Even though solar panels produce electricity during all hours of the day, they work best when the sun’s rays shine directly on them.

But exactly how many hours a day does that happen? And how is the amount of direct sunlight affected by location and time of year?

This is where the concept of peak sun hours comes in to play.

What are ‘peak sun hours’?

A peak sun hour doesn’t include just any hour when the sun is out in the sky. Instead, it refers to an hour in which your solar panels produce a certain amount of energy.

Each peak sun hour is defined as one hour when the intensity of sunlight (solar irradiance) reaches an average of 1,000 watts of energy per square meter (roughly 10.5 feet). 

Summer months and locations farther south will generally see more peak sun hours than wintry times and areas farther north. That’s because regions closer to the equator are also closer to the sun.

On the other hand, in latitudes farther north, when the sun is closer to the horizon, the sunlight is filtered through more layers of the atmosphere. In those places, the sunlight isn’t as strong by the time it reaches your solar panels, which results in lower peak sun hours. 

Peak sun hours also vary depending on where your solar panels are placed. In other words, the peak sun hours’ value for one part of the house might be different than its value for another part of the house. These factors can affect the number of peak sun hours:

  • Direction: The direction your solar panels are facing affects the intensity of the sunlight, as well as the total amount of sunlight received.
     
  • Shading: Even if all the solar panels face the same direction, they might experience sun hours at different times based on when a tree (or other obstruction) casts shade on them. 

How do we calculate total peak sun hours?

One peak sun hour = 1000 W/m2 of sunlight. However, when calculating the total amount of peak sun hours received at any location, you don’t just consider hours with 1000 W/m2 of solar radiation. Instead, you need to add the total amount of solar irradiance received by the location. You then express that in terms of the equivalent number of hours with 1000 W/m2.

It may sound complicated, but the concept is actually relatively simple to apply. For example, if a given location receives a total of 4,500 Wh/m2 of solar radiation over the course of a day, then that location gets 4.5 peak sun hours.

This table below from Solar Energy International illustrates this concept: 

The average solar irradiance depicted in the form of a 1000 Wh/m2 cup filled to different quantities throughout the day. The Peak Sun Hours value calculated by adding the solar irradiance for the day.

Solar irradiance throughout the entire day adds up and gives us the daily Peak Sun Hours value. Image source: Solar Energy International; for more in-depth information, check out their professional solar training courses.

As the image shows, adding up the total solar irradiance for a given location gives you the total peak sun hours value.  

You can calculate the irradiance for your location during different times of the year here: pveducation.org.

You can also check the average solar radiation for your location on this NREL page

How are peak sun hours different from regular sunlight hours?

Regular sunlight hours refer to any time the sun is shining during the day – the hours between sunrise and sunset. However, it doesn’t tell us anything about the strength/intensity of the sun’s radiation during those hours, and thus, is unhelpful when it comes to designing a solar panel system. 

That is why the concept of ‘peak sun hours’ has been developed. It precisely measures the amount of irradiance that will hit the solar panels, thereby allowing us to calculate the expected electricity generation. 

How many peak sun hours does a solar panel ideally need?

The more peak sun hours a solar panel gets, the more electricity it produces. In an ideal scenario for solar, panels would receive direct sunlight 24 hours a day, every day. Unfortunately, the sun does not stay at one spot in the sky, clouds do show up every now and then, and then there is the whole sunrise and sunset thing we can’t avoid.

Luke Skywalker gazes out towards a two-sun sunset

So let’s rephrase the question: How many peak sun hours do we then need to make solar power a viable option?

To tackle this question, let’s break down some numbers. In 2017, the average electricity consumption of a house in the US was 867kWh per month, which is about 28kWh per day.

We know that during peak sun hours, a solar panel should theoretically produce 1,000 W /m2. But, solar panels do not work at 100% efficiency. All solar panels these days come with a Standard Test Conditions (STC) rating, which is the amount of energy those panels can actually produce during peak sun hours.

A specifications sheet for an LG solar panel. The sheet shows a 300 watt Standard Test Conditions rating for the panel.

With this standard detailed specifications sheet, you also get its STC rating. This is a sample specifications sheet for an LG solar panel. Image source: solar-estimate.org

Assuming the panel above works at full STC efficiency, it can produce 300 watts in one hour. You would need a bit more than 3 such panels to produce 1 kWh, meaning 84 of these panels are needed to produce 28kW of energy during one peak sun hour. You can use this data and the number of sun hours your town/city gets to calculate how many solar panels you will need.

Before you start calculating, though, here is the catch: many other factors impact solar energy production. Some of them include the angle of your roof, real-world efficiency of the panels, and the trees/buildings around the house that block the sun rays.

In the United States, any location that gets around 4 peak sun hours is considered a good location to produce useful amounts of solar energy. Of course, if you get fewer peak sun hours, you can still supplement your utility power with solar, but it may not be quite as cost-effective.

Other important factors to consider are the electricity rates and net metering laws in your area. Residents in locations with low peak sun hours but with high electricity rates and net metering can save more money than residents with higher levels of peak sun hours but cheap electricity and no net metering.

Calculate how much you can save by going solar

What are the average peak sun hours for my state?

From the Pacific coast to the Atlantic, from cold northern states to the steamy south, the United States is filled with diverse climate conditions and varying peak sun hours. This list details the average peak sun hours for one city in each of the 50 states – the figures were obtained from solar irradiation maps provided by the National Renewable Energy Laboratory.

Peak sun hours by state
Location
Peak Sun Hours (PSH)
Alabama (Birmingham) 4.5 – 4.7 PSH
Alaska (Anchorage) 2.4 – 2.9 PSH
Arizona (Tucson) 7.5 – 7.9 PSH
Arkansas (Fort Smith) 4.9 – 5.0 PSH
California (San Diego) 5.8 – 6.7 PSH
Colorado (Grand Junction) 6.0 – 6.6 PSH
Connecticut (Hartford) 4.0 – 4.3 PSH
Florida (Tampa) 5.5 – 5.7 PSH
Georgia (Macon) 4.7 – 5.0 PSH
Idaho (Boise) 5.1 – 5.7 PSH
Illinois (Peoria) 4.3 – 4.4 PSH
Indiana (Indianapolis) 4.1 – 4.3 PSH
Iowa (Des Moines) 4.2 – 4.4 PSH
Kansas (Wichita) 5.2 – 5.8 PSH
Kentucky (Louisville) 41. – 4.4 PSH
Louisiana (New Orleans) 4.9 – 5.1 PSH
Maine (Portland) 4.0 – 4.3 PSH
Maryland (Baltimore) 4.2 – 4.5 PSH
Massachusetts (Boston) 4.3 – 4.5 PSH
Michigan (Lansing)  3.8 – 4.0 PSH
Minnesota (Minneapolis) 4.3 – 4.5 PSH
Mississippi (Jackson) 4.9 – 5.1 PSH
Missouri (Springfield) 4.9 – 5.0 PSH
Montana (Helena) 4.5 – 5.0 PSH
Nebraska (Lincoln) 4.9 – 5.2 PSH
Nevada (Reno) 6.4 – 7.1 PSH
New Hampshire (Concord) 4.0 – 4.3 PSH
New Jersey (Atlantic City) 4.0 – 4.3 PSH
New Mexico (Albuquerque) 7.0 – 7.5 PSH
New York (Syracuse) 3.6 – 3.9 PSH
North Carolina (Greensboro) 4.6 – 4.8 PSH
North Dakota (Bismarck) 4.5 – 4.7 PSH
Ohio (Columbus) 3.9 – 4.1 PSH
Oklahoma (Oklahoma City) 5.5 – 6.0 PSH
Oregon (Portland) 3.7 – 4.5 PSH
Pennsylvania (Harrisburg) 4.0 – 4.2 PSH
Rhode Island (Providence) 4.3 – 4.5 PSH
South Carolina (Columbia) 4.4 – 4.6 PSH
South Dakota (Huron) 5.0 – 5.3 PSH
Tennessee (Nashville) 4.2 – 4.4 PSH
Texas (Dallas) 5.2 – 5.9 PSH
Utah (Salt Lake City) 5.7 – 6.6 PSH
Vermont (Burlington) 3.8 – 4.0 PSH
Virginia (Richmond) 4.6 – 4.8 PSH
Washington (Seattle) 3.3 – 3.9 PSH
Wisconsin (Madison) 4.3 – 4.4 PSH
Wyoming (Lander)  5.2 – 5.7 PSH

As you can see, there are states with impressive peak sun numbers and those with scant peak sun hours. 

However, it is important to note that even though a state like New York gets less than the ideal 4 peak sun hours per day, it still is one of the most popular locations for installing solar panels in America. High electricity costs and terrific state solar incentives make solar energy a profitable proposition in New York and many other states with low peak sun hours.

4 simple steps to make the most of solar energy

While the peak sun hours for your location are not in your control, these simple steps will ensure that you get the most out of solar energy.

1. Do your research on different solar panel brands

With hundreds of companies out there selling solar panels, the first important question to consider is, “Which solar panels should you choose?”

Wouldn’t it be so easy if there was a brand of solar panel that was perfect for all situations? Unfortunately, that is simply not the case. The answer to the question, “What is the best solar panel?” will vary depending on what’s most important to you as a homeowner: expert assessment, popularity, efficiency, value for money, or some other factor.

Luckily, we have a blog that provides a comprehensive breakdown of the best solar panels based on various criteria.

2. Get multiple quotes and let the competition do the rest

Get multiple quotes from different installers and then choose the one that’s best for you.

This is the easiest way to ensure that you get the best deal on the market. Also, when installers know that you are shopping around, they are more likely to offer you their lowest prices.

Our solar calculator makes this process extremely easy. Enter some basic details to get a no-obligation quote from as many installers as you want.

Get live quotes from the best installers in your area

3. Use a qualified solar installer

A good solar installer could be the difference between solar panels that work at optimum levels and panels that don’t. A badly installed solar system will never reach peak efficiency, hence hampering your return on investment.

Again, it is best to get quotes from the best local installers and then select the one that is experienced, with the necessary licenses.

4. Don’t forget the tax rebate

The massive federal tax rebate on solar panels is set to expire in 2022. Currently at 26% in 2020, it goes down to 22% in 2021 reducing to 0% for residential installations in in 2022.

There will never be a better time to invest in solar panels than now. These rebates make it possible to recover the cost of the panels within a few years, saving you some serious cash for years to come.

Conclusion

In most parts of the US, there are enough peak sun hours to make getting solar panels a worthwhile investment. However, it’s best to do your research and make sure solar panels are the right decision for your home.

This NREL solar resource page provides an insolation map for the entire country. By calculating the average daily solar insolation, the map provides the solar production capacity of different locations in America (i.e. the peak sun hours).

The easiest way to ensure that you get the most out of your solar panels — do your research, get no-obligation quotes, and then choose the best deal.

Enter some basic details to get accurate and obligation-free solar quotes for your area!