Ever tried riding a bicycle up a steep hill and ran out of strength? That’s when an electric bike with a built-in battery might have come in handy and carried you to the top. GE Renewable Energy is now pioneering a similar solution for wind turbines. The batteries store power when there is low demand on the grid, say, on a Sunday or at night. The batteries discharge when the wind stops blowing and people and factories need power. But the battery in question isn’t the solid mass you’d find on a bike, though. It’s millions of gallons of water.
Four wind turbines of this design have just started spinning in Germany’s southwestern Swabian-Franconian Forest. Built by GE, they stretch up into the sky at a record-breaking 584 feet, almost double the height of the Statue of Liberty. Each has a large, concrete barrel-like container at its base capable of holding 1.6 million gallons of water. The turbines bring to mind a giant electric toothbrush with a AA battery at the bottom. Below each of the turbines is an even larger, underground reservoir holding five times as many gallons of water.
The giant battery at the base of each turbine can hold 70 megawatt-hours, equivalent to 20 hours’ worth of work by a single wind turbine. When demand on the grid spikes these reservoirs send water to a separate hydropower plant on the edge of the River Kocher, turning the stored water’s potential energy into electricity. The system reverses the process to recharge the battery, using electricity when demand is low to pump the water back up. (See image below. Click to enlarge.)
The clean-energy hybrid should help keep Germany’s electric grid more stable, says Thorsten Mack, GE’s project leader for the wind turbines project, and help the country reach its goal of getting nearly half its power from renewables by 2030. Electricity grids will often turn to other power sources like fossil fuels when the wind dies down, but in this case, they’ll be able to turn to another renewable energy.
The hydropower plant will be operational by the end of 2018, but even without the water-sourced power, each GE 3.4-137 turbine can already produce 10 gigawatt-hours, enough to supply 2,500 average German four-person homes. GE also provided software like the Digital Wind Farm application, which parses through turbine, grid and weather data to predict how much power should flow into the grid. Part of GE’s Predix platform, an app-building environment for the industrial internet, it can help crews plan maintenance more efficiently too.
GE built the wind turbines between March 2016 and December 2017 for Max Boegl Wind AG, and the team behind it finished two weeks early. “Everyone was home at Christmas,” Mack says.
Out of the 100 or so people who might be on the site at any one time, a brave handful would have to take an elevator to the very top of each windmill, leaving any fear of heights or claustrophobia at the door. The steel elevator, surrounded by metal brackets and cables, was so small only two people could fit inside, and typically they’d have to stand facing one another during the 8-minute ride. “You become very close friends,” says Mack, laughing. “It’s very, very small.”
The elevator takes its occupants to the top of the windmill’s stem and stops directly under the machine head, called a nacelle. Once at the top, some of these workers had the unenviable job of climbing out on top of the nacelle and guiding the 19-ton turbine blades into place. “The people on the top need to make sure the blades are installed in the right position,” Mack says. Each blade was installed on a blade bearing connected to center of the turbine’s rotor — precision work that had to be done to the millimeter, Mack says. All the while, his team had to carefully monitor the weather forecast. A sudden gust of wind at the wrong time could be dangerous. “You need to consider that the blade is not only very big,” he adds. “It is designed to catch wind.”
While that would be a terrifying job for most, these specialist workers typically have 10 or 20 years of experience under their belts. (Wind turbines are growing taller each year, though, so nerves of steel are increasingly in order.) The photo above shows one of the water battery turbines during construction in 2017, and a blade-installation tool (the yellow, crane alongside the shaft) lifting one of the turbine blades into position. Mack explains that the blades’ weight and vast length meant that it was difficult to install them without also breaching the limit of the crane’s capacity.
Just getting all the parts to the site was an adventure in itself. The wind turbines had “the biggest single-piece blades ever shipped over German streets by GE,” Mack remembers. The team hoisted the blades made by LM Wind Power onto an enormous truck with a trailer longer than the width of a football field, and planned out a slow, methodical drive through German highways and tiny villages in the Swabian forest.
“That was extraordinary,” he says. “It was a challenge to build such a blade, but another to transport it in one piece.”