IEEE Std 1679-2020 pdf download – IEEE Recommended Practice for the Characterization and Evaluation of Energy Storage Technologies in Stationary Applications.
3.1.2 Energy rating An energy rating expresses usable energy storage capacity of the device. For energy ratings to be meaningful, all limiting parameters such as rate, temperature, state of charge (SOC), and end-of-discharge voltage should be specifed. Energy ratings should be expressed in watt-hours (Wh). It is also recommended to know the coulombic storage capability for a given discharge rate. This is usually termed capacity and is expressed in ampere-hours (Ah). If the capacity is given in watt-hours, then the nominal voltage should also be specifed to allow calculation of the capacity in ampere-hours. The nameplate rating of the device in watt-hours or kilowatt-hours should be accompanied by the rate of discharge in watts or kilowatts or the time over which the rated energy can be discharged. Other rating methods may also be provided, such as specifc energy (watt-hours/kilogram [Wh/kg]), energy density (watt-hours/liter [Wh/L]), etc. If these parameters are specifed, the confgurations and conditions under which the rating is valid should be included. Energy ratings are normally based on products at the beginning of life. The manufacturer should state how available energy from the device may vary over service life (see also 3.2). 3.1.3 Power rating Power ratings for energy storage devices are specifed in a number of ways. In order to provide a rating that is useful for comparison of technologies, the rating should include all limiting parameters, such as the following: — The duration of the discharge — The operating voltage range — Temperature NOTE—In addition to power limitations in charge or discharge due to initial operating temperature, operation may also be restricted by temperature rise due to Joule heating.
3.1.5 Energy efciency The energy effciency of an energy storage technology is of utmost importance to many applications because it is a factor in cost of use. If the energy storage system requires additional system components to facilitate its proper function, the collateral losses of these components should be considered. Collateral losses may include the following: — Heating — Cooling — Pumping — Vacuum — Electronic systems for monitoring, control, and communication — Necessary power conversion, etc. Effciency should be defned as the useful energy output divided by the energy input to the system, and expressed as a percentage. This value includes all previously mentioned system losses as well as any electrochemical, electromechanical, or electrical ineffciency involved in the storage of the energy under normal operating conditions. If the effciency is affected by the time of storage, this time and its effect should be specifed. Because energy effciency is a function of power level on charge and discharge, the effciency should include the power ranges over which the value is valid. If appropriate, multiple effciency values should be provided to refect the full power spectrum over which the device is expected to be operated. In addition to the energy output/energy input effciency, it is desirable to know the coulombic effciency of the system expressed as the ratio of ampere-hours out of the system divided by the ampere-hours input to the system to store the energy. Again, all system losses should be included in this effciency.