How to calculate solar PV energy yield

You can estimate a PV system's annual energy with "system size × yield per kW". Depending on where you are, 1 kW of panels typically makes about 900 to 2,000 kWh a year. Below are the formulas, a worked example, and the factors that change the result.

The simplest formula

Annual energy (kWh) = system size (kWp) × peak sun hours per day (h) × 365Peak sun hours: how many hours a day the system would need to run at full rated power to make the same energy. Roughly 2.5 h in northern Europe, 3.5 to 4.5 h in much of the US, southern Europe and East Asia, and 5 h or more in deserts.

A 100 kWp plant with 3.6 peak sun hours makes 100 × 3.6 × 365 = about 131,000 kWh a year, or 1,314 kWh per kWp.

System size	2.8 h/day	3.6 h/day	4.5 h/day
5 kWp (home roof)	5,110 kWh	6,570 kWh	8,213 kWh
100 kWp	102,200 kWh	131,400 kWh	164,250 kWh
1 MWp	1,022,000 kWh	1,314,000 kWh	1,642,500 kWh

A better formula: irradiation and performance ratio

Annual energy (kWh) = system size (kWp) × annual irradiation on the panel plane (kWh/m²) × performance ratio (PR)PR is what is left after temperature, soiling, shading, cable and inverter losses. Well-built plants usually reach 0.75 to 0.85.

If the panel plane receives 1,650 kWh/m² a year and PR is 0.80, each kWp makes 1,650 × 0.80 = 1,320 kWh. You can get irradiation for any location from free sources such as PVGIS by the EU Joint Research Centre.

What changes the result

Orientation (azimuth): facing the equator is best. Output drops slowly as you turn east or west.
Tilt: the best annual tilt is usually a bit below your latitude. Too flat or too steep loses energy.
Shading: front rows, trees, buildings and hills, worst on winter mornings and evenings. See the shading guide.
Temperature: panels lose efficiency as they heat up, so hot climates lose more.
Row spacing: tighter rows fit more panels but add shading loss. See the row spacing guide.
Degradation: modules lose a little output every year, typically around 0.4 to 0.5 %. Include it in any 20-year estimate.

These are rough numbers. For a real project you need a simulation with the site's weather data, your layout and its shading.

Calculate it for your own site

Draw your site on the satellite map, panels are laid out automatically, and you get annual energy and daily peak hours with terrain and shading included. Free, nothing to install.

Try it free →

FAQ

How many kWh does 1 kW of solar produce per day?

Roughly the same as your peak sun hours: about 2.5 to 5 kWh per kW per day depending on location and season.

What does 3.6 peak sun hours mean?

It is the day's energy expressed as hours at full rated power. It is not the same as the number of daylight hours.

How much energy does a 5 kW home system make?

With good orientation and no shading, about 5,000 to 8,000 kWh a year in most temperate and sunny regions.