With ocean energy the next frontier for renewable energy, developments are happening at a fast pace, especially with the more mature wave and tidal energy technologies. [see e.g. Engerati-First Grid-Connected Wave Energy Array Operates In Australia]
Wave energy potential
Of the various ocean energy types, tidal energy is the most mature, followed closely by wave energy. [Engerati-Time to Put Wave Energy Back on the Power Map] With the potential of wave energy to contribute an estimated 2,000-4,000TWh/year of energy, more than 100 pilot and demonstration projects exist throughout the world, according to a recent study by the International Renewable Energy Agency (IRENA).
The best wave conditions for exploitation are in medium-high latitudes and deep waters (greater than 40m deep), where the wave energy is found to reach power densities of 60-70kW/m. To date the US has lagged behind other countries in wave energy technology development but maybe not for long. In what is a major development, the first third-party-validated, grid-tied wave energy device is now operating in North American waters, feeding renewable electricity to the US Navy’s Marine Corps Base in Hawaii.
Wave energy testing in Hawaii
The wave energy converting device, named Azura, is being developed by Northwest Energy Innovations (NWEI), with support from the US Department of Energy and the US Navy, which has installed it at its test site in Kaneohe Bay on the island of Oahu.
This follows testing of a prototype of the same scale in a controlled, open-sea area off the coast of Oregon in 2014.
The current 12-month phase of testing, which is with a 20kW device at a 30m berth, is aimed to gather performance and reliability data, which will be used to further optimize the performance and refine existing wave energy computer simulations, ultimately supporting commercialization of this technology. NWEI, with US$5 million in additional funding from the Energy Department, will apply lessons learned from this current phase of development to modify the design in order to improve its efficiency and reliability. NWEI plans to then test the improved design with a full-scale device rated between 500kW and 1MW at the Hawaii test site at deeper test berths of 60m to 80m over the next several years.
“As the first grid connected wave energy device in the US that will be tested and validated by an independent party, this deployment marks a major milestone for our team and the marine renewable energy industry,” said NWEI founder and CEO Steve Kopf. “Standards, rigorous testing and transparency are the foundations of our development programme for the Azura technology. We believe that independent verification of performance data is imperative to achieving commercialization.”
Azura is novel in that it is designed to extract power from both the heave (vertical) and surge (horizontal) motions of waves to maximize the energy capture. The system produces power as a result of the relative rotational motion between a hull and float. The float can rotate continuously through 360° or oscillate back and forth, which enables the device to extract energy in a wide variety of wave conditions. The float also provides a self-limiting power shedding effect, which makes the device inherently survivable in open ocean environments and helps to reduce loads in the mooring system.
The Navy’s Oahu test site is the nation’s only grid-connected open-water wave energy test site.
Wave energy in US
The wave energy potential off US coasts has been estimated by the Energy Department at over 1,170TWh/year, although not all of this resource potential can realistically be developed. With more than half of the US population living within 80km of a coastline, transmission from these resources is potentially more economical. With further progress towards commercialization, ocean energy technologies could make substantial contributions to our nation’s electricity needs.
A second company, Ocean Energy USA, has also been awarded US$5 million in Energy Department funding for testing of its Ocean Energy Buoy at the Navy test site. The Ocean Energy Buoy works by harnessing the energy from air that is compressed by the natural rise and fall of ocean waves, and converting it into electricity. Research objectives include validating the mooring design and device durability in the open ocean environment, measuring power output at full scale, and evaluating the levelized cost of energy produced by the device.
According to the Energy Department’s recent marine and hydrokinetic energy projects report, from 2008 to 2014 about US$133 million was awarded for 97 projects.