Peak Sun Hours by Location: The Complete 2026 Guide

Peak sun hours represent the equivalent number of hours per day when solar irradiance averages 1,000 watts per square meter. They vary by location based on latitude, climate, and weather patterns, directly affecting how much electricity your solar panels will produce annually. (Related: Federal Home Energy Tax Credits: A Guide to Claiming Expiring Solar Installation Incentives Before the Deadline) (Related: Solar Savings Calculator: Estimate Your Payback Period) (Related: Complete Guide to Solar Property Tax Exemptions by State 2026) (Related: How Permitting Costs Impact Solar ROI Calculations and What Automation Could Mean for Your Savings) (Related: Grid Tie vs Off Grid Solar: Which System Saves More?) (Related: Solar Loan Interest Rates 2026: The Complete Comparison Guide)

What Are Peak Sun Hours and Why They Matter

Peak sun hours are one of the most misunderstood concepts in residential solar planning — and one of the most important. Many homeowners assume “peak sun hours” simply means total daylight hours. It doesn’t. A cloudy 10-hour day in Seattle delivers far fewer peak sun hours than a clear 8-hour day in Phoenix.

The standard measurement threshold of 1,000 watts per square meter (W/m²) comes from solar irradiance testing standards used across the industry. This baseline is the same condition under which solar panel manufacturers rate their panels’ wattage output. So when a panel is rated at 400 watts, that rating assumes exactly 1,000 W/m² of irradiance hitting the surface.

When actual irradiance is lower — say, 500 W/m² on an overcast afternoon �� that same 400-watt panel produces roughly 200 watts. Peak sun hours essentially “compress” your day’s total solar energy into equivalent full-power hours, giving you an apples-to-apples number you can use in production calculations.

How Do Peak Sun Hours Affect Solar Panel Output?

The math is straightforward once you understand the concept. If your location receives an average of 5 peak sun hours per day, a 400-watt panel will theoretically generate 2,000 watt-hours (2 kWh) per day under ideal conditions. Scale that to a 10-panel, 4,000-watt system and you’re looking at approximately 20 kWh per day before accounting for system losses.

System losses — including inverter efficiency, wiring resistance, shading, soiling, and temperature effects — typically reduce real-world output by 15% to 25%. According to the U.S. Department of Energy’s Solar Energy Technologies Office, these de-rating factors must be incorporated into any accurate production estimate.

Peak Sun Hours by Geographic Location

Solar irradiance by location varies dramatically across the United States and globally. Here’s a practical regional breakdown based on long-term averages:

How Many Peak Sun Hours Does My Location Get?

Southwest U.S. (Arizona, Nevada, Southern California, New Mexico): 6.0 – 7.5 peak sun hours per day. This is the highest-performing region in the country. Phoenix, AZ consistently averages 6.5+ peak sun hours annually, making it one of the best locations for solar ROI.

Southeast U.S. (Florida, Georgia, Texas, Louisiana): 4.5 – 6.0 peak sun hours per day. Florida averages around 5.5 hours, while inland Texas cities like Dallas average closer to 5.2. Humidity and afternoon cloud cover reduce peak performance.

Mountain West (Colorado, Utah, Wyoming): 5.5 – 6.5 peak sun hours per day. Denver’s high altitude and over 300 sunny days per year push averages well above national norms despite cold winters.

Midwest (Illinois, Ohio, Missouri, Kansas): 4.0 – 5.0 peak sun hours per day. Chicago averages around 4.2 hours, while Kansas and Missouri cities can reach 4.8 to 5.0 due to fewer overcast days.

Northeast U.S. (New York, Massachusetts, Pennsylvania): 3.5 – 4.5 peak sun hours per day. New York City averages 4.1 hours. Despite lower solar irradiance by location, high electricity rates in this region still support strong financial returns.

Pacific Northwest (Oregon, Washington): 3.0 – 4.2 peak sun hours per day. Seattle averages around 3.5 hours. Seasonal variation is extreme — summer months can hit 6+ hours while winter dips below 2.

Alaska and Hawaii: These represent opposite extremes. Honolulu, HI averages 5.7 peak sun hours, while Anchorage, AK averages just 2.8 annually due to extreme seasonal daylight shifts.

How to Estimate Your Solar Panel Production

Knowing your regional peak sun hours gives you the foundation for accurate solar production estimates. Here’s the core formula used by solar engineers:

Daily kWh Production = System Size (kW) × Peak Sun Hours × System Efficiency Factor

The system efficiency factor accounts for real-world losses. A conservative figure of 0.80 (representing 20% total system losses) is widely used in residential calculations.

Example calculation for Denver, CO:

• System size: 8 kW
• Peak sun hours: 5.8 per day
• Efficiency factor: 0.80
• Daily production: 8 × 5.8 × 0.80 = 37.1 kWh/day
• Annual production: 37.1 × 365 = 13,542 kWh/year

Example calculation for Seattle, WA:

• System size: 8 kW
• Peak sun hours: 3.5 per day
• Efficiency factor: 0.80
• Daily production: 8 × 3.5 × 0.80 = 22.4 kWh/day
• Annual production: 22.4 × 365 = 8,176 kWh/year

That’s a difference of over 5,300 kWh per year from the same system — which translates directly into payback period and long-term ROI. At $0.13/kWh, Denver’s extra production is worth roughly $689 more annually.

Keep in mind that roof tilt, azimuth (compass orientation), and local shading from trees or structures will further adjust these estimates. South-facing roofs at a tilt angle matching your latitude typically capture the most annual irradiance.

Tools and Resources for Calculating Peak Sun Hours

Several reliable tools are available to look up solar irradiance data for your specific address. The most accurate publicly available resource is NASA’s POWER database, which provides decades of historical solar radiation data by GPS coordinates. The National Renewable Energy Laboratory (NREL) also publishes the PVWatts Calculator, a free tool that uses TMY (Typical Meteorological Year) data to model solar production estimates by address.

As noted by Energy.gov’s Solar Energy Technologies Office, using location-specific irradiance data rather than regional averages significantly improves the accuracy of payback and ROI projections — particularly in microclimates affected by coastal fog, mountain elevation, or urban heat islands.

When evaluating quotes from solar installers, always ask which irradiance dataset they used. TMY3 or NSRDB (National Solar Radiation Database) data is the current industry standard for residential proposals.

How to Use the Solar Production Calculator

Once you have your peak sun hours figure, plugging it into a solar production calculator gives you a complete picture — including estimated

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