Peak Sun Hours Calculator (by address, city, or zip code)

peak sun hours calculator

There is no doubt that solar power is powerful enough for any home, but before you install solar panels, you need to consider the weather you live in. In other words, is it sunny for most of the year? Do you deal with a lot of rain or clouds where you live?

These are all important questions to answer because solar panels need sufficient sunlight to work efficiently for you.

To answer all of these questions, all you need is to know how many peak sun hours you you typically get in your location.

To assess how many peak sunlight hours your location gets use our peak sun hours calculator :

Average Sunlight Hours Rank
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What Are Peak Sun Hours?

what are peak sun hours

The number of peak sun hours per day is not the same as daylight hours!.

In fact, peak sun hour describes an hour of exposure to direct sunlight with an intensity reaches an average of 1000 watts per square meter (1000 W/m²).

This intensity of 1000 W/m² is established as a standard to represent solar radiation received by the Earth's surface under ideal conditions, such as clear skies at noon.

More importantly, is that these value are used as a global standard for comparing the performance of solar panels from different companies and manufacturers. When measuring the efficiency of a solar cell or panel, it is done under assumed conditions, including sunlight intensity of 1000 W/m².

In other words, when you buy a 100-watt solar panel, it will produce 100 watt-hours (0.1 kWh) of electricity in one hour of exposure to sunlight with an intensity averages of 1000 W/m² (and under the standard temperature conditions).

Practical Application of Peak Sun Hours

To illustrate what peak sun hours are used for, let's assume you are considering installing a solar power system to offset your monthly electricity consumption estimated at 800 kWh, and you want to estimate the size of the solar power system.

  • Your monthly estimated electricity consumption is 800 kWh.
  • You want to estimate the size of the solar power system that can provide this amount of electricity.
  • first you need to know the number of peak sunlight hours at your location.
  • To estimate the system size, we can use the following equation:
System Size = Monthly Electricity Consumption / Monthly Peak Sunlight Hours

Let's assume you live in Austin, Texas, US.

    In Austin you can expect to receive about 4.9 peak sun hours per day on average.Once you calculate the system size, you can determine the number of solar panels or installed capacity needed to meet the energy requirements.

System Size = 800 / (4.9 * 30) = 5.44 kW

    So in an idealized scenario, you would need a 5.44 kW solar array to offset 27 kWh per day (800kWh/30day).

    This calculation assumes that the solar power system have an efficiency of 100% In reality, losses due to factors like shading, temperature, inverter efficiency must be taken into account when sizing the solar array.

    However, you will most likely install your solar array at an angle tilted from the horizontal, and this will allow the solar panels to capture more sunlight and generate more energy compared to installing them flat without tilt. This increase in power output can help offset a significant portion of system losses.

    Therefore, although the solar panels will not be installed horizontally, it is common to rely on the number of peak sun hours (horizontal irradiance) for a quick estimate of the potential solar energy generation in the area.

    By using the same method you can calculate, how many solar panels are needed for:
    Or you can do a reverse calculation to calculate how much energy can the solar panel generate in your area.

    How peak sun hour is Measured

    Peak Sun Hours Calculator

In reality, sunlight intensity varies greatly depending on weather conditions, geography, and time. In many areas, actual solar irradiance values (sunlight intensity) throughout the day may range between 200 and 800 W/m² during typical days. These values reflect the average intensity over the course of the day or under moderate weather conditions.

However, these numbers can vary significantly based on location, seasons, and individual weather conditions. Factors such as clouds, pollution, fog, distance from the equator, and time of day can all influence sunlight intensity, sometimes reducing it to levels below 200  W/m².

Despite the fact that in most regions sunlight intensity doesn't reach 1000 W/m² even for just one hour, you may wonder how some of these areas achieve 4-5 peak sun hours per day.

Peak Sun Hours Calculator

Firstly, it's important to note that a peak sun hour is a measure of energy quantity, wish is equivalent to:

1 peak sun hour = 1 hour of sunlight which the averages intensity is 1,000 W/m² = 1,000 Wh/m² = 1 kWh/m²

Thus, it represents the solar irradiance available over a specific period of time:

1 Peak sun hour = 1,000 Wh/m² = Intensity of sunlight (W/m²) x Duration 

So even in areas where sunlight intensity doesn't reach 1000 W/m², you can calculate the average peak sun hours during the day by summing the actual solar irradiance values for each hour of daylight.

How to Calculate Peak Sun Hours

When sizing a solar power system, peak sun hours value are relied upon to make estimates.

Many people find it difficult to determine the number of peak sun hours for their location when using solar calculators - such as PVWatts, Global Solar Atlas or PVGIS. These online tools provide several values, including Direct Normal Irradiance (DNI), Global Horizontal Irradiance (GHI), Global Diffuse Irradiance (GDI), and Global Tilted Irradiance (GTI). They may mistakenly calculate peak sun hours using the highest value provided, which is usually DNI.

It is important to know that DNI measures the the total amount of solar radiation absorbed on a surface perpendicular to the sun throughout the day, meaning it should only be relied upon when you want to install a solar tracks system.

Peak sun hours should be calculated using GHI that measures the total amount of solar irradiance received on a horizontal surface in a specific time.

Peak Sun Hours Calculator

GHI does not take into account the tilt angle of the solar panels from the horizontal. but in cases where the tilt angle of the solar panels is unknown or you want to make a simplified estimation of the suitable size of the solar power system. This value serves as a general estimate that you can rely on as a starting point for sizing your system.

It's important to note that one solar peak hour is equivalent to 1 kWh/m² of horizontal irradiation that the site gets. Therefore, while these tools may not explicitly mention "peak sun hours," they are actually represented by the average global horizontal irradiation. 

How can I calculate the peak sun hours for my roof?

When tilting your solar panels at the optimal tilt angle, they can absorber an additional 400 to 1000 Wh/m² of solar irradiation per day, which is equivalent to about a quarter to a full hour of peak sun hour.

So. If you know what angle your solar panels will be tilted at. For example, if you’re putting them on your roof and you know your roof pitch, you can use our solar irradiance calculator to calculate the peak sun hours for your roof?

This calculator allows you to enter the tilt angle or the roof pitch to determine the tilted irradiation at that angle in your location.

If you're just trying to figure out the size of your solar power system or your monthly solar arrays generation — after all, that's what peak sun hours are used for.


knowing how many peak sun hours on average your location receives is useful because it lets you easily estimate how many solar panels or installed capacity needed to fulfill your energy need. Or you can do a reverse calculation to estimate how much energy can the solar power system generate in your location.

One (1) kW of the solar power system can generate an average of 5 kWh per day in the areas with 5-6 peak sun hours per day. 

While in locations that gets an average of 3.5-4 peak sun hours per day. One (1) kW solar power system can generate an average of 3 kWh per day

From the above conclusion, it is clear that if you live in areas with fewer daily peak sun hours, solar panels receive less solar energy, so to generate one (1) kWh you will need an additional number of panels compared to someone who lives in location with peak sun hours.

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