# Nameplate capacity

Installed capacity is a term from the electricity industry. It indicates the maximum power ( nominal power ) installed at a power plant generators or installed in a country or a state total capacity of all power plants. It is expressed in units of Watts and multiples as megawatts ( MW) or gigawatts ( GW).

## Importance

From the installed capacity follows - given a known voltage - the current maximum generated and thus the necessary cross -section of the power cable when installing the system.

Some power plants only work on an hourly basis, so you have to calculate the energy produced and the mean duration over a longer period of time, usually one year, to be known. Determined in this way realistic, average yield is called the standard capacity and is essential for the assessment of the soundness of an investment. As a unit of energy, he is usually given in this context, in watt-hours or multiples thereof.

The quotient Q from the actually produced energy Eact and the determined from the installed capacity maximum possible energy release Emax is called efficiency. This quotient Q is always between 0% and 100 %:

Sometimes the efficiency is given as a full load hours, which indicate the billing interval, the number of hours under the assumption of a constant temporal performance decrease with the value of the installed capacity.

### Example

Consider a wind turbine with a rated power of 2 MW, with 8760 hours for a total of 8000 hours produced 4.5 GWh of electrical energy during a year. The in practice not achievable theoretical maximum annual production is 8760 h × 2 MW = 17.52 GWh. From the percentage of annual production at the theoretical maximum production, a capacity factor of 25.68 % and 2250 full load hours calculated.

## Limitations

Only when the current in base load power plants can be concluded from the installed capacity on the energy tax years into the grid (given in GWh). The resulting equity requirements in the amount of five to ten percent, and the failures must be taken into account by revisions in the amount of ten to fifteen percent of thermal power plants. In the current base load hydroelectric power plants, the losses must be calculated by means of weather-related low water levels, revision work or ice conditions.

In power plants, which are designed to cover peak load, no conclusions can be drawn on the duration yield from the installed capacity; some of which are operated per day just a few minutes or hours, while others may contribute technically much more for base load, but are needed and only switched on for peak loads. Pumped storage power plants also require electrical power to be "charged" for the peak demand.

## Installed capacity in Germany

In the following, the installed capacity in Germany ( gross electricity generation capacity) for the public grid in the years 2000, 2009, 2010 and 2011 as well as the absolute change from 2000 to 2011 is listed.

The installed capacity in the railway power supply is 3.2 GW.