October 2, 2007
TIDAL ENERGY TECHNOLOGY
By: Kevin E. McCarthy, Principal Analyst
You asked for background on tidal energy generators. You also wanted to know (1) what is the estimated cost of building such generators, (2) how much power they can produce, (3) whether the federal government provides grants to subsidize these costs, and (4) whether the Connecticut legislature has considered such generators or investigated their feasibility.
We have enclosed a 2006 study on relate issues prepared by the Electric Power Research Institute.
There are two types of tidal energy generator technologies currently in operation. A barrage uses a dam to funnel water through turbines which are used to generate power. Tidal turbines use devices that look like wind turbines to convert the energy in tidal currents into electricity.
There are currently only a handful of tidal energy generators worldwide and most of these are prototypes. The existing generators have a capacity ranging from several hundred kilowatts to 240 megawatts. A kilowatt is the amount of energy used by ten 100 watt light bulbs; a megawatt (MW) is one thousand kilowatts. In contrast, a typical new fossil fuel power plant has a capacity of 500 to 1,000 MW. We have incomplete cost information about the existing projects, but even small projects routinely cost tens of millions of dollars. The generating capacity and construction costs of a new facility would be very site specific.
The federal government does not currently have a program to subsidize tidal energy. However, there is funding for tidal energy technologies in both the House and Senate versions of the major energy bill that is currently before Congress.
Connecticut law (CGS § 16-245n), passed as part of the electric restructuring legislation, allows the state's Clean Energy Fund to financially support tidal energy technologies. Such support could take the form of grants, equity investments, and research funding, among other things. There is currently an application before the fund to support a tidal energy project which is in the early stages of review according to Lise Dondy, the fund's president. As noted in OLR Report 2006-R-0566, the fund has invested in a wave energy project off Point Judith, Rhode Island, which is in the development stage.
TYPES OF TIDAL GENERATORS
The two major types of tidal power technologies are barrages (dams) and tidal turbines. A barrage converts tidal energy into electricity by forcing the water through turbines, activating a generator. Gates and turbines are installed along the dam. When the tides produce an adequate difference in the level of the water on opposite sides of the dam, the gates are opened. The water then flows through the turbines. The turbines turn an electric generator to produce electricity. An example of this technology is located on the Rance River near St.-Malo, France. The facility has a peak generating capacity of 240 megawatts. The facility cost 620 million francs (approximately $100 million) when it was built in the 1960s and began operating in 1966. In 1997, the plant was upgraded by the installation of turbines able to spin during both the incoming and outgoing tides. Further information about this facility is available in English at http://www.edf.fr/html/en/decouvertes/voyage/usine/usine.html. In 1984 a barrage was completed in the Bay of Fundy in Canada, the site of the world's largest tides. This facility has a capacity of 20 megawatts and cost $100 million (Canadian). The facility is still being paid off and is not cost competitive according to Margaret Murphy, public affairs manager for Nova Scotia Power, the facility's owner. Further information about this facility is available at http://www.electricalline.com/images/mag_archive/18.pdf. A project near Murmansk, Russia has a capacity of 400 kilowatts. We have been unable to get cost data for this project. According to Roger Bedard, a staff person at the Electric Power Research Institute who conducts research on ocean energy, this technology raises a number of
environmental issues (for example, whales were trapped at the Canadian facility) and there are currently no projects under development using it anywhere.
A more recent technology uses the kinetic energy of tidal currents to generate power. These tidal turbines look like wind turbines and can be grouped together like wind farms. They function best where currents run at between 4 and 5.5 mph. The best locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).
Verdant Power has placed tidal generators using this technology on the bed of New York's East River along the eastern shore of Roosevelt Island. Tidal flows of about 6 feet per second spin the turbine blades, which turn a shaft that powers a generator. The six submerged turbines each have three blades and are five meters (16 feet) in diameter. Each turbine can generate 35 kilowatts. The turbines have been used to power a grocery store and parking garage on the island. The project has received funding from the New York State Energy Research and Development Authority.
The project has run into several problems. As reported in the New York Times, days after the first two turbines were lowered into the water, the river's currents sheared off the tips of several of their blades about a third of the way down. New cast aluminum blades were installed to replace the broken ones and four other turbines that were lowered into the river's eastern channel earlier in 2007. But the tides proved too strong even for the new blades, putting excessive strain on the bolts that hold them to the turbine hubs. To keep them from coming apart, all six of the turbines have been shut down for repairs and may not be back in operation until Spring 2008. Further information about this project is available at the August 8, 2007 edition of the New York Times, http://www.nytimes.com.
According to William Taylor III, president of Verdant, the company has a goal of bringing the cost of the turbines down to $2,400 per kilowatt.
A project using a similar technology is being installed at the mouth of Strangford Lough, near Belfast, Northern Ireland. This facility will have a capacity of 1.2 MW and is expected to go into operation by the end of 2007. The £8.5 million ($16.8 million) project received a £4.27 million ($8.4 million) grant from the British Department of Trade & Industry's Technology Program. The blades on this turbine will be substantially larger than those used in the New York project (11 meters or 36 feet). Finally, Nova Scotia Power is developing a 1 MW facility in the Bay of Fundy using a similar technology, which it estimates will cost $12 to $15 million (Canadian). The Canadian and U.S. dollar are currently nearly equivalent in value. The company believes the facility will begin trial operations in late 2009. This will be followed by a two-year evaluation of the facility's performance. If deemed successful, the company will consider expanding the project with additional turbines to a scale of 5 to 25 MW.