Winter sun by state
The short version
In its darkest month, a US state gets anywhere from 0.5 peak sun hours (Alaska) to 5.0 (Hawaii) on panels tilted toward the sun. Panels lying flat, like on a van roof, get about 40% less that month. In every state, the darkest month is December. Size solar for that month and it works all year.
Every state, darkest month
AK0.5
ME2.5
WI2.4
VT1.8
NH2.4
WA1.8
ID2.4
MT2.5
ND2.6
MN2.3
IL2.5
MI1.9
NY2.4
MA2.7
OR1.9
NV4.4
WY3.2
SD3.1
IA3.0
IN2.4
OH2.0
PA2.5
NJ2.8
CT2.6
RI2.6
CA4.1
UT3.2
CO4.3
NE3.3
MO3.2
KY2.8
WV2.5
VA3.4
MD2.9
DE3.0
AZ4.9
NM5.0
KS3.6
AR3.5
TN3.1
NC3.7
SC3.8
DC3.2
OK3.7
LA3.7
MS3.5
AL3.5
GA3.7
HI5.0
TX4.0
FL4.5
| State | Tilted panels, darkest month | Flat panels, darkest month | Summer, brightest month, tilted |
|---|---|---|---|
| Alabama | 3.5 | 2.3 | 5.5 |
| Alaska | 0.5 | 0.1 | 4.6 |
| Arizona | 4.9 | 3.1 | 7.6 |
| Arkansas | 3.5 | 2.2 | 5.6 |
| California | 4.1 | 2.6 | 7.5 |
| Colorado | 4.3 | 2.4 | 6.2 |
| Connecticut | 2.6 | 1.6 | 5.3 |
| Delaware | 3.0 | 1.8 | 5.4 |
| District of Columbia | 3.2 | 2.0 | 5.4 |
| Florida | 4.5 | 3.4 | 6.1 |
| Georgia | 3.7 | 2.5 | 5.6 |
| Hawaii | 5.0 | 4.1 | 6.7 |
| Idaho | 2.4 | 1.3 | 6.9 |
| Illinois | 2.5 | 1.5 | 5.5 |
| Indiana | 2.4 | 1.5 | 5.5 |
| Iowa | 3.0 | 1.7 | 5.7 |
| Kansas | 3.6 | 2.1 | 5.9 |
| Kentucky | 2.8 | 1.8 | 5.5 |
| Louisiana | 3.7 | 2.6 | 5.6 |
| Maine | 2.5 | 1.3 | 5.2 |
| Maryland | 2.9 | 1.8 | 5.4 |
| Massachusetts | 2.7 | 1.5 | 5.3 |
| Michigan | 1.9 | 1.2 | 5.6 |
| Minnesota | 2.3 | 1.2 | 5.6 |
| Mississippi | 3.5 | 2.4 | 5.6 |
| Missouri | 3.2 | 1.9 | 5.7 |
| Montana | 2.5 | 1.3 | 6.5 |
| Nebraska | 3.3 | 1.8 | 6.0 |
| Nevada | 4.4 | 2.6 | 7.5 |
| New Hampshire | 2.4 | 1.4 | 5.2 |
| New Jersey | 2.8 | 1.7 | 5.3 |
| New Mexico | 5.0 | 3.1 | 7.3 |
| New York | 2.4 | 1.5 | 5.2 |
| North Carolina | 3.7 | 2.3 | 5.5 |
| North Dakota | 2.6 | 1.2 | 5.9 |
| Ohio | 2.0 | 1.3 | 5.3 |
| Oklahoma | 3.7 | 2.4 | 6.0 |
| Oregon | 1.9 | 1.1 | 6.7 |
| Pennsylvania | 2.5 | 1.6 | 5.3 |
| Rhode Island | 2.6 | 1.6 | 5.5 |
| South Carolina | 3.8 | 2.5 | 5.7 |
| South Dakota | 3.1 | 1.6 | 6.1 |
| Tennessee | 3.1 | 2.1 | 5.5 |
| Texas | 4.0 | 2.8 | 6.1 |
| Utah | 3.2 | 1.9 | 6.8 |
| Vermont | 1.8 | 1.1 | 5.0 |
| Virginia | 3.4 | 2.1 | 5.5 |
| Washington | 1.8 | 0.9 | 6.5 |
| West Virginia | 2.5 | 1.6 | 5.2 |
| Wisconsin | 2.4 | 1.3 | 5.6 |
| Wyoming | 3.2 | 1.8 | 6.7 |
All values are for December, the darkest month everywhere, except Summer (the brightest month). Peak sun hours = kWh of sunlight per square meter of panel per day. Multiply by a panel's kW and about 0.77 (wires, heat, dust) to get kWh a day.
How these numbers were made
- Source: NASA Langley Research Center POWER Project, climatology API: long-term monthly averages of solar energy reaching a surface, from satellite data (power.larc.nasa.gov).
- Where: the table and map use one point per state, at its 2020 Census center of population (where the average resident lives). Big states vary a lot, so ZIP lookups and the guides use a finer point for each 3-digit ZIP area (890 areas, in the ZIP CSV).
- Tilted means panels facing south, tilted at the same angle as the latitude, the usual year-round setup for ground and roof mounts. Flat means lying horizontal, like most van and bus roofs.
- How the guides use it: every guide sizes panels for the darkest month here. Vans and buses use the flat number. More on the method
- Use it: free to reuse with credit to Liberty Offgrid and NASA POWER (CC BY 4.0).
What it means for your setup
Less winter sun means more panels for the same power. The guides do the math for your place.