Ars Innovation Spotlight

Inside (literally) wind turbines meant to work at the South Pole—and Mars

Ars visits Northern Power Systems to learn what goes into their wind turbines.

Enlarge / Roses are red, violets are blue, turbines use magnets to generate power which can be used to make light, and without light you are likely to be eaten by a grue.
Northern Power Systems

BARRE, Vermont—It started with Mars. In 1993, NASA gave a Small Business Innovation Research grant to Vermont-based Northern Power Systems (NPS) to build a very southern wind turbine—as in, a turbine that could reliably work at the South Pole.

NASA was interested in a wind turbine that could potentially provide power for human exploration of Mars, and the National Science Foundation was interested in some electricity at its South Pole station that didn’t require flying in fuel. NPS set about tackling both challenges in one fell swoop, designing a low-maintenance turbine using components that could survive the deathly Antarctic (or Martian) cold. A few years later, a 3 kilowatt turbine was spinning away at the South Pole.

Video: Ars visits Northern Power Systems to get our wind turbine learn on. Shot and edited by Jennifer Hahn.

Northern eventually scaled up that design to a 100 kilowatt turbine that could help power a small community. The company found interested customers in remote Alaskan towns that produced most of their power using diesel generators and, like the folks in Antarctica, needed something reliable in a harsh climate. Unlike the massive multi-megawatt wind turbines that utilities buy in bunches to set up in wind farm arrays, NPS mostly sells single turbines to individuals, businesses, or communities that want to produce some electricity for themselves. It's a category of energy production known as "distributed wind," and Northern is doing it with a slightly different kind of turbine—luckily, Northern was kind enough to let us stick our heads inside one recently to see for ourselves.

Magnets? How do they work?

Excluding solar panels, most electricity is produced using generators, which are really just motors run in reverse. The spinning of a rotor inside the generator (driven by wind, water, or the burning of fossil fuels) provides a rotating magnetic field that induces the flow of alternating current in the doughnut of coiled wire that surrounds it (and, hey presto! you've got electricity). Traditional wind turbines utilize a series of gears to spin an induction generator much faster than the blades of the turbine are turning in the wind.  But this isn’t the only way you can go. Instead of spinning the electrified coils of an induction generator, spinning actual magnets can do the job of inducing current in the outer part of the generator. With extremely potent magnets, these generators can be smaller and more efficient. (That's why permanent magnet generators/motors are common in hybrid and electric vehicles—except Tesla’s.)

Since a gearbox adds lots of moving parts that wear out or fail under duress, increasing the need for maintenance and repairs, another option is to ditch the gears. “Direct drive” turbines are comparatively simpler—the turbine’s blades attach to one end of a shaft, and the generator is on the other. The trade-off is that your generator will now turn only once for each turn of the wind turbine’s blades, but you can also increase the velocity of the spinning rotor somewhat by increasing its diameter. That is, completing a larger circle in the same amount of time means you go faster.

Northern's direct drive turbines produce “wild AC,” pumping out whatever the wind speed provides.

Pair permanent magnets with a direct drive, and you can get at least as much power as a traditional geared wind turbine while eliminating some trouble-prone complexity. This is the type of turbine that Northern built for the South Pole.

These powerful permanent magnets require rare earth elements, some of which have high and variable prices because they’re much rarer than others. But by tweaking things to keep the magnets a little cooler, Northern was able to leave out some of the more expensive elements (like dysprosium). These magnets can be ground up and recycled at the end of a machine’s life, too, making new magnets with different recipes rather than throwing out precious materials. Industrial rare earth magnets are a little trickier to order than your average part, NPS Director of Product Management Chris McKay told Ars. “The magnets either come magnetized, and then they’re in very special packing so that the forces are all offsetting one another, which is pretty interesting," he said. "Or, you can buy them unmagnetized, and once you put them in place you magnetize them.” So with the right (expensive) equipment, you can apply a large current to an inert brick and transform it into a super-magnet.

While some wind turbines are run at fixed speeds to match the desired frequency of electricity in the grid, Northern's direct drive turbines produce “wild AC,” pumping out whatever the wind speed provides. That creates a need for converters to smooth out the electricity so it’s suitable for the grid. NPS has worked pretty hard to build converters that can stand up to the elements and do their job without losing much energy in the process, and the company likes them enough that it also sells them on their own. Ruggedizing the converters for harsh conditions is partly a matter of finding tolerant components, which have improved over time themselves, and partly a matter of careful controls that might start up sensitive parts slowly or keep them warm when it's cold out, McKay said.

Enlarge / Putting together a large power converter unit.
Northern Power Systems

The 60 kilowatt and 100 kilowatt turbines the company produces are optimized for the range of wind speeds they’re going to see, which are lower than a much taller turbine might get. They sit atop 22 to 37 meter steel towers and sport about 12 meter long fiberglass blades. Because they’re built for lower wind speeds, the ratio of blade length to power output is higher than that of a big megawatt turbine—proportionally bigger sails to make the most of the slower wind. And while those big turbines often actively adjust the angle of each blade to adapt to wind speeds, that extra complexity isn’t economical for Northern's smaller turbines. Instead, the blades are shaped such that they begin to stall at high wind speeds, protecting the machine and preventing extreme power output. The generator itself can also be used to add some resistance and slow the blades, and there's a huge brake disc that can lock things down.

Other than occasional bouts with high winds, overheating is probably the turbine’s biggest enemy—even in Alaska. An air duct pulls some air up through the tower for cooling the hardware at the top, but the engineers also bank on cooling provided by the wind itself. Thick metal fins surround the generator housing, and a heavy-duty resistor that can be used to bleed off brief power peaks sits outside of the enclosed nacelle atop the tower—both are designed to cool off in the wind. In fact, McKay said that an initial indoors test of a recent design ran hotter than they anticipated until they realized they needed to point fans at the thing to simulate some wind.

Enlarge / An older version of Northern's 100 kilowatt turbine runs through some tests at the end of the assembly line.
Northern Power Systems

That kind of testing is the last step down on the surprisingly quiet but cavernous factory floor, where electric trains were manufactured before NPS moved in. The electrical components are built in smaller bays along the sides of the building. They come together on the main stage, where a single person can push the large nacelles down buttery-smooth trackways, moving from station to station to get their electronic and mechanical guts installed. There’s just enough space inside the nacelle for maintenance work to be done—a fact I can vouch for after ducking into one near the end of the assembly line. After climbing the ladder inside the tower, you would emerge in a wee room about the size of a chest freezer, with walls covered in circuit boards and heavy-duty electrical cabling, and a little floor space to kneel or sit. The generator itself sits inside an enclosed drum on the front of the nacelle, with a large braking disc used for locking down the blades the only moving part within the nacelle. For the rare occasions one needs to pop topside, there's a boat hatch that makes the nacelle feel a bit like a tiny submarine.

Simpler tasks like system resets can be done remotely, as all the turbines report back to NPS so that problems can be spotted quickly. But if Northern wants to sell turbines in a new part of the world, it has to set up a service center close enough to easily dispatch technicians and parts when something needs doing. A minor issue isn't so minor if you have to send someone halfway around the planet to deal with it.

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