Coo-Trois-Ponts Hydroelectric Power Station

The Coo-Trois-Ponts Hydroelectric Power Station is a pumped-storage hydroelectric power station located in Trois-Ponts, Province of Liege, Belgium. Located next to the Amblève River, the power station uses its water to support a power scheme where water is pumped from a lower reservoir to one of two upper reservoirs known as Coo I and Coo II. When energy demand is high, water can be released from these reservoirs for power generation. The water then returns to the lower reservoir and the process repeats as needed. The same machines that pump the water to the upper reservoirs at a higher elevation are also used as generators. The plant was commissioned in two stages, Coo I (1969) and Coo II (1978). It is owned by Electrabel and has an installed capacity of 1,164 MW.
Design and operation.
The lower reservoir for the power station has an elbow shape and was formed with two embankment dams, one high and the other . The maximum reservoir elevation of this reservoir is . Nestled in the hills above and west of the lower reservoir are the upper reservoirs, Coo I and Coo II. Each reservoir was formed with an earth-fill dike. Coo I and Coo II have maximum reservoir elevations of and , respectively. The active (or usable) storage of the combined upper Coo reservoirs is . The lower reservoir has the same active capacity as well. Water is transferred between the reservoirs by means of two penstocks, Coo I's being long and Coo II's at in length. The power station is located underground and contains the plant's six generators. The Coo I reservoir powers three 158 MW Francis pump turbines (FPT) with Coo II consisting of three 230 MW FPTs. The change in elevation between the two reservoirs affords a hydraulic head that varies between and , the effective head is .
The plant can go from a standstill to full operation in two and half minutes and switch to pumping mode in about seven minutes. It generates about 1 million MWh annually and consumes about 20 percent more in pumping mode. The plant usually pumps during periods of low demand, such as night time, when energy is cheap which makes it profitable. Its ability to quickly adjust to power demand makes it a peaking power plant.