Page 33 - Energize March 2021

TECHNICAL

Voltage control and regulation is usually handled by independent
voltage controllers but can also be dealt with by the storage
system. Some industrial smart BESS systems can provide
reactive power compensation to control the voltage supplied to
the load. With an accurate and rapid response, energy storage
systems improve power quality and protect downstream loads
against short-duration disturbances in the grid.
Active harmonic filtering is a feature of some BESS systems.
An active filter analyses the waveform of the current drawn and
injects a complementary current waveform into the supply to
reduce the harmonic content fed back to the grid.

Reliability of supply (spinning reserve)
In this application the BESS remains fully charged and responds
to generation or transmission outages. Depending on the Figure 5: Load reduction and demand response (ABB)
application need, the system can respond within milliseconds
or minutes. The BESS unit either supplies power until other
generation sources are started and running, enabling standby also known as load reduction, is a situation where the utility
generators to work at optimum power output (without the need limits the amount of power supplied to the consumer. The BESS
to keep idle capacity for spinning reserves) or may supply carries part of the load which exceeds the limit.
power for the whole duration of the outage, depending on the The BESS may also be used to implement the demand
size of the load and the capacity of the BESS. The load may be response function, which consists of reducing grid demand
split into interruptible and non-interruptible (NI) loads, and the by using the BESS to supply part of the load, in response to
BESS may be required to carry the full load for a short period, requests from the utility. This is usually a paid-for service by
or the NI load only for the full duration. With smart storage agreement with the utility.
coupled to an energy management system, full flexibility can be
achieved in this mode. Demand management (peak shaving)
Peak shaving is aimed at specific high demand peaks for
Demand side management (DSM) the purpose of reducing peak demand and for economy of
DSM is one of the most important functions of consumer BESS operation. The goal is to avoid installation of extra capacity
systems, and takes several forms. (see Figure 4). to supply the peaks of a highly variable load. Most facilities
do not operate 24 hours a day, and the energy demand
Energy tariff and charge management (arbitrage) remains relatively low for most of the period, rising only
This function is used to reduce demand during periods of high during operational hours. By charging an energy storage
energy tariffs, and stores energy when tariffs are low, reusing system during the off-hours of the day and discharging it
when tariffs are high. The function needs to be flexible as during the operational hours, the peak demand charge from
demand can vary from day to day and seasonally, as can tariffs. the utility can be reduced, and the peak demand on the
Use of the function also depends on the SOC of the battery. A electrical installation can also be lowered. Energy may also
typical example would be to fully charge the battery during the be stored in periods of low demand between consecutive
overnight low demand period and discharge during morning and peaks (Figure 6).
evening peaks (Figure 4).
Microgrid forming and black start capability
Load reduction, partial load shedding, and demand response Microgrids require a frequency reference for inverter-based
The BESS may be used to reduce loads in times of high demand and conventional generation plant to operate correctly. Under
on the grid and potential supply shortages. Partial load shedding, grid-connected conditions the grid serves as the frequency
reference. When disconnected from the grid, a stable local
frequency source is needed. This can be provided by using a
grid-forming inverter together with the storage system. A grid-
forming frequency source requires a stable supply for which
BESS is ideally suited.
Black start capability is required where generators need
a supply of power to start up. Although this application is
confined to large industries with large onsite generators, (gas or
co-generation), BESS systems have been successfully used as
a black start source. 3

On-site PV capacity firming
Many consumers are installing on site (rooftop) PV systems
to save costs and avoid power interruptions. Most urban
Figure 4: Demand management takes several forms (21stcentech.com) areas are subject to intermittent cloudy weather, and PV

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