Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC 13273-2-15:2019 – Common International Terminology for Distributed Energy Storage Systems
Technical Overview and Compliance Guidelines for the Latest Terminology Standard
Scope
IEC 13273-2-15:2019 is part of the international terminology series developed jointly by ISO and IEC to provide unambiguous definitions and classifications for energy systems. This particular part, Part 2-15: Distributed Energy Storage Systems, establishes a consistent vocabulary for describing, evaluating, and communicating about electrical energy storage (EES) systems that are connected to the distribution network or located behind the customer meter. The standard covers both electrochemical storage (e.g., lithium-ion, flow batteries) and non-electrochemical technologies such as pumped hydro, flywheels, compressed air, and thermal storage when applied to the electric power system.
The scope includes definition of capacity, power, round‑trip efficiency, state of charge, depth of discharge, cycle life, and self-discharge, along with classifications based on storage duration, application (e.g., bulk energy shifting, frequency regulation, power quality), and integration level (utility‑scale, commercial, residential). The standard is intended to serve as a reference for engineers, regulators, system operators, and manufacturers to ensure clarity in procurement contracts, performance guarantees, and regulatory filings.
Technical Requirements and Terminology Framework
Core Definitions
The standard sets out mandatory definitions and permissible synonyms. For example, “rated energy capacity” is defined as the maximum amount of electrical energy that can be withdrawn from a fully charged storage system under specified discharge conditions, expressed in watt‑hours (Wh). The term “usable energy capacity” accounts for operational constraints such as minimum state of charge required for auxiliary systems. Table 1 lists ten key terms defined in the standard.
| Term | Abbreviation | Definition per IEC 13273-2-15 |
|---|---|---|
| Round‑trip efficiency | RTE | Ratio of energy delivered to energy absorbed, measured over a full charge/discharge cycle under reference conditions. |
| State of charge | SoC | Percentage of usable energy capacity remaining relative to the maximum usable capacity. |
| Depth of discharge | DoD | Percentage of usable energy capacity that has been discharged from a fully charged state. |
| C‑rate | C·rate | Rate at which a battery is charged or discharged relative to its nominal capacity; e.g., 1C corresponds to one hour discharge. |
| Cycle life | n/a | Number of cycles the system can perform before usable capacity falls below a specified threshold (typically 80 % of rated capacity). |
| Self‑discharge rate | SDR | Fraction of stored energy lost per unit time under defined open‑circuit conditions. |
| Rated power | Prated | Maximum continuous power output (kW or MW) that the system can sustain for a defined duration without exceeding operational limits. |
| Response time | tresp | Time from receipt of a dispatch signal to when the system reaches 90 % of the requested power change. |
| Energy capacity retention | ECR | Percentage of initial rated energy capacity remaining after a specified number of cycles or years of operation. |
| Grid interconnection point | POI | Point on the electrical network at which the storage system connects, defining ownership and performance responsibilities. |
Classification of Storage Systems
The standard categorises systems by storage duration: short‑duration (seconds to minutes, e.g., flywheels), medium‑duration (minutes to hours, e.g., batteries), and long‑duration (hours to days, e.g., pumped hydro). It also defines application classes that link storage function to grid services. Each application class has a set of essential performance parameters that must be declared in technical datasheets.
Performance Declarations
For compliance with IEC 13273-2-15, manufacturers and system integrators must provide a datasheet that includes at least: rated energy capacity, rated power, round‑trip efficiency at rated power and at 50 % capacity, self‑discharge rate at 25 °C, cycle life at 80 % DoD, operating temperature range, and safety classification. The standard requires that all performance metrics be measured according to the test procedures defined in related IEC standards (e.g., IEC 62933‑2 for battery systems).
Implementation Highlights for Practitioners
Tip: When writing procurement specifications, refer directly to IEC 13273-2-15 definitions to avoid ambiguity. For example, use the term “usable energy capacity” rather than generic “capacity” to ensure consistent performance guarantees.
Engineers should note that the standard explicitly disallows the use of terms such as “capacity fade” without accompanying definition; instead, the term “energy capacity retention” (ECR) must be used to describe degradation. This facilitates clear communication between vendors and utilities.
Best Practice: For grid‑connected projects, align the project’s performance testing protocol with the classification tables in Annex A of the standard. The annex provides a matrix mapping storage types to typical test durations and ambient conditions, which reduces the need for case‑by‑case negotiation.
Software developers designing energy management systems should adopt the standard’s tag strings for parameters (e.g., storage.SoC, storage.RTE_avg) to enable interoperability with monitoring platforms. The standard includes a digital annex with a list of recommended parameter identifiers.
Compliance and Certification Notes
Conformity with IEC 13273-2-15 is assessed through a combination of documentation review and type testing. The International Electrotechnical Commission (IEC) Certification Body (CB) Scheme covers most electrical equipment, but storage systems often require additional verification by accredited laboratories per IEC 62933‑1 (safety) and IEC 62933‑2 (performance).
Warning: Some national regulations, including those adopted as CAN/CSA‑ISO/IEC 13273‑2‑15:2020 in Canada, mandate that any deviation from the standard’s definitions must be explicitly stated in the contract. Failure to do so can lead to disputes during acceptance testing.
Project developers should maintain traceable records of all declared parameters and test results. Third‑party certification marks such as the IECEE or national marks (e.g., CSA) indicate compliance. The standard is harmonised with the European EN 13273‑2‑15 and is recognised by many grid operators.
Critical: For systems using unconventional storage technologies (e.g., gravity‑based, hydrogen), the standard’s definitions may not directly apply. In such cases, a “compliance-by-equivalence” statement must be prepared, referencing the nearest applicable definitions and justifying any omissions. Without this statement, the system may be rejected from interconnection studies.
Regular updates to the standard (next planned revision 2027) will incorporate new definitions for hybrid systems and grid‑forming inverters. Stakeholders are encouraged to participate in the IEC TC 120/WG 4 working group.
Q: What is the difference between “rated energy capacity” and “usable energy capacity” in IEC 13273-2-15?
A: Rated energy capacity is the maximum amount of energy extractable under ideal test conditions, while usable energy capacity accounts for constraints like minimum SoC to protect the battery or power auxiliary loads. Usable capacity is typically 80–95 % of rated capacity.
A: Rated energy capacity is the maximum amount of energy extractable under ideal test conditions, while usable energy capacity accounts for constraints like minimum SoC to protect the battery or power auxiliary loads. Usable capacity is typically 80–95 % of rated capacity.
Q: Is the standard mandatory for all distributed storage installations?
A: The standard is voluntary at the international level, but many regulators (e.g., in the EU, Australia, and parts of Canada) mandate it as a basis for grid code compliance or incentive programs. Check your local jurisdiction.
A: The standard is voluntary at the international level, but many regulators (e.g., in the EU, Australia, and parts of Canada) mandate it as a basis for grid code compliance or incentive programs. Check your local jurisdiction.
Q: Does this standard cover thermal energy storage?
A: Yes, when the thermal storage is intended to supply electrical energy (e.g., via a turbine) or to reduce electrical demand. Purely thermal applications intended for heating/cooling are covered by other IEC terminology standards.
A: Yes, when the thermal storage is intended to supply electrical energy (e.g., via a turbine) or to reduce electrical demand. Purely thermal applications intended for heating/cooling are covered by other IEC terminology standards.
Q: How often should datasheets be updated according to the standard?
A: The standard recommends recalibration and declaration update every two years, or after any major modification (e.g., replacement of battery modules).
A: The standard recommends recalibration and declaration update every two years, or after any major modification (e.g., replacement of battery modules).
© 2026 International Electrotechnical Commission & International Organization for Standardization – This article is based on IEC 13273-2-15:2019 and its Canadian adoption CAN/CSA‑ISO/IEC 13273‑2‑15:2020.