Off-grid solar calculator
How many solar panels do you need, how big a battery, and what size inverter? List what you'll run, pick the nearest state capital, and the calculator does the rest.
How to use the results
- Start with daily kWh. It drives everything else. Cutting a big load, like an electric water heater or dryer, often shrinks the whole system more than any other change.
- Size the array for your darkest month if you'll live off-grid all year. Use the year-round average only for backup power or summer cabins.
- Pick a battery voltage. The calculator shows amp-hours at 12, 24 and 48 volts. Bigger systems usually run at 48 volts so the wires and currents stay smaller.
- Check surge. Motors, like well pumps and fridge compressors, draw extra power for a moment when they start. Compare that against the inverter's surge rating on its spec sheet.
Running a well? Our solar well pump sizing guide covers gallons a day, total head and real kit specs.
Where the starting numbers come from
- Appliance watts and hours start from the approximate wattages and average monthly hours in FirstEnergy's Understanding Electricity Usage & Costs fact sheet. We divided hours per month by 30. Your own devices will differ, so check their labels. Virginia Cooperative Extension's Estimating Appliance and Home Electronic Energy Use gives nameplate ranges, such as 250 to 1,100 watts for a deep well pump.
- Sun hours are NASA POWER's all-sky solar energy on flat ground, in kWh per square meter per day, averaged over January 2001 to December 2025 (NASA POWER Climatology API, checked November 3, 2026). One kWh per square meter is one "peak sun hour". Panels tilted toward the sun usually collect more than flat ground, especially in winter, so these numbers lean conservative.
- Losses, backup days, usable battery and inverter headroom are our starting assumptions, not measured data. Change them to match your gear: your battery's spec sheet lists its rated depth of discharge.
Peak sun hours by state
Average daily sun hours at each state capital, from NASA POWER (2001–2025, flat ground). "Worst month" is the darkest month of the year.
| City | Year average | Worst month |
|---|---|---|
| Montgomery, AL | 4.61 | 2.43 (Dec) |
| Anchorage, AK | 2.54 | 0.14 (Dec) |
| Phoenix, AZ | 5.85 | 3.08 (Dec) |
| Little Rock, AR | 4.44 | 2.28 (Dec) |
| Sacramento, CA | 5.23 | 1.97 (Dec) |
| Denver, CO | 4.85 | 2.29 (Dec) |
| Hartford, CT | 3.91 | 1.54 (Dec) |
| Dover, DE | 4.07 | 1.75 (Dec) |
| Tallahassee, FL | 4.78 | 2.79 (Dec) |
| Atlanta, GA | 4.51 | 2.37 (Dec) |
| Honolulu, HI | 5.68 | 3.93 (Dec) |
| Boise, ID | 4.56 | 1.39 (Dec) |
| Springfield, IL | 4.11 | 1.65 (Dec) |
| Indianapolis, IN | 4 | 1.56 (Dec) |
| Des Moines, IA | 4.09 | 1.67 (Dec) |
| Topeka, KS | 4.3 | 1.95 (Dec) |
| Frankfort, KY | 4.06 | 1.67 (Dec) |
| Baton Rouge, LA | 4.67 | 2.61 (Dec) |
| Augusta, ME | 3.7 | 1.28 (Dec) |
| Annapolis, MD | 4.24 | 1.92 (Dec) |
| Boston, MA | 3.81 | 1.49 (Dec) |
| Lansing, MI | 3.79 | 1.2 (Dec) |
| Saint Paul, MN | 3.86 | 1.31 (Dec) |
| Jackson, MS | 4.64 | 2.43 (Dec) |
| Jefferson City, MO | 4.24 | 1.91 (Dec) |
| Helena, MT | 4.01 | 1.17 (Dec) |
| Lincoln, NE | 4.31 | 1.89 (Dec) |
| Carson City, NV | 5.23 | 2.02 (Dec) |
| Concord, NH | 3.71 | 1.33 (Dec) |
| Trenton, NJ | 3.92 | 1.62 (Dec) |
| Santa Fe, NM | 5.43 | 2.89 (Dec) |
| Albany, NY | 3.74 | 1.3 (Dec) |
| Raleigh, NC | 4.47 | 2.31 (Dec) |
| Bismarck, ND | 4.03 | 1.3 (Dec) |
| Columbus, OH | 3.92 | 1.48 (Dec) |
| Oklahoma City, OK | 4.74 | 2.4 (Dec) |
| Salem, OR | 3.88 | 1.09 (Dec) |
| Harrisburg, PA | 3.86 | 1.52 (Dec) |
| Providence, RI | 3.99 | 1.55 (Dec) |
| Columbia, SC | 4.54 | 2.4 (Dec) |
| Pierre, SD | 4.18 | 1.52 (Dec) |
| Nashville, TN | 4.23 | 1.92 (Dec) |
| Austin, TX | 4.81 | 2.74 (Dec) |
| Salt Lake City, UT | 4.8 | 1.86 (Dec) |
| Montpelier, VT | 3.47 | 1.06 (Dec) |
| Richmond, VA | 4.27 | 2.07 (Dec) |
| Olympia, WA | 3.42 | 0.85 (Dec) |
| Charleston, WV | 3.94 | 1.59 (Dec) |
| Madison, WI | 3.85 | 1.32 (Dec) |
| Cheyenne, WY | 4.57 | 1.98 (Dec) |
This calculator is for planning. Have a licensed electrician check any system before you wire it, and follow your local code.