I have ALWAYS wondered this - thanks Tom :)<br><br>There are actually massive power-grid batteries in the form of pumped-storage hydroelectric plants (as you probably know!) but not nearly enough to cope with huge fluctuations. I think there's one in Wales. and Japan has loads of them.<br><br>Regarding high winds, though, I would've thought it would actually be safer to dynamically "brake" the windmills to prevent them turning beyond their operating capacity, since the load would be dynamically spread and partially extracted or converted, while switched off and static they'd be more vulnerable. But then, I suppose power-generation itself is a turbine-braking process, so if that's not enough to slow the buggers down to safe speeds then yeah, I guess they sometimes need to be locked down.<br><br><b>Disclaimer: I studied civil engineering, but am (clearly) no expert</b>,(reply>), They feather the blades, to minimize surface area, and don't just brake their rotation. By variably feathering the blades, they modulate the rotation to a fairly consistent speed in different wind strengths. This minimizes additional strain and increases average efficiency.<br>I am not an expert, but I have read about this.