Peak Sun Hours Calculator

Select your city — find your peak sun hours and calculate how much solar your system will produce.

Your location

Select your city?

Selected location: 4.5 peak sun hours/day — Good solar resource (near US average)

Your system

System size?

System efficiency?

Production for a 8 kW system at 4.5 peak sun hours

11,300 kWh per year

Daily production31.0 kWh

Monthly production942 kWh

Peak sun hours4.5 hrs/day

Solar resourceGood sun

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How to Use This Calculator

Select your city

Choose your nearest city from the dropdown to automatically set your peak sun hours (PSH). The calculator includes 45+ US cities with annual average PSH values from NREL's solar resource database. If your city isn't listed, select "Enter manually" and type your PSH value — you can find this from NREL's PVWatts tool or your solar installer's proposal.

Enter your system size

Enter your solar system size in kilowatts (kW). This is the sum of all your panel wattages divided by 1,000. A 25-panel system with 400W panels = 10 kW. If you don't know your system size yet, use our Solar System Size Calculator first.

Review system efficiency

The default 86% efficiency accounts for all real-world losses. Adjust this if you know your specific system efficiency from a monitoring platform or installer report.

Interpret the solar resource rating

The calculator rates your location's solar resource: Excellent (6.0+ PSH) covers Arizona, Nevada, and New Mexico. Very good (5.0–6.0 PSH) covers California, Florida, and Texas. Good (4.0–5.0 PSH) covers most of the contiguous US. Fair (3.0–4.0 PSH) covers the Pacific Northwest and Great Lakes region.

Peak Sun Hours by US City

Annual daily average peak sun hours for major US cities. Source: NREL National Solar Radiation Database.

City	State	PSH (hrs/day)	Rating
Phoenix	AZ	6.5	Excellent
Tucson	AZ	6.4	Excellent
Las Vegas	NV	6.3	Excellent
Albuquerque	NM	6.2	Excellent
Honolulu	HI	6	Excellent
El Paso	TX	6.1	Excellent
San Diego	CA	5.8	Very good
Los Angeles	CA	5.6	Very good
Miami	FL	5.5	Very good
Dallas	TX	5.1	Very good
Orlando	FL	5.3	Very good
Denver	CO	5	Very good
San Francisco	CA	5	Very good
Houston	TX	5	Very good
Atlanta	GA	4.8	Good
Washington DC	DC	4.4	Good
Minneapolis	MN	4.5	Good
New York City	NY	4.1	Good
Boston	MA	4.2	Good
Chicago	IL	4.1	Good
Detroit	MI	4	Good
Cleveland	OH	3.9	Fair
Pittsburgh	PA	3.8	Fair
Portland	OR	3.7	Fair
Seattle	WA	3.5	Fair
Anchorage	AK	2.8	Low

What Are Peak Sun Hours?

Peak sun hours (PSH) is one of the most misunderstood concepts in solar — and also one of the most important. Here's what it actually means:

Peak sun hours = Total daily solar irradiance (kWh/m²/day) at standard intensity Standard intensity = 1,000 W/m² (Standard Test Conditions) Example: A day with 5 PSH delivers the same energy as 5 hours at full 1,000 W/m² intensity, even if the sun is out for 12 hours. Production = System kW × PSH × System efficiency

A cloudy 12-hour day might only deliver 1.5 PSH. A clear summer day with intense sun might deliver 8.0 PSH. The annual daily average shown in this calculator smooths all of this out — hot Arizona summers, mild winters, seasonal variation, and typical cloud cover — into one representative number.

This is why PSH is the standard metric used by solar installers, NREL, and the National Renewable Energy Laboratory for system sizing. It's the most practical single number to represent your location's solar energy potential.

FAQ

What's the difference between peak sun hours and daylight hours? ▼

Daylight hours is simply the time between sunrise and sunset. Peak sun hours (PSH) is the equivalent number of hours of full-intensity sunlight (1,000 W/m²) that delivers the same total energy as your actual daily solar irradiance. A partly cloudy day with 14 hours of daylight might deliver only 3 PSH of actual solar energy — less than a clear day with 10 hours of daylight that delivers 7 PSH. Always use PSH for solar calculations, never daylight hours.

How do I find peak sun hours for my exact location? ▼

The most accurate method is NREL's PVWatts Calculator (pvwatts.nrel.gov) — enter your exact address and it returns location-specific irradiance data. The city values in our dropdown come from NREL's National Solar Radiation Database (NSRDB). For most residential solar calculations, using your nearest city's PSH value introduces less than 5% error — within the margin of other estimation uncertainties.

Do peak sun hours change by season? ▼

Yes — significantly. A location with 4.5 PSH annual average might get 6.5 PSH in June and only 2.5 PSH in December. For system sizing purposes, annual average PSH is the standard — it tells you total annual production, which is what determines your net metering offset and payback period. If you need to know winter production specifically (for off-grid sizing), use the December PSH value, which is roughly 40–60% of the summer value depending on latitude.

Why is Colorado's PSH higher than Florida's? ▼

Denver (5.0 PSH) outperforms Jacksonville, FL (5.0 PSH) for the same reason ski resorts are sunny: high altitude means less atmosphere to filter the sun, and Colorado's front range has very low humidity and many clear days. Florida has more total daylight hours in summer and is warmer, but the Gulf Coast humidity and afternoon thunderstorms reduce actual solar irradiance. Solar energy is about intensity, not just sun presence.

Is solar worth it in Seattle with only 3.5 peak sun hours? ▼

Yes — and Seattle homeowners often get excellent payback despite low sun. Why? Seattle's electricity rates are low (~$0.10/kWh) BUT neighboring Portland and California have high rates, and PSE (Seattle's utility) has net metering. More importantly, low sun means you need a bigger system, but the installation cost per watt is the same. The payback period in Seattle is longer (12–15 years vs. 7–9 in Phoenix), but the system still produces returns for 25+ years. The economics work — it's just not as slam-dunk as Arizona.