G for Grid Forming

In the context of the energy transition and the progressive decarbonisation of the national electricity system, the grid will be powered more and more by systems based on renewable energy sources. This is an essential step towards making the electricity sector more sustainable in the long term. However, the increased use of renewable energy to produce electricity brings with it certain technical complications, particularly in relation to the stability of the electricity grid. Non-programmable renewable sources, like solar and wind power as well as battery storage systems, do not produce electricity directly in the “format” used by the electricity grid. For this reason, they are connected to the grid through electronic devices called inverters.

These inverters serve to transform direct current (DC) — which may be generated by solar panels or stored in batteries, for example — into alternating current (AC), which is the type of electricity used in the grid, as well as in domestic and industrial systems. Essentially, alternating current is the standard for the distribution of electricity because it can be transported efficiently over long distances, and can be easily adapted to different voltage levels (high, medium or low) as needed.

Without this conversion from direct to alternating current, the electricity produced or stored could not be entered into the grid or used in ordinary electrical systems. By allowing this conversion, the inverters actually make it possible to integrate the energy produced by renewable sources like solar and wind power into the electricity system.

But there’s a but. The inverters most commonly used at present are the "grid-following" (GF) type, which work only when they are connected to an electricity grid which is already active, adapting to the frequency and voltage already present on that grid. In other words, they simply “follow” the lead of the existing conditions. This trait is a limitation, as it means that Grid-Following inverters alone cannot guarantee the safe and balanced functioning of the grid in the event of a problem (for example, a blackout). This is why the electricity grid is still largely reliant upon conventional thermoelectric power substations to ensure the stability and security of the system.

But these facilities in turn must rely upon fossil fuels in order to work, contributing to greenhouse gas emissions and, more generally, to the climate crisis. This dependence on traditional power substations is one of the main challenges for the energy transition, as it means that despite increasing the proportion of renewable energy in the system itself, it remains necessary to avail of traditional systems in order to guarantee grid stability.

For this reason, technological innovation and research in the electricity sector have concentrated in recent years on the development of a new generation of inverters, known as "grid-forming" (GFM) inverters. Unlike conventional GF inverters, GFM inverters do not simply follow the existing grid, but are able to actively set frequency and voltage, behaving similarly to traditional generators. This capacity makes them particularly suitable for guaranteeing the stability and reliability of the electricity system.

Although Grid-Forming technology is one of the most promising solutions in paving the way towards a stable and secure electricity grid based on renewable sources, it remains in the early stages of widespread implementation. In recent years, the technology has undergone experimental tests and studies conducted in various research laboratories. Yet the number of actually operative systems around the world which use Grid-Forming inverters stably integrated into the national electricity system remains low, for technical, regulatory and economic reasons.

Italy has recently taken significant strides in this arena thanks to Terna, which has put the nation’s first battery storage system using Grid-Forming technology into operation. The system has been installed and tested at the Storage Lab, the experimental laboratory dedicated to electrochemical storage systems, located within the electrical substation at Codrongianos, in Sardinia.

The project grew out of an innovation initiative more than three years ago. A stage of analysis and development was followed by the launch of testing conducted in the field. Thanks to the results, it will be possible to assess the functions of this technology with greater clarity. This is an extremely important advance, because Grid-Forming technology is considered crucial to the sustainable development of the electricity transmission grid.

«Grid Forming has become a topic of conversation within the context of the OSMOSE project, which stands for Optimal System-Mix Of flexibility Solutions for European electricity, part of the Horizon 2020 programme. Terna has played a crucial role as the leader of one of the most complex demonstrators, providing us with the opportunity to analyze and investigate the topic in greater detail both within the company and with our project partners. Thanks to the support of our colleagues who deal specifically with the monitoring, control and defence of the electricity system, the next step was to launch a fully fledged project line dedicated to Grid Forming, which has now reached a more practical stage», explains Luca Orrù, Innovation Roadmap & Technologies Manager at Terna’s Innovation Factory.

Moreover, in order to assess the maturity level of Grid Forming, one of the projects within Terna’s wider initiative of Energy System Innovation (ESI), the company led by CEO Giuseppina Di Foggia conducted a market survey aimed at industrial producers in the sectors of BESS (battery energy storage systems) and RES (renewable energy sources). 17 economic operators responded, covering around 60% of market players. In general, the survey revealed significant interest from the main players active in this area.

In addition to exploring Grid Forming with stakeholders, Terna — which has been actively engaged with the topic for years — has carried out activities ranging from collaborating with international grid operators interested in the technology to visiting the main systems currently in operation, in addition to the development of models and experiments in the field.

«These impressive results have been achieved thanks to close collaboration between Innovation and Dispatching, which pooled different skills and experiences for their mutual benefit», observed Giuseppe Lisciandrello, Terna’s lead person on the project and a member of the Innovation Factory System Operator team. «The activities of the work group encompass a variety of directions and initiatives. Based on the evidence gathered both during experimentation at the Storage Lab in Codrongianos and through the market survey, it will be possible to understand the limits and potential of a technology which, in the near future, will play a crucial role in the sustainable development of the electricity transmission grid».