This summer, a $2.10 billion energy storage project called Nant de Drance opened in Valais, Switzerland. The project, which some people call a "water battery (电池)", can store more energy than 400,000 car batteries.
The system works by gravity. There are two large water reservoirs high in the Swiss mountains. One is much higher than the other. The two are connected by a system of underground passages. When there is too much electricity, Nant de Drance can use that energy to send water from the lower reservoir to the upper one. To produce power, water goes down from the upper reservoir. Gravity pulls the water down into the passages, where it rushes through six large turbines. They produce electricity.
Though the system is quite a simple one, building it took 14 years and a lot of effort. The upper reservoir had to be doubled in size. Workers had to create 10.5 miles of large underground passages connecting the two reservoirs. That meant carving out huge amounts of rock from inside the mountains. The turbines are located over a third of a mile underground.
As the world turns more and more to renewable energy sources, being able to store energy is very important. Unlike oil, gas, or coal, many renewable energy sources only work some of the time and can not be burned to create energy any time. Solar panels only work when the sun is shining, for example. Wind turbines only create energy when the wind is blowing. Renewable energy must be stored if it's going to be ready to use at any time.
Using water to store and create energy isn't a new idea. But in the past, many water storage projects seriously changed or damaged rivers. Because Nant de Drance is almost completely underground, it's caused little damage to the local environment.
