Solar Insolation by Latitude
Sun-hours above the atmosphere and day length for any latitude and month: 8.8 sun-hours and 14.8 h of daylight at 40°N in June. Not peak sun hours. How it works
Use the Solar Insolation by Latitude
About the Solar Insolation by Latitude
At 40°N the top-of-atmosphere sun-hours are 8.8 hours a day in June and 2.7 in December, and the day from sunrise to sunset lasts 14.8 hours in June and 9.2 in December. The sun-hours figure is the sun’s daily energy on a flat surface above the atmosphere, counted in hours of full-strength sun (the solar constant) shining straight down. It is not peak sun hours and not what a panel on the ground receives, so do not use it to size an array or a battery bank.
Top-of-atmosphere sun-hours (hours a day) by month and latitude
| Month | 0° | 25°N | 40°N | 50°N | 60°N |
|---|---|---|---|---|---|
| January | 7.1 | 4.7 | 2.9 | 1.7 | 0.6 |
| February | 7.4 | 5.6 | 4.0 | 2.9 | 1.6 |
| March | 7.6 | 6.7 | 5.5 | 4.5 | 3.3 |
| April | 7.5 | 7.7 | 7.1 | 6.4 | 5.6 |
| May | 7.2 | 8.3 | 8.3 | 8.0 | 7.6 |
| June | 7.0 | 8.5 | 8.8 | 8.7 | 8.6 |
| July | 7.1 | 8.4 | 8.5 | 8.4 | 8.2 |
| August | 7.4 | 8.0 | 7.6 | 7.1 | 6.5 |
| September | 7.6 | 7.1 | 6.1 | 5.2 | 4.2 |
| October | 7.5 | 6.0 | 4.5 | 3.4 | 2.1 |
| November | 7.2 | 5.0 | 3.2 | 2.0 | 0.9 |
| December | 7.0 | 4.5 | 2.7 | 1.5 | 0.4 |
The values the page shows, to one decimal. They are sunlight above the atmosphere, not on the ground. A Southern Hemisphere latitude mirrors the seasons: −40° in December gives 8.8 and in June 2.7.
Day length, sunrise to sunset (hours) by month and latitude
| Month | 0° | 25°N | 40°N | 50°N | 60°N |
|---|---|---|---|---|---|
| January | 12.0 | 10.6 | 9.5 | 8.3 | 6.3 |
| February | 12.0 | 11.2 | 10.5 | 9.8 | 8.8 |
| March | 12.0 | 11.8 | 11.7 | 11.6 | 11.3 |
| April | 12.0 | 12.6 | 13.1 | 13.5 | 14.2 |
| May | 12.0 | 13.2 | 14.2 | 15.2 | 16.8 |
| June | 12.0 | 13.5 | 14.8 | 16.1 | 18.3 |
| July | 12.0 | 13.4 | 14.5 | 15.7 | 17.6 |
| August | 12.0 | 12.9 | 13.5 | 14.2 | 15.3 |
| September | 12.0 | 12.1 | 12.2 | 12.3 | 12.4 |
| October | 12.0 | 11.4 | 10.9 | 10.4 | 9.6 |
| November | 12.0 | 10.8 | 9.7 | 8.7 | 7.1 |
| December | 12.0 | 10.5 | 9.2 | 7.9 | 5.6 |
Astronomical day length for a point sun, 2 × sunset hour angle ÷ 15° per hour, on the same day per month. Refraction and the width of the sun’s disc make a real day a little longer, and it says nothing about cloud.
How to use this tool
- Type a latitude from −90 to 90, positive for the Northern Hemisphere. The page starts at 40.
- Choose a month. The page starts at June.
- Read the sun-hours and the day length for that month, then the chart and the table of all twelve months at the same latitude.
Frequently asked questions
- Is this the same as peak sun hours?
- No. Peak sun hours describe energy on the ground: a day with 1 kWh/m² is about one peak sun hour, and a Department of Energy slide notes that kWh/m² is sometimes called a sun-hour. This page works above the atmosphere, and clouds, haze and shading cut what reaches a roof. For ground-level figures at a US location, NREL’s PVWatts calculator draws on measured solar resource data for the address you enter.
- Why is the equator about 7 hours all year?
- Day and night at the equator are each about 12 hours in every month, and the noon sun is never more than about 23° from overhead, so the daily total changes little. The page gives 7.6 in March and September and 7.0 in June and December at 0°.
- Why does 60°N get more sun-hours than the equator in June?
- The June day at 60°N is far longer than 12 hours, and the extra hours outweigh the lower sun. The page gives 8.6 at 60°N in June against 7.0 at 0°. In December the same latitude drops to 0.4, because the sun is up for a short time and stays close to the horizon.
- What happens near the poles?
- The formula limits the sunset hour angle in polar night and midnight sun. At 90°N it gives 9.4 hours in June and 0 in December; at 70°N it gives 8.8 in June and 0 in December. Latitude must be from −90 to 90.
- Does it work for the Southern Hemisphere?
- Yes. Enter a negative latitude. At −40° the page gives 8.8 hours in December and 2.7 in June, the mirror of 40°N, because the seasons are reversed.
- How many hours of daylight are there at my latitude?
- The page shows the day length beside the sun-hours: twice the sunset hour angle, at 15° per hour. At 40°N that is 14.8 hours in June and 9.2 in December; at 60°N, 18.3 and 5.6; at the equator 12.0 all year. It is the time the sun is above the horizon, not hours of sunshine.
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