Solar Panel Output Calculator
Enter the system size, the direction the roof faces and its tilt, and get the estimated kWh per year and per month and their year-1 value, based on your state's average sun. *(ZIP-level output is planned: this version uses the state average. Don't show a ZIP field until v2 ships. See builder notes.)*
Solar panel output
D03Scenario A
Sets the electricity rate. Pick US average if you're not sure.
From EIA for US average. Use the rate on your bill if you know it.
Rate used: 18.4¢/kWh · US average · EIA reference 2025–26 · 1,350 kWh per kW of solar · export rule: varies (data as of 2026-09-26) ·
Estimated production per year
About 900 kWh a month on average in US average.
- kWh per year
- 10,800
- Average kWh per month
- 900
- Year-1 value (rate × net metering factor)
- $794.88
Estimate. Formula and sources are under “How it works”. Change any input; the result updates as you type.
2026 note: The federal 25C and 25D tax credits ended for installations after Dec 31, 2025. Our numbers use 2026 rules. State rebates, HEAR/HOMES programs and utility programs may still apply.
Formula
How it works
- kWh per year = kW × your state's kWh per kW per year × direction factor × tilt factor
- Average kWh per month = kWh per year ÷ 12
- Year-1 value = kWh per year × rate × net metering factor
Direction factors: south 1.00, southwest 0.96, west 0.87, east 0.86, north 0.65. Tilt factors: flat 0.90, low 0.98, latitude 1.00, steep 0.95. The net metering factor follows your state's rule: retail 1.0, net billing 0.6, limited or utility-dependent 0.5, anything else 0.4. The value is an estimate for year 1 only; the Solar Payback calculator adds degradation and rate changes.
Sources: production per kW per year by state from NREL PVWatts v8 (tilt = latitude, south, 14% losses); direction and tilt factors from NREL PVWatts US averages; electricity rate from EIA Electric Power Monthly table 5.6.A; net metering rules from DSIRE and state commissions.
Worked example
A worked example
Washington averages 1,050 kWh per kW per year. A 6 kW system facing west (0.87) on a low-pitch roof (0.98) makes an estimated 5,371 kWh a year, about 448 kWh a month. Washington has retail net metering in our data, so every kWh is worth the full 12.0¢: $644.57 in year 1.
Reference
By state, at the default inputs
Estimated production per year, with this page's default inputs and each state's reference prices (EIA reference 2025–26, data as of 2026-09-26).
| US average | 10,800 kWh | 18.4¢/kWh |
|---|---|---|
| Alabama | 10,800 kWh | 15.5¢/kWh |
| Alaska | 7,200 kWh | 25.0¢/kWh |
| Arizona | 13,600 kWh | 15.0¢/kWh |
| Arkansas | 10,800 kWh | 13.0¢/kWh |
| California | 12,400 kWh | 32.0¢/kWh |
| Colorado | 12,400 kWh | 16.0¢/kWh |
| Connecticut | 9,600 kWh | 30.0¢/kWh |
| Delaware | 10,000 kWh | 17.0¢/kWh |
| District of Columbia | 10,000 kWh | 19.0¢/kWh |
| Florida | 11,200 kWh | 15.0¢/kWh |
| Georgia | 10,800 kWh | 14.5¢/kWh |
| Hawaii | 12,000 kWh | 42.0¢/kWh |
| Idaho | 11,200 kWh | 12.0¢/kWh |
| Illinois | 10,000 kWh | 17.0¢/kWh |
| Indiana | 9,600 kWh | 15.5¢/kWh |
| Iowa | 10,000 kWh | 13.5¢/kWh |
| Kansas | 11,600 kWh | 14.5¢/kWh |
| Kentucky | 9,600 kWh | 13.0¢/kWh |
| Louisiana | 10,800 kWh | 12.5¢/kWh |
| Maine | 9,600 kWh | 26.0¢/kWh |
| Maryland | 10,000 kWh | 19.0¢/kWh |
| Massachusetts | 10,000 kWh | 29.0¢/kWh |
| Michigan | 9,200 kWh | 19.5¢/kWh |
| Minnesota | 10,000 kWh | 15.5¢/kWh |
| Mississippi | 10,800 kWh | 13.5¢/kWh |
| Missouri | 10,800 kWh | 13.0¢/kWh |
| Montana | 10,800 kWh | 13.0¢/kWh |
| Nebraska | 11,200 kWh | 12.0¢/kWh |
| Nevada | 13,200 kWh | 15.0¢/kWh |
| New Hampshire | 9,600 kWh | 27.0¢/kWh |
| New Jersey | 10,000 kWh | 22.0¢/kWh |
| New Mexico | 13,600 kWh | 15.0¢/kWh |
| New York | 9,600 kWh | 25.0¢/kWh |
| North Carolina | 10,800 kWh | 14.5¢/kWh |
| North Dakota | 10,400 kWh | 11.5¢/kWh |
| Ohio | 9,200 kWh | 16.5¢/kWh |
| Oklahoma | 11,600 kWh | 13.0¢/kWh |
| Oregon | 9,200 kWh | 14.5¢/kWh |
| Pennsylvania | 9,600 kWh | 18.5¢/kWh |
| Rhode Island | 10,000 kWh | 29.0¢/kWh |
| South Carolina | 10,800 kWh | 15.0¢/kWh |
| South Dakota | 10,800 kWh | 13.0¢/kWh |
| Tennessee | 10,400 kWh | 13.5¢/kWh |
| Texas | 11,600 kWh | 15.5¢/kWh |
| Utah | 12,000 kWh | 12.0¢/kWh |
| Vermont | 9,600 kWh | 22.0¢/kWh |
| Virginia | 10,400 kWh | 15.5¢/kWh |
| Washington | 8,400 kWh | 12.0¢/kWh |
| West Virginia | 9,200 kWh | 15.5¢/kWh |
| Wisconsin | 9,600 kWh | 17.5¢/kWh |
| Wyoming | 11,600 kWh | 12.5¢/kWh |
Questions
FAQ
How much does an 8 kW system produce?
At the US average of 1,350 kWh per kW, about 10,800 kWh a year, or 900 kWh a month, facing south at latitude tilt. In Texas it's 11,600 kWh a year (967 a month).
East vs west facing panels?
They're close: west produces 87% of a south-facing system and east 86%. For the US-average 8 kW system, that's 9,396 kWh (west) vs 9,288 kWh (east), against 10,800 kWh facing south. West-facing panels produce later in the day, which can matter on time-of-use rates.
Is a north-facing roof worth it?
It produces about 65% of a south-facing roof: 7,020 kWh a year for the US-average 8 kW system. That stretches payback a lot. Run the Solar Payback calculator with the smaller output.
Winter vs summer output?
This version gives the yearly total and the average month. Output is higher in summer and lower in winter; a month-by-month solar curve isn't in our data yet.
Why is my installer's number different?
Installers model your exact roof, shading and location. We use your state's average, so treat our result as a check on the quote, not a replacement for it.
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