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What is the kilowatt-peak?

The notion of kilowatt-peak is used to compare the performances of photovoltaic installations and to forecast the amount of electricity they can produce in optimum conditions.

Many factors can influence the amount of electricity that a photovoltaic installation can produce:

  • its installation location
  • its orientation
  • the direction of shade
  • the temperature on the roof

For this reason a standard has been established: the watt-peak (Wp) or kilowatt-peak (kWp).
(1 kWp = 1000 Wp ).

What does watt-peak mean?

The Wp represents the maximum electric power that can be supplied by one photovoltaic panel in standard temperature and sunshine conditions. In other words:

  • sunshine of 1000 watts/m²
  • an ambient temperature of 25°C (photovoltaic panels produce less output beyond this limit)
  • a clear sky, around noon for example

For a same surface area, the higher the number of Wp, the more efficient the photovoltaic panel.

What is the advantage of the watt-peak?

The watt-peak allows a comparison between the outputs of photovoltaic panels from different manufacturers. For a same surface area, the higher the Wp, the more efficient the panel.

The watt-peak is also used to calculate the necessary size for a photovoltaic installation according to the yield that is sought .

Caution, the sunshine conditions must also be taken into account in this calculation. A different output is achieved for 1 kWp of solar panels depending on the region where the photovoltaic installation is located and its sunshine conditions. Thus, on the roof of your house in Brussels, a 1 kWp installation will produce 900 kWh a year in optimum conditions (south-facing, 35° angle). Whilst on the roof of your holiday home in Southern Europe, it will produce 1250 kWh/year!

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