A U.K. battery station in Scotland proved crucial during a March power grid event, showcasing the potential of advanced energy storage.
SCOTLAND – A massive grid-scale battery in the Scottish Highlands sprang into action in March, just 11 days after its startup, when a generator in northern England unexpectedly shut down. The sudden loss of 1,877 megawatts of supply caused the grid’s 50-hertz frequency to plummet below its 49.8-Hz operating limit in a mere 8 seconds.
The 200-MW battery station responded within milliseconds, injecting power to stabilize the grid and prevent a wider collapse. This event marked one of the world’s first instances of a grid-scale battery being specifically commissioned for such a grid-stabilizing role. Traditionally, the inertia from spinning rotors in fossil-fuel generators provided this buffer against rapid frequency and voltage swings.
Batteries Mimic Generator Inertia
Table of Contents
The lithium battery storage site in Blackhillock, Scotland, the largest in Europe, simulates inertia using sophisticated power electronics. In a notable innovation, this battery site can also supply short-circuit current in response to grid faults, much like conventional power generators.
Four additional battery sites of this type are currently under construction in Scotland.
Grid-Forming Inverters Lead the Charge
These advanced grid-forming inverters are key to the batteries’ stabilizing capabilities. They convert direct current from lithium batteries into alternating current for the grid, and vice versa when charging. Unlike most grid-scale inverters that follow the grid’s frequency and voltage, grid-forming inverters maintain their own rhythm and can react faster than traditional generators.
“These grid-forming inverters that we’re installing in Scotland—nobody is doing that,” stated Julian Leslie, chief engineer and strategic energy planning director for the National Energy System Operator (NESO) in Warwick, England. Andy Hoke, an expert in grid-forming technology and principal engineer at the U.S. National Renewable Energy Lab, described Scotland’s battery additions as “super exciting projects” that push technological boundaries.
The UK’s Path to Gas-Free Operation
NESO is relying on these grid-forming batteries to help achieve its 2025 goal of demonstrating that the United Kingdom can operate without its crucial gas-fired power plants. The U.K. retired its last coal power plant last year and aims to prove its grid’s resilience without gas by the end of this year.
“By the end of the year we’ll have a couple of hours with zero carbon operation, which is going to be amazing,” Leslie said. This would represent the world’s largest demonstration of a fossil-free grid operation.
Did you know? The Blackhillock battery site alone is estimated to save consumers £309 million (US $418 million) over 15 years.
This transition isn’t just about environmental goals; increased stability from power electronics allows for greater integration of solar and wind power, minimizing the need to curtail their generation. London-based Zenobē, the grid battery operator for three of the new Scottish sites, provided the savings estimate for Blackhillock.
Scotland’s Decarbonization Challenge
Scotland is at the forefront of the U.K.’s grid decarbonization efforts. It has already phased out coal and gas plants. Its sole remaining nuclear plant, Torness, is slated for shutdown by 2030. Following Torness’s closure, Scotland’s grid stability will rely on its few small hydropower plants, whose rotating machinery has historically provided essential inertia. The country’s future energy mix heavily features wind and solar power, which typically use grid-following inverters that offer limited stability benefits.
To address this, grid operators globally are reinforcing their systems with synchronous condensers—standalone generators kept spinning to provide stored kinetic energy during grid disturbances. The Baltic states, for example, procured these stabilizers before transitioning their grid synchronization from Russia to Europe.
NESO, however, has adopted a proactive approach. Instead of solely relying on synchronous condensers, it sought innovative solutions for stability. Grid-forming batteries emerged as a strong contender in NESO’s 2022 tender. The £323-million ($427-million) package of winning bids included Scotland’s advanced grid-scale batteries and five synchronous condensers.
Innovation in Short-Circuit Current
A key innovation of these grid-forming batteries is NESO’s requirement for them to provide short-circuit current, mimicking synchronous generators. During grid faults, like those caused by falling trees, synchronous generators release a surge of current that supports voltage and triggers protective relays to isolate the affected segment.
Replicating this with power electronics is challenging. Grid-forming inverters maintain their own voltage and frequency by supplying necessary current. When voltage drops, their controllers allow more current through transistors. However, high currents generate heat that can damage power electronics. Inverters typically operate with only a 10-20% current margin above their rating, unlike synchronous generators which can surge up to 700% during a fault.
While adding more transistors can increase current capacity, it’s expensive for transmission-level converters. SMA Solar Technology, the German inverter producer for Blackhillock, developed a more cost-effective solution by leveraging the short duration of short-circuit currents.
Aaron Gerdemann, a business development manager at SMA, explained that Blackhillock’s inverter is programmed to deliver a 140-millisecond pulse at 250% above nominal current, as required by NESO. Afterward, the device reduces output to allow its circuits to cool.
Can Power Electronics Fully Stabilize the Grid?
Semih Oztreves, Zenobē’s global director of network infrastructure, predicts that grid-forming batteries will dominate the stability market due to their multifunctionality. While synchronous condensers often sit idle, Zenobē’s batteries generate revenue daily through activities like energy arbitrage—buying low and selling high.
However, the real-world performance of grid-forming batteries in providing short-circuit current remains untested. Doubts persist about how transmission relays will respond to these digitally controlled current surges. A report last year for Australian grid operator Transgrid cautioned against over-reliance on grid-forming inverters for short-circuit current, citing “high to very high risk.” Transgrid subsequently announced plans for both synchronous condensers and grid-forming batteries to strengthen its grid.
Given the high stakes, Hoke suggests that maintaining a mix of synchronous condensers might be the prudent approach, even if not the most cost-effective. “It might not be the cost-optimal solution, but it may be the wise solution,” he concluded.
From Your Site Articles
Related Articles Around the Web
