Artelys led the Assessment of Policy Options for Securing Inertia for the European Commission

The European Commission’s Directorate-General for Energy (DG ENER) selected Artelys (leader), Trinomics, and Tractebel ENGIE to study solutions for ensuring the future frequency stability of the European power system. The study report was published in August 2025 by DG ENER. 

This study analyses the role of inertia and its evolution in the context of asynchronous renewable energy deployment. This work establishes a shared understanding of inertia’s role in power system stability. 

Inertia plays a key role in frequency stability of the electricity system

The fastest reserves and defence plans require a few hundred milliseconds to activate. If frequency or Rate of Change of Frequency (RoCoF, frequency’s derivate) exceed critical thresholds during this interval, the system risks collapse (blackout) due to the tripping of assets for their own protection. 

Inertia immediately limits RoCoF, independently of any control system, thereby preventing critical RoCoF levels from being reached before any remedial action can take place. 

Workshop Assessment of Policy Options for Securing Inertia – May 6, 2025

Grid inertia is set to decline sharply in the long term without intervention

Historically, inertia relied on the natural adjustment provided by extracting power from the kinetic energy of synchronous machines, stored in rotating machines.

With the energy transition, an increasing share of assets are connected to the grid via power electronics inverter-based resources (IBRs: photovoltaic power plants, wind turbines, batteries, …) and account for a growing proportion of instantaneous generation, replacing synchronous thermal generation. These assets are traditionally equipped with grid-following inverters and thus do not provide inertia (although grid-forming technologies associated to energy storage can). 

A significant decline in system inertia is therefore anticipated across the European power system around 2030 as analysed by ENTSO-E, with needs increasing towards 2040-2050. 

Workshop Assessment of Policy Options for Securing Inertia – May 6, 2025

Securing adequate inertia levels is a technical, regulatory and economic challenge of growing importance as Europe undertakes its energy transition

Defining the framework for inertia service provision is thus necessary for establishing the long-term foundations of the European power system’s future resilience. To this end, it is necessary to:

Assess the evolution of the European power system’s inertia requirements based on the risk levels deemed necessary to cover, and define inertia targets to securely integrate IBRs into the grid in the short- to long-term; 

Establish common parameters for inertia products in the short-term, for instance through the revision of the Requirements for Generators (RfG), in a technology-neutral manner; 

Plan inertia provision and local stability services (voltage and short-circuit levels) in an integrated manner, as solutions can be shared; 

Examine the costs, benefits, and limitations of regional inertia exchanges for the medium-long term.

Upper-bound estimates for the long-term cost of providing inertia services reach up to €4 billion per year, though significant uncertainties remain, and solutions may prove less costly. 

Enabling renewable assets and storage to effectively and rapidly contribute to maintaining the European power system’s inertia, as well as to delivering local system services, is key. 

The report contains an in-depth analysis of inertia, based on a literature review organised by Artelys and feedback from stakeholders obtained through a webinar and interviews

These analyses notably covered the challenges and risks associated with frequency stability in the electricity system, the definition of inertia, the specification of the physical quantities required to ensure this stability, the fundamentals determining inertia requirements and the definition of associated services. Artelys also analysed the foreseeable evolution of inertia requirements with the energy transition, as well as the existing inertia and fast reserve markets. 

Discover the full report here.