There has a been a lot of activity in wave power recently, with the world’s first commercial tidal energy turbine installation completed in Northern Ireland last week, another project being developed in the Ontario River near Cornwall, Canada, and possible expansion of a small installation in New York City. The technology for the Ireland project was developed by British firm Marine Current Turbines, and the NYC and Canada installations were designed by Verdant Power, a New York-based company (read the Matter Network stories on Ireland here and Canada here).
Water turbines operate in much the same way as wind turbines, but the greater density of water presents somewhat different technological challenges. The increased density of water means that water turbine blades can function with smaller wingspans than air turbines. However, the effects of drag and wake formation are greater in water and can cause a large thrust force on the turbine blades, interfering with the flow through the turbine rotor. In addition, the flow rate varies significantly with the depth of the water.
Some of Marine Current Turbines’ patents seek to address these problems with their turbine installation designs. U.S. Patent No. 7,331,762 is directed to a turbine support structure having the turbine rotors situated between two parallel decks. The upper and lower deck each have a different streamlined cross-section, with one being more convex than the other. This design accelerates the flow of water over the more convex surface to eliminate the difference in flow rates between the upper and lower water streams, thereby reducing interference with the rotor.
U.S. Patent No.7,307,356 (‘356 patent) covers a bifurcated column design having a vertical gap designed to support twin turbine blades. The two blades spin in opposite directions to operate in bi-directional water flows (i.e., both ebb and flood tides). This setup also is beneficial because the two rotors offset each other’s torque. A horizontal turbine support structure extends perpendicular to the column with a portion extending through the vertical gap. This design minimizes water drag and wake formation so the bi-directional water flow doesn’t interfere with the rotor. The technology deployed in Northern Ireland, Marine Current Turbines’ SeaGen, appears to be an embodiment of the ‘356 patent.
Verdant Power’s patent application Pub. No. 2007/0063520 is directed to a system for generating power from slow moving water flows for use in non-tidal flowing water such as man-made canals or aqueducts. The system consists of a water flow flume with a network of slopes and curves, including an acceleration zone to increase flow velocity and create kinetic energy from water movement.
Looks like this is just the beginning for commercial tidal power installations and for Marine Current Turbines in particular, which has other projects slated for the next few years, including in Vancouver and Wales.