Solar Panel Output Calculator (PV System Yield)

How much does a solar panel produce?

The yield of a photovoltaic system is estimated as the product of three things: installed peak power, the solar irradiation on the panels and the efficiency left after system losses.

E = P_k × H × PR

• P_k: installed power, number of panels × panel rating (kWp)
• H: peak sun hours, the daily irradiation on the panel plane in kWh/m²
• PR: system efficiency (performance ratio)

What are peak sun hours?

They express the varying irradiation over a day as the equivalent number of hours at a constant 1000 W/m². A daily irradiation of 4.5 kWh/m² means 4.5 peak sun hours. The value depends on your location, the tilt and orientation of the panels and the season. The tool does not contain this data: take it from a reliable irradiation source for your site and enter it.

Example

Ten 550 W panels make 5.5 kWp. With 4.5 peak sun hours and 80 percent system efficiency the daily yield is 5.5 × 4.5 × 0.8 = 19.8 kWh and the annual yield 19.8 × 365 = 7227 kWh. That is 1314 kWh per installed kWp per year.

How many panels are needed?

Divide the daily consumption by peak sun hours times system efficiency. For 15 kWh a day with 4.5 peak sun hours and 80 percent efficiency you need 15 / 3.6 = 4.17 kWp. Eight 550 W panels (4.4 kWp) cover it.

Limits

The result is a first estimate based on an annual average. Winter yield falls clearly below the average and summer yield rises above it. Shading, panel temperature and inverter limits need an hourly calculation. Battery systems are sized for the worst month.