Page 32 - Energize March 2021

TECHNICAL

Storage parameters
All battery storage systems have several key parameters which need
to be considered when planning a BESS.
• Rated power capacity (the total possible instantaneous
discharge capability (kW or MW) of the BESS, or the maximum
rate of discharge which the BESS can achieve, starting from a
fully charged state.
• Energy capacity (maximum amount of stored energy (in kWh or
MWh). For chemical batteries, energy capacity depends on the Figure 2: Containerised BESS (ABB)
rate of discharge. The higher the rate of discharge the lower
the capacity. Irrespective of size, BESS will have the basic structure shown
• Storage duration (the amount of time storage can discharge at in Figure 3.
its power capacity before depleting its energy capacity). The configuration of the system will be customised to suit the
• Cycle life or lifetime before failure or significant degradation. application and can vary from high power, short duration to long
Cycle life is dependent on the number of charge\discharge duration, low power within the same container space. Generally,
cycles and the depth of discharge. the inverter and other protection devices are all mounted together
• Self-discharge, expressed as a percentage of charge lost over in a single cabinet or container. In some of the larger systems
a certain period, reduces the amount of energy available for (ABB, GE, Wärtsilä, etc.) the container only holds the battery and
discharge and is an important parameter to consider in batteries auxiliaries, while the rectifier/inverter and switchgear are mounted
intended for longer-duration applications. separately.
• State of charge, (SOC) expressed as a percentage, represents
the battery’s instantaneous level of charge and ranges from Applications
completely discharged to fully charged. The state of charge Applications differ based on whether the BESS is used for
influences a battery’s ability to provide energy or ancillary customer energy management services or distribution energy
services to the grid at any given time. management services. Customer energy management comprises:
• Round-trip efficiency, measured as a percentage, is a ratio of • Power quality management
the energy supplied to the battery to the energy recovered from • Reliability of supply (spinning reserve)
the battery. • Demand side management
- Energy tariff and charge management (arbitrage)
Technology and systems - Demand management (peak shaving)
Systems are designed as modular units, ranging in size from - Load reduction, partial load shedding and demand
hundreds of kW to several MW. They are mounted either in cabinets response
for internal applications (see Figure 1) or in transportable containers • Microgrid forming and blackstart capability
for external applications (see Figure 2). • On site PV capacity firming

Distribution network applications comprise the following
additional functions:
• Frequency support
• Voltage support
• Load levelling and investment deferment

Power quality management
Power quality issues such as voltage dips and sags, and current
harmonics, are of major concern in industrial applications, and can
cause a plant to shut down, devices to malfunction, and so on.

Figure 1: Cabinet-type BESS (Eaton) Figure 3: The general structure of a BESS.

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