Hydropower has a long record as the largest source of non-thermal electrical generation. But, after more than a century of use, the field is still far from achieving its full potential. While many of the best locations for traditional hydropower are already in production in developed parts of the world, there is still plenty of room to expand its use - in South America and Asia in particular. In addition, oceanic power sources have yet to be tapped beyond a few small-scale projects.
However, many areas with a resource that would support hydropower, also have a reliance on the fish swimming within the waters that would produce the power.
China's Yangtze River basin, for example, is home to about 360 species of fish, one third of that nation's total number of fish species. The 22.5 GW Three Gorges Dam across the Yangtze, which displaced 1.3 million people in creating a 360 mile reservoir behind the dam, also produced a 50% to 70% drop in the commercial harvests of four types of carp, and threatened several endangered species with extinction. Similar concerns have been expressed about power projects in the Mekong River and Amazon River basins.
“In Laos, people get 40% to 60% of their protein from fish caught in the Mekong,” says Dr. Glen F. Cada, a researcher in the Environmental Analysis Group at the US Department of Energy's (DoE) Oak Ridge National Laboratory, which specialises in the effects of hydraulic forces on fish. “They want the dams for the electricity, but don't want to destroy the fisheries people rely on for food.”
It's no surprise, then, to learn that research and development in the hydroelectric field has been dominated by the desire to increase turbine efficiency, while decreasing the negative impacts on the local fish populations.
For decades, the DoE, the Electric Power Research Institute (EPRI), turbine manufacturers and research laboratories have engaged in studies of how to get migratory fish safely up and down stream - past hydroelectric dams.
This research had been extended recently to include the hydrokinetic generation systems for use in tidal, run-of-river, and ocean thermal gradient generation systems. Part of the research includes the development of three new turbines, one for hydrokinetic applications; and two for use in traditional hydropower dams. All of these turbine designs are far safer for fish, without compromising output.
Gorlov hydrokinetic turbines
According to the DoE's December 2009 Report to Congress on the Potential Environmental Effects of Marine and Hydrokinetic Energy Technologies, “there are well over 100 conceptual designs for converting the energy of waves, river and tidal currents, and ocean temperature differences into electricity.” However, “most of these ocean energy and hydrokinetic renewable energy technologies remain at the conceptual stage.”
|Many areas with a marine resource that would support hydropower also have a reliance on the fish swimming within the waters that would produce this power.
But there are signs that commercialisation might not be too far away. One of these designs making it into the marketplace, for instance, is the Gorlov helical turbine (GHT). The GHT is based on the Darrieus turbine, which is used in vertical axis wind turbines as well as for hydropower applications.
The standard Darrieus design, with foils parallel to the axis, produces a sinusoidal power cycle depending on the angle of the foils to the direction of the air or water. The rotor speed must therefore be controlled so that it doesn't remain at the resonant frequency of the foils. In addition, the flow must be at a high enough speed to start the turbine spinning.
Developed by Alexander Gorlov, then a professor of mechanical engineering at Northeastern University, the GHT uses helical rather than strait foils. These foils then present a constant angle of attack, no matter what direction the flow is coming from. This eliminates the pulsing problem as well as allowing the turbine to spin at a lower flow velocity.
Almost two years ago, two GHTs installed in the free tidal flow of Uldolmok Strait (South Korea) began producing a combined 1 MW of electricity. A spherical form of the GHT was developed by Lucid Energy Technologies in 2009, for use inside water transmission pipelines.
This is now being marketed as the Northwest PowerPipe by the Northwest Pipe Company and Lucid. These units take the energy from the change in elevation along the pipeline route and convert it to electricity. A 60” pipe with a 12 ft. head drop and 7 ft./sec. velocity can reportedly produce 60 kW, more than 500MWH per year.
Fish friendly turbine
Much of the ongoing research in the hydropower sector is concerned with the attainment of the ideal turbine – one that combines efficiency with environmental friendliness. For example, one plausible alternative to the use of screens or other mechanisms to help fish avoid going through the turbine is to redesign the turbines so that fish can pass through them safely.
“It is all about flow,” says Steve Amaral, Ph.D. senior fisheries biologist for Alden Research Laboratories in Holden, Mass. “Fish react in different ways to different flow fields – turbulence, velocities, acceleration and flow. It is key to understand both the life stage of the fish and the species, and how they might react to different hydraulic conditions.”
Since the 1990s, the DoE's Advanced Hydropower Turbine Systems Program (AHTS) has researched methods of reducing mortality as fish interact with turbines.
“We analysed all the stresses that fish experience when they go through a turbine and are trying to redesign the turbine to reduce those stresses to values that fishes could survive,” says C ada.
A number of designs were proposed by a variety of vendors, and the DoE developed of two of these designs.
The first to make it out of the laboratory was the Voith Minimum Gap Runner (MGR) design from Siemens Voith Turbine. The MGR is based on a conventional Kaplan turbine, but with much smaller gaps between the runner and the turbine walls. Because of these smaller gaps, fish do not get trapped and crushed by the runner.
The first field testing of the MGR was done at the Bonneville dam in Oregon, and showed a 1.5% injury rate compared to a 2.5% injury rate at an adjacent Kaplan turbine.
More recently, the Grant County Public Utility District No. 2 installed an MGR at its 1,038 MW Wanapum Dam on the Columbia River. The tests found minimal differences between the mortality rates on the MGR and Kaplan turbines, which were already low. However the MGR allowed a 10% increase in electrical production.
Another approach developed by Alden Research Laboratory incorporates an integrated design, so that the runner blades are attached to a rotating shroud.
Since there is no gap between the blades' tips and the wall, this eliminates the low pressure vortices that occur near the blade tips, and also eradicates any chance of fish being caught between the blades and the turbine walls. In addition, in order to reduce the chance of blade strikes, this concept only uses three blades which are much longer than conventional blades and have nearly 180 degrees of wrap.
To test the principle, Alden constructed a 3:1 scale model of the turbine. These live fish tests found that American eels had a 100% survival rate, and that species such as sturgeon, trout, shad and herring would have a better than 98% survival rate when passing through a full-sized turbine.
The DoE has made an award of US$1.2 million to EPRI to conduct further engineering and testing of this turbine (EPRI Hydropower Project No. P58.003). Voith Hydro is building a full-scale version of the design and EPRI expects to have a test site selected this year.
“There is a lot of interest in these kinds of turbines,” says Cada. “Everyone would love it if you could put in a turbine that gives 98% survival for all species, and all sizes of fish, so you could pull out all the screens and run the turbine with a clear passage. That is the goal, and the limited testing of the Alden and Voith turbine looks like it might be a possibility.”
In addition to the three turbines discussed above, the DoE's Marine and Hydrokinetic Technology Database lists hundreds of other technologies at varying stages of development. Some of these are producing power for the grid, such as the Wavebob deployed in Ireland's Galway Bay in 2006, and the 0.45 MW Oceanlinx wave energy converter demonstration project near Port Kembla in New South Wales, Australia which operated for a few months in early 2010.
In addition, the DoE is funding research into new materials; coatings; and manufacturing techniques; to improve the performance of hydro plants, as well as new sensors and controls that will improve energy efficiency and environmental performance.
EPRI, meanwhile, is halfway through a four year project to evaluate greenhouse gas emissions from hydroelectric storage reservoirs, with a final report due at the end of 2012.
Drew Robb is a graduate of the University of Strathclyde in Glasgow. Currently living in Los Angeles, he is a freelance writer focusing on engineering and technology.
Renewable Energy Focus, Volume 12, Issue 2, March-April 2011, Pages 16-17