The Terna Group

Terna is the largest independent transmission system operator (TSO) in Europe and the seventh largest in the world in terms of kilometres of lines managed.

The Company’s registered office is in Rome and it is the main owner (99%) of the Italian national transmission grid (NTG), with more than 56,000 kilometres of high-voltage lines (more than 62,000 kilometres of three-phase conductors), 383 transformation substations, and 18 lines interconnecting with foreign grids as of December 31, 2009.

It owes its name to the set of the three conductors or groups of conductors – in Italian, a terna – used to transport each of the three phases of the three-phase electrical field in alternating-current grids.
In Italy, Terna is the government-licensed transmission system operator, responsible for transmitting and dispatching electricity on the high- and ultra-high-voltage grid throughout the country.

Terna is also responsible for the planning, construction, and maintenance of the grid.

After the sale of its shareholding in Brazil in November 2009, the structure of its equity interests is as follows:

The Terna Group


As of December 31, 2009, the Terna Group comprised: 

  • Sun Tergrid S.p.A. (formerly InTernational S.p.A.) and TELAT S.r.l., directly controlled, 100%-owned Italian companies;
  • RTR S.r.l., an Italian company indirectly controlled through SunTergrid S.p.A., which owns 100% of it;
  • two companies,  measured using the equity method, in which Terna S.p.A. has an equity interest: CESI S.p.A., an associate company (30.91% equity stake), and Elmed ÉTUDES Sàrl, a jointly-controlled company (50% equity stake).

CESI is the leading company in the market of testing and certifying electro-mechanical equipment and consultancy on electric systems. It covers all the stages of the life cycle of the electric system and offers companies therein (generation, transmission, and distribution), manufacturers of electrical and electronic equipment, large consumers of electricity, and local and national governments a complete range of services aimed at solving problems connected with the production processes of the entire electricity industry.

ELMED ÉTUDES is the company entrusted by Terna and the Tunisian electricity company STEG with the feasibility study on the Italy-Tunisia undersea interconnection.

In order to make the best use of its resources and maximise the profitability of its assets, in 2009 Terna instructed its subsidiary SunTergrid to undertake the construction and management of photovoltaic plants with about 100 MWp of total power on plant-free land next to transformation stations, leased from the Parent Company. At the end of the year, the new business was only minimally operative, with only a single plant in operation, in Ragusa. The production of electricity was absolutely negligible in 2009 and will be significant only beginning in 2010. The energy produced will be withdrawn and exploited by GSE S.p.A., according to the dedicated-withdrawal mechanism provided for by the energy account, thus ensuring Terna’s complete neutrality with respect to the sale of the energy on the electricity market.

In December 2009, SunTergrid set up a new company, Rete Rinnovabile S.r.l. (RTR S.r.l.), which will handle all the projects for photovoltaic production that will become operative by the end of 2010.

The corporate structure selected, which will be subsequently alienable, satisfies both the requirements of functional and accounting separation from the Parent Company and compatibility with Terna S.p.A.’s bylaws and license, as well as with the provisions of Legislative Decree no. 79/99 (the so-called “Bersani Decree”).

Today’s Terna is the result of the liberalisation of the electricity industry, which was begun in 1999, when the role of TSO was assigned to GRTN – Gestore della Rete di Trasmissione Nazionale, a government-controlled company. In November 2005, Terna – which already owned almost the entire National Transmissioni Grid – acquired the aforesaid role from the latter, together with the related human and material resources, as established by the Prime Minister’s Decree of May 11, 2004. The reunification of grid ownership (except for residual portions) and management also coincided with Terna’s independence from the Enel Group, to which it had previously belonged.

Size of the organisation as of December 31, 2009


Number of employees

Turnover in millions of euros1,360.7
Total capitalisation - (in millions of euros)5,989.10
km  of lines
underground cable  1,043
underwater cable