Wind and solar power will certainly be part of the bright green future, but they may be overshadowed by hydrokinetic power -- electricity generated from the movement of water. Tides, waves, even the flow of rivers can be harnessed to produce electricity, and most such sources are far more consistent than the wind and sun. And while dams have a variety of environmental drawbacks, newer forms of hydropower -- so called "free flow" hydro -- don't block the flow of water (and its inhabitants), and don't require the inundation of acres of land.
The Natural Resources Defense Council's OnEarth Magazine reports on a relatively new manifestation of free flow hydro: the Helical Turbine designed by Alexander Gorlov. While it's not the only free flow hydro technology trying to get investor attention, it has some unique properties, and an interesting history.
For its design, Gorlov credits in part French engineer Georges Jean-Marie Darrieus, who in 1931 received a U.S. patent for a turbine whose blade would be shaped in a way that was "analogous to that of the wings of birds." This, he knew, would increase efficiency and make the turbine spin much faster than the wind or water hitting it. On paper, the Darrieus turbine had magnificent potential, but the real world was too much for it. The ruler-straight blades had a tendency to pulsate wildly, rip from the axle, or snap in two. Gorlov corrected Darrieus's engineering error: By twisting the blades slightly, a bit like a strand of DNA, he eliminated the vibrations. Gorlov received his first patent for the turbine in 1994.
Today, the narrow blades are modeled on the airfoil profile of a Boeing 727 wing. That slight helical twist not only removes the vibrations but also makes Gorlov's turbine a champion spinner. Placed in a moving current, it kicks into motion almost instantly and within seconds will turn faster than the speed of the water hitting it. Tests conducted at the Marine Hydrodynamics Laboratories at the University of Michigan in 1998 and 1999 showed that the Gorlov Helical Turbine will take off in water moving as slowly as two knots and can capture about 35 percent of the kinetic energy of the current.
Gorlov's tests over the past decade have been promising, but slow. In 2002, however, the Republic of Korea began tests of a Gorlov Helical Turbine in the rapid tides of the Uldolmok Strait; the successful results have led to a new phase of the project, in which a 15' turbine will produce 1,000 kilowatts of power for a nearby island. If that goes well -- and all signs are it should -- the government of Korea plans to install a sufficient number of Gorlov turbines in the strait to produce 3,600 megawatts of electricity, the equivalent of four nuclear power plants.
Questions remain as to the cost of the systems -- a report at the website of the Boston Museum of Science from a few years ago pegged the cost per kilowatt as somewhat lower than nuclear, but higher than most other conventional sources -- and the impact on fish. Gorlov's dismissive statements ("Fish are not so stupid as to go through it") don't auger well, but tests on single units suggest that the rapid spin of the turbines produces a pressure barrier that repels fish -- it's less clear what will happen when fish encounter a cluster of turbines. There's also the question of what happens when major flows of water see a 35% reduction in energy. Gorlov suggests that 656 full-size turbines could capture sufficient energy from the Gulf Stream to power North America -- but what happens to the Gulf Stream after losing some portion of its kinetic energy?
Fortunately, the design appears to be as useful in a scaled-down, distributed form as it would be as a megaproject. The helical turbine can function in as little as a meter of water (traditional "axial" turbines need nearly three times that depth, according to the NRDC piece). The final phase of the Korean project may demonstrate the power generation potential of clusters of helical turbines, but it's the current form -- the single 15', one-megawatt turbine -- that strikes me as the ultimate way forward.
"Gorlov suggests that 656 full-size turbines could capture sufficient energy from the Gulf Stream to power North America -- but what happens to the Gulf Stream after losing a third of its power?"
Unless I'm missing something, this statement is incorrect. The Gulf Stream wouldn't lose one third of its power, only the water that would go through the turbines would lose 35% of its kinetic energy.
I seriously doubt that the whole Gulf Stream would go through his 656 turbines; he wasn't talking about capturing the whole stream but producing enough power to power North-America. Who knows how much of the Gulf Stream's kinetic energy that amounts to?
True. The complex of turbines would reduce the kinetic energy of the Gulf Stream by some amount, however. It's worth thinking about what that might mean before undertaking that particular project.
(Will fix text to reflect correct logical inference.)
Tne idea of trading gulf stream kinetic energy for electric power has some appeal, but if I remember correctly, isn't the gulf stream slowing down already, due to an overall slowing of surface and ocean currents attributed to decreasing salinity of North Atlantic waters? I'll try and find a link to that, but I seem to recall global warming activists claiming that melting ice is making surface waters less dense, slowing down surface/deep current exchange mechanisms, and messing with deep current oxygen levels.
You are right, the whole ocean current circulation depends on thermo-haline circulation, and if there are no differences in salinity then the currents won't flow. But if you anchor it close to beaches, whatever happens you get tidal flows.
Can this be put into huge sewers in cities?
It is probably pretty straightforward math to see how much energy is removed from a flow by a turbine.
So, whatever the site (be it a tidal race or a offshore current), you decide how much energy can be safely removed, and add that many turbines.
It could be that we end up with smaller turbine farms, but spread out in more places.
I guess the impact depends on how much of the gulf stream you use. If it's one percent of a percent or something like that, it's probably not much worse than all the cargo ships we have sailing around.
If it's a significant amount, then the impacts on the gulf stream should be taken into account.
But more important, is affecting the gulf stream with turbines better or worse than affecting it via global warming because of the use of coal and such dirty sources?
C'mon, Mikhail, that's a false comparison. The alternative to putting a bunch of hydrokinetic turbines in the Gulf Stream in order to power North America is not global warming disruption of the thermohaline flow, it's spreading out the hydrokinetic turbines across different water flows.
In any event, this is something of a sidetrack discussion -- there's little likelihood of the helical turbines being installed in a single massive cluster to power all of North America. The Gulf Stream will remain safe from this particular assult.
Sorry, I guess I went a bit too far on that line of thought. I don't believe for a second that we'll be faced with that problem, of course.
I'm wondering if a smaller version of the helical turbine could be used on shallow streams that have a short dam (say 3 to 4 feet) and a sluice way.