How We Calculate Your Solar Savings

1Location Resolution & Utility Mapping

We geocode your Washington address using the U.S. Census Bureau Geocoding API or match your 5-digit ZIP code directly against our curated database of Washington electric utility service territories. This automatically identifies your electric provider (Seattle City Light, Puget Sound Energy, Snohomish PUD, Tacoma Power, Avista, Pacific Power, or Clark Public Utilities).

2Energy Consumption Estimation

Electricity bills consist of a fixed monthly customer charge (typically $6.80 to $19.50 in WA) plus a volumetric per-kWh charge. We subtract your utility's specific fixed fee and divide the remainder by your effective residential rate:

3Solar Production Modeling (NREL PVWatts)

We utilize solar irradiance data from the National Renewable Energy Laboratory (NREL PVWatts v8) calibrated to Washington's distinct microclimates:

• Western WA (Marine): 1,040 to 1,120 kWh per year per installed 1 kW DC (assuming standard 25° roof tilt).
• Eastern WA (Inland): 1,350 to 1,450 kWh per year per installed 1 kW DC.
• Roof Orientation Multipliers: South (1.00), East/West (0.84), Flat/Low Pitch (0.72).

4Installation Cost Baseline

We use EnergySage 2026 Washington statewide market data showing an average turnkey cost of $2.54 per Watt DC (including tier-1 monocrystalline panels, microinverters or optimizers, city permitting, and professional installation). Users can adjust this figure directly in the assumptions drawer.

5Washington State Sales Tax Exemption (RCW 82.08.962)

Unlike most states, Washington provides a 100% exemption from all state and local retail sales and use taxes on solar machinery, equipment, and installation labor for systems up to 100 kW through December 31, 2029. In King and Pierce counties with ~10.3% combined sales tax, this eliminates thousands in taxes at the time of purchase.

62026 Federal Tax Credit Status (The Truth)

Almost all solar websites in 2026 still display a 30% federal tax credit under Section 25D. This is inaccurate. Under federal legislation enacted in July 2025 (P.L. 119-21), Section 25D was terminated for systems placed in service after December 31, 2025.

- Cash or Loan Purchase: 0% federal tax credit in 2026.
- Third-Party Owned (Leases / PPAs): Eligible for the commercial clean electricity investment credit under Section 48E, which solar companies claim and pass through as lower monthly payments.

725-Year Compound Cashflow Modeling

We project savings year-by-year across 25 years with conservative financial modeling:

• Utility Rate Inflation: Compounded at 3.5% annually (consistent with recent UTC filings).
• Panel Degradation: 0.5% per year (standard tier-1 panel warranty guarantee).
• Inverter Replacement Reserve: -$1,500 deducted at year 13 to account for inverter maintenance.