Solar Irradiance to kWh Calculator

Turn a site's solar resource (peak sun hours) into the daily and yearly energy a PV array will produce, either from the array size in kWp or from the panel area and efficiency.

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How to use this calculator

Enter Values

Array size (kWp) — or use panel area + efficiency below

Panel area (m², if array size not known)

Panel efficiency (%, with panel area)

Peak sun hours PSH (h/day = daily irradiance in kWh/m²/day)

Performance ratio PR (0–1, default 0.75)

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter the array size in kilowatts-peak (kWp), or leave it blank and enter the panel area (m²) plus panel efficiency (%) to derive it.
Enter the peak sun hours (PSH) for your location — the same number as the daily solar irradiation in kWh/m²/day.
Set the performance ratio (default 0.75) for real-world losses; read the daily and annual energy.

How it works

Daily energy (kWh/day) = array size (kWp) × peak sun hours × performance ratio. Annual energy = daily × 365. If you supply panel area and efficiency instead of kWp, the array size is found from the Standard Test Conditions reference of 1 kW/m²: kWp = area × 1 kW/m² × efficiency.

Worked example

Worked example. A 6.6 kWp array at a site with 4.5 peak sun hours and a 0.75 performance ratio makes 6.6 × 4.5 × 0.75 = 22.275 kWh/day, or about 8,130 kWh per year.

Common mistakes

Using a performance ratio of 1 — that ignores inverter, temperature, soiling and shading losses; 0.75–0.8 is typical for a well-installed system.
Confusing peak sun hours with daylight hours — PSH is the equivalent hours of full 1 kW/m² sun, usually far fewer than the hours of daylight.
Mixing up kW and kWh — kWp is the array's power rating; kWh is the energy it produces over time.

Frequently asked questions

What are peak sun hours?

Peak sun hours (PSH) is the number of hours per day that, at full 1 kW/m² sunlight, would give the same total energy as the real day. It equals the daily solar irradiation in kWh/m²/day, so a site with 4.5 kWh/m²/day has 4.5 peak sun hours.

What performance ratio should I use?

The performance ratio captures real-world losses (inverter, wiring, heat, dust, shading, mismatch). A good rooftop system is around 0.75–0.8; use a lower value for hot, shaded or dusty sites.

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Tip: Enter any known values to calculate the remaining results.

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