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Wave energy is energy captured from the motion of waves either on the surface or by the pressure changes below the surface. Ocean waves contain tremendous energy potential. Devices either floating on the surface of the ocean or anchored on the bottom capture this energy. Wave energy technologies can be installed in three separate areas, each with their own environmental impacts: nearshore, offshore and far offshore. Typically, energy units are given in gigawatts (GW) or killawatt-hours (kWh), but wave and tidal energy is often given in terawatt-hours/year (TWh/yr). Wave energy is still a relatively new technology with projects underway across the world. There are a variety of applications for the wave energy devices each having their own benefits and impacts.
- 1 Four Types of Wave Energy Devices:
- 2 Current Global Wave Energy Projects
- 3 See also
Four Types of Wave Energy Devices:
- Terminator Devices
- Point absorbers
- Overtopping Devices
A terminator device is attached perpendicular to the waves captured or reflects the wave energy. This device takes up relatively little space in the ocean, but does use up coastline. Some of the best coastline for wave energy is either residential or pristine wilderness. These devices tend to be onshore or nearshore; however, floating designs have been made for offshore application. Water column oscillation is a driver of terminator devices, where water enters into a chamber through an opening, trapping air above. Outside wave motion causes the captured water to move up and down, like a piston, thus forcing the air to turn a turbine and generate power. Terminator devices tend to have power ratings of 500 kW to 2 MW, depending on wave motion and device parameters.
Long, segmented floating cylinders built parallel to wave direction, which flex at segment connections with the height of the waves as the waves move past them. To produce electricity, the segments connect to a hydraulic pump (or other energy converter). Power is fed to shore through a common sub-sea cable. This device does not use valuable coastline space, but it has to be brought ashore for any type repair. This presents difficulties in transportation of energy from the harvesting location.
A floating buoy structure attached to a fixed cylinder. Its components move with rising and falling wave height to produce electricity. The up and down motion of waves drive electro-mechanical or hydraulic converters to generate power. The anchors provide substructures for marine life to grow. These devices also take up space in the ocean which could otherwise by used for commercial purposes such as fishing.
These devices are composed of reservoirs with up to 14,000m^3 of water filled from incoming waves. The reservoirs fill and build up pressure, similar to a dam. The water is released from the reservoir and gravity drives the falling water to turn the hydro-turbines and generate energy. Offshore overtopping devices have wave reflectors that concentrate waves which increases the wave height. Overtopping devices can also be built as a floating platform which creates electricity via wave energy funneled through turbines inside of the platform.
Current Global Wave Energy Projects
Pelamis; Pelamis Wave Power
Location: Coast of Portugal
Project: 2.25 MW multi-unit commercial wave farm that was ready for use in the summer 2008. Each device has the ability to generate 750KW with 25-40% of that power being constantly generated.
How it Works: This energy device is is constructed of cylinder shaped sections that are connected by hydraulic joints. The device is partially submerged in the ocean water. Wave motion in the hydraulic joints is resisted by ram pumps which pump oil into the hydraulic motors. These motors drive the electricity generation for the device.
Archimedes Waveswing; AWS; Ocean Energy
Location: Pre-commercial wave energy plant to be tested in Scotland
Project: 250KW point absorber device planned to be tested at Orkney's European Marine Energy Center in Scotland.
How it Works: Buoys moored on the seabed. Devices have air-filled casings that are submerged where waves move over the devices and press against the cylinders with compressed air. The compressed air is what drives the hydraulic system and generators to produce electricity.
CETO; Renewable Energy Holdings
Location: First device tested in Western Australia in January 2008
Project: Wave energy technology that produces freshwater from sea water;projected to be commercially available in 2009
How it Works: Completely submerged device that is moored to seabed. High pressure sea water is brought to the shore through pipes. Reverse osmosis is used to desalinate the water which is then used to drive the hydroturbines.
The LIMPET; OWC
Location: Islay, Scotland
Project: Oscillating Water Column (OWC) terminator device prototype currently operating at 75kW, with a maximum capacity of 500kW.
How it Works: A wave capture chamber is built into the shore's rock face. Tidal wave power forces water into the capture chamber. The air inside of the device is compressed and decompressed by the oscillating water column. The rushes of air drive the Wells turbine, thus generating power.
Environmental Impacts of Wave Energy
Animals: entanglement in the cords; fouling organisms expected to colonize the mooring lines; Gray and Humpback migration disruption
- All devices can cause the seabed to be disrupted by drilling and running of cables to the shoreline.
- Attenuator hydraulic pumps attached to center could potentially leak.
- Sounds pollution; test done in Kaneohe bay showed that Humpback whales, two species of dolphins and green sea turtles could be affected.
- Wave height reduction 10-15% behind plant
- New hard structures in pelagic and soft sediment environments.
- Device could effect habitat. Example: Kelp; amount of wave energy affects which species of kelp are present. Macrocystis pyrifera found in areas of low wave energies
- Nereocystis luetkeana located in more exposed habitats.
- Reduction of wave energy levels reaching the coast may reduce longshore sediment transport. This reduces erosion in the vicinity of wave energy plant but increases erosion down coast. This is significant only if it is within 2 km of shoreline.
- Beach characteristics may affect beach spawning fishes such as the Surf Smelt or Night Smelt who spawn on the beach slope and deposit their eggs beneath the surface of the sand.
- According to Previsic and Bedard (2007) once wave energy conversion devices reach a base of about 25,000 megawatts they will produce a megawatt hour of electrical energy at or below the cost of energy generated from on shore wind technology.
- Displacement of safe transit lanes for ships.
- New jobs, income and tax revenue resulting from WEC facility.
- Degradation of aesthetic resources resulting from changing patterns of coastal erosion.
- Loss of jobs, income and tax revenue from impacts to fisheries and recreation such as whale watching from displacement.
- Loss of sites with other commercial values such as Aquaculture or dredge spoil disposal.
- For sites scaled to a commercial level generating 300,000 MWH/yr the Cost of energy depending on location $0.10 kwh for areas of high wave energy and 10.40 kwh for areas of lower level wave energy
- Bedard, Roger, comp. Offshore Wave Power in the US: Rep. no. E2I Global EPRI-007-US. Ed. George Hagerman. Global Energy Partners, 2004. Print.
- Cruz, Joao, ed. Ocean wave energy current status and future prepectives [i.e. perspectives]. Berlin: Springer, 2008. Print.
- Foster, Ms, Schiel, DR (1985) The ecology of giant kelp forests in California: a community profile. US Fish and Wildlife Biological report 85(7.2)
- McMurray, Gregory. "Ocean and Coastal Management Program Oregon Department of Land Conservation and Development." 2007. MS. Oregon State University, Corvalis.
- PIER 2007. Summary of PIER Funded Wave Energy Research, California Energy Commission, PIER Program. CEC‐500‐2007‐083.Soerensen, Hans C., Lars K. Hansen, and Rune Hansen. European Thematic Network on Wave Energy. Rep. no. NNE5-1999-00438. Comp. Tim Thorpe/AEA Technology and Pat Mc Cullen/ESB International. Blegdamsvej: EMU, 2003. Print.
- United States of America. U.S. Department of the Interior. Minerals Management Service Renewable Energy and Alternative Use Program. Technology White Paper on Wave Energy Potential on the U.S. Outer Continental Shelf. 2006. Print.