How many kWh does a solar panel produce per day?
1.55 kWh a day from one 400 W panel at 4.5 peak sun hours with 14% system losses, or 565 kWh a year. In Texas (5.3 hours) it is 1.82 kWh a day, in London (3.48) 1.2 kWh. Panel kW × sun hours × (1 − losses) is the whole formula; the tables below run it for one panel at 3 to 6 sun hours, for systems of 1 to 12 kW, and for a panel and a 10 kW system in every US state.
Open the solar output calculator
How many kWh does one 400 W panel produce per day, month and year?
Per day = 0.4 kW × peak sun hours × 0.86; per month = per day × 365 / 12; per year = per day × 365. Peak sun hours are the kWh/m² a day that reach the panel: about 3 in the cloudiest US states and UK cities, 6 or more in the desert Southwest.
| Peak sun hours | kWh per day | kWh per month | kWh per year |
|---|---|---|---|
| 3 | 1.03 kWh | 31.4 kWh | 377 kWh |
| 3.5 | 1.2 kWh | 36.6 kWh | 439 kWh |
| 4 | 1.38 kWh | 41.9 kWh | 502 kWh |
| 4.5 | 1.55 kWh | 47.1 kWh | 565 kWh |
| 5 | 1.72 kWh | 52.3 kWh | 628 kWh |
| 5.5 | 1.89 kWh | 57.5 kWh | 691 kWh |
| 6 | 2.06 kWh | 62.8 kWh | 753 kWh |
How much does a 3, 5, 6, 8 or 10 kW system produce per day?
The same formula with the system’s DC size instead of one panel’s. Each cell shows kWh per day / kWh per year. A 10 kW system is 25 panels of 400 W.
| System size | 3.5 sun hours | 4.5 sun hours | 5.5 sun hours |
|---|---|---|---|
| 1 kW | 3 kWh / 1,099 kWh | 3.9 kWh / 1,413 kWh | 4.7 kWh / 1,726 kWh |
| 3 kW | 9 kWh / 3,296 kWh | 11.6 kWh / 4,238 kWh | 14.2 kWh / 5,179 kWh |
| 4 kW | 12 kWh / 4,395 kWh | 15.5 kWh / 5,650 kWh | 18.9 kWh / 6,906 kWh |
| 5 kW | 15 kWh / 5,493 kWh | 19.4 kWh / 7,063 kWh | 23.7 kWh / 8,632 kWh |
| 6 kW | 18.1 kWh / 6,592 kWh | 23.2 kWh / 8,475 kWh | 28.4 kWh / 10,359 kWh |
| 8 kW | 24.1 kWh / 8,789 kWh | 31 kWh / 11,300 kWh | 37.8 kWh / 13,812 kWh |
| 10 kW | 30.1 kWh / 10,987 kWh | 38.7 kWh / 14,126 kWh | 47.3 kWh / 17,265 kWh |
| 12 kW | 36.1 kWh / 13,184 kWh | 46.4 kWh / 16,951 kWh | 56.8 kWh / 20,717 kWh |
How many kWh does a solar panel produce per day in each US state?
Peak sun hours by state from NREL data (Unbound Solar table). One 400 W panel and a 10 kW system; for another size, scale the 10 kW column. For UK cities the output calculator uses the PVGIS month-by-month figures.
| State | Sun hours | Panel / day | Panel / year | 10 kW / day | 10 kW / year |
|---|---|---|---|---|---|
| Alabama | 4.6 | 1.58 kWh | 578 kWh | 39.6 kWh | 14,439 kWh |
| Alaska | 3 | 1.03 kWh | 377 kWh | 25.8 kWh | 9,417 kWh |
| Arizona | 6.5 | 2.24 kWh | 816 kWh | 55.9 kWh | 20,404 kWh |
| Arkansas | 4.5 | 1.55 kWh | 565 kWh | 38.7 kWh | 14,126 kWh |
| California | 5.6 | 1.93 kWh | 703 kWh | 48.2 kWh | 17,578 kWh |
| Colorado | 5.5 | 1.89 kWh | 691 kWh | 47.3 kWh | 17,265 kWh |
| Connecticut | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| Delaware | 4.4 | 1.51 kWh | 552 kWh | 37.8 kWh | 13,812 kWh |
| District of Columbia | 4.4 | 1.51 kWh | 552 kWh | 37.8 kWh | 13,812 kWh |
| Florida | 5.3 | 1.82 kWh | 665 kWh | 45.6 kWh | 16,637 kWh |
| Georgia | 4.8 | 1.65 kWh | 603 kWh | 41.3 kWh | 15,067 kWh |
| Hawaii | 5.8 | 2 kWh | 728 kWh | 49.9 kWh | 18,206 kWh |
| Idaho | 4.9 | 1.69 kWh | 615 kWh | 42.1 kWh | 15,381 kWh |
| Illinois | 4.3 | 1.48 kWh | 540 kWh | 37 kWh | 13,498 kWh |
| Indiana | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| Iowa | 4.4 | 1.51 kWh | 552 kWh | 37.8 kWh | 13,812 kWh |
| Kansas | 5 | 1.72 kWh | 628 kWh | 43 kWh | 15,695 kWh |
| Kentucky | 4.3 | 1.48 kWh | 540 kWh | 37 kWh | 13,498 kWh |
| Louisiana | 4.7 | 1.62 kWh | 590 kWh | 40.4 kWh | 14,753 kWh |
| Maine | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| Maryland | 4.4 | 1.51 kWh | 552 kWh | 37.8 kWh | 13,812 kWh |
| Massachusetts | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| Michigan | 4 | 1.38 kWh | 502 kWh | 34.4 kWh | 12,556 kWh |
| Minnesota | 4.3 | 1.48 kWh | 540 kWh | 37 kWh | 13,498 kWh |
| Mississippi | 4.6 | 1.58 kWh | 578 kWh | 39.6 kWh | 14,439 kWh |
| Missouri | 4.6 | 1.58 kWh | 578 kWh | 39.6 kWh | 14,439 kWh |
| Montana | 4.7 | 1.62 kWh | 590 kWh | 40.4 kWh | 14,753 kWh |
| Nebraska | 4.8 | 1.65 kWh | 603 kWh | 41.3 kWh | 15,067 kWh |
| Nevada | 6.4 | 2.2 kWh | 804 kWh | 55 kWh | 20,090 kWh |
| New Hampshire | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| New Jersey | 4.3 | 1.48 kWh | 540 kWh | 37 kWh | 13,498 kWh |
| New Mexico | 6.5 | 2.24 kWh | 816 kWh | 55.9 kWh | 20,404 kWh |
| New York | 4 | 1.38 kWh | 502 kWh | 34.4 kWh | 12,556 kWh |
| North Carolina | 4.7 | 1.62 kWh | 590 kWh | 40.4 kWh | 14,753 kWh |
| North Dakota | 4.5 | 1.55 kWh | 565 kWh | 38.7 kWh | 14,126 kWh |
| Ohio | 4.1 | 1.41 kWh | 515 kWh | 35.3 kWh | 12,870 kWh |
| Oklahoma | 5.1 | 1.75 kWh | 640 kWh | 43.9 kWh | 16,009 kWh |
| Oregon | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| Pennsylvania | 4.1 | 1.41 kWh | 515 kWh | 35.3 kWh | 12,870 kWh |
| Rhode Island | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| South Carolina | 4.8 | 1.65 kWh | 603 kWh | 41.3 kWh | 15,067 kWh |
| South Dakota | 4.7 | 1.62 kWh | 590 kWh | 40.4 kWh | 14,753 kWh |
| Tennessee | 4.4 | 1.51 kWh | 552 kWh | 37.8 kWh | 13,812 kWh |
| Texas | 5.3 | 1.82 kWh | 665 kWh | 45.6 kWh | 16,637 kWh |
| Utah | 5.5 | 1.89 kWh | 691 kWh | 47.3 kWh | 17,265 kWh |
| Vermont | 4 | 1.38 kWh | 502 kWh | 34.4 kWh | 12,556 kWh |
| Virginia | 4.5 | 1.55 kWh | 565 kWh | 38.7 kWh | 14,126 kWh |
| Washington | 3.8 | 1.31 kWh | 477 kWh | 32.7 kWh | 11,928 kWh |
| West Virginia | 4.1 | 1.41 kWh | 515 kWh | 35.3 kWh | 12,870 kWh |
| Wisconsin | 4.2 | 1.44 kWh | 527 kWh | 36.1 kWh | 13,184 kWh |
| Wyoming | 5.2 | 1.79 kWh | 653 kWh | 44.7 kWh | 16,323 kWh |
What the tables leave out
- Seasons: the state figures are yearly averages. In London one panel makes 52.4 kWh in June and 15.8 kWh in December; the calculator shows the twelve months for UK cities.
- Orientation, tilt and shade: the sun hours assume a south-facing array at a good tilt. An east or west roof gives 15-20% less (Energy Saving Trust); raise the losses in the calculator for shade.
- Temperature and the inverter: PVWatts models panel temperature and a 96% inverter separately from the 14% losses, so its own estimate runs a few percent below this formula.
- The other direction: to go from the kWh you use to the panels you need, the power-a-house guide and the panel calculator do that; for a daily target, the 30 kWh a day guide counts the panels for 5 to 50 kWh a day.
Sources
US sun hours: Unbound Solar, "Peak Sun Hours by US State", table built from NREL's PVWatts data; "A peak sun hour is one hour of sunlight at an average intensity of 1,000 watts per square meter". UK sun hours: European Commission Joint Research Centre, PVGIS 5.2, PVcalc for the city's coordinates at the optimal slope and azimuth. Panel: A 400 W panel is the middle of the Trina Vertex TSM-DE09 range and the common residential class in 2026; Trina Solar, Vertex TSM-DE09 data sheet, product range 390-405 W. Losses: NREL, PVWatts Version 5 Manual, section 11 System Losses, Table 6. Output decline: NREL, PVWatts Version 5 Manual, section 11. Average home use: U.S. Energy Information Administration, FAQ "How much electricity does an American home use?". All read 2026-09-20; the full text of each source, with links, is under the calculator.
Frequently asked questions
- How many kWh does a 400 W solar panel produce per day?
- 1.55 kWh at 4.5 peak sun hours: 0.4 kW × 4.5 × 0.86 (after 14% losses). At 3.5 hours 1.2 kWh, at 5.5 hours 1.89 kWh. That is a yearly average; a summer day gives more and a winter day less, and a north-facing or shaded panel gives less again.
- How much does a 10 kW solar system produce per day?
- 38.7 kWh a day at 4.5 sun hours, 1,177 kWh a month and 14,126 kWh a year. In Texas it is 45.6 kWh a day; the state table gives every other state. 10 kW is 25 panels of 400 W.
- How do I convert solar panel watts to kWh?
- Divide the watts by 1,000 to get kW, multiply by the peak sun hours of the day, then by (1 − losses). A 5 kW array in a 5-sun-hour place: 5 × 5 = 25 kWh before losses and 21.5 kWh after the 14% NREL default. Watts are power at one instant; kWh are energy over the day, which is why the sun hours matter more than the label.
- How many kWh does a solar panel produce per month?
- Per day × 365 / 12. One 400 W panel at 4.5 sun hours makes 47.1 kWh a month on average. Where the source publishes monthly sun hours the months differ a lot: in London one panel makes 52.4 kWh in June and 15.8 kWh in December (PVGIS).
- How many panels does it take to make what a house uses in a day?
- The average US home buys 899 kWh a month (EIA), 29.6 kWh a day. At 4.5 sun hours that is 29.6 kWh / 1.55 kWh = 20 panels. The power-a-house guide runs that for every state and for smaller and larger homes.
- Does a panel make less each year?
- Slowly. NREL describes long-term degradation of about 0.5% a year, and the Trina data sheet used for the panel size warrants 0.55% a year, so in year 25 a panel makes about 89% of what it made in year one. The figures on this page are year-one output.
More guides
- How much electricity does a 4 kW solar system generate in the UK?
A 4 kW solar system produces about 4,369 kWh of electricity a year in London (12 kWh a day): 3,616 in Glasgow to 4,897 in Brighton. Month by month.
- How much electricity does a 3 kW solar system generate in the UK?
kWh a day, month and year from a 3 kWp system in every UK city, month by month in three cities (PVGIS), and against Ofgem household use.
- How much electricity does a 5 kW solar system generate in the UK?
kWh a day, month and year from a 5 kWp system in every UK city, month by month in three cities (PVGIS), and against Ofgem household use.
- How many solar panels for 2,000 kWh a month?
2,000 kWh a month is 65.8 kWh a day: 43 panels of 400 W (17.2 kW) at 4.5 sun hours, about $44,720 installed. Every US state and UK city.
Last updated 2026-10-03. Estimates from published averages (NREL, EIA, Ofgem, industry cost surveys), each with its source and date: an installer's site survey and shading analysis replace them. Not financial advice.