Your Easy Guide To Peak Sun Hours

Peak sun hours are an important factor for homeowners who want to go solar. Solar installers will need to consider the peak sun hours available in a given area when determining the size and location of clients’ solar installations.

Let’s take a look at what you need to know about peak sun hours so you can explain the concept and it’s 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

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 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 Are The Peak Sun Hours In Different States?

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

Source: https://www.nrel.gov/gis/assets/images/solar-annual-ghi-2018-usa-scale-01.jpg

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:

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 Clients Need

The average household used just over 29 kilowatt-hours (kWh) of electricity each day, or about 10,632 kWh per year in 2021, according to the U.S. Energy Information Administration.

A good approach is to review client utility bills. 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.

The Bottom Line: Peak Sun Hours Help Determine The Number Of Solar Panels Clients Need

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 home.