Peak sun hours is a standardized measurement used in the solar industry to quantify the amount of usable solar energy a location receives per day. One peak sun hour equals one hour of sunlight at an intensity of 1,000 watts per square meter — the level used to rate solar panel output under Standard Test Conditions.
It's important to note that peak sun hours are not simply the number of hours between sunrise and sunset. While a location might experience 12 hours of daylight, the actual solar intensity varies throughout the day. Morning and evening sun is weaker and angled, producing less energy than midday sun. Peak sun hours compress all of a day's solar energy into equivalent hours of maximum intensity.
In the Northeast United States, most locations receive between 3.5 and 5.0 peak sun hours per day on average, accounting for seasonal variation. Summer months may see 5–6 peak sun hours, while winter days might deliver only 2–3. Annual averages factor in cloudy days and seasonal changes.
Solar installers use peak sun hour data to accurately estimate how much electricity a system will produce. For example, a 7 kW system in an area averaging 4 peak sun hours daily would produce approximately 28 kWh per day, or about 10,200 kWh per year.
Understanding your location's peak sun hours helps set realistic expectations for solar production and ensures your system is properly sized to meet your energy goals. Despite having fewer peak sun hours than the Sun Belt, Northeast states remain excellent candidates for solar thanks to strong incentives and high electricity rates.