The concept of Peak Sun Hours plays an essential role in determining the maximum amount of energy that can be produced by a solar energy system. With the growing adoption of solar in households, understanding peak sun hours can equip installers and homeowners to derive not just the right placement but also the optimal number of solar panels for maximum energy production.
What are peak sun hours and why do they matter?
Solar panels turn sunlight into electricity, and the amount of sunlight that reaches your roof impacts the amount of electricity your panels generate. Peak sun hours are essentially a measure of the amount of sunlight received by a location. We receive 1000W/m² on a clear day at noon, which is the standard testing conditions (STC) used for PV sizing. The concept of peak sun hours was developed to accurately measure the amount of solar irradiance hitting the Earth’s surface or a solar panel placed at that given location.
Scientifically, we can say that if an area receives sunlight with the intensity of 1000 watts per square meter or 1kW/m2 in one hour, it is equal to 1 peak sun hour.
1 Peak Sun hour = 1000 Watts/m2 over an hour or
1 Peak Sun hour = 1 kWh/m2
So, if the same area receives 500 watts of sunlight over a course of two hours, then that is also 1 peak sun hour. In essence, if a location receives 4 peak sun hours, that means the total sunlight received in that area could be 1000 watts per square meter for 4 hours or could also be 500 watts per square meter for 8 hours.
Identifying your location’s peak sun hours allows you to calculate the right system size for you or also detect if your panels are generating optimum energy for your location.
Peak sun hour vs sunlight hours – what’s the difference?
Peak sun hours are different from sunlight hours, which are also known as total daylight hours. Total daylight hours are the time measured from sunrise to sunset in hours per day, which varies based on your location.
How to find the average peak sun hours per day in your area
The amount of Peak sun hours in your area is impacted by several natural factors like time of day, weather, seasonality, cloud cover, and latitude, as well as man-made factors like pollution. As peak sun hours are essentially the intensity of sun or solar irradiance, your distance from the equator also plays a crucial part, as the sun hits the earth at a more direct angle, projecting sunlight at a higher intensity for a longer period of time.
To know the peak sun hours of your location, you can refer to standardized tables and charts published by reputable organizations like, the NREL shows the peak sun hours by state across the country, averaged over the year.
Each state in the US has a unique number of peak sun hours due to varying climate conditions. Like, despite being further south, Florida experiences lower peak sun hours due to natural variables like cloud cover, while the Southwest states experience the highest peak sun hours due to clearer skies in the deserts. The sunnier days you have, the higher your peak sun hours.
The average peak sun hours in a year in Las Vegas, Nevada, is 6.41, while in Cleveland, Ohio is 3.94. However, this does not mean that you have to move states if you live in Cleveland and want to get solar panels installed; it just means you will require a greater number of panels to generate the same amount of electricity as a house located in Las Vegas.
How to calculate solar system size using peak sun hours
You can calculate your solar energy system size using the peak sun hours of your region as follows:
Step 1: Identify your region’s peak sun hours through the map or table
For example, you live in Texas, and your peak sun hours are 5
Step 2: Determine the average electricity usage of your house from your electricity bills.
Let’s say it is around 30000kWh for the last year.
Which is 30000kWh / 365 days = 82.19kWh per day
Step 3: To determine your PV system size, you can simply divide your average electricity usage per day by your region’s peak sun hours.
82.19kWh / 5PSH = 16.43kW=
So, you should probably get a 16.5kW system for your house.
How to combine peak sun hours and shading for accurate system design
While PSH is great for rough estimation and calculation of your system size, it does not account for something crucial – shading. In a realistic scenario, to estimate your system size accurately, precise site assessments or satellite-based data capture obstructions surrounding your house that cause shading on your roof.
Shaded areas are not ideal for placing your panels, as they inhibit maximum energy production by blocking sunlight. To accurately calculate the right area for panel placement, the real available sunlight needs to be determined through calculating the Solar Access Value or SAV.
To be even more precise, the Total Solar Resource Fraction or TSRF value is calculated, which accounts for both shading as well as tilt and orientation of the panels to determine actual solar capture value and accurately evaluate energy production.
How can installers do more?
Using advanced software like Solargraf, installers can model 3D solar layouts, detecting obstructions like trees and other houses. The tool also utilizes solar irradiance metrics like SAV, TOF, and TSRF to determine the optimal panel placement for maximum energy capture. Features like the System Visualiser calculate energy output for every hour for each panel across all seasons, making it easy to get a realistic production estimates for better system optimization.
Conclusion
The concept of Peak Sun Hours is a great way to roughly estimate your PV energy production and a standardized metric to determine solar irradiance at any location on the Earth in an ideal case. However, in real PV sizing estimations, metrics like SAV, TOF, and TSRF are used to more accurately measure the solar capture while accounting for shading, tilt, and orientation.
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