Calculator › Seattle, Washington
Solar panels in Seattle, Washington
Seattle receives 3.48 peak sun hours a day and 1,270 kWh/m² of solar energy a year. That is measured satellite data for Seattle's coordinates, not a national average — and it changes the panel count.
Seattle solar data
3.48peak sun hours/day
1,270annual irradiance (kWh/m²)
1.15kWh/day from one 400 W panel
419kWh/year from one 400 W panel
Monthly solar irradiance in Seattle
| Month | Peak sun hours/day | Share of year |
|---|---|---|
| January | 0.96 | 0.1 |
| February | 1.64 | 0.1 |
| March | 3.09 | 0.3 |
| April | 4.56 | 0.4 |
| May | 5.41 | 0.5 |
| June | 6.05 | 0.5 |
| July | 7.07 | 0.6 |
| August | 4.83 | 0.4 |
| September | 3.68 | 0.3 |
| October | 2.31 | 0.2 |
| November | 1.12 | 0.1 |
| December | 0.85 | 0.1 |
Source: NASA POWER daily point API, parameter ALLSKY_SFC_SW_DWN (global horizontal irradiance), year 2024. Coordinates 47.6062, -122.3321.
How many solar panels does Seattle need?
For a typical US household using 900 kWh a month, Seattle needs about 27 panels of 400 W (10.44 kWp), with a south-facing roof. That is more panels than the same household would need in a city with 4.5 peak sun hours.