^{Aerial view of Europe’s largest battery site, located in Blackhillock, Scotland. The site began commercial operations in March 2025 (photo: Zenobē)}

When a coal or gas-fired power station closes, the electricity it generated can increasingly be replaced by wind farms, solar parks and batteries. What does not automatically reappear are the invisible grid-stability services provided by its enormous rotating generator.

That spinning mass helps keep an electricity grid at a stable frequency. It resists sudden changes, supports voltage and contributes current when faults occur. Remove enough conventional generating plants and the grid can become more sensitive to disturbances—even when it has ample renewable electricity available.

Grid-forming inverters offer a possible answer. Through a combination of power electronics, sensors and control software, batteries and renewable plants can begin to provide some of the stabilising behaviour once delivered mechanically by fossil-fuel turbines.

The technology is already moving into commercial infrastructure. In March 2025, Great Britain’s first grid-forming battery began operating at Blackhillock in Scotland. By summer 2026, seven units from the second phase of the National Energy System Operator’s Stability Pathfinder programme (a mixture of grid-forming batteries and synchronous condensers) were live, with the remaining units expected to follow by the end of the year.

So can a renewable electricity grid remain stable without relying on the spinning turbines of conventional power stations?

Why renewable grids lose physical inertia

Electricity grids must maintain a near-constant balance between generation and demand. In Europe, that balance is reflected in a nominal system frequency of 50 hertz.

When a large generator suddenly fails, supply falls below demand and the frequency begins to drop. Traditional power stations provide an immediate buffer because their heavy turbines and generators continue rotating. The stored kinetic energy slows the initial rate of change, giving grid operators and other power plants time to respond.

This physical inertia has long been an automatic feature of the electricity system. Nobody had to instruct a turbine to possess mass.

Solar panels produce no rotating inertia. Wind turbines clearly do rotate, but modern machines are generally connected to the grid through power-electronic converters. These decouple the mechanical rotation of the blades from the electrical frequency of the grid, so wind turbines do not automatically respond like conventional synchronous generators.

Most existing renewable plants and batteries use grid-following inverters. They measure the voltage waveform already present on the network, synchronise with it and inject current accordingly. This works well when large power stations or other equipment are maintaining a strong reference signal.

Now imagine a large generator suddenly disconnecting. Frequency begins to fall, but thousands of conventional renewable inverters are designed to follow the grid rather than establish it. As voltage and frequency become less stable, those inverters may have greater difficulty maintaining synchronisation and responding reliably.

In a weak or low-inertia grid, disturbances can produce rapid frequency movements, voltage instability or unwanted interactions between multiple inverter control systems. Grid operators may then keep gas plants running partly for their stabilising properties, even when their electricity is not otherwise needed.

Grid-forming inverters are intended to remain a stable reference during precisely this kind of disturbance.

How grid-forming inverters work

A grid-forming inverter behaves more like a controlled voltage source. Rather than waiting for an external voltage waveform to follow, its software maintains an internal voltage reference and adjusts the inverter’s output when external conditions change.

When connected to a battery, the inverter can draw on stored energy to provide a rapid burst of active power if frequency falls. It can absorb power when frequency rises, support voltage with reactive power and help damp oscillations.

Some systems use a virtual synchronous machine control strategy. Mathematical models reproduce aspects of the behaviour of a rotating generator, including its response to changes in frequency and electrical angle. The inertia is synthetic rather than mechanical, but it can be tuned through software.

That does not make grid-forming batteries electronic replicas of power stations. Conventional generators can produce several times their rated current during a fault. Inverters are generally restricted to a much smaller amount above their normal output because of the physical limits of their semiconductor components.

These different fault characteristics can also affect the protection equipment that detects faults and disconnects damaged parts of the network.

The battery must meanwhile maintain sufficient charge and spare power capacity to respond in either direction.

Grid-forming controls can nevertheless react very rapidly and potentially combine several grid services in one installation. A battery can store surplus electricity, supply power during periods of high demand and support the network when a fault or sudden imbalance occurs.

In some configurations, grid-forming inverters can also provide black-start capability: energising part of a dead network without first receiving a stable external supply.

Scotland becomes a proving ground for grid-forming batteries

The Blackhillock battery provides the clearest European demonstration of how grid-forming technology is becoming commercial infrastructure.

Owned and operated by battery specialist Zenobē, the site’s first phase provides 200 megawatts of power and 400 megawatt-hours of storage. A second phase is intended to bring the project to 300MW and 600MWh.

Finnish technology group Wärtsilä supplied the energy-storage system and its GEMS digital energy-management platform. German inverter manufacturer SMA supplied 62 medium-voltage power stations equipped with battery inverters and the grid-forming control system.

SMA says its equipment can provide 116 megavolt-amperes of short-circuit contribution and 370 megawatt-seconds of inertia. In practical terms, the first figure describes the battery installation’s contribution to strengthening the network during a fault. The second indicates the scale of its inertia-like response when frequency changes suddenly.

The project completed Britain’s compliance process for grid-forming equipment before entering operation.

The commercial model is as significant as the engineering. Blackhillock is not providing stability as an incidental side effect. Zenobē holds a long-term contract with the National Energy System Operator to deliver it as a paid service.

Under the second phase of the Stability Pathfinder programme, the operator awarded ten contracts worth £323 million: five for grid-forming batteries and five for synchronous condensers. The latter are rotating machines similar to generators but operate without producing electricity.

Together, the projects were contracted to provide 11.55 gigavolt-amperes of short-circuit level in Scotland and 6.75 gigavolt-ampere-seconds of inertia across Great Britain. The operator estimated that the ten-year contracts could produce approximately £500 million in savings compared with alternative ways of securing the same services.

Zenobē, Wärtsilä and SMA are also working on a 300MW battery at Kilmarnock South, another Scottish Stability Pathfinder site. For these companies, grid support is becoming an additional revenue stream alongside energy trading and conventional balancing.

Which companies are developing grid-forming inverter technology?

Several of the world’s largest electricity-equipment suppliers are developing their own grid-forming systems.

Hitachi Industrial Equipment Systems placed three grid-forming inverters into operation at its Narashino factory in Japan in 2025. The units coordinate solar generation and battery storage in an alternating-current microgrid. If the external electricity supply fails, the system is designed to maintain power to selected equipment, including water pumps and internal communications.

Hitachi Energy is taking the technology into larger power-system equipment. It offers grid-forming controls across battery installations, static synchronous compensators and high-voltage direct-current systems, with functions including voltage regulation, rapid frequency response and operation in weak or isolated grids.

Siemens Energy and GE Vernova are also integrating grid-forming, synthetic-inertia and black-start functions into commercial battery and converter platforms. These offerings show how the capability is becoming part of mainstream power-equipment portfolios, although a product specification is not the same as demonstrating performance across an entire renewable-heavy grid.

Australia has become another important testing ground because some regions combine large amounts of wind and solar with relatively weak transmission networks. Neoen’s 300MW/450MWh Victorian Big Battery, built with Tesla Megapacks, is being converted from grid-following operation using Tesla’s Virtual Machine Mode.

The retrofit has generated practical lessons about firmware, fault ride-through, inertia settings and regulatory modelling. As of April 2026, however, the project was still in the later stages of the application required to move formally into grid-forming operation.

These projects show that grid-forming inverter technology is no longer confined to simulations and small pilots. Yet deployments remain concentrated in markets where grid operators have defined technical requirements and created a way to pay for stability.

Software-defined grid stability introduces new dependencies

Replacing physical behaviour with programmable control brings advantages. Synthetic inertia can respond rapidly and be adapted to local grid conditions. A battery can perform several functions without consuming fuel or keeping an otherwise unnecessary thermal plant running.

It also makes electricity-system stability increasingly dependent on software design.

Grid operators need to know how different manufacturers’ inverters will behave during the same disturbance. Hundreds of systems responding simultaneously could interact in ways that are difficult to predict from individual tests. Control settings must continue working as network conditions change, and firmware updates may alter the performance of infrastructure expected to remain in service for decades.

There is also no single grid-forming algorithm. Virtual synchronous machines, droop control and oscillator-based approaches can all create grid-forming behaviour, but their responses are not identical. Common testing procedures, technical definitions and grid-code requirements are still evolving.

Britain’s system operator currently calls grid-forming batteries an emerging technology. It allows qualifying assets to compete for stability contracts and is considering whether grid-forming capability should eventually be required from new plants, but has not imposed a universal mandate.

Nor can advanced inverters solve every grid problem. They do not build new transmission lines or remove physical congestion from overcrowded networks. Europe will still need cables, substations, interconnectors, flexible demand and several forms of storage.

Grid-forming technology addresses a more fundamental problem: ensuring that the electrical system remains stable enough for all those assets to operate.

A renewable grid may therefore function without relying on the synchronously connected turbines of coal and gas plants. That does not necessarily mean eliminating every rotating grid asset: synchronous condensers and some conventional generators may continue to support the system alongside inverter-based technologies.

But the grid will no longer need to obtain all its stability from machines that burn fuel to keep spinning.

An increasing share of that responsibility will sit inside the power semiconductors and control software of an inverter—machinery with no rotating mass, programmed to provide some of the behaviour the grid once received automatically.

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