As wind turbines have a rotor as well as steam turbines, this energy storage device can be tapped by an intelligent control of the power electronics that serve as electronic gearbox between the speed of the rotating blades and the speed of the grid frequency. The mechanical starting time is even bigger, ca 20 to 30 seconds vs. ~10 s with steam or gas turbines combined with a synchronous generator.,(reply>), There are technical issues with this synthetic inertia response. I don't want to get to technical but for instance, if we provide synthetic inertia during frequency drop, we slow down the wind turbine rotor. This causes a lower aerodynamic efficiency, which means lower output after the inertia support than prior to it (if pitch angle corrections are npt available - operating below the rated power). This can have adverse effects like second frequency dip. In certain situations, a control feature like this can do more harm than good.<br><br>A better option is to keep an active power reserve by lowering efficiency through speed control, pitch control or a combination of these two (depending on the operational state). Overspeeding being the best option: if there is a need for additional power, you inject more power, slowing the rotor down. By doing this the aerodynamic efficiency rises. At the same time the surplus kinetic energy is injected into the grid. Then stabilise the turbine at peak efficiency - at optimal rotational speed. Of course, during normal operation we are spilling a fraction of clean energy this way.