From its creation, the mission of Energie de l'Ouest-Suisse (EOS), founded in 1919 by the electricity companies of Western Switzerland as a limited company, was to exploit the hydropower of the region rationally and intensively.

EOS milestones – a chronology

2006: Completion of the contracts relating to the purchase of the Motor Columbus shares of UBS following the authorization obtained from the Swiss and European competition authorities at the end of February 2006.

2005: Pôle Suisse Occidentale: EOS Holding is part of a majority-Swiss consortium acquiring the 55.6% UBS share of Motor-Columbus with a view to subsequently merging Atel and EOS.

2002:

• 26 March – Incorporation of EOS Holding, the result of a profound reorganization of EOS, whereby the company becomes a strategic holding company, structured on the basis of its core businesses, with a mission to operate and consolidate the key operations of electricity generation, transmission, marketing and sale in Switzerland and abroad

• 25 June – creation of HYDRO Exploitation SA, the company mandated by EOS, Grande Dixence SA and FMV SA to operate their hydropower facilities
  

1993-1998: Construction of the complementary Cleuson-Dixence scheme, the capacity increase enabling twice as much of the water stored at Dixence to be turbined. The scheme comprises a new water intake in the Grande Dixence dam, collecting works, a steel-lined shaft and the Bieudron powerhouse.

from 1974: Construction of the 380 kV very high voltage network of Western Switzerland with a view to interconnection with the major European grids. However, completion of the projects is much delayed by objections and red tape.

1969-2005: From CEG I to Renov CEG, 35 years of change and development at the Dispatching Centre (Centre d'Exploitation et de Gestion – CEG).

• 2005 - installation of SCADA, a system with the capacity to manage an almost unlimited number of data items

• 1972 - establishing of a remote control system to operate the hydropower machinery and most of the circuit breakers and earthing switches from Lausanne

• 1970 - establishing of a digital data transmission system

• 1969 - introduction of the electromechanical coder that replaced manual meter reading and telephone transfer of the readings to Lausanne

1963-1972: Building of the pump turbine hydropower scheme at Hongrin-Léman. Pumping water from Lake Geneva into the Hongrin reservoir at off-peak times and sending the water back through the turbines during heavy grid loading periods means that the excess energy generated at the Vouvry thermal power plant and by the Swiss nuclear power plants can be used to the full.

1963-1965: Vouvry thermal power plant (CTV) at Chavalon, a rocky spur dominating Vouvry; a conventional thermal power plant is built with two boilers, two turboalternator units each with a capacity of 150 MW, four cooling towers and a 10.5 km pipeline from the oil refineries at Collombey.

1951-1961: Construction of Grande Dixence, the highest gravity dam in the world. A more than 100 km network of tunnels brings water to Lake Dix from most of the glaciers east of Dix Valley, forming a catchment area of 420 km2. The first Dixence dam and its reservoir of 50 million m3 of water disappears, submerged beneath the additional 350 million m3 of water stored behind the new dam built 500 m downstream of the old one.

1950-1953: Beginnings of a Western Switzerland 220 kV high-voltage grid. Commissioning of the Mörel-Simplon-Italy (1952) and Chandoline-Mörel (Upper Valais) (1953) lines.

1947-1952: EOS, together with Lonza S.A., founds its first joint-venture: Salanfe SA. Construction of the dam at the entrance to the Salanfe plateau, at the foot of the Dents du Midi mountains. Commissioning of the underground power plant at Miéville (Vernayaz).

1930-1944: Expansion of the 130 kV grid and interconnection with France and German-speaking Switzerland.

1929-1935: Construction of the Dixence-Chandoline hydropower complex, the biggest storage facility yet built, intended to supply energy to regulate the grid in French-speaking Switzerland.

1927-1929: Completion of the Fionnay-Champsec scheme. for the first time, EOS is a hydropower plant builder.

1924-1927: Connection of power plants in canton Valais to consumption centres in western Switzerland; construction of the Romanel and Vorziers transformer plant (1925)

1922: Energy production begins: EOS buys the Martigny-Bourg electricity generating station and its back-up plant at Fully (storage facility, which for a long time boasted the world’s biggest gross head of water at 1650 m), and the concessions and capital equipment works in progress for the Dranse power facility between Fionnay and Champsec in Bagnes Valley.

1920: Construction of the 130 kV line between Pierre-de-Plan (Lausanne) and Chèvres (Geneva), the first part of the high-voltage grid (provisionally operated at 65kV) of French-speaking Switzerland, enabling excess energy to be routed to Geneva from Services industriels de Lausanne and Société Romande d'Electricité.

1919: A majority of local and regional electricity companies in Western Switzerland founded EOS at the instigation of Jean Landry, its future Chairman and CEO. According to its articles of association, “the purpose of the company is to ensure the rational and intensive use of the hydropower resources of Western Switzerland. It is to buy energy from and sell it to the participating electricity power stations or to other companies, and to that end shall construct and operate a major electricity transmission and distribution grid,...”