There are a variety of incentives available in Washington State that significantly reduce the cost of a solar system – and help maximize your Return on Investment.
Washington State Production Incentive
The Washington State Production Incentive is funded by the state government and managed by your local utility. This program pays you for every kWh you produce, whether you consume that solar electricity in your house or not.
The program has been so successful that in many utility districts the funding limit has been reached.  Some smaller utilities have closed the program to new applicants.  Seattle City Light, Puget Sound Energy, and Snohomish PUD will be prorating the incentive to divide up the total fund available among the kilowatt hours that are applying for it.
For a 5-kW system in Seattle, on a South-facing 4:12 roof with 95% solar access, the annual production would be around 5263 kWh per year,
Production Incentives are paid on top of the Net Metering benefit you’re already receiving and is capped at $5,000/yr until June 30,2020, when the program is set to expire.
Net Metering
Net Metering is a contract that you sign with your utility allowing you to trade power with them at retail rates. When you produce more energy than you consume the excess kilowatt hours are fed into the grid and credited to your account. When you produce less than the consume, you purchase electricity from the utility. See: Net Metering Explained.
Sales Tax Exemption
Washington State extended the Sales Tax Exemption for solar systems under 10kW until 2018. This means you pay no sales tax on the full invoice for installing a solar photovoltaic or solar hot water system for systems smaller than 10kW. This saves you 8.5-10% on your system price.
For systems over 10kW, the full sales tax must be paid first, and then the the customer may apply for a rebate of 75% of the tax. This remittance expires at the end of 2019.
Income Tax Credit
The Federal Government allows you to claim an Income Tax Credit of up to 30% of your total system cost. What is more, you can roll it over, meaning that if you can’t use the full value in the first year, you can claim the remainder in the next year. The ITC is applicable to your Alternative Minimum Tax (AMT) as well. This incentive is is good through 2019 and then is reduced after that.
Rebates, or "cash back incentives," for solar systems in Washington vary from utility to utility. Check out your utility's website to determine if rebates are available in your service area.