How does solar permitting work in Seattle?

Solar permits in Seattle are handled by the Seattle Department of Construction and Inspections (SDCI). SDCI integrates the building permit and solar interconnection review process — both are submitted through the SDCI portal. Residential solar under 15 kW may qualify for SolarAPP+ review for faster approval. All systems must use equipment on Seattle City Light's Approved Equipment List. SDCI's permit process is more integrated with the utility than most US cities.

Does Seattle use SolarAPP+ for solar permits?

Seattle SDCI has accepted SolarAPP+ for qualifying residential solar systems. SolarAPP+ provides automated plan review, potentially reducing permit turnaround for eligible residential systems under 15 kW. Confirm current SolarAPP+ status with SDCI before submitting — Seattle's SolarAPP+ participation may be subject to program updates.

How does Seattle City Light net metering work?

Seattle City Light is a municipal utility subject to Washington State's net metering law (RCW 80.60). SCL credits excess solar generation at the full retail rate. Monthly credits carry forward throughout the year. On April 30, unused annual credits are forfeited — not paid out. Right-sizing the system to avoid large annual excess is important in Seattle's moderate climate (150+ rainy days per year means annual production is lower than sunnier markets).

What are the solar energy incentives available in Seattle?

Seattle solar incentives: (1) Washington State sales tax exemption on solar equipment and installation labor (approximately 9–10.5% savings in Seattle's combined state/local rate). (2) Washington net metering under RCW 80.60 (retail-rate credits). (3) Federal ITC (30% residential, up to 50% commercial). Seattle/Washington has no state income tax credit. Seattle City Light also offers a Green Power program and time-of-use rates that can optimize solar self-consumption.

Seattle Solar Permit Guide 2026: SDCI Permits, Seattle City Light Interconnection & NEC 2023

Q: What is Seattle City Light's Approved Equipment List?

Seattle City Light (SCL) maintains an Approved Equipment List (AEL) of solar inverters and related equipment. Solar systems in Seattle City Light territory must use inverters from the AEL to receive interconnection approval. Using a non-AEL inverter can prevent interconnection — even if the inverter is UL-listed and compliant with NEC 2023. Always verify that the specified inverter is on the current SCL AEL before finalizing system design.

Seattle’s solar permitting is more integrated than most US cities — SDCI and Seattle City Light coordinate the permit and interconnection review, and the utility’s Approved Equipment List is a hard prerequisite. The mild, cloudy climate means lower production per kW than southern markets, but the combination of Washington’s sales tax exemption, federal ITC, and net metering provides reasonable economics.

Seattle Solar Snapshot

NEC Edition: 2023 (WA early adopter) | Utility: Seattle City Light (municipal) | Net Metering: RCW 80.60 (retail rate; April 30 excess forfeited) | State Incentive: Sales tax exemption (~9–10.5%) | SCL AEL: Must use approved equipment list

NEC 2023 in Seattle

Washington adopted NEC 2023 statewide. Seattle (SDCI) enforces NEC 2023 for all solar permits:

NEC 2023 Section	Seattle Application
690.12 PVHCS	Alternative RSD path available — confirm SCL/SDCI interpretation
690.7 string voltage	Mild climate: T_min = -9°C
690.8 conductor sizing	Mild derating (0.82 factor for SCL area)
690.41 grounding	NEC 2023 reorganized language
Article 706 storage	Updated for solar-plus-storage systems

Seattle Climate Engineering

Seattle’s mild climate makes conductor sizing less aggressive than desert markets:

Parameter	Value
ASHRAE max air temp	29°C
+ 22°C rooftop adder	+22°C
Effective conductor temp	51°C
THWN-2 (90°C) correction factor	0.82

Seattle has the most favorable conductor derating of any major US city — 10 AWG at 0.82 factor = 40 × 0.82 = 32.8A available.

Seattle NEC 690.7 String Voltage

Seattle T_min = -9°C:

For Voc = 45.0V, β_Voc = -0.28%/°C:

Factor = 1 + (-9 - 25) × (-0.0028) = 1 + 0.0952 = 1.0952
Max modules (600V) = 600 / (45.0 × 1.0952) = 12.16 → 12 modules
Max modules (1000V) = 1000 / (45.0 × 1.0952) = 20.3 → 20 modules

Seattle’s cold minimum requires about the same maximum string count as LA — both limit to 12 residential modules, but for different reasons (Voc in Seattle; conductor derating in LA).

Seattle City Light Approved Equipment List

The SCL AEL is a mandatory prerequisite:

SCL publishes the AEL at seattle.gov/city-light/solar
List includes approved inverters, meters, and other interconnection equipment
Updated periodically — always check the current list
Equipment not on the AEL is not eligible for SCL interconnection, even if UL-listed

Why SCL has an AEL: SCL is a municipal utility with its own interconnection standards. The AEL ensures equipment meets SCL’s technical requirements for grid protection, power quality, and communication protocols (including SunSpec/DER communication requirements).

Seattle City Light Interconnection Process

System Size	Process	Timeline
Under 10 kW residential	Standard	15–25 business days
10 kW–30 kW	Engineering review	20–30 business days
Over 30 kW	Distribution study	60–90 days

Interconnection application requires:

SCL solar interconnection application form
One-line electrical diagram (NEC 2023)
Site plan with module layout
Inverter spec sheet (verify AEL status)
SDCI permit number (or SolarAPP+ certificate)

SDCI and SCL Review in Parallel

Unlike most US markets where the permit and utility interconnection are separate sequential processes, Seattle’s SDCI and SCL coordinate their reviews. Submit both applications simultaneously — this parallel process can save weeks vs. sequential submission. The SDCI permit references the SCL interconnection application and vice versa.

Washington Net Metering for Seattle

Parameter	Details (RCW 80.60)
Eligible size	Up to 100 kW residential; up to 1 MW commercial
Credit rate	Full retail rate
Monthly carryover	Yes
Annual true-up	April 30 — excess credits forfeited
Utilities covered	All utilities including SCL (municipal)

April 30 credit forfeiture: Seattle’s net metering does not pay out excess annual credits — they are simply zeroed out. This is different from Oregon (market rate payout) or Minnesota (retail rate payout). System right-sizing is important: a system that exports heavily in summer (Seattle’s sunnier months) may see those credits forfeited if not self-consumed or stored.

SDCI Permit Process

SolarAPP+ Track

SDCI has accepted SolarAPP+ for qualifying residential systems:

Submit through SolarAPP+-compatible software
Automated approval
Submit SolarAPP+ certificate to SDCI
SDCI issues permit
Install + inspections
SCL net meter activation

Standard Track

Submit through SDCI Permit portal (Seattle.gov/sdci)
Upload electrical one-line, structural drawings, equipment specs
SDCI and SCL coordinated review
Plan review: 10–20 business days
Install
Schedule SDCI inspections
SCL net meter activation

SDCI Permit Fees

System	Approximate Fee
Residential (simple)	$150–350
Commercial	Valuation-based

Seattle Historic Districts

Seattle has several historic districts and landmark buildings:

Seattle Landmarks and Historic Districts

If the project is on a Seattle Landmark or in a historic district, the Seattle Landmarks Preservation Board must review the solar installation application before SDCI can issue a permit. This can add 4–8 weeks and may restrict panel placement to rear/non-visible roof surfaces. Identify potential historic designation early using the Seattle Landmarks database.

Washington Sales Tax Exemption

Seattle solar installations qualify for Washington’s sales tax exemption:

Seattle combined sales tax rate: approximately 10.25–10.5%
Exemption applies to solar equipment and installation labor
Exemption taken by installer at time of sale (no customer application needed)
Savings of ~10% on total system cost

Seattle Solar Permit Packages — SCL AEL Compliant

SurgePV generates NEC 2023-compliant permit packages for Seattle SDCI — with SCL Approved Equipment List verification, coordinated permit and interconnection documentation, and Washington net metering modeling.

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Frequently Asked Questions

Does Seattle use NEC 2023?

Yes — Washington adopted NEC 2023 as an early adopter state. SDCI enforces NEC 2023 for all Seattle solar permits. Key NEC 2023 feature: PVHCS as alternative rapid shutdown path — confirm interpretation with SDCI.

What is Seattle City Light’s Approved Equipment List?

SCL’s AEL is a mandatory list of approved inverters and equipment for SCL interconnection. Using an inverter not on the AEL prevents interconnection regardless of UL listing. Always verify AEL status for the specified inverter before finalizing equipment selection.

What happens to unused Seattle net metering credits?

April 30 annual reset: unused monthly credit carryforwards are forfeited (zeroed out). Unlike Oregon or Minnesota, Washington does not pay out annual excess credits. Right-size the system to minimize annual credit forfeiture in Seattle’s moderate production climate.