China-based Huaneng Group connected a dual-flywheel frequency regulation system to the grid at its Lanzhou combined heat and power plant on Nov. 6, completing a roughly year-long commissioning process that the group says validates large-scale flywheel storage for coal-fired generation assets.

The system comprises two flywheel units with a combined rating of 5.5 MW and 1.375 MWh. The primary unit — a 5 MW, 1.25 MWh flywheel spinning at up to 3,200 rpm on five-axis active magnetic levitation — is claimed by Huaneng to be the highest-power single flywheel unit in China. A secondary 0.5 MW, 125 kWh inertia flywheel handles smaller frequency deviations alongside it.

Huaneng says the paired design achieves a grid response time below 100 milliseconds and a regulation accuracy above 99.5%, figures the company attributes to the system’s proprietary control integration with the plant’s distributed control system. These performance figures have not been independently verified.

The pairing matters because flywheel storage is not designed for bulk energy delivery — 1.375 MWh is a small buffer — but for speed. Where a lithium battery frequency regulation system typically responds in a few hundred milliseconds, the flywheel array’s sub-100-millisecond response allows the thermal unit to react to grid disturbances faster than its own mechanical inertia would normally permit. The 5 MW primary flywheel handles large frequency excursions, while the smaller unit manages the finer, continuous corrections that would otherwise wear down the larger machine.

Technical development was led by the Xi’an Thermal Power Research Institute, Huaneng’s internal R&D arm, which has accumulated experience across several earlier thermal-storage combined frequency regulation demonstration projects. Equipment installation and the mandatory 168-hour continuous trial run were completed in December 2025; the system then operated under monitored conditions before the formal commercial grid connection this month.

The Lanzhou plant sits within Gansu province, a core zone of northwest China’s wind and solar buildout. Northwest China’s grids have faced persistent frequency stability challenges as variable renewable capacity has grown faster than conventional dispatchable generation. Thermal plants like the Lanzhou facility are under increasing pressure to act as regulating rather than baseload assets, and grid operators assess financial penalties under China’s two-part ancillary services assessment rules when frequency response falls short of benchmarks.

Huaneng’s stated rationale for the flywheel investment is partly to reduce those penalty costs while earning ancillary services revenue.

Flywheel storage carries structural advantages for this role — no chemical degradation, a claimed cycle life of tens of millions of charge-discharge cycles, and no fire risk — but remains more capital-intensive per megawatt than lithium battery alternatives at current prices.

Whether the dual-flywheel architecture proves economically replicable across other thermal plants will depend on how the ancillary services market values the importance of millisecond-range response.

From ESS News