The rate is why the numbers work here
Puget Sound Energy is an investor-owned utility with a supply mix leaning more on natural gas than the hydro-heavy municipals, and it has charged around 17.7 cents per kWh for residential power.
Seattle City Light, a short distance west, has charged around 11 cents. That is a difference of roughly 60 percent in what a displaced kilowatt hour is worth, on identical hardware and identical weather.
This is the single most important thing to establish about a western Washington quote: which utility bills the address, and whether the projection used that utility actual rate rather than a state average of about 15 cents.
A projection built on the state average understates a PSE project and overstates a City Light one. Both errors are common and both come from the same lazy input.
And the trajectory is steeper still
PSE has proposed raising electricity rates by roughly 17 percent next year and by close to 30 percent over the next three years. A proposal is not an approved order, and regulators frequently allow less than is asked, but the direction is set.
For a twenty-five year asset that trajectory is the substance of the case. Every point of rate increase raises the value of the entire remaining output of the system.
Ask what escalation rate the savings model applied and whether it was grounded in the utility own filings or in a generic assumption. Those two approaches produce very different answers over a long horizon.
Ask also to see the projection at zero escalation. In Bellevue that version is likely to look reasonable on its own, which is a much stronger position than a case that depends on the increases arriving as proposed.
Sizing against the April 30 forfeit
Under RCW 80.60 excess kilowatt hours are credited at the retail rate on the following period bill, and on April 30 each year any remaining unused credit from the previous year is granted to the utility without compensation.
A higher retail rate raises the value of every kilowatt hour you consume yourself, and it does nothing at all for a kilowatt hour that sits in credit until April and is forfeited. The gap between those two outcomes is wider in PSE territory than anywhere else in the region.
So the sizing discipline matters more here rather than less. Build from your last twelve months of bills, ask what percentage of annual usage the design covers, and treat capacity beyond that as needing a specific reason.
Ask for the monthly profile as well as the annual total, with the credit balance tracked through to April 30. An annual figure that balances can still leave credit stranded on the wrong side of that date.
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 Bellevue 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 under RCW 82.08.962 covering equipment and installation labour on systems up to 100 kW AC through December 31, 2029, and retail-rate net metering with the April 30 forfeit.
Then add the electricity you stop buying at the actual PSE rate rather than a state average, with the escalation assumption stated. In Bellevue that last term is doing most of the work, which is exactly why it should be the number you check hardest.