With Wind Turbine Generators, As Is the Case with All Things, There Is No Such Thing as a Free Lunch

What happens in the nacelle, that box-like thing shown here at the top of a wind turbine?  In its simplicity, it’s where we convert mechanical into electrical energy, i.e., it’s the home of the generator.  From there, however, things get a bit more complex, when one considers the trade-offs between various options for the nacelle’s guts, particularly, direct drive and geared systems.  

Imagine you have a shaft turning at the low speed of the turbine blades themselves, but with incredibly high torque, which is created by huge volumes of fast-moving air turning blades of enormous length.  (This gives you a certain amount of power, which, as we recall from physics, is the product of speed and torque; here we have low speed and high torque.) You can run that shaft directly into a generator, but to function efficiently, it requires extremely strong (and heavy) permanent magnets, meaning lots of rare earth metals.

You can also insert a system of gears that raises the speed (while lowering the torque, since power is conserved) of the turning shaft.  Now you need simpler, lower-cost generators, but you also have lots of moving parts that add weight and require maintenance.

That’s the trade-off, but where is all this going?  Well, in both cases, it’s all about weight; you never want heavy things that need to be supported, especially at the extreme heights that come with today’s huge, offshore wind turbines, as this would mean adding all kinds of structural materials.

Here’s what’s being done to drive down weight from both the direct drive and geared systems.