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Battery Energy Storage

1.1    Scope

The scope for battery energy storage (BES) systems covers industrial and commercial applications. A BES system is a stand-alone package unit connected via cable to the local grid. This can include basic components such as battery subsystem, enclosure, power conversion subsystem, control subsystem, auxiliary subsystem, and connection terminal. 

1.2    Definitions

Battery energy storage is an electrochemical device that stores energy and provides electricity by discharging that energy at later times. In the wider electricity system, a BES system can defer the consumption of electricity generation to a later time, allowing for more cost-effective and sustainable generation sources to be maximised.

Battery energy storage is available in a range of different electrochemical designs and efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of higher efficiency products.
The ETL Scheme covers three categories of Battery Energy Storage products:

  • Office building (< 20,000 kWh)
  • Small Industrial/ Large business (< 90,000 kWh)
  • Large Industrial (< 250,000 kWh)

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.3    Requirements

1.3.1    Eligibility requirements

To be eligible, products shall:   

  • Have a capacity of no less than 100kWh

1.3.2    Performance requirements

Products shall have:   

  • An energy density of no less than 150 kWh/kg (kg to refer to total BES mass)
  • A lifespan no less than 10,000 cycles before reaching 60% of rated capacity
  • A round trip energy efficiency of no less than 95%

1.4    Measurement and Calculations

1.4.1    Measurement standards

The following standards shall be used to test product performance:

  • BS EN IEC 62933-2-1:2018

1.4.2    Standard testing conditions

As defined in BS EN IEC 62933-2-1:2018, tests shall be performed in the following conditions:

  • Ambient air temperature 25° Celsius 
  • Altitude ≤1000m
  • Humidity ≤ 95% with no condensation

1.4.3    Test Requirements

In line with the eligibility and performance requirements above:

  • The capacity of the BES system shall be calculated following the "actual energy capacity test" found in the standard BS EN IEC 62933-2-1:2018 at 6.2.1.
  • The energy density of the BES system shall be calculated following the "Input and output power rating test" found in the standard BS EN IEC 62933-2-1:2018 at 6.2.2.
  • The lifespan of the BES system shall be provided by the supplier as described in the standard BS EN IEC 62933-2-1:2018 at 5.2.4.
  • The roundtrip efficiency of the BES system shall be calculated following the "roundtrip efficiency test" found in the standard BS EN IEC 62933-2-1:2018 at 6.2.3.

1.5    Verification for ETL Listing

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing 
  • Acceptance Tests or Field Trials 
  • Independent testing
  • Representative testing (see clause 1.5.1 below)     

Further information regarding the first three routes can be found in the ETL Testing Framework.

1.5.1    Representative testing

Where applications are being made for two or more models that are variants of the same basic design, test data may be submitted for a single ‘representative model’ provided that all variants:

  • Use the same power conversion subsystem, control subsystem, auxiliary subsystem, and connection terminal. 
  • Use the same battery technology for energy storage scaled to different capacities by adding/removing cells of the same battery technology. 

It should be noted that:      

  • If a manufacturer voluntarily removes the representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL. 
  • If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative model will be removed from the ETL.

1.6    Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity assessment programme in order to ensure listed models continue to meet the ETL requirements. 

1.7    Review

1.7.1    Indicative review date

This specification is scheduled to be reviewed during the 2025/26 review cycle.

1.7.2    Illustrative future direction of the requirements

The first technical review of these criteria will consider:

  • Uptake of the BES technology listed on the ETL.
  • The setting of a minimum power discharge rate.
  • The setting of a maximum self-discharge rate.
  • Market developments for the technology in the UK.
  • The use of distributed BES systems in conjunction with solar PV and wind.