Grid Stability Is Becoming a Service in the Renewable Energy Era

WEG Business Development Manager Mark Newman explains how resilience is being restored in changing power systems

As wind and solar power rapidly increase their share of electricity generation across Europe, the retirement of conventional thermal power plants is making grid stability one of the central challenges of the energy transition. This changing generation mix is redefining not only the sources from which electricity is produced, but also how frequency, voltage and overall system resilience are maintained. Mark Newman, Business Development Manager at integrated energy systems manufacturer WEG, examines how system operators are beginning to treat grid stability not as a natural by-product of power generation, but as a distinct service that must be planned, procured and managed.

For decades, grid stability was largely a by-product of conventional power generation. Large synchronous machines inherently provided inertia, reactive power and short-circuit capacity—all essential foundations of a stable and resilient electricity grid. Today, that assumption no longer holds. System operators must instead rethink stability as something that needs to be actively procured and managed, rather than passively inherited.

In this new environment, “stability as a service” is emerging as a defining feature of modern power systems.

From Rotating Mass to Power Electronics

At the heart of this transformation lies the physical structure of power generation.

Traditionally, electricity systems relied on turbines with large rotating masses connected to synchronous generators. These machines naturally provided the system with inertia, supplied high short-circuit currents and helped maintain grid voltage levels.

By contrast, electricity generated from renewable energy sources is largely connected to the grid through power electronic converters. Although these technologies are indispensable for converting and controlling variable wind and solar energy, they do not inherently provide the same grid stability characteristics as synchronous generators.

As a result, grids are becoming electrically “weaker.” Reduced inertia leads to faster and more pronounced frequency deviations. Lower availability of reactive power increases the risk of voltage instability. Declining short-circuit capacity weakens the system’s ability to withstand faults and recover rapidly. Taken together, these changes make grids more sensitive to disturbances and more complex to operate.

This is not a distant or theoretical concern. The consequences of declining system stability are already being felt. A major blackout on the Iberian Peninsula in 2025 affected large parts of Portugal and Spain, demonstrating how vulnerable modern power systems can become when stability margins are stretched. Although the causes of the incident were numerous and complex, it reinforced the importance of maintaining frequency and voltage stability, as well as sufficient system response capability, in a grid increasingly reliant on renewable generation.

In the United Kingdom, wind is already one of the largest contributors to electricity generation, while the share of electricity supplied by renewable sources continues to increase each year. In 2025, renewables generated a record 44 per cent of the country’s electricity, supplying more than 127 terawatt-hours (TWh) in total—the highest figure ever recorded.

Similar trends can be observed across Europe. The International Renewable Energy Agency reports that the region has 934,334 MW of renewable energy capacity. The direction of travel is clear: renewable energy is no longer a supplementary element but lies at the heart of the system. The principal challenge, therefore, is no longer energy supply alone, but system stability.

Defining Stability in a System Undergoing Transformation

To address this challenge, system operators are adapting their approaches. Rather than relying on generation assets to provide stability indirectly, they are defining, valuing and procuring specific services that keep the grid secure and operational. In the United Kingdom, the National Energy System Operator (NESO) has formalised this model by establishing markets for ancillary and balancing services designed to maintain system reliability, effectively operationalising stability as a service.

Five fundamental system requirements lie at the heart of this approach. The first is frequency stability. Electricity systems must operate at a constant frequency—typically 50 Hz in Europe. Any imbalance between supply and demand causes deviations which, if left uncontrolled, can lead to system instability or even widespread blackouts. As system inertia declines, frequency can change more rapidly, requiring faster and more precise intervention. Operators are consequently procuring increasing volumes of active power response services capable of reacting to disturbances almost instantaneously.

The second requirement is voltage control. Maintaining voltage within acceptable limits is vital for the safe operation of equipment and the integrity of the grid. Reactive power plays a central role in this process, but its availability is declining as conventional generators are retired. Dedicated voltage support services that keep transmission nodes within their operational limits, even under dynamic conditions, are therefore becoming critically important.

The third requirement is system strength, encompassing inertia, fault level and overall robustness. A strong system can absorb disturbances, dampen oscillations and recover rapidly from faults. A weak system, by contrast, is more susceptible to cascading failures. As the inherent contribution of synchronous machines declines, system operators are explicitly procuring services that replicate or replace these characteristics, ensuring resilience in a grid increasingly dominated by power electronics.

The fourth requirement is constraint management. As renewable electricity generation expands, power flows across the grid become more complex and less predictable. Whether thermal or stability-related, transmission constraints can limit the ability to move electricity from where it is generated to where it is needed. Managing these constraints requires flexible resources capable of relieving congestion and maintaining secure operation without unnecessarily curtailing renewable generation.

Finally, there is system restoration. Although a total or partial system shutdown is unlikely, the ability to restart the grid safely and efficiently following such an event is vital. Traditionally, this function relied on large conventional power plants equipped with black-start capabilities. Today, new technologies are being developed and procured to fulfil this role in ways that reflect the changing generation mix.

Together, these five fundamental elements form the basis of “stability as a service.” They represent a shift towards a more granular, market-based approach to grid reliability, in which specific capabilities are defined, valued and delivered through a range of technologies.

From Concept to Procurement

This transition is already being reflected in large-scale procurement programmes. NESO’s “Long-term 2029 Network Services” tender, for example, combines the simultaneous procurement of stability, reactive power and network restoration services, illustrating how these markets are developing in both scale and complexity. For technology providers and partners, this represents a clear shift towards long-term, system-level solutions—an area in which WEG is actively involved.

This development is also encouraging innovation in the way stability is provided. Technologies such as synchronous condensers and battery energy storage systems (BESS) are playing an increasingly important role. By closely replicating the characteristics of conventional generators, synchronous condensers can provide physical inertia, reactive power and short-circuit strength.

Meanwhile, according to RenewableUK, the United Kingdom already has more than 6.8 GW/10.5 GWh of operational battery storage capacity. This segment continues to expand rapidly as grid operators turn to flexible, fast-responding resources to support system stability. Battery systems can simultaneously address several power-system requirements by delivering ultra-fast frequency response, synthetic inertia, voltage support and independent black-start capability.

Crucially, these technologies are not merely substitutes for conventional assets. They form part of a broader transition towards a more flexible, dynamic and digitalised energy system. Grid stability is therefore becoming less of an inherent characteristic associated with a single generation technology and more of an outcome achieved through the coordinated integration of different assets, services and system-management solutions.

Building Resilient Power Systems for a Carbon-Neutral Future

Beyond the United Kingdom, this model is being adopted with increasing frequency across Europe. As countries pursue more ambitious decarbonisation targets and raise the share of renewable energy in their electricity systems, the need for clearly defined grid stability services will become increasingly apparent. In response, regulatory frameworks and market mechanisms are evolving to incorporate these services, creating new opportunities for investment, innovation and the development of technological solutions.

However, this transition is not without challenges. Designing effective markets for grid stability services requires a balance between the system’s technical requirements, economic incentives and coordination among the electricity sector’s various stakeholders. It also demands a paradigm shift: grid reliability is no longer regarded as a natural consequence of conventional generation, but as an objective that must be planned, managed and continuously secured.

It is clear that the energy transition has entered a new phase. The central challenge is no longer simply to increase installed renewable energy capacity, but to ensure that the electricity system as a whole remains secure, resilient and capable of meeting the requirements of an increasingly decarbonised energy landscape.

Treating grid stability as a service is not merely a technical concept. It represents a fundamental redefinition of how modern electricity systems operate. As renewable energy generation continues to grow, specialised stability services will play an increasingly central role in securing electricity supplies across Europe.

To learn more about WEG’s synchronous condenser and BESS technologies, and their role in power-grid stability, visit WEG’s website.