The 10-kW prototype of ABB’s magnetically geared generator—illustrated above—was tested at ABB’s Corporate Research lab in Raleigh, North Carolina. Test results indicated the generator could be ideal for low-speed, high-torque applications like wave energy. The prototype was part of an Energy Department-funded project to research novel direct-drive generators that could eliminate hydraulic components in some wave energy power take-off systems.
As a source of energy, ocean waves are particularly complicated. On one hand, waves possess immense power—that’s a good thing for making electricity. On the other hand, they’re slow and widely spaced. This dichotomy of high power and long intervals presents a unique engineering challenge, making it a natural focus for technology development efforts.
One project funded by the Water Power Technologies Office (WPTO) has taken steps to overcome this challenge. ABB and project partners, including Texas A&M’s Advanced Electrical Machines Lab and Resolute Marine Energy (RME), developed an integrated magnetic-gear generator with the potential to convert low-speed, high-torque (meaning extremely powerful) waves into grid-ready electricity more economically than current solutions, according to ABB.
The advancement was necessary because a majority of today’s generation devices work with fast-moving, constant sources of power. In nuclear plants, for example, powerful steam—heated by the high-energy splitting of uranium atoms in a process known as nuclear fission—forces generators to spin. Inside hydropower plants, falling water moves a turbine that spins a generator.
In the ocean, however, slow-traveling waves encounter energy converters only five times a minute on average. Making consistent energy from a resource like that has, in the past, vexed device developers. To be suitable for grid connections, electrons must come from a power source in a neat and orderly fashion—they can’t come in surges, as they naturally would from ocean waves. Typically, this challenge is handled electrically through power conditioning or other forms of energy storage.
ABB’s answer to this challenge was to design an integrated magnetic-gear generator for use in RME’s wave surge converter device. Essentially, the device is a big flap that extends upward from the ocean floor and moves back and forth with waves. To make it more economical, the company sought ways to reduce cost and improve the efficiency of the generator.
The key difference between ABB’s system and previous generators is the lack of mechanical gearing. To create electricity, generators typically require fast-spinning rotors. In applications like ocean energy, gears are required to step up—meaning, make faster—the motion from the waves, so the generator rotors can turn even faster. The higher rotor speeds lets the ocean wave system create electricity using a smaller and more economical generator.
In the ocean there is also a lot of variability in the waves, with a 4:1 ratio typical of the difference between maximum and average values for both the force (or torque) applied by the wave, as well as the wave period (or speed) of the wave. This means a machine is needed that can create smoother energy output whether experiencing normal waves or a storm crashing to shore. What’s more, having mechanical gearing increases the need for operations and maintenance, which can get expensive at sea.
ABB’s machine bypasses mechanical gears altogether, replacing them with inner and outer rotors that are magnetically coupled to drive faster speeds inside the generator.
Because it’s still in development, it’s too early to tell how or if this generator will be used in commercial wave energy devices, but researchers note that the innovation possibly could be applied to tidal energy and wind power, as well.
The Office of Energy Efficiency and Renewable Energy accelerates development and deployment of energy efficiency and renewable energy technologies and market-based solutions that strengthen U.S. energy security, environmental quality, and economic vitality. Visit water.energy.gov to learn more about the Water Power Technologies Office.