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, 26% 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).
Example of 4 kW system calculation in Minnesota for electricity bill $100