Nominal power (photovoltaic)
Watt peak ( engl. peak " peak ") is a commonly used in the field of photovoltaics, non-standard term for the electric power ( unit: watt ) of solar cells. Also common multiples as megawatts peak. As abbreviations Wp or kWp MWp be used.
Use
With Watt peak is defined as the output of solar electric power under standard test conditions ( STC) with the following parameters:
- Cell temperature = 25 ° C
- Irradiance = 1000 W / m²
- Sunlight spectrum according to AM = 1.5.
The phrase " The photovoltaic system has an output of 10 kWp " is colloquial. Correctly states: " The photovoltaic system has a rated output of 10 kW. " Accordingly, the notation " Pnom = 10 kW " spelled " P = 10 kWp " preferable because a attachment of additions of unit characters is non-standard.
Example
"It is per kWp requires an area of about 6 to 10 m. " This means that for a desired system output of 1 kW under standard test conditions an area of 6 to 10 m is required.
Criticism
The irradiance of 1000 W / m² is in Central Europe averaged statistically over a year not frequently ( the further south, the more frequently ), usually only during the lunch hours of a cloudless summer day. Every minute measured frequency distributions of the irradiance in Germany also show selective values about it, but play due to the short availability in terms of energy yield not matter. The maximum of the solar constant E0 is 1367 W / m².
In normal operation, have solar panels or solar cells at an irradiance of 1 kW / m² usually a much higher operating temperature than those provided for in the test 25 ° C and therefore an up to 20% lower efficiency and a correspondingly lower actual output power. In addition, the cells are usually not precisely oriented perpendicular to the incident light, whereby the power further reduced.
With data in watts peak can therefore was slightly equal-area solar modules are compared from different production in its efficiency, however, these data are in principle not for the characterization of stationary photovoltaic systems. Since this for the energy yield and the efficiency of the plant essential parameters like the site, that is, the latitude, and thus linked not be observed, the average irradiance or the prevailing climatic conditions at the site as the temperature. Have data in watts peak as a result of a seemingly higher " power rating " result, since they are obtained under artificial test conditions in the laboratory, but which are not achieved under certain circumstances in the investment actually realized as a peak value of the instantaneous power.