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.
HOW IT WORKS
The most promising of all hydro energy technologies, 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.
(Pictured at Right) The world's first commercial-scale and grid-connected tidal stream generator – SeaGen – in Strangford Lough, Ireland. The strong wake shows the power in the tidal current.
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:
- Coastal ocean currents worldwide contain power equal to 1/4 of the world's energy needs.
- Pneumatic devices use wave motion to compress air and drive a turbine.
- Buoyant devices move on the surface with the waves, exerting tension against a an anchor line to harness energy.
- Raft devices tethered to each other or to pontoons use the relative motion of each other moving with the waves to harness wave energy.
- Spillover devices capture water and power from breaking waves
- Commercial-scale wave energy is yet to become a reality though test projects average costs of 6-8 cents per kilowatt hour. Though some are much closer to commercial deployment than others.
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 of sub-sea power connections and therefore increase their cost efficiency, paying back energy dividends more quickly.
Ocean Thermal Energy
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.
WAVE POWER IN MARYLAND
While there are several trail, built projects internationally in England, Ireland, and India, and one project located in Maine at the mouth of the Bay of Fundy, there are currently no tidal energy projects located in Maryland. In 2008, UEK Delaware was award a grant by the Delaware Department of Natural Resources (DNREC) Green Energy Office to construct a tidal turbine power plant in the Indian River Inlet, but the proposed project was swamped by strong local opposition from fisherman and other community groups.
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.
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:
- Efficiently converting wave motion into electricity. Waves have intermittent power surges, while most turbines operate on steadily streaming power;
- Constructing affordable devices that can survive storm damage and saltwater corrosion;
- Reducing the high total cost of electricity—including the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs;
- Impacts on the marine environment, such as noise and visual appearance;
- Potential for some installations to displace commercial and recreational fishermen from productive fishing grounds, can change the pattern of beach sand nourishment, and may represent hazards to safe navigation.
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.
New Research in Tide-Wave-Hydro Power
In 2013, the Department of Energy made $16 million in grants for 17 different projects to help sustainably and efficiently capture energy from waves, tides and currents. Together, these projects will increase the power production and reliability of wave and tidal devices and help gather valuable data on how deployed devices interact with the surrounding environment.
For more on research and testing of tide, wave and other hydro technologies, visit the DOE Marine and Hydrokinetic Technology Development and Testing page on the energy.gov website.