4. Low Inertia Systems


The kinetic energy of synchronous rotating machines is crucial for the stability of the power system. Current grid control and backup methods are based on this physical characteristic. In the case of solar and wind power plants, the production is injected into the grid through electronic circuits that have no inertia and therefore do not contribute to grid stability. As a consequence, the massive development of renewable energy solutions and other resources connected by power electronics leads to a decrease in the share of synchronous rotating machines in the electrical system that will cause a change in grid control and backup methods.


Today, the inverters of renewable energies behave in a grid-following way. They synchronise themselves with the grid to produce the desired active and reactive power (depending on the primary resource). Depending on the connection level and requirements, they can “support” the grid by providing certain system services (voltage). European grid codes require some new groups to know how to provide system service frequency which requires grid-forming inverters (and other smart functions: reactive power at night, etc.).

Challenges and opportunities for DSOs

  • What are the critical thresholds beyond which the safety criteria and the collapse mode of the system change?
  • What are the solutions to ensure the stability of the operation of an electrical system with lower inertia?
  • Which solutions are there to restore the system after a generalised incident?

EDSO Considerations

  • In terms of grid stability, in the context of high penetration of renewable sources (partly connected to the distribution grid), the coordination between TSOs and DSOs becomes fundamental.
  • DSOs must undertake an ambitious research and development program to find solutions to operate a low-inertia electrical system with the level of reliability and resilience required. Part of the work will have to be carried out in cooperation with the TSOs.

Last update: 28 September 2023