The Linthal hydropower plant is accessible only by cable car, after a scenic jaunt through winding mountain roads. The mouth of the tunnel that descends to the subterranean hydroplant is located at 1,800 meters (5,900 feet) above sea level. At the command of the plant’s operator, Swiss utility Axpo, massive steel valves are opened, allowing water to flow from Lake Mutt to Lake Limmern, which are separated by a 2,000-foot cliff. The pump is twice the height of the Eiffel Tower. Nearly 23 billion gallons of water stop behind a dam in the valley, creating a temporary reservoir that feeds the plant’s four variable speed hydro generators.

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When demand for power is low, the flow on the valve is simply reversed, pumping water from the lower reservoir back up to Lake Mutt, where it can be stored until it’s time to generate more electricity. In this way, General Electric touts the power plant as a kind of natural battery. “It’s the only grid-scale method of storing energy,” says Maryse François, the hydrotechnology leader at GE Renewable Energy, which developed the technology powering the site.

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The Linthal plant marks the first place GE has installed its variable-speed technology, which takes the common concept of pumped storage to a whole new level. Having this sort of control over a massive renewable energy power plant can make a world of difference to the local power grid. The valves controlling the water make it possible to change the plant’s net energy output, absorb spikes in demand, as well as help utilities stabilize the grid and reduce brown-outs.

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The system’s efficiency also makes it a big win, not only for clean energy but for the local economy as well. At its peak, the overall cycle efficiency can reach as high as 80 percent. When all four generators are in operation, the plant will churn out a whopping 1,450 megawatts of renewable electricity. That’s enough to power a million Swiss homes during peak consumption times, which accounts for nearly one-third of the country’s population.

+ GE Reports

Images via General Electric