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What Are PSH and PSP? How to Accurately Calculate Real Sun Hours for Your Area
If you have been wondering why your solar system produces less energy than expected, or how to calculate the right number of solar panels to cover your consumption, the answer lies in a term called PSH. Many technicians confuse daylight hours with effective sun hours, and that mistake leads to a weak system that fails to charge batteries in winter. Today, we will break down in simple engineering terms what PSH and PSP mean, and how to calculate them accurately for your area.
Peak Sun Hours (PSH) is the number of hours during which solar irradiance reaches 1000 W/m². It is not the same as daylight hours! Relying on the correct PSH (typically between 3 to 6 hours depending on the region and season) ensures you design a system that meets your needs and charges batteries even on the least sunny days.
The Theory: The Difference Between Irradiance and Energy (PSP vs PSH)
Let us distinguish between two fundamental terms based on international standards (IEC 61724 for system performance monitoring):
- Peak Solar Power (PSP): This is the instantaneous solar power reaching the Earth, measured in
W/m²(watts per square meter). During a clear summer noon, this number reaches 1000 W/m², which is exactly the value used in Standard Test Conditions (STC) to evaluate panels perIEC 60904-3. - Peak Sun Hours (PSH): This is the total solar energy accumulated throughout the entire day. Simply put, it is as if you add up all the energy that came down during the day and divide it by 1000 W. The result is a number of hours.
In other words, if you have a day that yields 5000 Wh/m² as total accumulated energy, that day provides 5 Peak Sun Hours (PSH = 5).
The Practice: How to Calculate PSH for Your Area
1. The Daylight Hours Mistake
Some people say: "The sun is up for 10 hours a day in our country, so we have 10 PSH." That is completely wrong! In the morning, the sun is weak (200 W/m²), at noon it is strong (1000 W/m²), and then it weakens again. When you do the math, the average peak comes out to only about 4 to 5 hours.
The biggest disaster happens when an engineer designs the system based on summer PSH (5.5 hours). In winter, PSH drops to 3 hours or less. The system will fail to run your loads and the batteries will get damaged. The golden rule: always design based on the lowest PSH of the year (the worst month).
2. How to Use PSH in System Calculations
Let us assume you need 15 kilowatt-hours (kWh) per day to power your home, and your area gets 4 PSH at worst (winter). To find the required panel capacity, we use this formula:
Panel Capacity (kW) = Daily Consumption (kWh) ÷ [PSH × System Efficiency]
The system efficiency (Performance Ratio - PR) is typically around 0.70 to 0.85 depending on the region and climate. In hot regions (the Gulf, North Africa in summer), efficiency drops to 0.70 due to high temperatures, while in temperate regions (the Levant, Europe) it can reach 0.80-0.85. For more technical details, check out the solar cable sizing guide, which explains how wiring losses affect overall efficiency.
Here is the calculation (using 0.75 efficiency for a hot region):
15 ÷ (4 × 0.75) = 15 ÷ 3.0 = 5.0 kW (meaning you need about 5 kW of panels)To avoid these mistakes, and because every area has different numbers, we always recommend using the comprehensive solar system calculation guide or relying on the engineering calculator to avoid complex manual calculations. You can also verify solar irradiance data for your area through PVGIS - European Commission (a globally trusted source).
| Season / Region | Daylight Hours (approx.) | Actual PSH (average) | System Efficiency (PR) |
|---|---|---|---|
| Summer (clear inland region) | 13 hours | 6.5 - 7 hours | 0.75 - 0.80 |
| Winter (clear inland region) | 10 hours | 3.5 - 4 hours | 0.80 - 0.85 |
| Winter (cloudy coastal region) | 10 hours | 2 - 2.5 hours | 0.70 - 0.75 |
| Summer (extremely hot region - Gulf) | 13 hours | 6 - 6.5 hours | 0.70 - 0.75 |
* Numbers are approximate and depend on exact geographic location and local weather conditions. Data sourced from PVGIS and NREL databases.
3. The Effect of Tilt Angle on PSH
PSH changes depending on the panel tilt angle. If the panel is flat, it loses a lot of morning and evening irradiance because it does not face the sun perpendicularly. To ensure you harvest the maximum possible PSH, you need to set the right angle. You can learn this topic in detail by reading the solar panel orientation and tilt angle guide.
💡 Calculate Your Area's PSH Automatically!
No need to struggle with tables and maps. Our calculator provides accurate solar irradiance (PSH) data for your city and designs your system with reliability.
Open Calculator ⚡Conclusion
Understanding PSH (Peak Sun Hours) is what separates an engineer from a technician. Relying on regular daylight hours or designing a system based on summer energy will ruin your investment. Always design based on the worst month of the year (lowest PSH), use an appropriate tilt angle to maximize irradiance, and you will guarantee a solar system that runs efficiently 365 days a year.
Frequently Asked Questions (FAQ)
What is the difference between daylight hours and Peak Sun Hours (PSH)?
Daylight hours are the number of hours from sunrise to sunset, while Peak Sun Hours (PSH) are the number of hours during which solar irradiance reaches 1000 W/m². PSH is always less than actual daylight hours.
Why is calculating PSH important in solar system design?
Calculating PSH accurately determines how much energy your solar panels will produce each day. Relying on regular daylight hours leads to an undersized system that fails to charge batteries during winter.
How do Peak Sun Hours (PSH) change across seasons?
PSH changes drastically between summer and winter. In summer, PSH reaches its peak (up to 6-7 hours), while in winter it drops significantly (down to 2-3 hours) due to shorter days and a lower sun angle.