There are three main types of wave energy technologies. One type uses floats, buoys, or pitching devices to generate electricity using the rise and fall of ocean swells to drive hydraulic pumps. A second type uses oscillating water column (OWC)devices to generate electricity at the shore using the rise and fall of water within a cylindrical shaft. The rising water drives air out of the top of the shaft, powering an air-driven turbine. Third, a tapered channel, or overtoppingdevice can be located either on or offshore. They concentrate waves and drive them into an elevated reservoir, where power is then generated using hydropower turbines as the water is released. The vast majority of recently proposed wave energy projects would use offshore floats, buoys or pitching devices.
Until recently, the common model for tidal power facilities involved erecting a tidal dam, or barrage, with a sluice across a narrow bay or estuary. As the tide flows in or out, creating uneven water levels on either side of the barrage, the sluice is opened and water flows through low-head hydro turbines to generate electricity. For a tidal barrage to be feasible, the difference between high and low tides must be at least 16 feet. La Rance Station in France, the world’s first and still largest tidal barrage, has a rated capacity of 260 MW and has operated since 1966. However, tidal barrages, have several environmental drawbacks, including changes to marine and shoreline ecosystems, most notably fish populations.
These turbines would be placed offshore or in estuaries in strong tidal currents where the tidal flow spins the turbines, which then generate electricity. Tidal turbines would be deployed in underwater ‘farms’ in waters 60-120 feet deep with currents exceeding 5-6 mph. Because water is much denser than air, tidal turbines are smaller than wind turbines and can produce more electricity in a given area.7 A pilot-scale tidal turbine facility – the first in North America – was installed in New York’s East River in December 2006. The developer, Verdant Power, hopes to eventually install a 10 MW tidal farm at the site.
Unlike fossil-fueled power plants, wave and tidal energy facilities generate electricity without producing any pollutant emissions or greenhouse gases. Since the first wave and tidal energy facilities are currently being deployed, the full environmental impacts of wave and tidal power remain uncertain but are projected to be small. Concerns include impacts on marine ecosystems and fisheries. Environmental impact studies are currently underway and several pilot and commercial projects are undergoing environmental monitoring. The East River tidal turbine pilot project includes a $1.5 million sonar system to monitor impacts on fish populations, for example.9 Careful siting should minimize impacts on marine ecosystems, fishing and other coastal economic activities. Wave and tidal facilities also have little or no visual impact, as they are either submerged or do not rise very far above the waterline.
One type of alternative energy source that can be used to provide electricity to the earth’s population is tidal energy. As the focus shifts more and more to environmentally friendly, reusable, and more sustainable energy sources, energy sources such as tidal energy begin to receive more attention in order to determine if they can be used in the long term.
Tidal energy is the creation of energy from the flow of water that is created by the changing of the tides. The idea is that when the tide changes, water either flows in towards land or it flows away from land, so water turbines are installed at the ocean bottom in areas where the flow is at it's greatest.
Electricity is created with water turbines that are strategically placed in order to capture the kinetic energy which is created by the flow of water past turbine blades. As water flows through the turbine, the blades spin which in turn spin an internal shaft that extends into a generator. This generator is what produces electricity. Since the tides are always changing, the process is always repeating itself and a constant source of energy is being created due to tidal changes.
While tidal energy is a viable option for providing a constant source of sustainable energy, there are some environmental consequences associated with the installation of tidal turbines, mainly with the animal population that exists in the ocean.
Although tidal energy can provide a very sustainable and valuable energy supply, it is still a solution that is yet to be fully explored. One of the reason why it is not being used more as a viable energy source is because of the high costs associated with being able to create an infrastructure that can support the mass production and distribution of electricity created with this type of energy source.
Waves are produced by winds blowing across the surface of the ocean. However, because waves travel across the ocean, their arrival time at the wave power facility may be more predictable than wind. In contrast, tidal energy, which is driven by the gravitational pull of the moon and sun, is predictable centuries in advance.
Worldwide potential for wave and tidal power is enormous, however, local geography greatly influences the electricity generation potential of each technology. Wave energy resources are best between 30º and 60º latitude in both hemispheres, and the potential tends to be the greatest on western coasts.
The United States receives 2,100 terawatt-hours of incident wave energy along its coastlines each year, and tapping just one quarter of this potential could produce as much energy as the entire U.S. hydropower system. Oregon and Washington have the strongest wave energy resource in the lower 48 states and could eventually generate several thousand megawatts of electricity using wave resources.2 Several sites in Washington’s Puget Sound with excellent tidal resources could be developed, potentially yielding several hundred megawatts of tidal power.