Off-grid solar in Washington
In Washington's darkest month, December, panels tilted toward the sun get about 1.8 peak sun hours a day, from 1.6 to 2.0 depending on where you are. Sized for that, a typical off-grid home needs about 24 panels and 4 batteries; a cabin, 4 panels and 1 battery. Flat panels, like on a van roof, get 48% less that month.
Answer a few taps in a guide and every page like this shows the numbers for your own setup. Start
Every setup, sized for Washington
Each guide's usual answers, with Washington's December sun. Tap one to change the answers to yours.
| Setup | Panels | Batteries | About |
|---|---|---|---|
| Off-grid home | 24 × 410 W | 4 | $11,000 – $13,500 |
| Backup for my house | 4 × 410 W | 2 | $9,000 – $11,500 |
| Tiny house | 10 × 410 W | 2 | $6,500 – $8,000 |
| Cabin or shed | 4 × 410 W | 1 | $4,000 – $5,000 |
| RV, bus or skoolie | 8 × 410 W | 2 | $6,000 – $7,500 |
| Van | 4 × 200 W | 3 | $6,000 – $7,500 |
| Just emergencies or camping | 4 × 200 W | Power station | $3,500 – $4,500 |
Van and RV numbers use flat-roof sun (0.9 h) and are capped by roof space, so they lean on driving and a generator in December. Costs are the gear only.
Sun in Washington, month by month
Tilted at latitude Flat. December gets 28% of the sun of the brightest month (6.5 h). Size for December and the rest of the year has spare.
Across Washington
Darkest-month sun differs by place. The 14 ZIP areas range from 1.6 hours in the 982xx ZIP area to 2.0 in the 989xx ZIP area. That's 29% more panel output for the same panels.
Common questions
How many solar panels do I need to live off grid in Washington?
Sized for Washington's darkest month (December, about 1.8 peak sun hours on tilted panels), a typical off-grid home needs about 24 panels (410 W each) and 4 server-rack batteries; a cabin about 4 panels and 1 battery. Your own loads change this; the guides size it for you.
How many peak sun hours does Washington get in winter?
About 1.8 a day in December on panels tilted at latitude, and 0.9 on flat panels (NASA POWER, at the state's center of population), ranging from 1.6 in the 982xx ZIP area to 2.0 in the 989xx ZIP area.
Does off-grid solar work in Washington in winter?
Yes, if it's sized for December: that month gets about 28% of the sun of the brightest month, so a system sized for December has plenty the rest of the year. Below about 2 sun hours, most owners add a small generator for the darkest weeks rather than doubling the panels.
Data: NASA Langley Research Center POWER Project, long-term monthly averages at Washington's 2020 Census center of population and at each 3-digit ZIP area. Method and downloads.