Wind blows. Water falls. But for the first time, one is now powering the other. Engineers in Germany are storing water for hydroelectricity inside wind turbines allowing the towers act like massive batteries once the wind stops blowing. It’s the first major example of the two technologies being physically integrated to supply reliable renewable energy.

The four-turbine project, announced by General Electric this month, stores energy from the spinning blades by pumping water about 100 feet up inside the turbine structure itself. Basins around each base will store another 9 million gallons. When the wind stops, water flows downhill to generate hydroelectric power. A man-made lake in the valley below collects water until turbines pump the water back up again.

Typically, wind farms don’t store excess energy at all because storage is too expensive to be viable; excess energy harvested goes straight to the grid (driving energy prices into low or even negative territory), or the turbines get shut down. This project creates an affordable way to store excess energy in a natural reservoir, and integrates the source and storage into one system.

Max Boegl Wind The four wind turbine sites will be connected by a channel that takes the water down to the valley.

The wind farm in Germany’s Swabian-Franconian forest will feature the tallest turbines in the world at 809 feet (246.5 meters). At full capacity, it should produce 13.6 megawatts, along with another 16 megawatts from the hydroelectric plant. The project is being built by German firm Max Boegl Wind AG and GE Renewable Energy. The wind farm should connect to the grid by 2017, and hydropower units will be finished by the end of 2018.

Germany is in the midst of its energiewende, or energy transition, as it attempts to virtually eliminate fossil fuels. The nation has said it aims to draw 45% of its energy from renewables by 2030 and reach 100% by 2050. Last year, the average renewable mix was 33%, reports Agora Energiewende, a German clean energy think tank.

GE says this wind farm is the first major project that integrates water storage in the turbines themselves, although there are a few examples of combined wind and pumped-water storage in the world. If successful, it should prove to be a template for other projects. Boegl says it plans to add one to two new more wind-hydro projects in Germany annually after 2018, and new sites may be found the around the world as the technology can use either fresh and saltwater.