Peak Sun Hours & Solar Energy

Peak sun hours are a key factor to consider when you have a solar energy system. The amount of sunlight your solar panels receive directly affects their efficiency. Peak sun hours refer to the time during the day when sunlight is at its most intense, and this varies depending on where you live.

To get the most out of your solar system, it's important to understand the peak sun hours in your area. This will help you determine the best size and setup for your system. The more peak sun hours you get, the more solar energy your system can generate and use, making it easier to meet your energy needs.

Peak Sunlight Hours: An Easy Definition

A peak sun hour or peak sunlight hour isn't about the total number of sunlight hours a location gets. It's a way to measure how much sunlight falls on a given area, known as solar irradiance or solar insolation.

A peak sun hour happens when the sun’s intensity averages 1,000 watts of photovoltaic power per square meter. This usually occurs during the middle of the day when solar panels receive the most direct sunlight.

For example, Illinois averages 3 – 4 peak sun hours per day. During this time, your solar panels will get close to 1,000 watts of solar energy per square meter. In comparison, Texas averages 4.5 – 6 peak sun hours per day, meaning a solar system in Austin could generate more energy than the same system in Chicago.

Why Peak Sun Hours Are Important for Solar Energy

Knowing the peak sun hours in your area is important for understanding how much energy your solar panels can generate. The more peak sun hours you get, the better the potential return on investment for your solar system.

But it's not just about the sun—several other factors can affect your solar investment, including:

• Government incentives such as the federal solar tax credit: These incentives can lower the upfront cost of your solar system, potentially speeding up your payback period. It's a good idea to consult a tax professional to see if you qualify for these benefits.

• Rebates from a utility company: Many utility companies offer rebates or incentives for solar homeowners, such as equipment rebates or special rate plans for those who produce clean energy. Understanding the offers available from your local utility company can add more savings to your solar investment.

• Utility company net metering policies: Some utilities compensate customers for the energy they send back to the grid. In some cases, they may pay the full retail value for the excess electricity your system produces, which can further offset your energy costs.

In locations with fewer sunny days, generous incentives can still make solar panels worth it. Illinois, for example, has a low sun number. However, the state government’s aggressive push for renewable energy can make solar panels a solid proposition for ratepayers.

Regions With the Most Peak Sun Hours

If you're in the southwestern United States, including states like Arizona, California, Nevada, New Mexico, and parts of Texas, you're in a region that gets some of the highest peak sunlight hours. These areas benefit from strong sun intensity and great weather conditions, making them perfect for solar energy production. The combination of high solar insolation and mostly clear skies helps your solar system perform at its best.

Regions With the Fewest Peak Sunlight Hours

If you live in the Pacific Northwest, parts of the Midwest, or the Northeast, you’re likely to experience fewer peak sun hours. States like Washington, Oregon, Alaska, Maine, New Hampshire, and parts of the Great Lakes region tend to have less direct sunlight due to their higher latitudes, frequent cloud cover, and varying weather patterns. As a result, your solar panels may not receive as much sunlight as systems in sunnier areas.

How to Calculate Peak Sun Hours

Peak sunlight 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.
  

Peak Sunlight Hours by Location

You might be wondering how many peak sun hours you get at home. The number of peak sun hours can vary a lot depending on where you live, as it's influenced by factors like 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

Several factors can impact how many peak sunlight hours you receive at home, including latitude and weather conditions. If you look at a map of peak sun hours in the U.S., you’ll see that areas in the Southwest typically have the highest peak sun hours. The desert regions benefit from clearer skies compared to places like Florida, which, while farther south, often experiences cloudier conditions.

Peak sun hours also vary by season. During the summer months, when the sun stays up longer, you’ll get more peak sun hours. In contrast, the shorter days of winter provide fewer. For example, in Austin, Texas, you can expect an average of 2.73 peak sun hours in December, but this increases to 6.77 peak sun hours in July.

Here’s a sample of peak sun hours in different locations across the country from the National Renewable Energy Laboratory (NREL).

At What Times Does a Location Experience Peak Sun Hours?

You’ll typically receive the most solar energy when the skies are clear, and the sun is high in the sky, usually around midday. This is when the sun’s intensity is at its peak, providing the most direct and intense sunlight. During this time, solar irradiance and energy production are maximized, which is ideal for your solar panels.

Locations closer to the equator tend to get more consistent and intense sunlight year-round compared to areas farther away. However, factors like cloud cover and atmospheric pollution can also affect the amount of solar energy you get at any given time, impacting peak sunlight hours.

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

Solar installation companies should factor in peak sun hours when estimating solar system output. Many companies use solar software or resource data incorporating peak sun hours and geographic information to make accurate production estimates. For instance, the  PVWatts calculator utilizes average solar radiation data specific to the location to predict solar energy production.

Do Peak Sun Hours Vary by Season?

Peak sunlight hours can vary by season due to changes in the sun's angle and the length of daylight. For instance, summer months typically offer more peak sun hours as the sun is higher in the sky and days are longer, while winter months provide fewer peak sun hours due to lower sun angles and shorter days.

Other Factors That Affect Peak Sunlight Hours

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.
  

What is Solar Radiation in Relation to Peak Sunlight Hours?

Solar radiation is the energy the sun emits through electromagnetic waves, including ultraviolet (UV), visible light, and infrared (IR) radiation. This energy is the main driver behind Earth’s climate, influencing weather patterns, photosynthesis, and the water cycle.

Solar radiation is closely linked to peak sunlight hours, which is the time of day when the sun’s energy, or solar irradiance, is at its peak. These hours usually occur when the sun is at its highest point in the sky and when there are minimal obstructions like clouds. Understanding peak sun hours is crucial for getting the most out of your solar energy system, ensuring it captures the highest possible amount of solar radiation.

How Many Solar Hours Per Day Do Solar Panels Need?

Your solar panels generate electricity whenever sunlight is available, but the amount of power they produce depends on how intense that sunlight is. "Full sun" or "peak sun" conditions occur when sunlight provides about 1,000 watts per square meter. While solar panels can still generate power during lower light conditions, the output will be lower.

To assess how well your solar panels are performing, peak sun hours and peak sunlight hours are used to measure the number of hours each day when sunlight intensity is equal to or greater than 1,000 watts per square meter. These hours can vary based on location, weather, and the time of year.

On average, your solar panel system might produce significant power during 4 to 6 peak sun hours per day, though this can differ depending on where you live and the specific conditions of your home. Even on cloudy days, your solar panels will still generate electricity, but the output won’t be as high as it is during peak sunlight hours.

Peak Sun Hours Help Determine The Number Of Solar Panels

Solar power systems can work effectively nearly anywhere in the United States, even in areas with fewer peak sun hours. However, in these areas, you might need more solar panels to meet your power needs.

While having fewer peak sun hours can lengthen the payback period of your solar system, you’ll still benefit from reduced carbon emissions, lower electricity bills, and potentially higher home value.

Is your solar system in need of maintenance or repairs? GreenLancer can help troubleshoot and address any issues, ensuring your system continues to run smoothly. Whether you need diagnostics, repairs, or regular maintenance, we're here to support you and keep your solar system performing at its best.