World’s first battery storage system to provide full active and reactive power services comes online

In February 2023, construction began on 200 MW of a 300 MW/600 MWh battery energy storage system (BESS) site in Blackhillock, Scotland. Project proponents wanted it to be the world’s first transmission system-connected BESS to offer grid stability. Rather than boost or replace wires, Blackhillock will provide full active and reactive power services.

On March 3, 2025, Zenobe, one of the UK’s leading owners and operators of transmission system-connected grid-scale batteries or so-called grid boosters, announced that Blackhillock began commercial operations as Europe’s largest battery site.

The Blackhillock site is launching in two phases. Phase 1 comprises of 200 MW which went live on Monday and will be followed by a further 100 MW in 2026.

However, what is even more impressive than the project size is the type of services it will provide. Blackhillock was procured under Stability Pathfinder 2, the first tender of its kind in the world to procure stability services, such as short circuit levels (SCL) and inertia, from inverter-based resources.

Four companies secured 10 contracts under the tender in April 2022, to address insufficient SCL – the amount of current flowing during faults – across Scotland. The winning bidders also committed to offer “green” inertia to balance supply and demand after events such as trips at power stations, which change system frequency. Five synchronous condensers and five battery sites secured GBP 323 million worth of contracts.

At the time, National Grid offered to pay up to EUR 6,500 ($6,852) per megavolt ampere of short circuit power per year with the successful bids averaging around EUR 4,000/MVA. This created a strong revenue potential besides the already existing reactive power contracts for battery-based energy storage.

Now, Zenobe said that the site is expected to save consumers over GBP 170 million ($216 million) over the next 15 years. 

The GBP 8 million of savings from the Stability Pathfinder assumes that the contract secured for the Blackhillock project will avoid the use of combined-cycle gas turbines (CCGTs) to provide inertia and SCL.

Another GBP 164 million will come from providing balancing services and constraint management to the grid and helping reduce price volatility, cycling the battery two times a day with degradation over the lifetime considered.

Blackhillrock deploys Wärtsilä’s Quantum energy storage system technology and GEMS Digital Energy Platform with SMA grid forming inverters. EDF Wholesale Market Services will be the Route to Market provider for the site, through its market leading trading platform, Powershift, working hand in hand with Zenobē’s battery optimization experts. 

To support the construction of phase one, 200MW/400MWh of Blackhillock, Zenobē secured GBP 101m debt financing via a log-term debt facility from a club of five banks. 

Blackhillock is not the only BESS project Zenobe secured in the Pathfinder 2 procurement. The company will also develop the 300 MW/600 MWh Kilmarnock South site due in 2025 and a 400MW/800 MWh Eccles facility the following year. The gigawatt of batteries should provide 4.4 GVAs (gigavolt ampere seconds) of inertia – 5% to 10% of Britain’s requirement.

“The reason why we were so competitive is that we were able to stack the revenues that we would generate from day-ahead and intraday markets, frequency response services, reactive power, balancing mechanism, and other services in combination with stability services,” says Semih Oztreves, director of network infrastructure at Zenobe, told pv magazine in 2023. “When you stack these services up, you can provide stability services almost at one tenth of what it would cost to provide it exclusively. Stability services are an additional revenue stack without a lot of additional capex (capital expenditure) and opex (operating expenditure). It’s about utilizing your BESS to the maximum.”

At Zenobe, for instance, stability contracts account for only 10% of battery site revenue.