Sunshine
How much sunlight reaches the ground — or your panel — where you live? Solar irradiance week by week, month by month or year by year, from satellite data of 2005–2020: direct sunlight and diffuse sky light, the best and worst periods, and what it means in peak sun hours.
Direct Sunlight and Sky Light
Above the atmosphere the sun delivers about 1361 W/m². On a clear day at noon roughly 1000 W/m² reaches the ground: that is “one sun”. Part comes straight from the sun’s disc (direct), part is scattered by air and clouds and comes from the whole sky (diffuse). On an overcast day nearly all of it is diffuse, and much less.
Add the irradiance up over time and you get irradiation in kWh/m². A day with 3 kWh/m² is as much light as 3 hours of full sun: 3 peak sun hours. North-west Europe gets about 1000–1150 kWh/m² a year on flat ground, Madrid about 1750, the deserts of Arizona and Egypt more than 2100.
Sunshine Through the Year, Step by Step
kWh/m²Assumptions of This Model
| Assumption | In reality… |
|---|---|
| Month and year: the measured monthly sunshine and diffuse share of every year 2005–2020 (PVGIS, from satellite images) | checked: for Amsterdam 1079 kWh/m² a year against 1073 measured by KNMI at Schiphol (2005–2020), with the same dullest (2012) and sunniest (2018) year; for 24 of the 26 built-in places within 5% of the Global Solar Atlas. Outside satellite coverage PVGIS uses the ERA5 weather model, which is less accurate under tropical clouds: for Singapore it gives 13% more than the Global Solar Atlas. The years after 2020 are not included |
| Week and the average days: the typical year (PVGIS TMY), built from the most typical month of each calendar month in 2005–2020 | a real week can be much sunnier or darker than the typical one; use month or year to see the spread between years |
| A tilted panel: direct light by the angle to the sun, sky light with the Perez model, ground reflection 20%; for other years the typical year’s gains of direct and sky light are applied to that year’s own sunshine | checked against PVGIS: the same year-to-year pattern within about 1%; shade from buildings and trees is not included |
| The place is a 0.1° cell (about 10 km), including the shading of the terrain horizon | valleys, coasts and cities can differ within that distance |
Key Relations
The direct beam Gb,n falls at the sun’s zenith angle θz; the diffuse light Gd comes from the whole sky.
Irradiance (W/m²) added up over the hours gives the energy per square metre (kWh/m²).
The day’s sunlight as hours of full sun. A panel of 1 kWp makes about PSH × performance ratio kWh a day (see Solar panels).
Sources & Verification
- PVGIS 5.2, European Commission Joint Research Centre — monthly irradiation and diffuse share per year 2005–2020 (MRcalc), hourly typical meteorological year. PVGIS © European Union, 2001–2026.
- KNMI, daily station data Schiphol (240) and De Bilt (260), global radiation 2005–2020 — ground measurements used as a check (Schiphol 1073 kWh/m² a year on average).
- Global Solar Atlas 2 (World Bank / ESMAP, Solargis) — long-term GHI used as a second check for all 26 built-in places.
- G. Kopp & J. L. Lean, “A new, lower value of total solar irradiance”, Geophysical Research Letters 38, L01706 (2011) — 1360.8 W/m² above the atmosphere.
- R. Perez et al., Solar Energy 44(5), 271–289 (1990) — sky light on a tilted panel.
Frequently Asked Questions
How much sunlight does my location get?
On flat ground about 1080 kWh/m² a year in Amsterdam (KNMI measured 1073 at Schiphol over the same years), 1790 in Madrid and 1830 in Singapore (PVGIS, average of 2005–2020; for Singapore the satellite-based Global Solar Atlas gives about 1610, as the weather model PVGIS uses there overestimates tropical sunshine). Pick your place or enter its coordinates to see it per week, month or year.
What are peak sun hours?
The day's sunlight expressed as hours of full sun (1000 W/m²): a day with 3 kWh/m² has 3 peak sun hours. Amsterdam averages about 2.95 a day over the year, from about 5.6 on an average June day to 0.5 in December.
How much less sun is there in winter?
It depends strongly on the latitude. In Amsterdam June brings about 10 times as much sunlight per day as December; in Madrid about 3.8 times; in Singapore, near the equator, the sunniest month has only about 1.3 times the darkest.
What is diffuse sunlight?
Light scattered by the air and clouds, coming from the whole sky instead of straight from the sun. In cloudy climates it is about half of all sunlight: 52% in Amsterdam, against 31% in sunny Madrid. Solar panels use it too, which is why they still produce under clouds, only much less.
How much does the sunshine vary from year to year?
In Amsterdam the sunniest year of 2005–2020 (2018, 1174 kWh/m²) had about 14% of the average more than the dullest (2012, 1021 kWh/m²). Choose year by year to see every year for your place.