Explainer
Peak sun hours explained
The number that turns panel watts into daily watt-hours.
Published
- One peak sun hour equals 1,000 W/m² of sunlight for one hour.
- Much of the U.S. sees roughly 3–6 peak sun hours a day, varying by season.
- Winter values can be far lower than the annual average.
What it means
Panels are rated under standard test conditions of 1,000 watts per square meter. Peak sun hours compress a day of changing sunlight into equivalent hours at that intensity.
Finding your number
NREL's free PVWatts calculator and solar resource maps give estimates for your location, tilt and orientation. Use the worst month you need to cover, not just the annual average, for off-grid designs.
Shade and orientation
Even partial shade on part of a panel can cut output sharply. In the northern hemisphere, south-facing panels at a tilt near your latitude are a common starting point.
FAQ
Where do I go next?
Try the power planner to put numbers to your own situation, or see the product picks on the deals page.
Terms used here
- Watt (W)
- Rate of power use or production.
- Watt-hour (Wh)
- Energy: one watt for one hour.
- Peak sun hours
- Hours of equivalent 1,000 W/m² sunlight per day.
This guide is informational and based on published specifications and general references, not hands-on testing. Check the manufacturer's current specs before you buy.