With Tesla adding its Powerwalls and Powerpacks to houses, businesses, and the grid itself, one might think that Li-ion batteries are the ultimate in energy storage systems. That theory doesn’t hold water – but what does hold water is the world’s tallest wind turbine: a 3.4 megawatt GE 3.4-137, sitting atop a Max Bögl tower whose base includes a reservoir for a pumped hydro energy storage system, which the company calls a “water battery.”
Pumped hydropower is a well-established energy storage technique; it’s also one of the most efficient energy storage technologies, which is why pumped hydro represents 95% of the US grid’s energy storage capacity. The concept is simple: when electricity is abundant (production exceeds demand), a pump moves water uphill and stores it in a reservoir. During peak demand times, the water flows downhill, turning the pump into a generator. This is typically done in areas where the natural geography provides both an upper and a lower reservoir. In some cases, a man-made reservoir serves as either the upper or lower vessel.
When the town of Gaildorf, Germany, decided to put four wind turbines on some nearby mountains, officials wanted to incorporate an energy storage system. While the area has a natural body of water in the valley, an artificial reservoir was needed at a higher elevation. Engineers at Max Bögl, a German company that makes hybrid steel and concrete turbine towers, saw an opportunity to increase the wind turbines’ generating capacity and satisfy the need for an upper reservoir at the same time. They designed an innovative tower base that increases the turbine height by forty meters and holds 40 million liters (10.5 million US gallons) of water. The additional tower height allows each turbine to capture strong higher-altitude winds, while the “water battery” can store 70 MWh worth of electricity with a peak power output of 16 MW.
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