What is wave energy?
First, we need to explain how waves are created. Wind is caused by differences in temperature due to the solar heating of the earth’s atmosphere. When this wind skims over the sea, an interaction is caused in which energy is exchanged between the wind and the sea surface. At first, little ripples arise on the surface. Then, the wind that skims along these ripples causes higher air pressure at the front of the wave than at the back. As a result the ripples change into small waves.
As this process continues, the waves become higher and the distance between the tops (wave length) becomes longer. The amount of converted energy depends on the wind speed, the time the wind blows over the waves, and the distance it covers. During a wave’s voyage, it shapes into a more regular wave, commonly referred to as a swell. At ocean shores, swells are very regular and discernable, even when the sea is calm.
Wave energy, then, can be seen as a concentrated form of solar energy. During this process of conversion, the energy is concentrated more and more, up to a power level of over 100 kW per meter of wave front.
What does a wave energy converter do?
Basically, it converts the mechanical energy of a wave into electrical power.
How does the PowerBuoy™ work? What is so unique about it?
The PowerBuoy™ is an offshore wave energy converter which is submerged more than a meter below the water’s surface. Inside, a piston-like structure moves as the PowerBuoy™ bobs with the rise and fall of the waves. This movement drives a generator on the ocean floor, producing electricity, which is sent to the shore by an underwater cable. An OPT “power plant” will consist of an array of identical PowerBuoys™ that are electrically connected to provide the desired power capacity.
OPT’s “smart” PowerBuoy™ utilizes computer-based, proprietary technologies. Technological innovations include: patented electronics systems for control and power conversion patented wave energy conversion and transfer systems unique generating systems that function effectively at low and variable speeds and a modular construction process.
What is done to assess the environmental effects of putting a system like this near the shoreline?
A comprehensive Environmental Assessment (EA) is prepared before any construction phase of a project begins. Great care is put in the planning and design phases to ensure there are no negative environmental effects.
How is the buoy mounted to the sea floor?
The PowerBuoy™ is mounted on the sea bottom using a proprietary anchoring system that avoids any damage or threat to the sea bed or sea life.
Is any part of the PowerBuoy™ visible above sea level?
As dictated by local marine regulations, an OPT power plant will have a few PowerBuoys™ with masts that rise above the surface of the water, with navigational aids attached, such as a radar reflector, day mark, and warning light to help aid mariners in the vicinity.
How deep is the water in which the system is installed?
The buoy is designed to be deployed in approximately 100 feet (30 meters) of water.
What are the effects on fishermen in the area?
The presence of the buoys does not cause any significant restrictions to fishing. In fact, the buoys serve as an artificial reef and attract fish and other marine life. In some parts of the world, conventional buoys are deployed to serve as “Fish Attracting Devices”.
How will the buoy affect sea turtles and other marine life in the area?
Possible impact on threatened or endangered species in the area by the placement of the buoys is addressed in the Environmental Assessment phase of the project. For example, in Australia, an independent study found that the OPT system had no negative impact on sea life, including migratory patterns of whales.
How will the buoy affect swimmers in the area? Will they be electrocuted if they swim nearby?
Although the buoys generate electricity, all the electrical generating and transmitting devices are housed in insulated enclosures and the standard underwater cable is shielded to prevent stray electrical currents. The system is designed to prevent any loss of electricity or emissions of electromagnetic fields.
What is the impact on the shoreline?
The power is brought to shore by a standard submarine transmission cable which has a small diameter. It is brought through the surf zone by conduit and the cable terminator at a standard grid connection box located near the shoreline. There is effectively no impact to the shoreline or to any sea life in the vicinity.
Overview of Power Wave Technology
OPT’s PowerBuoy™ wave generation system uses a “smart,” ocean-going buoy to capture and convert wave energy into a controlled mechanical force which drives an electrical generator
The rising and falling of the waves off shore causes the buoy to move freely up and down. The resultant mechanical stroking drives the electrical generator. The generated AC power is converted into high voltage DC and transmitted ashore via an underwater power cable.
The PowerBuoy™ is enhanced with sensors which continuously monitor the performance of the various subsystems and surrounding ocean environment. In the event of very large oncoming waves, the system automatically disconnects. When the wave heights return to normal, the system reconnects and recommences energy conversion and transmission.
Ocean Wave Generating Costs
The total operating cost of generating power from an OPT wave power station is projected to be only (US) 3-4¢/ kWh for 100MW systems and (US) 7-10¢/kWh for 1MW plants, including maintenance and operating expenses, as well as the amortized capital cost of the equipment.
State of the Technology
Ocean Power Technologies, Inc. currently has a test PowerBuoy™ in operation in Hawaii and has tested PowerBuoy™ off the coast of New Jersey. The company is currently petioning the state of New Jersey for permission to install a 100 MW PowerBuoy™ plant off the coast of Atlantic City, New Jersey.
Ocean Power Technologies, Inc. (OPT) is the leader in cost-effective, advanced, and environmentally sound offshore wave power technology. The electrical power generated by OPT’s technology is key to meeting the energy needs of utilities, independent power producers and the public sector. OPT’s PowerBuoy™ system extracts the natural energy in ocean waves, and is based on the integration of patented technologies in hydrodynamics, electronics, conversion mechanics, and computer control systems.
The result is a leading edge, ocean-tested, proprietary system which generates reliable, clean, and environmentally-beneficial electricity. Ocean Power Technologies, Inc. Ocean Power Delivery LTD. [OPD] is another major player in this industry and is arguably further along than OPT or others. OPD’s office is located at 104 Commercial Street in Edinburgh, United Kingdom. Ocean Power Delivery Ltd has developed a novel offshore wave energy converter called Pelamis. Building on technology developed for the offshore industry, the Pelamis has a similar output to a modern wind turbine. The first full-scale pre-production prototype has been built and is being tested at the European Marine Energy Centre in Orkney.
It is anticipated that future `wave farm’ projects would consist of an arrangement of interlinked multi-machines connected to shore by a single subsea cable. A typical 30MW installation would occupy a square kilometre of ocean and provide sufficient electricity for 20,000 homes. Twenty of these farms could power a city such as Edinburgh.