Solar power in Washington has expanded to over 27 MW in 2013, largely due to a 30% federal tax credit, and declining installation costs. Washington also pays a feed-in tariff of up to $5,000/year of 15 cents/kWh, which is increased by a factor of 2.4 if the panels are made in the state and by an additional 1.2 if the inverters are made in state.
When you install your solar system, 30% of your project expenses apply toward a credit to offset any taxes you owe that year. This federal tax credit is a major incentive to go solar, but it is being phased out by 2022.
Most people are eligible to claim this credit (you must owe federal taxes to be eligible).