The exemption, and why it is bigger than it looks
From July 1, 2019 through December 31, 2029, residential purchasers receive a 100 percent exemption from state and local sales and use tax on machinery and equipment used directly in generating electricity by a solar energy system capable of no more than 100 kW AC, under RCW 82.08.962 and 82.12.962.
The detail that makes it larger than most such exemptions is that it covers installation labour, not only hardware. Labour is a substantial share of a residential solar project, so an exemption that stops at equipment would be worth considerably less.
Washington combined state and local sales tax rates are high by national standards, which further increases what the exemption is worth on a system in the twenty to thirty thousand dollar range.
It also has an end date. The authorisation runs through December 31, 2029, and while such provisions are often renewed, a renewal is a legislative decision rather than a certainty.
How to confirm your quote reflects it
Because there is nothing to claim, the only way to verify the exemption is to look for what is not on the quote. Ask directly whether the quoted price includes any Washington state or local sales tax.
If it does, ask which component it was applied to and why. There may be a legitimate answer for an item outside the exemption, but it should be an explanation rather than a shrug.
This is also a place where two quotes can look closer than they are. If one seller has handled the exemption correctly and another has not, the difference is not in the workmanship, it is in the paperwork.
Confirm the system is within the 100 kW AC ceiling, which any residential array will be by a wide margin, and keep the documentation with your records in case the treatment is ever queried.
Cheap power is the counterweight
Tacoma Power is a municipal utility with low rates, and low rates are the reason Washington payback periods run long. The exemption reduces what you pay for the system; it does not change what a kilowatt hour is worth once the system is running.
So the honest framing for a Tacoma project is that the up-front cost is genuinely reduced and the ongoing return is genuinely modest, and both of those should be visible in the numbers you are shown.
Ask for the payback calculated from your actual Tacoma Power rate rather than a state or national average, since municipal rates sit well below both.
Ask what escalation the model assumed. Utilities across Washington have proposed steep increases for the coming years, so escalation is a live question rather than a formality, but the assumption should be stated and you should see the projection without it too.
Rebuilding the Washington arithmetic
The 30 percent federal Residential Clean Energy Credit under Section 25D expired for property placed in service after December 31, 2025, so a cash or loan purchase in Tacoma receives no federal tax credit. Section 48E survives at 30 percent for third-party owners under leases and power purchase agreements.
Washington has no state income tax and therefore no state solar credit.
What exists is the sales and use tax exemption on equipment and labour through December 31, 2029, retail-rate net metering under RCW 80.60 with the April 30 forfeit, and whatever programmes Tacoma Power itself may run, which is worth asking the utility about directly.
Then add the electricity you stop buying at your actual municipal rate. Ask for the projection with the rate and the escalation assumption both stated on the page.