Behind the Meter: Battery Energy Storage Concepts, Requirements, and Applications
By Sifat Amin and Mehrdad Boloorchi
Battery energy storage systems (BESS) are emerging in all areas of electricity sectors including generation services, ancillary services, transmission services, distribution services, and consumers' energy management services.
Applications of the BESS in the electricity sector are divided into three categories: front-the-meter (FTM), behind-the-meter (BTM), and off-grid, which for long-term operation have to be supported by an off-grid generator.
FTM BESS are those that are integrated into a generation facility, distribution network, or a transmission system for the applications that are summarized in Table 1.
Table 1- FTM BESS Applications
BTM BESS are connected behind the utility service meter of the commercial, industrial, or residential consumers and their primary objective is consumer energy management and electricity bill savings. The BTM BESS acts as a load during the batteries charging periods and act as a generator during the batteries discharging periods.
The application of BTM BESS could be for the fulfilling one or more of the following purposes:
- Peak shaving and demand charge management
- Time-of-use energy cost management
- Continuity of energy supply during the outage of electricity supply utility
- Power quality management and limitation of upstream disturbances
- Reactive power compensation
- EV fast charging
BTM BESS Concept
BTM BESS, which is in parallel with the utility supply network should be used solely on the consumer side and there should not be any power flow back to the grid. In addition to the BTM BESS, there might be BTM PV or other types of distributed energy resources (DER) in consumer's facility, as well.
General flow of power in an industrial facility containing BTM BESS and BTM PV system is shown in Figure 1.
Figure 1. Power Flow in a Facility Containing BTM BESS
It is necessary to ensure that BTM BESS is not discharging real power to the grid. To meet this requirement, BESS system shall continually monitor the facility load and adjust the BESS discharge not to exceed the facility consumption. In addition to this measure, a reverse power monitoring relay shall be used at the utility supply point to prevent power injection to the utility network in case of failure of BESS monitoring system.
Like the FTM BESS or DER, BTM BESS shall be equipped with the Islanding detection and anti-islanding protection system where BESS inverters cannot meet the anti-islanding requirements as stipulate in IEEE Std 1547, a separate remote or local anti-islanding detection system might be required.
BTM BESS inverters shall be bidirectional in order to be able to be charged and to discharge. In addition, these inverters shall be bi-modal, i.e. to be able to operate as a grid forming generator in case of the grid outage and necessity for off-grid operation of BTM BESS. There are several control methods for operating the BTM BESS inverter in grid forming mode. Careful consideration and examination of the control system for off-grid operation of the BTM BESS inverter is required where the bump-less transfer of facility load from the utility supply system to the BESS system in off-grid condition is required. Uninterruptible power supply (UPS) system is a special case of BESS application which is being used in industries for providing continuous supply to critical loads. However, UPS system requires two individual AC/DC (rectifier/ charger) and DC/AC (inverter) power conversion systems.
Description of BTM BESS applications
Peak shaving and demand charge management is the use of BTM BESS by the consumer for peak shaving, or smoothing of own peak demand, to minimize the part of their invoice that varies according to their highest power demand, and reducing the overall costs for electric service by reducing demand charges during peak periods specified by the utility.
Time-of-use energy cost management is charging of BTM BESS when the rates are low and discharging it during peak times, with the aim of reducing the utility bill.
Continuity of energy supply relates to the ability of the BTM BESS to substitute the network in case of interruption, thus, reducing the damage for the consumer in case of a blackout.
Power quality management has the objective of using BTM BESS to provide a high level of power quality above and beyond what the utility offers where the facility’s critical loads are very important. In addition, BTM BESS could be used for the limitation of disturbances transmitted at upper levels.
Compensation of the reactive power refers to the ability of BESS inverter/ converter ability to locally compensate the reactive power, hence, influence the supply voltage.
Electric Vehicles (EV) fast charging Integration is the BESS in parallel with DC converted grid supply for charging of electric vehicles or ferries or supplying the peak DC loads. If BTM BESS is being used for this application only, its inverter is not required to be bidirectional.
This article edited by Mehrdad Rostami
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