Adding a control system more than doubles energy amount absorbed by a marine energy device

By adding a control system to a previous test version of a wave energy converter (WEC) that did not have the control system, Sandia National Laboratories has more than doubled the amount of energy its WEC was able to absorb.

The project’s cost was not immediately available, but it is part of a multi-year project funded by the Department of Energy’s Water Power Technologies Office.

In its Oct. 30 announcement, Sandia said it used a marine energy model developed and validated in fall 2016, which is a “large 1-ton ocean buoy with motors, sensors and an onboard computer built at a scaled-down size for a testing environment.”

Engineers from Sandia’s Water Power program used a combination of modeling and experimental testing to refine how the WEC moves and responds in an ocean environment to capture wave energy. The testing also considered how to improve the resiliency of the device in a harsh ocean environment.

The team wrote and applied multiple control algorithms to learn whether the device could capture increased energy amounts and then tested which control system would attain the best results.

Researchers did not release baseline amounts of energy doubled, but Sandia said its team is analyzing the testing data and considering further options to refine the control systems to maximize energy transfer.

In August, the team tested the WEC’s new control methods in an ocean-like environment at the maneuvering and sea-keeping (MASK) basin at the Naval Surface Warfare Center’s Carderock Division (NSWCCD) in Bethesda, Md. The facility houses a 360-foot-long by 240-foot-wide tank in which a wave maker device generates precisely measured waves for hours at a time, which simulates various ocean environments, according to Sandia.

“This year, the device can move forward, backward, up and down, and roll in order to resonate at the frequency of the incoming waves,” said Sandia engineer, Giorgio Bacelli.

The control system uses 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 in response to the variety of waves.

“All degrees of freedom were actuated, meaning there are motors in the device for each direction it can move, Bacelli said. “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.”

“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,” said Sandia engineer, Ryan Coe. “By getting more energy out of the same device, we can reduce the cost of energy from that device.”

Sandia used the MASK wave tank at NSWCCD to simulate a full-size ocean environment off the coast of Oregon, located in the Northwestern United States, but scaled down to 1/20th the size of typical ocean waves to match their device.

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Gregory B. Poindexter formerly was an associate editor for HydroWorld.com.

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