Photo by Randy Montoya Sandia National Laboratories water power engineers Giorgio Bacelli, left, Dave Patterson, center, and Ryan Coe with Sandia’s wave energy converter buoy.
Researchers may have found a new way to capture wave energy that can be used to make electricity.
A team from Sandia National Laboratories are working on designing, modeling and testing a new control system that may double the amount of power a wave energy converter can absorb from ocean waves by applying a classical control theory, robotics and aerospace engineering design principles to improve the converter’s efficiency.
The researchers are using a combination of modeling and experimental testing to refine how a wave energy converter moves and responds in the ocean to capture wave energy, while also considering how to improve the resiliency of the device in a harsh ocean environment.
“We are working to create methodologies and technologies that private companies can harness to create wave energy devices that will enable them to sell power to the U.S. grid at a competitive price,” Sandia engineer Ryan Coe said in a statement. “By getting more energy out of the same device, we can reduce the cost of energy from that device.”
The wave energy converter is a one-ton ocean buoy with motors, sensors and an onboard computer built at a scaled down size for a testing environment. Commercial wave energy converters can be large and are generally part of a group of devices including wind farms with multiple turbines.
“These devices can be in open ocean and deep water, maybe 50 to 100 miles off the coast,” Coe said. “An array of wave energy converters, maybe 100 devices, connected to an underwater transmission line would send the wave energy back to shore for consumption on the grid.”
A wave energy converted moves and bobs in the water, absorbing power from waves when they generate forces on the buoy.
The researchers used their model and applied multiple control algorithms to see if the converter could capture more energy.
“A control algorithm is a set of rules you write that prompts an action or multiple actions based on incoming measurements,” Sandia engineer Giorgio Bacelli said in a statement. “The sensors on the device measure position, velocity and pressure on the hull of buoy and then generate a force or torque in the motor.
“This action modifies the dynamic response of the buoy so that it resonates at the frequency of the incoming waves, which maximizes the amount of power that can be absorbed.”
The control system used a feedback loop to respond to the behavior of the device, by taking measurements 1,000 times per second to continuously refine the movement of the buoy to follow and then test which control system would get the best result.
“Controls is a pretty big field,” Sandia engineer Dave Patterson said in a statement. “You can operate anything from planes to cars to walking robots.
“Different controls will work better for different machines, so a large part of this project is figuring out which control algorithm works and how to design your system to best take advantage of those controls.”
The researchers ran a baseline test to see how the converter performed with a simple control system—directing its movements and actions— and ran a series of tests to study how the various control algorithms they had designed affected the ability of the device to absorb energy.
“This year, the device can move forward, backward, up and down and roll in order to resonate at the frequency of the incoming waves,” Bacelli said. “All degrees of freedom were actuated, meaning there are motors in the device for each direction it can move.
“During testing we were able to absorb energy in each of these modes, and we were able to simulate the operating conditions of a device at sea much more accurately.”
The researchers found that the control algorithms were able to more than double the amount of energy the wave energy converters were able to absorb without a control system.
