Power or electrical power is defined as the energy required or produced in a specific period of time (per second as standard) and is expressed in watts [W].
For example, this indicates the current energy consumption of a consumer or the current production of electrical energy, for example a photovoltaic system.
In contrast to capacity (kWh), the output does not provide information about the amount of energy used/produced, but only how much is currently used/produced.
For example, if a photovoltaic system currently produces 2 kW (2000 watts), this is a statement about how much energy is currently being produced per second.

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

Examples and comparisons:

In order to classify the magnitudes of watts, kilowatts or megawatts, the following infographic provides examples of both power generation/storage and electricity consumption.

For example, at peak times (morning and evening), a household needs an output of around 14 kW in order to be able to operate all appliances (stove, refrigerator, hair dryer, television, etc.).

Kyon's large battery storage systems, large intermediate storage systems for electrical energy, can, on the other hand, draw powers of around 5 MW up to 100 MW both from the grid and feed them back into the grid. (1MW = 1,000,000 W) With this power, such a storage system could supply, for example, the entire district of Regensburg with around 195,000 inhabitants, including all households, industry and municipal facilities, as they require an average electrical output of 100 MW or 100,000 kW.

As described in the definition, however, this power does not provide any information as to how long the battery storage systems could supply the district, simply that the energy requirement can be met by the storage system in a moment.
If the duration for which the storage facility could supply the district is to be determined, the capacity must also be considered in addition to the output. This indicates how much energy can be stored in total.
For more details, see the glossary entry for “Capacity”

What are the most important terms about performance?

Useful power:

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

Power loss:

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.


Efficiency indicates the ratio of net power and power loss. The higher the share of useful power in the total electrical power consumed, the higher is the efficiency. The power loss should therefore always be kept as low as possible for high efficiency. A well-known example of efficiency is light from light bulbs and LEDs. While LEDs with high efficiency convert most of the energy into light, light bulbs draw significantly more energy for the same amount of light because the majority has been converted into heat.

Kilowatt peak:

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