Solar irradiance converter
Convert between W/m² and kWh/m² per day, the two numbers every solar calculation needs, and see what a panel would make.
That's about the same as full midday sun. A two-square-meter panel at 20% would make about 400 W.
What it means
How much sun is that?
Panels are rated at 1,000 W/m², called one sun. kWh/m² per day here is averaged over 24 hours, not over daylight only.
Every unit
Your irradiance in every unit
Learn
Three things worth knowing
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One sun is 1,000 W/m²
Every panel’s wattage is measured at exactly that. A 400 W panel makes 400 W in full sun and proportionally less in cloud.
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The langley
Named after astronomer Samuel Langley, it measures a calorie per square centimeter. Older climate records are full of langleys per day.
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Peak sun hours are not daylight hours
A place with 12 hours of daylight may only get 4 peak sun hours. The measure already accounts for angle, haze and cloud.
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Popular irradiance conversions
Background
About irradiance units
Irradiance is power per area: W/m². Full midday sun at the surface is about 1,000 W/m², and above the atmosphere it is 1,361, the solar constant.
Solar planners prefer kWh/m² per day, also called peak sun hours, because it folds a whole day of weather into one number.