Resurgent Technology Can Maintain Grid Stability in the Renewable Era
Renewables are taking over, but they are shaking up grid stability. As fossil fuel plants shut down, we are also losing the vital inertia they provide. The result? A hidden engineering challenge that undermines the reliability of clean power.
By Kristina Carlquist, Head of Synchronous Condenser Product Line, ABB Large Motors and Generators, Sweden
That is why a technology from the last century is making a comeback. Synchronous condensers (SCs) may not seem exciting, but they deliver exactly what today’s renewable-heavy grids need – spinning inertia to keep frequency stable, voltage steady, and the lights on, no matter the wind or sun conditions.
Increased Grid Instability
Fossil fuel plants provided something vital beyond electricity – rotational inertia – the mechanical stability inherent in large spinning turbines. This inertia, also known as kinetic reserve, has historically been crucial for maintaining grid frequency and voltage stability. It acts as a buffer against sudden surges or drops in electricity demand and protects the system from the effect of disturbances.
With renewables now dominating new energy projects, power grids increasingly face instability. While essential for clean power generation, solar panels and wind turbines typically offer no mechanical inertia, leaving grids vulnerable to frequency fluctuations and voltage dips and increasing the risk of disruptions or blackouts. As the proportion of traditional power plants shrinks, maintaining grid stability has become one of the major technical challenges of the energy transition.
Synchronous Condensers Make a Come Back
Against this backdrop, SCs, a technology once considered outdated, are making an unexpected comeback as a critical infrastructure tool. SCs are rotating electrical machines that resemble synchronous generators in their design. But they are neither motors, as they do not drive a load, nor generators, because they do not generate electricity.
Originally widespread in early electricity generation systems going back to the last century, SCs fell out of favour as their main role was performed by power electronics. Now, in a world dominated by renewable energies, the SC’s value is clearer than ever.
Unlike battery storage and electronic-based grid stabilisation solutions, SCs utilise actual spinning masses to deliver immediate frequency and voltage support. With real mechanical inertia at their core, SCs enable power grids dominated by renewable energy to maintain steady frequency, voltage stability, and superior fault protection, responding instantaneously during transient events.
Why Grid Operators are Turning Back
Grid operators increasingly face the challenging task of stabilising and securing electricity networks originally built around inertia-rich fossil fuel plants. They need solutions to manage today’s grid and proven, future-ready technologies that can reliably manage fluctuations and disturbances in renewable-intensive grids for decades.
SCs represent a critical available technology that enables higher penetration of renewables while maintaining the stability and resilience essential to modern electrical infrastructure.
Transmission planners, grid operators, and renewable developers can strategically position SCs at weak nodes or grid edges or directly adjacent to large wind or solar farms.
Stabilising High-Renewable Grids
High wind and solar power penetration, typically connected through inverter-based or grid-following technologies, has introduced significant challenges. Without the intrinsic rotating inertia of traditional generators, grids become ‘weak’, characterised by low inertia, declining fault levels, growing voltage instability, and vulnerability to frequency fluctuations during sudden changes in demand or production.
Inverter-based wind turbines and solar photovoltaics contribute limited or no inertia to the grid. Conversely, SCs consistently deliver stable frequency by injecting or absorbing kinetic energy precisely when the grid needs it, mitigating instability before it becomes critical.
Operators now recognise these rotating machines as uniquely valuable assets for renewable-dominated grids.
Cost-Effective, Long-Term Resilience
SCs can economically fit into existing grid locations or substations, avoiding the need for extensive transmission network rebuilds or expansions. They provide utility operators with a quick-win solution, boosting grid resilience without requiring large-scale overhauls. This advantage translates into crucial savings in investments and timelines, enabling faster integration of renewable projects and rapid improvements in network reliability.
Moving Faster Towards Net-Zero Goals
With national and global net-zero commitments driving aggressive renewable deployment, there is little room for slowing the energy transition. Yet, grid reliability remains paramount; outages or instability would severely dent public confidence in sustainable energy efforts.
SCs enable operators to confidently increase renewable capacity, secure in the knowledge that grid stability is maintained. Offering assured real-time stability, they help accelerate transition towards ambitious renewable-powered targets without sacrificing operational security or system performance.
Proven Capabilities and Complementary Roles
Although new technologies such as grid-forming inverters promise long-term possibilities, they are still in developmental or early scale-up stages, lacking the maturity necessary for widespread adoption. In contrast, SCs are a proven, established technology that is available and ready for immediate deployment.
A good example is the 2023 commissioning of ABB’s turnkey project for Statkraft, Europe’s largest renewable power generator, to help restore the missing system inertia and stabilise the UK power grid. The project features two ABB high-inertia SC systems installed at the Lister Drive Greener Grid Park in Liverpool. The two units provide a total of more than 900 megawatt-seconds inertia.
Another example is the Faroe Islands, which are relying on SCs to reach an ambitious 100% renewable energy target by 2030. ABB has already installed two SC units for the North Atlantic island group’s power utility, SEV, with a third on the way.
Evolving Grid Roles and Policy Context
As renewable energy capacity grows rapidly, many countries are adapting their requirements for new power generation projects. For instance, Australia’s electricity market now explicitly considers inertia provision in its grid connection requirements. Similarly, the UK National Grid’s innovative Pathfinder tenders specifically solicit grid stability solutions, highlighting the urgency of addressing inertia deficits and reactive power shortfalls as renewables accelerate.
This regulatory push is elevating SCs from a niche option to a widely accepted and necessary technology. SC deployments are gaining momentum because they offer predictability, robustness and a long lifetime, often reliably functioning for 30 to 40 years or more. Far from being limited to developing nations or weak-grid regions, SCs are now embraced globally.
A Resilient Grid Foundation
SCs might not capture headlines or inspire the same excitement as ambitious battery storage initiatives or futuristic grid-forming inverter technologies but their role remains essential. Quietly and reliably operating in the background, SCs stabilise renewable-heavy grids by passively contributing inertia, reactive power support, and fault current support.
Advances in remote monitoring, digital diagnostics, and smart control technologies are increasingly applied to SC installations, further enhancing their integration into intelligent grid management systems. As wind power capacity expands, SCs offer a solid, technically sound baseline on which to layer advanced grid controls and energy storage solutions.
Biography of the Author
Kristina Carlquist is Head of Synchronous Condenser Product Line at ABB Large Motors and Generators. She has extensive experience in the power industry and leads ABB’s efforts to enable stable, renewable-heavy grids. With a background in engineering and leadership, she is passionate about driving the transition towards sustainable and resilient energy infrastructure.
