You know solar panels need the sun to make electricity. But, if you’re just starting to think about going solar, you might not know that the sun being in different places and at different times of the day and year all makes a difference.
If you’ve never heard of peak sun hours, a measurement that quantifies the strength of sun a specific area receives over time, we’ll help you understand what they are and why they’re a factor in designing any new solar power system.
Peak sun hours measure the intensity of sunlight on an exact area—down to the size of your home’s roof. Knowing your location’s peak sun hours is part of knowing the efficiency and financial benefit of a system before you decide to go solar.
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What is the Definition of Peak Sun Hours?
One peak sun hour is a measure of the time, not necessarily a full hour or consecutive hours, when the sun is giving 1,000 watts of power per square meter—say, onto a solar panel.
There isn’t a peak sun hour of the day to a given region or day of the calendar. Instead, it’s a measure of the intensity of the sun’s rays over time. If a location gets 1,000 watts of sunlight over an hour, that’s a peak sun hour. If that same location gets 500 watts of sunlight over two hours, that’s also a peak sun hour. If a location gets five peak sun hours a day, it means the total power it receives from the sun is equivalent to five hours of sunlight at a power of 1,000 watts.
The amount and intensity of sunlight is also termed “solar insolation” or “solar radiation.” In the US, average peak sun hours range from 3.5 a day in western Washington and Oregon up to 6 a day in Las Vegas, southern inland California, and western Arizona. Most of the continental US gets 4.2-5.5 peak sun hours a day.
Peak sun hours are not the same as total daylight hours, or all the time from sunrise to sunset. The most intense sunlight (when most of the peak sun hours are generated is typically midday into the early afternoon, when the sun’s rays hit the Earth’s surface at the most direct angle. This is good for solar power generation. It would be bad if you were stranded in Death Valley.
In scientific terms:
1 peak sun hour = 1000 W/m² (or 1 kW/m²) of sunlight over an hour.
In other words, if your location receives 6 kWh/m² of solar radiation in a day, and it could, for example, be 6 kWh/m² in a span from 8:30 a.m. to 6:30 p.m., then you get 6 peak sun hours.
What Should I Understand About the Peak Sun Hours?
Knowing the peak sun hours for your region can help you determine the ideal size of the solar panel system for your roof. It can also help you understand how solar will be a worthy investment. Equally, if you plan to benefit from net metering, you need to figure out your area's peak sun hours to know if you can generate excess electricity.
To help you decipher what peak sunlight hours mean to solar installation, think of them as those weather insights you rely on to choose and plan your next trip. Peak sun hours help you recognize when your solar panels will be more productive so you can better plan for your long-term energy needs.
For example, if you know when your solar panel system will be most effective, you can calculate when and how you need to use energy in the home. This especially comes in handy regarding the extra energy you might be storing from those peak sun hours.
What Are Peak Sun Hours by State?
Each state in the USA has a unique number of average peak sun hours due to the variation in the different climate zones.
Often, the number of peak sunlight hours increases the closer you are to the equator and generally during the summer months. The table below shows the peak sun hours by state across the country.
| State | Peak Sun Hours | State | Peak Sun Hours | State | Peak Sun Hours |
|---|---|---|---|---|---|
| Alabama | 3.5-4 | Louisiana | 4-4.5 | Ohio | 2.5-3.5 |
| Alaska | 2-3 | Maine | 3-3.5 | Oklahoma | 4.5-5.5 |
| Arizona | 7-8 | Maryland | 3-4 | Oregon | 3-5 |
| Arkansas | 3.5-4 | Massachusetts | 2.5-3.5 | Pennsylvania | 2.5-3.5 |
| California | 5-7.5 | Michigan | 2.5-3.5 | Rhode Island | 3-4 |
| Colorado | 5-6.5 | Minnesota | 3.5-4.5 | South Carolina | 4-4.5 |
| Connecticut | 2.5-3.5 | Mississippi | 4-4.5 | South Dakota | 4.5-5 |
| Delaware | 3-3.5 | Missouri | 4-4.5 | Tennessee | 3.5-4.5 |
| Florida | 3.5-4.5 | Montana | 4-5 | Texas | 4.5-6 |
| Georgia | 4-4.5 | Nebraska | 4.5-5 | Utah | 6-7 |
| Hawaii | 5.5-6.5 | Nevada | 6-7.5 | Vermont | 3-3.5 |
| Idaho | 4-4.5 | New Hampshire | 3-3.5 | Virginia | 3.5-4 |
| Illinois | 3-4 | New Jersey | 3.5-4 | Washington | 2.5-5 |
| Indiana | 2.5-4 | New Mexico | 6-7 | West Virginia | 2.5-3.5 |
| Iowa | 3.5-4.5 | New York | 3-3.5 | Wisconsin | 3-4 |
| Kansas | 4-5.5 | North Carolina | 4-4.5 | Wyoming | 5.5-6 |
| Kentucky | 3-4 | North Dakota | 4-4.5 |
You can view this data on the detailed irradiance maps for the United States created by the National Renewable Energy Laboratory.
Solar companies use this factual information about the average daily peak sun hours your area gets, such as an insolation map, to help you make better decisions about the right solar panel system for your home in terms of the energy you need.
Why Do Peak Sun Hours Vary By Location?
Peak sun hours vary by latitude and seasonality. Very generally speaking, the closer to the equator (in the US that means south) the more peak sun hours your area will get. The sun hits the Earth at a more direct angle for longer periods of time the closer you get to the equator.
Then solar radiation changes by season. The average peak sun hour number falls to 25-50% below the yearly average in winter, and is 25-50% above the average in summer.
Within the US, take Las Vegas where the average peak sun hours is 6.41 hours a day. The yearly range is 5.84-7.13 hours. In Cleveland, the average for a year is 3.94 hours and the range is 2.69-4.79 hours.
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How Will Peak Sun Hours Impact My Solar Panels?
Knowing your region's average peak sun hours can be a useful gauge of your home’s solar potential. Using the example below, let's see how you can use peak sun hours to calculate how much electricity you need your solar panel system to create:
- Peak sun hours = 7
- Your home used 25,000 kWh of electricity last year
- 25,000 kWh / 365 days = 68.49 kWh per day
- 68.49 kWh per day / 7 peak sun hours per day = 9.78 kWh
- You should install a 10kW solar PV system
Your solar panels need the direct sunlight of peak sun hours to generate the maximum electricity possible for your home. However, you don’t need to move to a state with the highest number of peak sun hours to enjoy the perks of solar power. It just means that a home in Massachusetts that uses 25,000 kWh a year will need more solar panels in their rooftop array to generate that much electricity than a home in Arizona with the same amount of annual usage.
Other factors besides average daily peak sun hours impact your solar panel system energy production capacity, including:
- Home consumption: Home energy consumption remains the biggest factor in determining the size of a solar panel system. Even if you live in an area with an abundance of peak sun hours, you still need the right amount of solar panels to generate the necessary power for your home.
- Solar panel efficiency: This is the ability of a solar panel system to convert the absorbed sunlight into electricity. The average solar panel is roughly between 15% and 20% efficient, with high-quality solar panels in some cases exceeding 22% efficiency. The age of your solar panels and the type of material used to capture solar energy will determine the efficiency of your panels.
- Storage capacity: To meet your energy usage needs, you can add battery storage to your solar panel system so you can prepare for times when your panels don’t generate enough electricity to meet your needs.
- Future growth: You may decide to install more panels on your roof than you currently need if you anticipate your energy needs will increase in the future.
If you talk to the solar experts at Palmetto, you can be sure all details will be considered when we design a solar power system for your home. Our team of solar specialists will answer your questions and help you make the right solar choices for your needs.
How Much Sunlight Do My Solar Panels Need?
The short answer is “As much as they can get.” Solar panels are designed to generate electricity from sunlight. Even on a cloudy day, they will still generate some electricity.
But why then do you need to remember that peak sun hours vary if a solar panel system can still create power with any amount of sunlight? Because it’s important that your solar panels reach their maximum effectiveness when they are most productive.
Thus, peak sun hours help you calculate the size of the solar power system that’s ideal for your home.
Ways To Take Advantage of Peak Sun Hours in Your Home
Now that you know what peak sunlight hours are and why they should matter to you, let's learn how to get the most out of them, especially when the sun is strongest.
- Store more electricity. Your solar panels will reach their maximum effectiveness when the sun's intensity is highest. They will likely produce excess electricity at this time. Installing a solar battery system can ensure you can use all the energy you generated.
- Leverage net metering. If your solar panels are creating more electricity than you’re using, you can benefit from net metering. All of that extra energy will get sent to the electricity grid, and the credits you earn can be used to offset your utility bills. To learn more, check out our Guide to Net Metering for Home Solar.
- Reduce your appliance usage during peak hours. To maximize the electricity generated during the peak sun hours for storage or net metering, you should look for opportunities to use less energy during peak hours and shift that usage to other parts of the day.
Key Takeaways
Knowing the peak sun hours for your area helps you design a solar panel system that will generate the electricity you need. You can also use that information to develop a system that will yield extra electricity for storage, future growth, and net metering.
Talk to Palmetto today or get your free solar savings estimate to learn more about how your home can best utilize peak sun hours. Our experts can assist with your solar panel decisions by taking into account different factors, including your preferences and budget, to ensure you install the right solar panel system for your needs. We'll do everything we can to make sure you take advantage of peak sun hours with a top-of-the-line solar power system.
Peak Sun Hours FAQs
Which places in the US have the most peak sun hours?
The desert southwest—Arizona, New Mexico, and parts of Nevada, California, Texas, Utah, and Colorado—gets the most peak sun hours.
Which places in the US have the least peak sun hours?
Alaska, where some parts of the state for some months of the year get no peak sun hours, gets the least peak sun hours. In the lower 48, coastal Washington and Oregon, New England, and Michigan, Pennsylvania, West Virginia, Ohio, and Indiana, get the lowest averages of peak sun hours.
Do solar panels work on cloudy or rainy days? What if I live in a cloudy area?
It’s a common misconception solar panels won’t work in cloudy, rainy, or snowy areas. In reality, solar panels can still capture and generate power from indirect light. During the initial survey and design process, we’ll examine your overall electricity usage relative to your potential solar energy production and structure your array to optimize savings. Geography and weather are key factors in this process. In some cases, we may recommend integrating battery storage with your solar energy system to make your energy more dependable.
Are peak sun hours important if I’m going solar?
Yes. Knowing your region’s peak sun hours is an important factor in making your new system efficient and the right financial decision.
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Cory O'BrienSenior Director - Growth MarketingCory brings over 8 years of solar expertise to Palmetto, and enjoys sharing that knowledge with others looking to improve their carbon footprint. A dog lover residing in Asheville, NC with his wife, Cory graduated from UCSB. If you run into him, ask him about the company he founded to rate and review beer!
