BESS & Energy Storage Glossary — Key Terms Explained
The battery energy storage industry comes with its own language. Whether you’re a business exploring BESS deployment for the first time or a battery supplier navigating new markets, understanding the terminology is essential. This glossary covers the key terms, concepts, and technical definitions you’ll encounter across procurement, installation, grid connection, and energy storage technology — explained clearly by the JS Energy team.
A
3 terms
AC (Alternating Current)
Electrical current that periodically reverses direction; used by the grid.Ancillary Services
Grid-support services such as frequency regulation, voltage support, and reserve capacity.Availability
Percentage of time a system is operational and capable of delivering power.
B
6 terms
BESS (Battery Energy Storage System)
A complete battery storage installation including batteries, PCS/inverters, EMS, transformers, HVAC, and controls.Battery Rack
Structural frame holding battery modules inside a container or cabinet.Battery Module
Assembly of battery cells grouped together.Battery Cell
Smallest electrochemical energy storage unit.Black Start
Ability of a power system to restart without external grid supply.BoP (Balance of Plant)
All auxiliary equipment outside the core battery system, including transformers, cables, switchgear, and HVAC.
C
6 terms
Capacity (kWh / MWh)
Total amount of energy the battery can store.C-Rate
Battery charge/discharge rate relative to capacity. A 1C rate means the battery fully charges or discharges in one hour.Commissioning
Process of testing and validating a system before operation.Containerized BESS
Battery storage system housed in shipping-container-style enclosures.Curtailment
Reduction of PV output due to grid or operational constraints.Cycle Life
Number of charge/discharge cycles before battery degradation reaches a specified limit.
D
6 terms
DC (Direct Current)
Current flowing in one direction; produced by batteries and PV panels.DC-Coupled
Configuration where PV and battery are connected on the DC side before inversion.Depth of Discharge (DoD)
Percentage of battery capacity used during a discharge cycle.DER (Distributed Energy Resource)
Decentralized power resources such as PV systems and batteries.DSO (Distribution System Operator)
Entity responsible for operating the local electricity network.Dynamic Tariff
Electricity pricing that changes based on market conditions or time of day.
E
4 terms
EMS (Energy Management System)
Supervisory control system that optimises battery and PV operation.EPC (Engineering, Procurement & Construction)
Contractor responsible for full project delivery from design through to completion.Efficiency (Round Trip Efficiency)
Ratio of energy recovered from the battery versus the energy charged into it.Export Limitation
Restriction on how much power a site can export to the grid.
F
2 terms
Frequency Regulation
Grid-support service used to stabilise grid frequency within acceptable limits.Fire Suppression System
Integrated safety system designed to detect and mitigate thermal events within a BESS.
G
3 terms
Grid Forming
Inverter capability to independently establish voltage and frequency without an existing grid signal.Grid Following
Inverter operating mode that synchronises to an existing grid signal.General Certificate / Overall Certificate
Compliance certificate covering the complete integrated system.
H
2 terms
HVAC (Heating, Ventilation & Air Conditioning)
Thermal management system used to regulate temperature inside BESS containers.Hybrid Inverter
Inverter capable of handling both PV and battery systems simultaneously.
I
3 terms
Inverter / PCS (Power Conversion System)
Equipment that converts DC power from batteries or PV into AC power for grid or load use.Island Mode / Islanding
Operating mode where a system functions independently from the main grid.IP Rating
Protection rating indicating a system’s resistance to dust and water ingress.
K
4 terms
kW (Kilowatt)
Unit of power.kWh (Kilowatt-hour)
Unit of energy.kVA (Kilovolt-ampere)
Unit of apparent power.kWp (Kilowatt-peak)
Peak output rating of a PV system under standard test conditions.
L
2 terms
LFP (Lithium Iron Phosphate)
Common lithium battery chemistry used in BESS installations due to its safety characteristics and long cycle life.Load Shifting
Strategy of charging batteries during low-cost periods and discharging during high-cost periods to reduce energy bills.
M
3 terms
Load Shifting
Strategy of charging batteries during low-cost periods and discharging during high-cost periods to reduce energy bills.MPPT (Maximum Power Point Tracking)
PV inverter function that continuously adjusts operation to maximise solar energy output.MV (Medium Voltage)
Network voltage range typically between 1 kV and 36 kV.
N
3 terms
NA Protection (Netz- und Anlagenschutz)
German grid protection system ensuring safe disconnection from the network under fault conditions.NMC (Nickel Manganese Cobalt)
Lithium battery chemistry offering higher energy density than LFP.NOC (Network Operator Consent)
Permission required from the utility or grid operator before connecting to the network.
O
2 terms
Off-grid
Independent operation without any connection to the public electricity network.On-grid
Connected to and operating in parallel with the public electricity network.
P
4 terms
Peak Shaving
Reducing a site’s maximum power demand by discharging the battery during peak consumption periods.PCS (Power Conversion System)
Inverter and associated conversion equipment used to interface the battery with the grid or load.PPA (Power Purchase Agreement)
Long-term contract for the supply of electricity at agreed terms.PV (Photovoltaic)
Technology that converts sunlight directly into electricity.
R
3 terms
Ramp Rate
Speed at which a system’s power output can increase or decrease.Reactive Power
Power used for voltage control in AC electrical systems.Round Trip Efficiency (RTE)
Overall efficiency of storing and recovering energy, expressed as the ratio of energy output to energy input.
S
5 terms
SCADA (Supervisory Control and Data Acquisition)
Monitoring and control platform used to manage and oversee energy systems remotely.SOC (State of Charge)
Current battery charge level expressed as a percentage of total capacity.SOH (State of Health)
Measure of battery condition relative to its original capacity.String
Group of PV modules electrically connected in series.String Inverter
Inverter that serves one or more PV strings.
T
3 terms
Thermal Runaway
Uncontrolled increase in battery temperature that can lead to failure or fire if not mitigated.Transformer
Equipment used to step voltage up or down between different parts of the electrical system.Turnkey Project
Fully delivered operational project where the contractor manages all stages from design to handover.
U
1 term
UPS (Uninterruptible Power Supply)
Backup power system that provides instantaneous power during grid outages.
V
1 term
Voltage Ride Through
Ability of a system to remain connected to the grid during voltage disturbances.
W
1 term
Warranty Throughput
Total energy throughput covered under a battery manufacturer’s warranty.Common Industry Abbreviations
Abbreviation
Meaning
Abbreviations
BESS
Battery Energy Storage System
PV
Photovoltaic
PCS
Power Conversion System
EMS
Energy Management System
SCADA
Supervisory Control and Data Acquisition
DSO
Distribution System Operator
EPC
Engineering, Procurement & Construction
HVAC
Heating, Ventilation & Air Conditioning
SOC
State of Charge
SOH
State of Health
DoD
Depth of Discharge
MV
Medium Voltage
LV
Low Voltage
RTE
Round Trip Efficiency
PPA
Power Purchase Agreement
LFP
Lithium Iron Phosphate
NMC
Nickel Manganese Cobalt
Still Have Questions About BESS or Energy Storage?
Whether you’re a battery supplier looking to grow in new markets or a business ready to deploy energy storage, our team is here to help. Get in touch with JS Energy today and let’s talk through your specific goals, challenges, and next steps.