Protection technology ensures safe, reliable battery storage for renewables
EDITOR’ S CHOICE PROTECTING THE POWER SHIFT
CRESSALL
Protection technology ensures safe, reliable battery storage for renewables
In the UK, the share of electricity generation from renewable sources during the second quarter of 2025 reached a new record level of 54.5 per cent of all generation, according to the Department for Energy Security and Net Zero. But as we shift closer to a net-zero energy system, it becomes critical to have a robust storage solution to harness the energy we produce. Here, Mike Torbitt, managing director of resistor manufacturer Cressall, explores the technology behind battery energy storage systems( BESS).
The Government’ s Clean Power 2030 Action Plan, introduced in December 2024, looks to ensure that clean sources produce“ at least as much power as Great Britain consumes in total” and“ at least 95 per cent of Great Britain’ s generation”. Achieving this will rely on a blend of offshore wind and solar energy deployed at scale.
But this transformation hinges on flexibility. As wind and solar dominate, BESS is becoming the backbone of grid stability, absorbing excess renewable energy and releasing it during demand peaks. Lithium-ion technology leads the way here, comprising 95 per cent of UK BESS projects, thanks to its rapid response and scalability.
The BESS landscape
Higher renewable penetration has driven demand for energy storage. As of September 2025, RenewableUK reports 1,943 active battery storage projects in the UK, with 6.8 gigawatts( GW) of operational capacity— a 509 per cent increase since 2020.
Even larger projects are underway. Tillbridge Solar in Lincolnshire will deliver 1.5 GW of solar PV and three GWh of BESS, while Pembroke Battery in Wales will become the UK’ s largest storage facility when construction begins in early 2026.
These assets will provide fast frequency response, peak shaving and renewable firming. Their success, however, depends on safe, reliable integration into mediumvoltage( MV) grids. Systems typically connect at 6 – 36 kV, where grid code compliance, fault studies and earthing design are critical. Without robust protection, the promise of storage could falter under grid physics.
MV challenges
MV grids are fault energy rich environments. In solidly earthed MV systems, a single line to ground fault can drive very high currents, imposing severe thermal and mechanical stress on step up transformers, converter valves and switchgear.
For BESS, rapid dispatch and high-power flows amplify risks such as inrush currents, transient overvoltages and earth faults escalating in milliseconds, posing compliance and protection challenges under the GB Grid Code. Without controlled earthing, fault magnitudes can exceed clearing times and equipment limits, risking outages and costly repairs.
As grids add high voltage direct current( HVDC) links to ferry offshore wind and remote solar, and as BESS ties into converter stations or MV collectors, abnormal conditions like DC faults reflected into AC neutrals demand predictable neutral behaviour. Limiting ground fault current is
32 PECM Issue 79