately $1,500-2,800 over 20 years for a typical system depending on county. In King County, where home values are highest, the annual tax savings per dollar of system value is somewhat lower due to the state's tax levy limits, but the absolute dollar savings are still meaningful.

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