As we stated at the beginning of this chapter, wind turbines produce electricity efficiently without going through a steam cycle. The generators in the nacelles are basically electric motors run in reverse, so that instead of electricity causing something to turn, the turning of the blades causes electricity to be generated. Of course, it is not that simple, and this gets a little technical. The pitch of the blades is varied to keep them turning at the same speed as the wind varies. The rotor is connected to the generator through a gearbox. The gears are needed to increase the rotational speed of the rotor (about 5 rpm, say) to the speed of the generator (about 1,000 rpm, say). The gearbox tends to wear out before anything else, and new turbines are being developed to do the switching electronically, without moving parts. Since it takes a second or two to change the pitch of the blades, gusts of wind will make the rotor turn faster, and the generator has to handle that.

The next problem is to match the electric output from the generator to the AC grid. Though there are different kinds of generators, it is not always possible for them to turn out AC at the same frequency as the grid. The generator’s output will vary with the wind and may be nowhere near the 50- or 60-cycle frequency of AC power. It will also be reactive. That is, the voltage and current of the output will not be in phase, varying nicely together as they should. To manage this, the generator’s output is processed by a converter. The AC is first converted to DC, and then the DC is converted to 50- for 60-cycle AC so that it can be sent into the grid. We com­monly use converters on a small scale. The power bricks that charge our cell phones and laptop computers convert AC to DC. There are small devices for cars which can convert the DC from the cigarette lighter into AC to run a portable household appli­ance. But for a 5-MW turbine, the electronics and capacitors to handle this conver­sion would fill a small factory. Basically, a sizable electric substation has to be built at the base of the tower or inside it. Five megawatts is a lot of power; it is equivalent to 6,700 HP. The switching of this much power requires some heavy-duty transis­tors, and there is a proposal to develop silicon carbide (SiC) switches, which can handle this better than ordinary silicon.19 These large components needed to convert wind power to grid power are a part of the cost and environmental impact that people do not usually know about.