Solar Panel Calculator for Seattle, WA
Estimate the cost, savings and payback of solar panels in Seattle, WA, using local NREL sunshine data, Washington prices and electricity rates.
Your result
Enter your numbers and press the button. Your result appears here.
Seattle gets about 3.96 peak sun hours a day on a south-facing roof, so each kW of panels makes about 1,093 kWh a year. That ranks #108 of the 111 cities on this site. Output peaks in Jul and is lowest in Dec.
Sunshine in Seattle by month
What an 8 kW system makes in Seattle
| Month | Sun hours a day | Output | Bill savings |
|---|---|---|---|
| Jan | 1.37 | 272 kWh | $39 |
| Feb | 2.62 | 472 kWh | $68 |
| Mar | 3.83 | 752 kWh | $108 |
| Apr | 5.03 | 920 kWh | $133 |
| May | 5.90 | 1,096 kWh | $158 |
| Jun | 6.17 | 1,088 kWh | $157 |
| Jul | 6.41 | 1,152 kWh | $166 |
| Aug | 5.95 | 1,072 kWh | $155 |
| Sep | 4.63 | 832 kWh | $120 |
| Oct | 2.76 | 528 kWh | $76 |
| Nov | 1.60 | 312 kWh | $45 |
| Dec | 1.30 | 256 kWh | $37 |
| Year | 3.96 | 8,744 kWh | $1,261 |
Savings at 14.42¢ per kWh (Washington average), with every kWh credited at that price.
Cost and payback by system size
At $2.47 per watt, the Washington average, before incentives.
| System | Cost | Year 1 savings | Payback | 25-yr gain |
|---|---|---|---|---|
| 4 kW | $9,880 | $630 | 16.3 yrs | $4,971 |
| 6 kW | $14,820 | $946 | 16.3 yrs | $7,456 |
| 8 kW | $19,760 | $1,261 | 16.3 yrs | $9,941 |
| 10 kW | $24,700 | $1,576 | 16.3 yrs | $12,427 |
| 12 kW | $29,640 | $1,891 | 16.3 yrs | $14,912 |
How many panels you need in Seattle
| Monthly use | System | 400 W panels |
|---|---|---|
| 500 kWh | 5.49 kW | 14 |
| 750 kWh | 8.23 kW | 21 |
| 1,000 kWh | 10.98 kW | 28 |
| 1,500 kWh | 16.47 kW | 42 |
| 2,000 kWh | 21.96 kW | 55 |
Covering 100% of a year's use at 1,093 kWh per kW.
Common questions
Is solar worth it in Seattle?
At local averages an 8 kW system costs about $19,760 before incentives, saves about $1,261 in its first year and pays back in about 16.3 years.
How many peak sun hours does Seattle get?
About 3.96 a day over the year on a south-facing roof at 20°, from 1.3 in Dec to 6.4 in Jul, according to NREL's PVWatts model.
How much does a 1 kW solar system produce in Seattle?
About 1,093 kWh a year, or 91 kWh a month on average.
Is there a federal solar tax credit?
Not for homeowners who buy their system. The 30% Residential Clean Energy Credit ended for systems installed after December 31, 2025.
Sources
- NREL PVWatts V8 API (south-facing, 20° tilt, 14% losses, typical-year weather): https://developer.nlr.gov/docs/solar/pvwatts/v8/
- EnergySage, Solar panel cost by state (updated November 6, 2026): https://www.energysage.com/local-data/solar-panel-cost/
- U.S. EIA, Electric Power Monthly, Table 5.6.B (residential price, Jan–Aug 2026): https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_b