Solar insolation measures the total solar energy received on a surface over a specific time period, typically expressed in kilowatt hours per square meter per day (kWh/m²/day). Unlike irradiance, which measures instantaneous power, insolation represents cumulative energy delivery. It is the primary metric for predicting solar system annual energy production.
Technical Details
Insolation values are location-specific and vary seasonally. The continental United States averages 4-6 peak sun hours daily, translating to 4-6 kWh/m²/day insolation. Southern states like Arizona and Florida receive 5-6 kWh/m²/day annually, while northern states receive 3-4.5 kWh/m²/day. Solar resource maps, such as NREL’s PVWatts tool, provide precise insolation data by geographic location. Seasonal variation affects winter production—December insolation values can be 50% lower than June values in northern climates.
Practical Significance
Insolation data enables accurate energy production calculations for solar system design. A 10kW system in a 5 kWh/m²/day location produces approximately 50kWh daily or 18,250 kWh annually. Understanding local insolation helps homeowners evaluate system economics and establishes realistic performance expectations.