Proponents of wave and tidal power say these renewable energy technologies have great potential but still must prove themselves before they can be widely deployed.

Exactly how do wave and tidal power differ? Wave energy technology uses the movement of ocean surface waves to generate electricity. Tidal power, on the other hand, is based on extracting energy from tidal movements and the water currents that accompany the rise and fall of the tide.

Wave and tidal energy have two significant advantages over other renewable resources. First, ocean tides are predictable and regular. Second, wave energy could be more abundant than tidal energy, while being less intermittent than wind or solar power.

However, wave and tidal energy installations also face some disadvantages. Primary among these is that fact that conditions along coastlines or on the ocean surface can be hard on wave and tidal installations. Generation assets must be built with operational hazards – such as crashing waves and corrosive salt water – in mind.

Wave and tidal potential

 According to the European Marine Energy Centre (EMEC) at Scotland's Orkney Islands, the best wave climates – with yearly average power levels of 20 to 70 kW per meter of wave front or higher – are where strong storms occur. Experts say the most energetic wave resources are along the coasts of the Americas, Europe, Southern Africa, Australia, and New Zealand. However, the extent to which these resources will prove practical to harness depends upon the successful development of near-shore and deep-water technologies.

Because wave and tidal technologies can be three to four times more expensive than wind power per megawatt, many installations are being developed and supported with government financial backing. The United Kingdom is one of the largest sponsors of wave and tidal power. The government has earmarked more than US$35 million for a new Marine Renewables Proving Fund. This fund is to support initial project prototype development through to early-stage commercial generation. A further US$15.7 million is going to develop the Wave Hub off Cornwall, and US$13.2 million for EMEC. Wave Hub's electrical "socket" on the seabed is to allow ocean energy developers to conduct large-scale testing of their equipment before going into commercial production.

Once projects in the United Kingdom have reached early-stage commercial generation, they are eligible for money from the Marine Renewables Deployment Fund. The United Kingdom government granted US$3.8 million to wave and tidal power from a US$83 million pot created under this fund, which began in 2004.

Setbacks to deployment

In 2008, Scottish firm Pelamis Wave Power Ltd. (which changed its name in 2007 from Ocean Power Delivery) launched the Agucadoura wave farm in Portugal. The project featured three of the company's P1-A marine energy converters. These converters consist of 150- to 180-meter-long floating tubes that move with wave motions. Generators positioned along the tubes then convert movement into energy.

The company installed the converters 3 miles off the coast of northern Portugal in September 2008. However, all three units were removed from the ocean in mid-November 2008, after leaks were discovered in the buoyancy tanks.

Compounding Pelamis' woes with Agucadoura, the company could not get the financial support to relaunch the units once the technical problems were solved. As a result of the global economic downturn, sponsor Babcock & Brown withdrew from the project. By March 2009, the Agucadoura project was taken offline indefinitely, with about US$13 million spent on the project.

However, Pelamis' work on other projects is gaining momentum. In February 2009, the company won an order from British renewable company E.ON for one unit of the next generation of Pelamis converters, called P-2s. The 750-kW machine will be built at Pelamis' facility at Leith Docks, Edinburgh, and tested at EMEC.

In addition, in December 2009, Swedish energy company Vattenfall announced plans for a joint venture with Pelamis to develop a marine energy farm near the Shetland Islands in the eastern Atlantic. This project could achieve an installed capacity of up to 20 MW by 2014, Vattenfall said. This could provide electricity to about 9,000 homes annually.

Projects taking shape

Despite the technological and economic challenges, there are still wave and tidal projects taking shape. Three companies – Ocean Power Technologies, OpenHydro, and Blue Energy Canada Inc. – are among those making progress.

In November 2009, Ocean Power Technologies (OPT) won a US$61 million grant from the Australian government for a utility-scale project. The company said work on the 19-MW project is expected to begin by the second quarter of 2010. Further funding will be needed to complete the project, the company said.

OPT's PowerBuoy unit floats freely with the rising and falling of offshore waves. The resulting motion is converted with a power take-off to drive a generator. The generated power is transmitted ashore via an underwater power cable. A 10-MW OPT power station would occupy about 30 acres of ocean space. The technology is scalable up to 100 MW, the company said.

In October 2008, OPT won a US$2 million award from the U.S. Department of Energy (DOE) in support of the company's 1.5-MW wave power project in Reedsport, Ore. This was the first award for the building of ocean wave energy systems by the DOE, according to the company. In December 2009, OPT chose Oregon Iron Works to construct the first 150-kW PowerBuoy PB150 unit to be installed at Reedsport.

An Irish tidal energy company, OpenHydro, also is moving forward on project development. OpenHydro's turbine is mounted on the seabed below the ocean waves. Each unit has a maximum capacity of 1 MW. In October 2009, OpenHydro won a grant of nearly US$3 million from Sustainable Energy Ireland's Ocean Energy Prototype Research and Development Program. OpenHydro will use the grant to design and develop a 16-meter Open Center Turbine, subsea base, and installation barge.

Also in 2009, OpenHydro paired with Nova Scotia Power to deploy a 1-MW tidal turbine in the Bay of Fundy in Canada. The project will serve as part of Nova Scotia's tidal power test facility. The Open Center Turbine was manufactured in Ireland by OpenHydro. The turbine rests directly on the ocean floor using a subsea gravity base fabricated by Cherubini Metal Works.

Another company working in Canada is Blue Energy Canada. In September 2009, the company began developing its tidal turbine technology. This 1-MW unit, called a tidal bridge turbine, is powered by ocean currents and is designed to allow fish to pass through freely, the company said. Once Blue Energy Canada determines a location for this unit, the company plans to build ten more units as the base model for a 200-MW ocean energy project. Blue Energy says its tidal bridge turbine can provide a route across large bodies of water for cars and tracks; can be used as a platform for offshore wind turbines; and can support gas, phone, or power lines.

Shoreline devices

Two companies that are working to develop shoreline wave energy conversion devices are Aquamarine Power Ltd. and Wavegen.

Aquamarine's Oyster wave energy converter has been tested and deployed at the New and Renewable Energy Centre near Newcastle, England. The Oyster converter is an onshore, commercial-scale pumping cylinder with a capacity of 170 kW. A full-scale Oyster uses two pumping cylinders and can deliver in excess of its capacity of 350 kW.

Oyster is designed to capture the energy found in near-shore waves up to depths of 12 meters. A 15-MW commercial farm of Oyster devices could provide clean renewable energy to 9,000 homes. In November 2009, Aquamarine launched the Oyster at EMEC, and the unit began producing power.

Aquamarine also has an agreement with Airtricity, the renewable energy division of Scottish and Southern Energy. Under this agreement, by 2020 Aquamarine will develop sites suitable for deployment of Oyster.

Wavegen, a unit of Voith Hydro, produces a shoreline wave energy conversion unit called Limpet. The technology used is called an oscillating water column. Ocean waves move air in and out of chambers in a breakwater. This compressed air drives Wavegen's turbine, known as the Wells turbine, to generate electricity. The 18.5-kW modules are meant for use in breakwaters, coastal defenses, land reclamation schemes, and harbor walls. The technology has been connected to Scotland's power grid since 2000.

In 2006, Wavegen teamed up with Npower Renewables to plan a wave power plant for the Lewis Island in Scotland. The 4-MW Siadar Wave Energy Project earned the approval of the Scottish government in January 2009.

Ocean wave and tidal power is a valuable resource. Companies are making progress toward harnessing this resource to provide electricity to homes in North America and throughout the world. However, more work is needed to advance this technology and bring it to commercial-scale electricity production. 

Jeff Postelwait is associate editor with Electric Light and Power, a PennWell Corporation publication. This article was adapted from the December 2009 issue of Electric Light and Power.