Scientists from the Universitat Rovira i Virgili (URV) in southern Catalonia have created a novel energy-harvesting device that captures the vibrations of a pendulum driven by ocean currents to generate usable electrical power.
The pendulum-based approach is less efficient than existing “blue energy” harvesters that resemble underwater wind turbines. However, the system’s design is also simpler and functions with most of the hardware above the ocean surface, reducing the damaging effects of water and marine life that adds cost and complexity to other approaches.
“The beauty of this system is that only the cylinder is in the water; everything else—the shaft, the transmissions, and eventually the generator—can be outside,” explained Francisco Huera, a researcher in the Department of Mechanical Engineering at URV.
Although the breakthrough energy-harvesting system is designed to work with ocean currents, the team behind its creation suggests that the approach could be adapted to rivers or other channels of moving water that can induce vibrations in the immersed pendulum.
How a Pendulum Converts Vibrations into Electrical Energy
Engineers and scientists searching for sustainable forms of power generation have begun to explore more unconventional approaches that tap forces of nature, including wind and solar power. Axial-flow or cross-flow turbine-based systems resembling underwater wind turbines also exist and are designed to extract usable energy from ocean currents.
However, underwater turbines are complex and operate in harsh environments that can rapidly degrade materials and components, increasing maintenance and downtime costs. Such systems are still in the prototype phase, limiting the number of commercially available energy-harvesting options.
According to the study detailing the new pendulum-based system, their design captures the energy from vibrations caused by vortices that form in the water as it passes by a submerged cylinder.
Engineers who design large-scale oceanic structures, such as pipelines connecting oil platforms to the seabed, have dealt with the adverse effects of current-induced vibrations, including fatigue and degradation of installation integrity.
Notably, Francisco Huera has previously worked on a system to combat these vibrations, including obtaining a patent for his designs. Now, the researcher has found a way to capture the energy from those negative vibrations and turn them into usable electricity.
Tests Confirm the Design’s Simplicity and Establish Its Energy Harvesting Efficiency
After building a test version of their pendulum-based energy-harvesting system, the research team submerged its calendrical pendulum in a water channel representing the flow of an ocean current. To capture the energy from the vibrating pendulum, the submerged portion of the system was connected to a shaft that rotates on air bearings.
As the water flowed around the cylinder and induced the expected vibrations, the research team monitored the effects using a sensor that measured the device’s oscillation angle. The team also employed an electromagnetic brake on the shaft to measure the mechanical power available from the vibrations.
After performing several tests, Huerta’s team found their design captured around 15% of the available energy. The team said these results were consistent with tests on previous designs that used cylinder vibrations for harvesting.
While the system’s measured efficiency was roughly half of the 25-35% achieved by underwater turbine-based systems, the research team said their design’s reduced size and increased simplicity make it a viable alternative to those approaches.
When highlighting other advantages of their approach compared to turbine-based designs, the researcher noted that all the complex mechanics of his team’s energy harvester, such as generators, transmissions, and control systems, can stay above water on a floating platform, since only the cylinder needs to be submerged.
“At the end of the day, it’s just a tube hanging from an axle,” Huera explained.
Approach Could Be Adapted to Other Energy Harvesting Systems
Although the research team offered detailed descriptions of their pendulum-based system’s design and behavior, they conceded that they did not explore the design of a “complete generator” that converts vibrations into usable electricity.
“We have described the system theoretically and conducted laboratory tests to demonstrate that it works, but we have not made large-scale prototypes or cost studies,” Huera explained.
When discussing possible uses of their energy-harvesting approach, the researchers suggested using this design in environments where conventional turbines are technically impractical or difficult to maintain. They also note that their ocean current-based approach could be adapted to any waterway with sufficient flow and “suitable cross sections,” or to harness energy from wind-induced vibrations.
Up next, the research team plans to optimize the performance of their current design. According to the team’s statement, these include “adjusting the brake torque according to position or hydrodynamic load,” studying the limits of useful speed range, and exploring how multiple devices could be tasked to work together to “increase the energy obtained per unit area.”
The study “Energy harvesting from vortex-induced vibrations using a pendulum” was published in the Journal of Fluids and Structures.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.