A Newly Developed Coaxial Turbine May Someday Make the Energy World Go ‘Round

Based at the Coastal Studies Institute, the North Carolina Renewable Ocean Energy Program (NCROEP) seeks to use renewable ocean energy wisely and effectively while contributing to North Carolina’s Blue Economy. As a result, NCROEP helps to support interdisciplinary researchers from UNC System Schools- specifically NC State University, East Carolina University, UNC-Charlotte, and NCA&T State University- and their projects to advance marine energy solutions.

Last year, researchers from NC State University and East Carolina University/ Coastal Studies Institute tested an underwater energy harvesting kite at Lake Norman in Charlotte. Now this fall, another device- a small coaxial turbine that relies on a water current to spin the turbine blades to generate energy- has been tested in the waters just off the shores of the Coastal Studies Institute.

Arriving early one morning in December at the Coastal Studies Institute, Saurabh Agrawal, a mechanical engineering Ph.D. student in the Engineering Mechanics and Space Systems Laboratory (EMSSL) led by Dr. Andre Mazzoleni at NC State, and Aditya Varanwal, an M.S. student from the same lab, were greeted by Oceanography and Marine Hydrokinetic (MHK) Energy Lab members Spencer Wilkinson and Trip Taylor. The team boarded CSI’s R/V “Blackbeard” and began their work for the day.

While the turbine had previously been tested in the lab and by boat in Lake Norman, the operations conducted at CSI marked the first time the device had been in any sort of saline environment. On that occasion, the coaxial turbine was again tethered to the boat and towed, simulating a current that the device depends on to generate power.

Because of the unpredictable nature of open water testing, “all the components of the turbine were designed to allow for easy integration and interchangeability…. The system was designed to be robust and built in such a way as to allow for quick assembly and tear down”, Agrawal explains. He and others at NC State- Drs. Matthew Bryant and Kenneth Granlund, as well as Ph.D. students Vinson Oliver Williams and Mehedi Hassan and M.S. student Xinyang Tong- worked together to bring the project to life.

The first tow test in the Croatan Sound was a big milestone for the group and for the device as it demonstrated operational feasibility in an open water setting. Over the course of the day, the coaxial turbine was tested under two different towing speeds for each of three different electrical resistive loads. The device had to be taken from the water each time the resistance load was switched which also allowed time for the downloading of recorded data from the device.

“Overall, this open water trial was incredibly successful. We were able to successfully demonstrate the ability to extract power, system robustness, and waterproofing capabilities during underwater operation,” said Agrawal.

Eventually, the goal is to have the device deployed off of Jennette’s Pier. There it would sit in the water column attached to a surface marker buoy from above and anchored to the seafloor below. An electric cable, running from the turbine parallel to the anchor line, across the seafloor, and up to the pier, would transmit the energy generated from the turbine to a microgrid.

While the above scenario might still seem distant, the testing done at CSI in December is not without importance. This work provided researchers insight into the robustness of the device, how it might operate in certain conditions, and how it could be improved. Their next steps will be to optimize the turbine’s current design so that, in the future, it will generate greater power.

When asked about the Oceanography and MHK Energy Lab’s collaboration with the researchers at NC State, Dr. Mike Muglia shared, “We’ve really enjoyed working with this group of professors and students on the coaxial turbine project. We are excited to see this go from paper to deployment and look forward to a longer-term ocean deployment at Jennette’s Pier very soon.”