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Peak Sun Hours & Solar Energy


peak sun hours

Peak sun hours are an important factor for homeowners who want to install solar panels. Therefore, solar installers need to consider the peak sun hours available in a given area when determining the size and location of a solar installation.


Let’s take a look at what you need to know about peak sun hours so you can explain the concept and its importance to prospective clients.


Peak Sunlight Hours: An Easy Definition


A peak sun hour isn’t a measure of time or how many hours of sunlight a location receives. It’s a measurement of the amount of sunlight that falls on a given area – a concept also known as solar irradiance or solar insolation.


A peak sun hour is when the sun’s intensity is an average of 1,000 watts of photovoltaic power per square meter. Typically, the intensity of sunlight is greatest in the middle of the day. That’s also when solar panels receive the most direct sunlight.


Illinois, for example, averages 3 – 4 peak sun hours per day. During those hours, solar panels will receive close to 1,000 watts of solar energy per square meter. Texas averages 4.5 – 6 peak sun hours per day, so a solar array in Austin could produce more energy than the same-sized system in Chicago.


Why Peak Sun Hours Are Important for Solar Energy


Knowing the peak sun hours of your service area can help you determine whether solar panels will offer a good return on investment for a client. That’s just one piece of the puzzle, though. A few other factors you’ll want to discuss with clients include:


  • Government incentives such as the federal solar tax credit: Incentives can reduce the cost of a solar panel system, potentially shortening the payback period. We suggest installers advise clients to consult a tax professional to see if they qualify for certain incentives.

  • Rebates from a utility company: Utility companies may have incentives for solar homeowners, and these incentives can range from rebates on equipment to special rate plans for homeowners who produce clean energy. Installers should have a good understanding of offers available from utility companies in their area.

  • Utility company net metering policies: Some utility companies have policies that compensate customers for the energy they generate. In some cases, electricity providers may pay the full retail value for electricity that homeowners add to the grid.


In locations that don’t have as many sunny days as Arizona, generous incentives can make solar panels still worth it. Illinois, for example, has a low sun number. But the state government’s aggressive push for renewable energy can make solar panels a solid proposition for ratepayers.


What Regions of the U.S. Have the Most Peak Sun Hours?


The southwestern United States, including Arizona, California, Nevada, New Mexico, and parts of Texas, experiences some of the highest peak sun hours. These regions benefit from abundant sunlight and favorable weather conditions, making them ideal for solar energy production. The combination of high solar insolation and clear skies contributes to the optimal performance of solar installations in these areas.


What Regions of the U.S. Have the Fewest Peak Sun Hours?


Regions with the fewest peak sun hours in the United States are typically found in the Pacific Northwest and parts of the Midwest and Northeast. States like Washington, Oregon, Alaska, Maine, New Hampshire, and parts of the Great Lakes region may experience fewer hours of direct sunlight due to higher latitudes, more frequent cloud cover, and varying weather patterns.


How to Calculate Peak Sun Hours


Peak sun hours are not simply the number of daylight hours. They are the equivalent number of hours when the sun is shining at its maximum intensity. The formula for calculating peak sun hours is:


Peak Sun Hours = Total Daily Solar Insolation/Solar Noon Duration


  • Find the average daily solar insolation (sunlight intensity) for your location. This information is often available from solar resource maps or databases.

  • Solar noon is the time when the sun is at its highest point in the sky.

What Are The Peak Sun Hours In Different States?


Some clients may ask you how many peak sun hours they get. Peak sun hours vary widely by location due to latitude and climate.

STATE

AVERAGE PEAK SUN HOURS

Arizona

7-8

California

5-7.5

Colorado

5-6.5

Florida

3.5-4.5

Georgia

4-4.5

Illinois

3-4

Maryland

3-4

Massachusetts

2.5-3.5

Michigan

2.5-3.5

Missouri

4-4.5

Nevada

6-7.5

New Jersey

3.5-4

North Carolina

4-4.5

Ohio

2.5-3.5

Pennsylvania

2.5-3.5

Rhode Island

3-4

South Carolina

4-4.5

Texas

4.5-6

Utah

6-7

Virginia

3.5-4



A few factors, including latitude and weather conditions, can impact how many peak sun-hours an area receives. If you look at a map of peak sun hours in the U.S., you’ll notice that the areas with the highest peak sun hours are in the Southwest. The desert areas have clearer skies than areas like Florida, that are further south, but they often have cloudier conditions.


Peak sun hours will also vary by season. In the summer months, when the sun stays up longer, there will be more peak sun hours than the shorter periods of daylight in the winter months. For example, Austin, Texas, ranges from an average of 2.73 peak sun hours in December to 6.77 peak sun hours in July.


Here’s a sample of peak sun hours at locations throughout the country from solar company Palmetto:

peak sun hours map


Do Solar System Production Estimates Take Peak Sun Hours Into Account?


Yes, solar installation companies should use peak sun hour data when estimating solar system output. Many solar companies use solar software or solar resource data when estimating solar production and output, which both factor in peak sun hours.


Other Factors That Affect Average Daily Peak Sun Time


A solar panel system should operate at its peak output rating in lab conditions. In real-world conditions, the system will have some output loss caused by high temperatures, among other factors. Other factors that impact how efficient and productive a solar system can be include:

  • Roof orientation: South-facing roofs typically have the most optimum angle for sunlight.

  • Shading: Properties with large trees or buildings obstructing the roof can block some sunlight from reaching a photovoltaic system.

  • Time of day: When the sun is low in the sky, sunlight has to filter through more of the atmosphere. This reduces the intensity of solar radiation.

How Many Solar Panels A Home Needs


The average household used just over 29 kilowatt-hours (kWh) of electricity each day, or about 10,791 kWh per year in 2022, according to the U.S. Energy Information Administration. On average, a solar-powered home needs about 20 to 25 solar panels to meet the energy needs of a typical home.


A good approach is to review client utility bills before sizing a solar system. It may be helpful to review client utility bills together, explaining the different parts of the electricity bill to your clients. And with this information, installers should be able to design a system that meets or exceeds client energy needs. It’s also a good idea to discuss any potential changes to energy usage the client anticipates in the future, such as adding an electric vehicle (EV) to the household.


How many Hours of Sunlight Do Solar Panels Need?


Solar panels can generate electricity whenever there is sunlight, but the solar output depends on the intensity of sunlight. "Full sun" or "peak sun" conditions are considered to be around 1,000 watts of sunlight per square meter. However, solar panels can still generate power under lower light conditions.


In terms of hours, solar panels are often rated based on "peak sun hours," which represent the number of hours during a day when sunlight intensity is equivalent to or greater than 1,000 watts per square meter. The actual number of peak sun hours can vary based on geographic location, weather patterns, and other factors.


As a rough estimate, a typical solar panel system might generate significant power during 4 to 6 peak sun hours per day on average. This can vary depending on the region and specific site conditions. Keep in mind that solar panels can still produce some electricity during cloudy or overcast days, but the output will be lower compared to bright, sunny days.



Peak Sun Hours Help Determine The Number Of Solar Panels


Solar power systems are viable nearly anywhere in the United States, even in areas with fewer peak sun hours. These areas may need more solar panels to meet a homeowner’s power needs, though.


While a lower number of peak sun hours may increase the payback period of a PV array, homeowners will still reduce their carbon footprint, lower their electric bill, and raise the value of their homes.




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