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Oceans and rivers possess tremendous amounts of energy in the form of waves, currents, tidal flows and temperature gradients. Estimates for the energy contained in currents and tidal flows alone range from 280,000 Terawatt-hours (TWh) to over 700,000 – many times over the electric power generation of the entire world, which is approximately 16,000 TWh. Prevailing ocean currents hug populous continental coastlines, making approximately 4,000 TWh—one quarter of the world’s current electricity demand – accessible.
Likewise, similar power resides in major rivers – and right in our own Chesapeake Bay.
Wave energy is produced when electricity generators are placed on the surface of the water. Energy output is determined by factors such as wave height, wave speed, wavelength, and water density. Wave energy can be harnessed through a number of devices that operate on different principles:
R&D is also underway to use these devices to provide a mounting platform for wind turbines – offering the possibility of a hybrid wind-wave device. Hybrids have the potential to maximize the use of sub-sea power connections and therefore increase their cost efficiency, paying back energy dividends more quickly.
Tidal stream devices operate below the surface to extract energy from the tides. Unlike wave power, tidal streams are predictable – though cannot always be matched to hours of peak demand. Current tidal technology involves dam projects, which are expensive to build and disrupt the environment.
New technologies include tidal turbines, which resemble wind turbines and are mounted on the sea floor. Unlike dams, they operate in freely flowing current and require no large-scale construction, lowering the cost of development and minimizing the impact on the marine ecosystem. But in order to capture the diffuse nature of tidal energy, this also means that large numbers of turbines spread over large areas are required to generate significant power. R&D is underway to test large grid-connected systems to unlock further potential in this technology.
This form of energy uses the temperature difference that exists between deep and shallow ocean waters to run a heat engine for power. Rather than using fossil fuels to run the engine, ocean thermal energy uses the sun’s warming of the surface water.
The total energy available from this method is perhaps twice as high as wave energy, but in order to generate the highest output, large temperature differences between the surface and deep waters must exist. These differences are greatest in the tropics, and the most promising projects are operating in Hawaii and the Pacific rim, where deep water is more accessible and surface waters are consistently warm.
Commercial energy from waves and tides is still under development. Technology to support it is costly to develop, and unlike solar, geothermal, or even wind, it is not a solution that a homeowner can implement.
Considerations and challenges for implementing wave-hydro systems include:
As we look at ways to generate more and more energy from renewable sources, we need to consider all sources. With the vast water resources of the Chesapeake Bay and its major rivers and tributaries and the Atlantic Ocean coast, wave and tidal energy are both viable technologies for Maryland’s energy needs.
Just as the Chesapeake Bay has been a vital economic force for Maryland since the beginning, it also has the power to be a vital energy force. As we harvest crabs, rockfish, and oysters, we can also harvest renewable energy.
Ireland-based Wavebob, Inc. has pronounced Maryland an “ocean energy” cluster because of our marine natural resources. A project is under development between Wavebob and the U.S. Naval Academy to generate wave energy, and other companies are exploring opportunities in the lower Bay and along the Atlantic coast.
See the MCEC R&D in Maryland page for descriptions of organizations, projects, and institutions advancing research and development in all types of renewable energy resources.
The Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) lists renewable energy and efficiency news and websites specific to Maryland.