The capacity or electrical power is defined as the energy required or produced in a certain period of time (per second by default) and is specified in the unit watts [W].
This therefore indicates, for example, the current energy consumption of a consumer or the current production of electrical energy, for example of a photovoltaic system.
In contrast to the Capacity (kWh), the power does not provide any information about the amount of energy consumed/produced, but only how much is currently being consumed/produced.
For example, if a photovoltaic system is currently producing 2 kW (2000 watts), this provides information about how much energy is currently being produced per second.

Physically, the electrical power P is calculated from the product of voltage U [volts] and current I [amperes].
P = U * I

Examples and comparisons:

In order to classify the orders of magnitude of watts, kilowatts or megawatts, you will find examples of both electricity generation/storage and electricity consumption in the following infographic.

For example, at peak times (morning and evening), a household needs a power of about 14 kW to operate all appliances (stove, refrigerator, hairdryer, TV, etc.).

By contrast, Kyon's large-scale battery storage systems, which are large intermediate storage facilities for electrical energy, can draw power from the grid and feed it back into the grid at rates of approx. 5 MW to 100 MW. (1MW = 1,000,000 W) With this power, such a storage facility could supply the entire district of Regensburg with approx. 195,000 inhabitants, including all households, industry and municipal facilities, since these require an average electrical power of 100 MW or 100,000 kW.

However, as described in the definition, this capacity does not indicate how long the battery storage could supply the county, only that at one moment the energy demand can be met by the storage.
If the duration is to be determined in which the storage could supply the district, then the capacity must be considered in addition to the power. This indicates how much energy can be stored in total.
You can find more details in the glossary entry of "capacity".

What are the most important terms related to performance?

useful power:

The useful power describes the electrical power that is effectively used by a consumer. In reality, however, the total energy consumed is usually higher, as a consumer always has a certain power loss.

Power loss:

The power loss is the electrical power that is consumed in addition to the useful power and is usually "lost" in the form of heat or can no longer be used.


The efficiency indicates the ratio of useful power to power loss. The higher the proportion of useful power in the total electrical power consumed, the higher the efficiency. The power loss should therefore always be kept as low as possible to achieve high efficiency. A well-known example of efficiency is light from light bulbs and LEDs. While highly efficient LEDs convert most of the energy into light, incandescent bulbs draw significantly more energy for the same amount of light, as most of it is converted into heat.

‍Kilowatt peak:

The maximum output of a photovoltaic system is specified in kilowatt peak (kWp) and is used to compare PV modules. PV modules are characterized by the fact that they produce different electrical outputs under different conditions.
The maximum output in kWp specified for PV modules from different manufacturers, on the other hand, is achieved under defined conditions. Here, the solar radiation, air mass and cell temperature are specified and the electrical output achieved is stated. Modern PV modules achieve outputs of 300-400 Wp.