Because no other question is asked more often to Solar Washington under various forms that the one about the availability of solar incentives, we have written a page on this website that answers it thoroughly.

If you are a homeowner:  consult Current Solar Incentives in Washington (solarwa.org)

If you are a business owner, most of those items will apply to you, but you can also check: Solar for Washington Businesses (solarwa.org)

The main solar incentives in Washington State are:

• The Individual Tax Credit (ITC) is a 30 percent federal tax credit for solar installations, and this now includes stand-alone energy storage devices that have a capacity rating of 5 kilowatt hours or greater. 
• Net Metering lets customers of power companies offset their electricity consumption with a credit if they produce more electricity than they use, or they are charged if they purchase more than the produce.  Under the current law, net metering is available from individual electric companies as long as they have not reached a certain threshold capacity.  Updated status is available on this WSU website.

Check the Incentive page for additional incentives and check with your utility company for any local incentive.