Peak Sun Hours by City
Find average peak sun hours for 60+ major US cities and use them in solar calculations.
| City | State | Peak Sun Hours / Day | Rating |
|---|
What Are Peak Sun Hours?
Definition
A peak sun hour is one hour during which the sun's intensity averages 1,000 watts per square meter (1 kW/m²). A location with 5 peak sun hours per day receives the equivalent of 5 full hours of direct noontime sun, even if the actual daylight is 10+ hours.
How It Affects System Sizing
Peak sun hours directly determine how much energy your solar system will produce. A 8 kW system in Phoenix (6.5 hrs) produces about 70% more annual energy than the same system in Seattle (3.8 hrs). This is why the same system size costs the same everywhere but delivers very different value depending on location.
The Formula
Daily production (kWh) = System size (kW) × Peak sun hours × System efficiency (typically 80%). Multiply by 365 for annual production.
Factors That Affect Local PSH
Peak sun hours vary by latitude, altitude, seasonal cloud cover, humidity, and local air quality. Desert Southwest cities consistently lead the US, while the Pacific Northwest and Alaska have the fewest. Data shown represents annual daily averages — summer values are significantly higher, winter values lower.
Source Note
Values are based on NREL (National Renewable Energy Laboratory) long-term solar resource data and are representative annual daily averages for each metro area.