Kilowatt-peak (kWp) describes the maximum output a solar system achieves under so-called Standard Test Conditions (STC): 1000 watts of solar irradiance per square metre, a module temperature of 25 degrees and a defined angle of light incidence. The addition of "peak" means exactly that – a peak. The figure is a laboratory reference value, not the actual continuous yield on your roof. It is what makes systems from different manufacturers and of different sizes comparable in the first place.\n\nIn everyday use, the actual electricity yield depends on location, roof orientation, tilt, shading and weather. In Switzerland, a system typically delivers a certain annual yield in kilowatt-hours (kWh) per installed kWp – and this varies considerably between the Mittelland, the Alpine region and Ticino. So kWp measures power (the size of the system), while kWh measures the electricity actually produced.\n\nYou need the kWp figure as soon as you plan a photovoltaic system: for sizing, the quotation, the building permit and the calculation of subsidies such as the one-off remuneration. The capacity of a battery storage unit is also often matched to the kWp.\n\nBe careful not to confuse kWp with the annual yield – a larger system is not automatically more economical. Factor your self-consumption, available roof area and a sound yield forecast into the planning, and obtain several quotes from certified solar specialists.
Kilowatt-peak (kWp)
Kilowatt-peak (kWp) is the unit of measurement for the rated power of a photovoltaic system under standardised test conditions. It indicates how much peak electrical power the solar modules can deliver under ideal circumstances.
Example
A family in Wetzikon wants to equip their detached house with a solar system. The solar specialist assesses the south-facing, slightly tilted roof area and plans a system of around 10 kWp. Based on the kWp figure, they calculate the expected annual yield, the appropriate battery storage and the amount of the one-off remuneration – allowing the family to realistically estimate costs and self-consumption.
Frequently asked
What is the difference between kWp and kWh?
kWp (kilowatt-peak) indicates the installed peak power of your solar system under test conditions – in other words, its size. kWh (kilowatt-hour) measures the amount of electricity actually generated over a given period. Put simply: kWp is the potential, kWh is the real yield.
How much electricity does 1 kWp deliver per year in Switzerland?
This depends heavily on location, roof orientation, tilt and shading, and varies considerably between the Mittelland, mountain regions and Ticino. A certified solar specialist will prepare a sound yield forecast based on your specific roof situation – generic figures should be treated with caution.
How many kWp do I need for my house?
The right size depends on your electricity consumption, your desired self-consumption, the available roof area and your budget. A larger system is not automatically more worthwhile. Seek advice from a specialist and obtain several quotes.