How big can wind turbines get? New technologies will be needed to get to 10 MW, and possibly beyond
Anti-wind groups won’t be happy to read this, but for the rest of us — the majority — who see wind energy as part of the solution to a low-carbon future, then you’ll be happy to read about efforts underway to make wind turbines that are more powerful, lighter and more reliable. I explore some of these in my latest piece for MIT Technology Review.
This is particularly crucial if we are to responsibly tap into the vast wind resources located in offshore locations. Going offshore offers the ability to harness much stronger and more consistent winds with larger and higher performing machines, but it also makes it more difficult to do maintenance and repairs. Most onshore wind turbines of 2 or 3 megawatts in size have gearboxes to match the slower turbine rotor speed with the high speeds of its internal generator. Gearboxes, by design, have more moving parts and therefore need regular maintenance. They’re also more prone to malfunction. This is okay when onshore, because it’s easier to access the turbines for repair. Offshore, it’s not so easy. It costs tremendous amounts of money to rent barges that will take repair crews to these remotely located turbines, and that’s assuming the weather is cooperating.
Some turbine manufacturers — Siemens, Enercon, Goldwind, Alstom — are now making direct-drive turbines, meaning no gearboxes. They’re less complex, have fewer moving parts, so are more reliable. Problem is, they’re super heavy. For direct drive you need to have a generator that can pump out the same amount of power at a much lower speed of operation, meaning you have to build a larger generator that has more surface area for the permanent magnets inside to sweep across the stator coils (a movement that induces current in the coils). This means more magnets, meaning much more weight and an increased reliance on rare-earth materials.
So, while direct-drive is ideal for offshore locations because of lower need for maintenance, getting to machines that are 10 MW in size will create generators that are simply too heavy to be economically deployed. One solution being explored, as you’ll read in my Technology Review piece, is to use superconductivity technology that creates super powerful and efficient electromagnets. This will eliminate the need for permanent magnets and therefore rare-earth materials, and it will create a much more powerful magnetic field at a fraction of the weight of conventional direct-drive designs. Both GE Global Research and Advanced Magnet Labs, two of six recipients of DOE funding for research in this area, believe they can make direct-drive wind turbine generators with a 10 MW capacity but weighing only 70 or so tons. A conventional direct-drive generator would weight over 250 tons.
Anyway, it’s all interesting stuff. At the moment, there are commercial direct-drive designs out there ranging from 6 to 10 MW in size. Siemens just announced its 6 MW version in June. But whether those can be manufactured and deployed on a large scale economically is still unclear. Something new will be needed to crack this new barrier for wind, and while it might not come this decade, it will come.