Solar · guide
How much less do solar panels make in winter?
In the worst month, panels make 78% (in New Mexico) to 13% (in Alaska) of what they make on a day in the best month. That’s why anything off-grid is sized for winter: covering 1 kWh a day in Tennessee takes about 490 W of panels in December but 350 W in an average month.
Best and worst month, by state
kWh per kW of panels per day, facing south at the best tilt. The last column is the worst month as a share of the best.
| State | Best | Worst | Worst ÷ best |
|---|---|---|---|
| Alabama | April 4.8 | December 3.2 | 66% |
| Alaska | June 4.9 | December 0.7 | 13% |
| Arizona | April 5.9 | December 4.4 | 74% |
| Arkansas | July 4.7 | December 3.2 | 68% |
| California | August 5.6 | December 3.8 | 68% |
| Colorado | September 5.2 | December 4.0 | 77% |
| Connecticut | July 4.6 | December 2.8 | 61% |
| Delaware | July 4.6 | December 2.9 | 64% |
| District of Columbia | June 4.5 | December 3.1 | 68% |
| Florida | April 5.1 | December 3.8 | 74% |
| Georgia | April 4.8 | December 3.3 | 68% |
| Hawaii | September 5.1 | December 3.8 | 75% |
| Idaho | July 5.7 | December 2.2 | 39% |
| Illinois | July 4.8 | December 2.4 | 50% |
| Indiana | June 4.7 | December 2.3 | 49% |
| Iowa | July 4.7 | December 2.5 | 53% |
| Kansas | July 4.9 | December 3.3 | 68% |
| Kentucky | June 4.7 | December 2.5 | 54% |
| Louisiana | May 4.7 | December 3.3 | 70% |
| Maine | August 4.5 | December 2.5 | 56% |
| Maryland | June 4.5 | December 3.0 | 66% |
| Massachusetts | July 4.5 | December 2.7 | 60% |
| Michigan | July 4.7 | December 1.8 | 38% |
| Minnesota | July 4.7 | December 2.3 | 48% |
| Mississippi | April 4.7 | December 3.2 | 68% |
| Missouri | June 4.7 | December 3.0 | 63% |
| Montana | July 5.5 | December 2.2 | 41% |
| Nebraska | July 4.8 | December 2.9 | 61% |
| Nevada | April 5.9 | December 4.2 | 71% |
| New Hampshire | July 4.5 | December 2.7 | 60% |
| New Jersey | July 4.5 | December 2.8 | 63% |
| New Mexico | April 5.8 | December 4.5 | 78% |
| New York | July 4.6 | December 2.9 | 62% |
| North Carolina | April 4.8 | December 3.4 | 70% |
| North Dakota | July 5.0 | December 2.2 | 44% |
| Ohio | June 4.6 | December 2.0 | 45% |
| Oklahoma | July 4.9 | December 3.5 | 72% |
| Oregon | July 5.4 | December 1.6 | 30% |
| Pennsylvania | July 4.5 | December 2.7 | 61% |
| Rhode Island | July 4.5 | December 2.9 | 64% |
| South Carolina | April 5.0 | December 3.5 | 69% |
| South Dakota | July 5.0 | December 2.8 | 55% |
| Tennessee | June 4.7 | December 2.9 | 61% |
| Texas | August 4.7 | December 3.3 | 69% |
| Utah | June 5.5 | December 2.7 | 49% |
| Vermont | July 4.6 | December 1.8 | 39% |
| Virginia | April 4.7 | December 3.3 | 70% |
| Washington | July 5.3 | December 1.4 | 27% |
| West Virginia | June 4.5 | December 2.2 | 49% |
| Wisconsin | July 4.8 | December 2.2 | 47% |
| Wyoming | June 5.2 | December 3.4 | 65% |
Size panels and a battery for your worst month →
FAQ
How much less do solar panels make in winter?
In the worst month, panels make 78% (in New Mexico) to 13% (in Alaska) of what they make on a day in the best month. That’s why anything off-grid is sized for winter: covering 1 kWh a day in Tennessee takes about 490 W of panels in December but 350 W in an average month.
Should a home system be sized for winter?
A grid-tied home is usually sized on the year, because the grid covers the winter shortfall and (depending on your utility) credits the summer surplus. Off-grid systems have no such backup, so they’re sized for the worst month.
Sources and assumptions
- Solar output (kWh per kW of panels, by month): Global Solar Atlas 2.0, long-term averages to 2025 (data version 2.2.68, updated 2026-04-01), for crystalline-silicon panels facing south at the best fixed tilt, after typical system losses. Data obtained from the “Global Solar Atlas 2.0, a free, web-based application is developed and operated by the company Solargis s.r.o. on behalf of the World Bank Group, utilizing Solargis data, with funding provided by the Energy Sector Management Assistance Program (ESMAP). For additional information: https://globalsolaratlas.info” Licensed CC BY 4.0; we rounded and combined it as described here. Not affiliated with or endorsed by Solargis or the World Bank Group.
- State figure: population-weighted average of the state’s three largest cities (U.S. Census Bureau Vintage 2024 population estimates; coordinates from the 2020 Census Gazetteer). Hawaii and DC use one city.
- Cross-check: NASA POWER sunshine climatology (2001–2025), tilted with a standard isotropic-sky model × 0.80. States more than 12% apart were reviewed by hand; the gaps are explained on our methodology page.
- Home use: EIA Table 5A, 2024 average monthly residential kWh by state. Rates: EIA Electric Power Monthly, August 2026.
- Tax credit: IRS FAQ on the One, Big, Beautiful Bill (FS-2025-05, Aug. 21, 2025).
- Assumptions: 85% charging efficiency into a battery, 85% from battery to appliance, panel counts rounded up, off-grid sizing for the worst month.