The relevance of energy storages for an autarky of electricity supply ...

4.2 Evaluation Criteria
Following criteria can be used to assess storage technologies (Neupert, 2009):
Rated power (W)
Rated power describes the maximum available energy per unit of time.
Energy content of the system (Wh)
Theoretical energy content in Joule or Watt hours does not include losses due to
technical execution, which are considered within the practical energy content.
Furthermore, the dischargeable energy content accounts for energy, which has to stay
in the storage to secure functionality.
Energy density (kWh/l or kWh/kg or kWh/m 3 )
Energy density describes the usable energy content related to mass or volume. It can
refer to the system or only to the storage.
Self-discharge rate/losses
Losses can occur during loading and unloading or time-dependent as self-discharge
rates expressed in percentage per time interval.
Availability/Response time
The availability of a system describes the timeframe within it is possible to produce
50 % of the power.
Efficiency
To evaluate the efficiency of energy storage technologies the whole system including
conversion steps has to be considered. Useful energy from a storage system is the
result of renewable energy input minus operational energy minus energy losses
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