Grid Connection Requirements for BESS

A battery connected to the public grid is, from the network operator’s point of view, a power plant and a load in one. Before it can be energised, it must show that it will not make the grid less stable, that it will ride through disturbances the grid is designed to survive, and that its protection will behave. The documents that define this are the grid codes, and for storage they apply on top of the product safety standards covered on the Battery Energy Storage Systems hub.

What a grid code asks of a storage asset

Fault ride-through: staying connected, and in many codes injecting current, during a voltage dip or surge, rather than tripping and making the disturbance worse.
Voltage and reactive power control: holding a voltage set point or following a reactive power or power factor schedule within a declared capability range.
Frequency response: reducing or increasing active power as frequency moves outside a dead band, and tolerating rate-of-change-of-frequency events without tripping.
Power quality: limits on harmonics, flicker and DC injection at the point of connection.
Protection and settings: agreed trip settings, anti-islanding behaviour, and remote disconnection or curtailment on instruction.

A battery adds two points that other generation does not. It can both import and export, so the code applies in each direction. And its available power depends on state of charge and temperature, so the declared capability has to hold across the operating range the owner intends to use, not only when the battery is full.

The main codes by region

UK. Storage connected to the distribution network is covered by the Engineering Recommendation G99, which classifies plant into types by size and connection voltage and sets the evidence needed at each level.^[1] Larger plant connected to the transmission network is covered by the Grid Code itself.

European Union. The Requirements for Generators network code sets the common minimum requirements, grouped into types A to D by size and voltage, and each member state sets national values within it.^[2] The EN 50549 series (part 1 for low voltage, part 2 for medium voltage) supplies the technical detail for plants connected to distribution networks.

United States. IEEE 1547 covers resources connected at distribution level, and IEEE 2800 covers large inverter-based resources connected at transmission level, including batteries.^[3] The distribution case is covered on the site in IEEE 1547.

Showing compliance

Compliance is shown in layers. The owner submits design data and, for larger plant, a validated simulation model of the plant so the operator can study its effect on the network. Type testing of the inverter gives evidence for the product, and commissioning tests on the finished plant prove the installed system matches. Sites tested well in the factory still need the on-site tests described in the page on site acceptance testing and commissioning, because settings, cabling and the real network are only present there.

Moving towards grid-forming

Conventional inverters follow the voltage and frequency the grid already provides. As synchronous generation retires, operators want some inverters to behave as a voltage source instead, which supports the grid when it is weak. Batteries are well suited because they can deliver the extra current and energy. The difference is explained in Grid-Forming vs Grid-Following Inverters. In Great Britain a minimum specification for grid-forming capability has been developed through the Grid Code modification process, and other regions are moving in the same direction.^[4]