Chapter 3: Electricity Generation from Open Water
(Draft date: 07 Dec. 07)
Author's note: This is a preliminary draft and a work in progress. (Further explanation.)
3.A: Electricity Generation Using Helical Turbines in Open Water
Alexander Gorlov’s patented “Gorlov Helical Turbine” received the 2001 Thomas A. Edison Patent Award, given each year by the American Society of Mechanical Engineers. The Society hailed the potential of the Gorlov turbine to “alleviate the world-wide crisis in energy.” Gorlov’s turbine design is based on the 1931 invention of a turbine whose blades were modeled after the wings of birds by French engineer George Jean-Marie Darrieus. This permitted the blades to turn faster than the wind or water striking them. Darrieus’ invention suffered from vibration which destroyed his turbines; Gorlov twisted the blades a bit like a strand of DNA, eliminating the vibration. The twist also improved the capacity of the turbine to spin in water; when put into a current of water it starts spinning instantly and within seconds is turning faster than the current of water hitting it. Gorlov received his first patent for his helical turbine in 1994. In 1998-99 studies at the Marine Hydrodynamics Laboratories at the University of Michigan found the Gorlov Helical Turbine will generate in water moving as slowly as two knots and captures about 35 percent of the kinetic energy of the current.
Gorlov’s Helical Turbine can harness the kinetic energy of slow-moving currents in open water. It does not require a dam; some refer to this form of electric generation as “free-flow hydropower.” The Gorlov turbine looks like an oversized eggbeater: a “cross-flow” turbine. (The type of turbine used in wind installations that looks like a boat propeller is an “axial flow” turbine.) Unlike axial-flow turbines, a cross-flow turbine can be mounted either horizontally or vertically, stacked in rows like spools on a string, in as little as three feet of water. Cross-flow turbines will turn equally well in current flows from any direction, making them ideal for tidal current hydropower. The capacity of a water turbine to generate electricity is due to the fact that water is some 850 times denser than air; wind turbines work best in humid conditions for this reason. William Taylor of Verdant Power in Virginia estimates that helical turbine installations will ultimately deliver hydropower for $1,500 per kilowatt, about the same price as current Danish wind turbines.
According to the United Kingdom’s Department of Trade and Industry, global potential for power generation from ocean currents is 3,000 gigawatts, of which 90 gigawatts is economically recoverable using current technologies. The currents flowing through San Francisco’s Golden Gate could produce 2 gigawatts per day, more than twice what the city consumes at times of peak demand. In September, 2003, the first commercial free-flow ocean turbine began operation in Hammerfest, Norway. The United Kingdom has plans for many installations, and is currently installing its first free-flow turbine complex at Devon. On March 19, 2002, the Korean Ocean Research and Development Institute lowered its first experimental Gorlov turbine into the Uldolmok Strait between the Korean Peninsula and Jindo Island, which has tidal currents of 12 knots. In the fall of 2004, South Korea installed a second 15-foot Gorlov turbine, with the goal of generating 1,000 kilowatts of power for the 40,000 people of Jindo Island. If these installations go well, the Koran government plans thousands of ocean Gorlov turbine installations to harvest 3,600 megawatts of power - the equivalent to the output of four nuclear power plants.
In a report issued in April, 2003, the U.S. Department of Energy assessed the amount of electricity that turbines could generate from America’s rivers and streams. Excluding waters running through national parks and other off-limits sites like wilderness, the DOE estimated 170 gigawatts capacity, more than four times the average amount now generated per year by all U.S. hydroelectric facilities. Not all that 170 gigawatts would be economically recoverable. Verdant Power is currently installing six Gorlov turbines in New York City’s East River.
Gorlov insists his turbines generate a pressure barrier which will repel fish from being caught and killed in his turbine blades, but this has not been proven. Monitoring of a single Gorlov turbine in a freshwater stream showed fish swimming around it rather than being sucked into it. No one has evaluated what happens when fish encounter a field of spinning Gorlov turbines.
The commercial future of Gorlov Helical Turbines will also depend on what these pioneering installations experience by way of maintenance and interruptions in service due to damage. The underwater environment is harsh, full of sediments, corrosive agents, and debris. Joseph Sayer, project manager at the New York State Energy Research and Development Association, asks: “What happens if there’s a storm? What about a log?”
In November, 2006, Crest Energy, Ltd., applied to build a 200-megawatt tidal power plant just north of Auckland in the mouth of Kaipara Harbour. The generating facility would consist of 200 marine turbines on two 20-mile DC cables, sited 15 feet below the ocean surface - the harbour has no commercial ship traffic. The facility would generate power from the four tides each day, with eight hours of non-generation. The DC turbines (selected because high-voltage DC produces 5 percent of the electromagnetic emissions of AC, which minimizes disturbance to sea creatures) will feed by cable to a DC-AC converter and substation on land at the Hoteo River. When completed in 2011, the $400 million project would generate 4 percent of New Zealand’s annual energy supply.
In Florida, six ocean power projects using turbines to capture energy from the strong currents along Florida’s long coastline are now being planned.
Another approach to capturing the kinetic energy of ocean water: in Hawaii, a power generator uses a pump driven by the bobbing motion of waves. This demonstration system has not been expanded to commercial scale yet.
Chapter 3.B: Ocean Thermal Energy Generation
In Hawaii, researchers have used the large difference in temperature between cold, deep water and warm surface water to generate electricity in a demonstration project. This system has not been upsized for commercial application yet.