A new class of elastic energy converters is emerging, with the ability to capture energy from a variety of different motions. The National Renewable Energy Laboratory (NREL) is pushing to deploy them, first in a series of strange, bendy wave energy designs.
The NREL says its DEEC-Tec (distributed embedded energy converter technologies) designs will sit around in the water, letting the waves deform them in all directions, and harvesting electricity from "almost all physical motions or dynamic shape changes."
Rather than driving turbines, or combining to drive an external generator, they'll be built using lots of small, flexible generators, each acting a bit like a muscle fiber to produce its own output.
One such type of generator uses dielectric elastomers, which first surfaced in the late 1990s. According to a 2020 review published in Advanced Intelligent Systems, these essentially consist of a layer of deformable, elastic, dielectric material, coated with electrodes to form a variable capacitor.
These have their lowest capacitance in their unstressed state, and any deviation from their original state increases their capacitance, whether this is stretching, twisting, compressing or bending in any direction. At peak deformation, they're primed with a charge through the electrodes, bringing their capacitance up equal to their unstressed state, and the elastic works against the electric charge to bring them back to their state of lowest capacitance, producing more energy than was used to create the charge in the first place.
As with turbine-style generators, these things can work in both directions, either harvesting energy from externally-supplied deformation forces, or spending energy to work as actuators. They can also essentially act as sensors, providing constant feedback on how far they're stretched from their normal state and essentially giving a brain/battery unit information from which to deduce how much charge to apply at a given time.
In 2019, a dielectric elastomer generator in the form of a rubber membrane on the end of an air tube was tested in Scotland. It demonstrated an ability to harvest energy both when high wave pressure pushed air up into the tube, blowing the rubber up a bit like a balloon, and when low wave pressure sucked at the air column and pulled the membrane down with it.
But the NREL's plans go much further. Waves do a lot more than going up and down, they produce nearly random movement in just about all directions. DEEC-Tec generators will have the minimal possible solid structure to them. They'll be almost entirely flexible, allowing them to harvest kinetic energy whenever it arrives.
A wobbly, flexible structure built from hundreds or thousands of tiny elastomeric generators, each requiring precise applications of charge at precise moments, could certainly be tricky to control. But it's not unreasonable to think an AI deep learning system could figure it out, and adapt quickly to changing conditions.
And the nature of these dielectric elastomers as sensor, generator and actuator all in one would give the control system an unprecedented ability to reshape the structure like a soft robot wherever there's an advantage in taking a different form.
Mind you, dielectric elastomer generators are not the only option here; the team is just as happy to incorporate ionic dielectric elastomer generators, magnetostrictive generators and whatever else might be relevant to a given project, perhaps in combination.
It's pretty remarkable stuff; NREL proposes wall-shaped and snake-shaped designs for wave energy capture, as well as a heavy ball inside a balloon filled with gridded elastic generators, which could harvest inertial energy from movement as well as from deformations of the balloon shape. The team says it could also eventually be used in energy harvesting clothing, and even buildings or roads.
The NREL team says these things can be manufactured easily from low-cost, sustainable materials. They offer a degree of redundancy, in that even if several generators in a given structure break and stop working, there will still be hundreds of others online. All in all, the team hopes to prove this kind of wave energy generator is cheap, safe, low-maintenance, scalable and capable of making a worthy contribution to the energy grid.
There are many unknowns, including which materials, transducers and designs will result in the best power conversion efficiencies, durability, and resistance to the corrosive nature of seawater.
It's still early days yet, but with a fresh patent in the bag, the NREL's DEEC-Tec team, led by senior engineer Blake Boren, is pushing to develop the concept, both in-house and with external collaborators and industry. We're fascinated to see what they come up with.
Source: NREL