Photo of an orange and purple sky while the sun is setting during early evening hours.

What Are Peak Sun Hours?

Solar energy has gained loads of attention as one of the most sustainable energy sources — after all, sunlight is free and abundant! But what are peak sun hours?

You might wonder about this if you own solar panels or are debating going solar. And if you want to maximize your solar panels’ efficiency and accurately estimate their energy production, understanding this concept is important. 

Here, we’ll explore the fundamentals of peak sun hours:

  • What peak sun hours are 
  • Average daily peak sun hours (with some state examples) 
  • How to calculate peak sun hours 
  • Why peak sun hours matter in the solar energy realm 

We’re giving you the info, but you don’t have to do the math. We’ll do it for you.

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Defining Peak Sun Hours

“Peak sun hours” refers to the amount of sunlight a particular location receives. The standard peak sun hour is 1,000 watts (W) of energy per square meter (roughly 10.5 feet) within one hour. It’s basically a lot of direct, intense sunlight midday in a short amount of time.

Think of strong, direct sunlight to panels as creatine (a pre-workout drink mix) to a workout. Both a peak sun hour and creatine energy powder serve as catalysts for a high energy output, whether via panels or physical exercise!

However, don’t confuse peak sun hours with total daylight hours — they’re not the same. Daylight hours make up the entire time between sunrise and sunset. Peak sun hours  are specifically the period when the sun’s intensity is sufficient for highly effective solar power generation.

[Related: Sun Number: Is Your House Suitable for Solar?]

Factors Influencing Peak Sun Hours

Several factors influence how you calculate sun peak hours.

Solar Angle

As we know, global rotation changes the angle at which sunlight strikes the Earth’s surface throughout the day. That angle also varies based on your geographic location and the time of year. 

Basically, Sunlight is most intense when the sun is directly overhead, which leads to higher energy production during that time!


Not to take us back to high school geography class, but latitude — your distance from the equator — is a key factor in calculating peak hours of sun intensity. 

Why? Locations closer to the equator receive more direct sunlight annually (and are typically much hotter than those farther from it). 

As you move toward higher latitudes, the angle at which sunlight hits the Earth becomes less direct. This reduces the number of peak sun hours.

Time of Year

When are peak sun hours? Well, there are a few things to consider (and another quick geography lesson). 

The tilt of the Earth’s axis causes the sun’s angle to change throughout the year. This leads to seasonal variations, so you should expect variations in peak sun hours by month. 

For example, the sun is highest in the sky during the summer solstice, which causes more intense peak sun hours in certain locations. As for the winter solstice … you get the drift. 

Weather Conditions

Oh, the weather outside is … hopefully sunny!

Cloud cover, atmospheric conditions and even pollution affect the amount of sunlight that reaches the Earth’s surface. As you’d expect, regions that see a high number of overcast days with frequent cloud cover (such as Seattle) have fewer peak sun hours than clear, sunny areas like Houston, Tampa and Norfolk.

Importance of Peak Sun Hours in Solar Energy

So, why are peak sun hours so important when it comes to solar panels?

Accurate Energy Production Estimates

Manufacturers rate solar panels according to their efficiency in converting sunlight into electricity. 

To estimate how much energy your solar panels can produce, you need to consider your location’s peak sun hours based on the factors above. 

Accurate estimates help you make informed decisions about the system and panel size to buy to meet your energy savings standard. 

[Related: How Many Solar Panels Do I Need?]

Sizing Solar Systems

Peak sun hours play a crucial role in determining the appropriately sized solar panel system that will meet your energy needs. When you’re ready to buy, that information is invaluable.

For example, a too-small system likely won’t generate enough power to meet your needs. Meanwhile, an oversized system may generate excess energy that you don’t use.

Note: Backup power solutions are a great investment alongside a quality solar panel system. Although a large system may produce more energy than you need, you can always store that energy in a solar battery. For example, the SunPower® SunVault or Tesla Powerwall lets you use stored energy at night, on cloudy days or during power outages.

[Related: Solar Panel Size Guide]

Project Viability

For both homeowners and businesses considering solar projects, knowing your location’s peak sun hours is vital when assessing your potential return on investment.

Is solar worth it? Will it pay off? 

Use a peak sun hours calculator and see whether solar suits your unique circumstances. 

Note: Don’t worry — you don’t have to figure all this out yourself. Energy consultants will do the math for you!

Optimal Panel Placement

Knowing peak sun hours helps you determine the best placement for your solar panels. Specifically, you’ll know the ideal angle and orientation to maximize energy production. 

When a trusted solar provider installs your panels ideally (and properly), you’ll enhance their efficiency and reduce long-term energy losses. Of course, you’ll save money, too.

[Related: Tips To Save on Energy Costs]

How To Calculate Peak Sun Hours

So, how do you find your peak sun hours? Here’s a fairly simple three-step method to calculate peak sun hours. 

Again, you don’t have to do it yourself — a solar installation company can take care of it!

Step 1: Collect Solar Irradiance Data

Solar irradiance is the amount of solar energy that reaches a specific area over a unit of time. 

You usually measure this data in watts per square meter (W/m²). You can find solar irradiance data from reliable sources like the National Solar Radiation Database. It provides U.S. and international solar radiation data and information about the meteorological year. 

Step 2: Choose a Benchmark

Select a solar irradiance value that represents the minimum sunlight level necessary for efficient energy production. The standard value is 1,000 W/m², which is the amount of optimal solar energy received under clear, direct sunlight.

Step 3: Use a Peak Sun Hours Calculator 

Now, calculate the peak sun hours. Divide the total solar energy received during one day in watt-hours per square meter (Wh/m²) by the benchmark irradiance in W/m².

Yes, that’s a mouthful. Here’s an equation to bookmark:

Peak Sun Hours = Total Solar Energy (Wh/m²) / Benchmark Irradiance (W/m²)

Let’s say you have total solar energy of 8,000 Wh/m² for one day and a benchmark irradiance of 1,000 W/m²:

  • Peak sun hours = 8,000 Wh/m² ÷ 1,000 W/m² 
  • Peak sun hours = 8 hours

In this example, your location sees eight peak hours of sun for that day (imagine the southern West Coast). But remember that the peak sun hours by state vary — the U.S. is large, and some states cross climate regions different from their neighbors. 

The peak sun hours by zip code vary too, so make sure you (or your solar installer) don’t leave out any details when determining your peak hours of sun!

[Check out our Solar Potential Calculator]

Contact Freedom Solar Power To Find Your Peak Sun Hours and Perfect Solar Panels

Knowing your peak sun hours is helpful if you’re debating going solar

For starters, they help you decide whether investing in a system is highly viable (it is). They also help you decide a system size that’s ideal for your home or business. Plus, you can find the best way to place your panels for optimal performance. 

Granted, taking all these factors and calculations and customizing them to your location are … tough. That’s where Freedom Solar comes in.

By harnessing the power of peak sun hours, we can unlock solar’s full potential. When you’re ready to make the jump, contact us! We provide market-leading solar panels to ensure you have only the best equipment. 

Call us at (800) 504-2337 or complete our online inquiry form. One of our expert energy consultants will be in touch! And you can put down the calculator, scratch paper and pencil.

Featured image via Pixabay