Coo: recognised expertise in energy storage

Coo power station has played a core role in ENGIE Electrabel’s energy mix for over 30 years. It is vital to covering the growing need for flexibility triggered by the energy transition, which ENGIE would like to lead in Europe. An extension of Coo is currently being studied.

ENGIE Electrabel Coo jbcConstruction of the Coo power station began in 1967; it took place in two phases and aimed to guarantee the optimum integration of nuclear generation onto the Belgian grid. The first phase, which ended in 1972, resulted in the commissioning of three turbo gensets with a total capacity of 474 MW (Coo 1). The second phase (the installation of three additional gensets with a total capacity of 690 MW) came to an end in 1979 (Coo 2). The lower reservoir was left as it was, with two dams to cut off the natural meander of the Amblève. Two artificial lakes that make up the upper reservoirs were built at the top of the plateau.

All other facilities (i.e. the two penstocks supplying water from the upper reservoirs to the power plant and the machine room housing the six turbo gensets) were designed to be built underground.

Coo power station has played a core role in ENGIE Electrabel’s energy mix for over 30 years and actively helps to cover the growing need for flexibility triggered by the energy transition.

A simple and efficient mechanism

The operation of a hydroelectric power plant is very simple: running water (kinetic energy) turns a turbine (mechanical energy) which then turns a generator. The generator transforms the mechanical energy into electrical energy. Coo’s gensets are reversible, meaning that they can work either in turbine mode or in pump mode by reversing the system.

Pumps shift the water into the upper reservoirs during periods of low energy consumption (e.g. during the night and weekends). In contrast, during peak consumption periods the water is poured from the upper reservoirs to the lower reservoir via the machine room housing the turbines and generators, which produce the electricity needed.

When in turbine mode and running at maximum capacity, almost 500,000 litres of water from the upper reservoirs pass through the turbines every second, with a volume of water equal to that of an Olympic swimming pool passing through every five seconds. Maximum capacity can be achieved in under two minutes. The power station is completely controlled by operators at a dispatching centre in Brussels; they decided when and how the various sets should run.

The overall yield of the power station is approximately 75%, meaning that 75% of energy extracted during off-peak hours is restored during peak hours.

Flexibility: a key to grid stability

Renewable energies have taken off in recent years. ENGIE Electrabel is also Belgium’s top generator of green energy. These energies help to cut the sector’s carbon emissions but are intermittent by nature, as they only generate energy when there is wind or sun. As such, energy generation can fluctuate considerably from one moment to the next, which may have a major impact on grid stability. The need for flexibility and storage is growing as a result of the energy transition and this trend will only become more pronounced in the years and decades to come.

Pumped-storage accounts for 99% of electricity stored worldwide and is currently the only way to store electricity on a large scale. In the long term, batteries combined with increasingly decentralised means of generation will doubtless offer a partial solution, though this will not eliminate the need for pumped-storage power stations, which are currently the main technology used worldwide as well as being one of the most mature.

Although balance on European grids is the responsibility of system operators (Elia in Belgium), ENGIE Electrabel helps by operating diversified, local and flexible generation facilities. ENGIE Electrabel anticipates as far as possible the intermittent nature of solar and wind power by constantly analysing temperatures, wind speed and sunshine in Belgium and neighbouring countries to guarantee balance between its customers’ electricity supply and demand.

Coo power station plays a key role in this balance. Initially planned as a complement to nuclear power, it then became essential to managing the intermittent nature of wind and solar power. The turbines can quickly be started up at any time to offset a sudden drop in generation (e.g. during the unexpected shutdown of a power plant) or to absorb excess electricity. More specifically, Coo can virtually instantaneously stand in should the biggest unit in Belgium’s generation infrastructure trip. ENGIE Electrabel utilises this flexibility to optimise its electricity generation, while Elia uses it in its ancillary service contracts. Lastly, Coo can also be mobilised to restart the Tihange power plant in case of blackout.

Could we see Coo 3 in the future?

Technically the Coo site could be extended, turning it into a key stakeholder in the energy transition and security of supply. A third upper reservoir (Coo 3) could be built and connected to two additional turbines with a total capacity of 600 MW. These turbines could be installed underground or in a new building. This project represents a local investment estimated at €600 million.

ENGIE Electrabel’s teams are currently analysing the feasibility of this project; they are experts in the technology involved and the project itself dovetails with the ENGIE Group’s desire to lead the energy transition in Europe. Nevertheless, rolling out a project of this scale requires a clear and stable regulatory and economic framework in the long term. Some aspects that hinder the development of electricity storage in Belgium have to be considered. Grid prices are one such example. Storage involves both generating and consuming electricity and is therefore doubly hit by, for instance, taxes and surcharges which specifically target this activity that is so essential to preventing blackouts.

Before being able to make a decision about such a capital-intensive investment, it is also essential that ENGIE Electrabel has a more accurate overview of future flexibility needs, the strategy that authorities intend to introduce to satisfy these needs, and the development of alternative storage solutions, especially decentralised solutions.

Requiring an estimated investment of €600 million, the Coo 3 project will have a positive impact on employment in the region, economic momentum, and our competencies and expertise in the strategic field of energy storage.

Leader of the energy transition

ENGIE wants to lead the energy transition in Europe and to become the benchmark energy supplier in countries experiencing considerable growth. To this end, the Group is speeding up its transformation by taking into account four major factors of the energy transition, namely decarbonisation, decentralised generation, digitisation and energy efficiency.

Renewable energies are one of ENGIE’s strategic priorities, with a view to becoming leader of the energy transition in Europe. As such, the Group plans to double the capacity of its renewable sources of electricity to 16 GW between 2015 and 2025. ENGIE is a global leader with over 20 GW of installed capacity in renewables, almost 20% of its total installed capacity.

ENGIE is innovative in the field of energy storage, which is a key element of the aim to decarbonise the use of energy and decentralise generation facilities through various projects in France, Italy, Germany and Norway. In Belgium, the Group has developed an energy storage competency centre and, through ENGIE Electrabel, operates the Coo pumped-storage power station, which plays a key role in maintaining balance on the grid.

Coo in figures

  • Maximum installed capacity: 1,164 MW for Coo 1 and 2.
  • Total volume of the two upper reservoirs: 8.5 million m³, i.e. 8.5 billion litres.
  • Total volume of the lower reservoir: over 8.5 million m³.
  • Operating time: six hours at full power.
  • Maximum flow: equal to 10 Olympic swimming pools per minute.
  • Time to maximum power: under two minutes.
  • Coo 3:
    • Approximately €600 million in investment at local level.
    • Two 300-MW turbines.
    • An additional upper reservoir holding 5 million m³.
    • Enhanced expertise in the strategic field of storage.
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