Waves, Currents &
Electrical Potential


The TidGen Power System is designed to generate electricity in shallow tidal and deep river sites. Image: Ocean Renewable Power Company

Billions of watts of power continuously flow down rivers and streams, or wash up on U.S. shores, just to dissipate. Part of the ocean waves and flowing currents, this form of energy tends to be more reliable than solar and wind, and is abundant in certain regions. It’s also immensely challenging to exploit: How can engineers tap this vast, restless resource to create sustainable energy that competes with fossil fuels and is compatible with existing power grids?

According to Pike Research’s January 2012 report, Hydrokinetic and Ocean Energy Renewable Power Generation, the U.S. still has plenty of untapped hydropower resources – enough to “generate from 85,000 to 95,000 more megawatts, with 23,000 MW available by 2025.”

Verdant Power’s free flow system turbine is bidirectional. Passive yawing orients the device to operate optimally during both ebb and flood tides. Image: Verdant Power

The upside potential for “technically recoverable wave energy alone could provide about 25 percent of U.S. electricity demand,” said Christopher Mahoney, director of communications for the Electric Power Research Institute in Charlotte, NC.

This kind of notice is starting to bring the technology of hydrokinetics out from the shadows of wind turbines and solar panels.

Hydrokinetics studies how kinetic energy is generated by the natural movement of water – surface waves, tidal currents, and rivers, streams, and ocean currents – and how to convert that energy to electricity. Hydrokinetic devices are placed directly in the flow and generate energy only from the power of the moving water; no dam or diversion structure is required to increase hydraulic head to drive a turbine.

Hydrokinetics is a rapidly developing field where both big companies and startups can compete equally in engineering and design.

“Various approaches to harvesting ocean wave energies have been developed that focus on maximizing wave-energy capture, maximizing the output of the electromechanical power conversion process, and optimizing the overall system performance from a cost, reliability, and value proposition standpoint,” said Gregory Lennon, director of business development-utility scale for Ocean Power Technologies, a Pennington, NJ, wavepower technology firm.  “Significant focus has also been given to solutions that are grid-connect-ready, as well as the ones that serve as autonomous power sources for localized loads.”


February 2013

by Mark Crawford, ASME.org, for Mechanical Engineering