A huge bright pink tarpaulin sits in the middle of the vast engine room of the Coo hydraulic power station, located on a hill in the Amblève valley, near Liège in Belgium. Underneath lies a brand new rotor weighing around 300 tonnes. In a few weeks, this centerpiece will be installed on one of the six turbines of the factory inaugurated in 1972.
Owned by the French group Engie, this power plant with a power of one gigawatt (roughly the equivalent of a nuclear reactor) is the subject of a major extension project requiring 67 million euros. investments. Objective: increase its storage volume, by expanding the upper basin, and its power by 7.5%, by renewing the machines, to cope with the increasingly significant penetration of renewable energies in the European electricity system, which generates new needs for flexibility.
The Coo power plant is a turbine and pumping station or “STEP” in the jargon. Made up of two upper basins and a lower basin, it allows both to produce electricity using hydraulic energy, but also to store this energy. During peak consumption, in the morning and at the end of the day around 7 p.m., the water goes down from one of the two upper basins to the lower basin where the hydraulic power plant is located. The water travels one kilometer over a drop of 275 meters via a gallery 8 meters in diameter and hits the turbines, which activate a rotor which transforms mechanical energy into electrical energy. “The equivalent of an Olympic swimming pool passes through the turbines every five seconds”, specifies Paul-Etienne Verheven, who manages Engie’s flexible power plants in Wallonia. The device then makes it possible to bring a power of one gigawatt onto the network in just 2 minutes.
Increased demand on STEPs
Conversely, when there is too much electricity on the network, for example due to high production from solar and wind farms and relatively low consumption (which happens at night, on weekends or even, during the week, on summer afternoons), the hydraulic power station brings the water up to one of the two upper basins. This action consumes a lot of electricity, which makes it possible to absorb excess electrons on the network, while building up a stock of water which can be used later to produce electricity during a future peak in consumption.
STEPs, which circulate water in a closed circuit, are often compared to huge batteries. Engie operates four others around the world for a total capacity of 3 gigawatts (GW). All are located in Europe. The two based in the United Kingdom and the one located in Germany also date from the 1970s. The latter was recently acquired in Portugal.
These assets are set to play an increasingly important role within the electricity system of the Old Continent, faced with the growing penetration of intermittent renewable energies, whose production peaks do not necessarily correspond to consumption peaks. However, to ensure the proper functioning of the electricity network and avoid a blackout, electricity production must correspond to electricity consumption at all times. The electricity network will therefore need more and more flexibility tools to ensure this delicate balance. Especially since power plants running on natural gas, which historically play this role of flexibility, are not expected to develop further for climatic and energy sovereignty reasons.
Boost existing STEPs rather than building new ones
The evolution of the operating mode of the Coo power plant illustrates this trend very well. While the plant’s machines made 8,000 starts in 2010, the STEP should total some 18,000 starts this year. At the same time, the average time spent using machines has decreased, from 2.5 hours 13 years ago to less than 2 hours today. “The power plant is in increasing demand but to produce less and less electricity”summarizes Sébastien Arbola, deputy general manager in charge of Flex Gen and retail activities at Engie, the group’s number two.
In the control room, monitoring of the machines shows a succession of cycles, alternating turbines and pumping, within the same day. When it was created, pumping phases were only observed during the night to absorb excess nuclear electricity. “From now on, in summer, the power plant pumps every afternoon to absorb electricity production from photovoltaics”explains Marc Locht, the plant’s operations manager.
In addition to the development of intermittent renewable energies, global warming, which leads to an increase in intense weather events, also increases the need for flexibility. “During the last autumn storm, the winds were such that the wind farms in the North Sea had to stop, causing 300 megawatts of power to disappear from the network at once. It was the Coo power plant which took over”reports Sébastien Arborla.
STEPs therefore appear to be the holy grail for the electricity system of tomorrow. “It’s a holy grail, once the work is built”, shade Sébastien Arbola. These projects are, in fact, very capital intensive and civil engineering generates a lot of uncertainty. Added to this are questions of environmental impact and acceptability. For its many reasons, Engie did not follow up on the studies carried out in Europe to develop new STEPs. Its strategy therefore consists of increasing the capacities of those already created.
Develop 10 gigawatts of battery storage
At the same time, the French group is also banking on another type of asset to bring flexibility to the network: battery storage. A technology which has the advantage of being able to absorb and release electricity in a few thousandths of a second, compared to a few seconds for a STEP and around fifteen minutes for a power plant running on gas. Engie has set itself the goal of reaching a capacity of 10 GW in 2030 and is expected to invest nearly 2 billion euros in this activity by 2025. “Today we have 600 megawatts installed and we plan to have 3 GW in 2024”, indicates Sébastien Arbola. In this market Engie mainly targets the United States, Chile, Australia and Europe.
Today, its projects are mainly concentrated in California and Texas, which respectively aim for a penetration of renewable energies of 50% and 35% by 2030. To build muscle in this area, Engie acquired the American company Broad Reach Power last August. “Based on a renewable energy penetration rate of 20% on the network, we estimate that 100 MW of renewable capacity should give rise to 15 MW of storage capacity”specifies the number 2 of the French group.
France, not a priority
In addition to this factor, Engie is targeting markets where the difference in the price of electricity during the same day is significant. If prices are very low in the morning due to significant solar production, for example, it is in his best interest to store electricity on his batteries. It can even be paid to absorb this surplus when the price of the megawatt hour becomes negative on the markets. The idea then is to return these electrons when demand increases and thus resell them at a much higher price. “We believe that battery storage is relevant when the spread (the difference in electricity prices on the markets, editor’s note) reached 60-70 dollars during the day »indicates Sébastien Arbola.
Today, the group is developing battery storage projects in Chile, the United Kingdom, Italy and Belgium. He also looks at the Netherlands. For the moment, no project is being studied in France, where the “spread” is not significant enough. Especially since France already has means of flexibility, such as its nuclear fleet, its numerous hydraulic dams or even its gas power plants, which will nevertheless have to be decarbonized…
