Underwater Ocean Kites To Harvest Tidal Energy 203
eldavojohn writes "A Swedish startup has acquired funding for beginning scale model trials of underwater kites, which would be secured to a turbine to harness tidal energy for power. The company reports that the kite device allows the attached turbine to harvest energy at 10 times the speed of the actual tidal current. With a 12-meter wingspan on the kite, the company says they could harvest 500 kilowatts while it's operational. This novel new design is one of many in which a startup or university hope to turn the ocean into a renewable energy source."
Re:Stupid question, but one that's always bugged m (Score:5, Informative)
short answers: No, there is. The sun. No.
Re:Global consequences of tidal energy harvesting (Score:1, Informative)
no, the scale is too large even if you deploy hundreds of them you're talking hundredths of points of degree change.
The real strawman er I mean issue could potentially be the net effect on the moon's orbit. (It will slow marginally with the increased drag.) So will we get into a static orbit with the moon sooner than 1 billion years for now or not if we deploy these all over the ocean floor.
Re:10x the speed? (Score:3, Informative)
No, power is measured in joules/second. They're both rates. 10x higher speed means 10x higher rate.
It's not the best choice of words, but it works okay I guess. :/
Re:Unintended consequences... (Score:3, Informative)
Re:Another energy-diffuse, capital-intensive syste (Score:4, Informative)
Explanation video on YouTube (Score:5, Informative)
http://www.youtube.com/watch?v=1qCDRj8TE9Y [youtube.com]
Re:dem dang numbers (Score:3, Informative)
My impression is that the tethered kite will fly back and forth in the current, allowing the little turbine strapped to the bottom of it to spin faster (10x, per TFA). I guess they'll just go ahead with their trial to see if it all works out, but it seems like it could be a way to make use of the power of the currents without building huge turbines.
Re:dem dang numbers (Score:5, Informative)
Thats not how it works.
The kite is really a steerable sail that moves back and forth across the current, thereby increasing the velocity through the attached turbine.
An animation is available at http://www.ebase.se/minesto/animation.htm [ebase.se]
fava
Re:dem dang numbers (Score:2, Informative)
The kite is not moving, it is hovering - tethered - and the energy is generated by the turbine attached to the kite. The "flying" is probably just to lift it to optimal position, drag and angle. The energy is generated by water moving HORIZONTALLY in and out of the bay, not UP and DOWN. You don't need a high tide, you need bay with a lot of horizontal water movement.
The advantage about this method to other sea methods, is you can lift the kite out of the water in a storm or for maintenance, it doesn't have to stay down there. The only infrastructure you need down on the seabed is a hook to hold it, not gates or turbines.
Re:Stupid question, but one that's always bugged m (Score:3, Informative)
Is it possible to exhaust the wind or sea's natural momentum, if there is such a thing? Where does the energy ultimately come from? In other words, is it theoretically possible to have so many wind farms (or, in this case, tide farms) that the atmosphere becomes still?
(captcha: "universe". heh.)
I think we're OK for a while. There's many 'renewable' energy sources that can, and are, being tapped, and we're nowhere near extracting any significant fraction of them so far:
1. Tides, as in this article, come from the sun & moon interacting with the earth; http://en.wikipedia.org/wiki/Tides [wikipedia.org]
2. Sunlight; there's plenty to spare: http://en.wikipedia.org/wiki/Solar_energy [wikipedia.org] "Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on earth. Only a minuscule fraction of the available solar energy is used."
3. Let's not forget geothermal: http://en.wikipedia.org/wiki/Geothermal_power [wikipedia.org]
Of course, that last one, being strictly a gift of today's Earth, could be compared to 'traditional' energy sources such as hydrocarbons (oil, gas, coal) and nuclear. We're nowhere near running out of those yet either.
Re:Maintenance (Score:3, Informative)
Keep 'em deep enough, and nothing will grow. (No sunlight)
Corrosion will of course be a problem, as will be keeping the electrical generating and transmission bits nice and watertight.
Re:Stupid question, but one that's always bugged m (Score:1, Informative)
If moon is doing the tide then how come there's high tide 2 times a month.
So actually sun contributes at least as much as the moon or a bit more. And the interference max of those is the high tide.
But earths rotation and continents actually make it meaningful.
Re:dem dang numbers (Score:3, Informative)
Re:dem dang numbers (Score:3, Informative)
You're not making simplifying assumptions. You are completely misrepresenting the mechanism, and your numbers are meaningless. You are wrong, the posters who called you on your original post are right, and snarky comments about "basic physics" aren't going to cover that up.
Re:dem dang numbers (Score:4, Informative)
And as with all numbers, the devil is in the detail.
Tide power is generated by water flowing through a turbine. As a result, what matters is the surface of the turbine times the apparent water speed. That gives you a volume over time, which in turn controls how fast the turbine spins. Considering that apparent water speed depends not only on the size of the tide, but the local ocean floor geometry, and the output of the turbines can vary wildly depending on where they're located.
Finally, you made a key mistake in your calculation: a tide turbine doesn't capture the up and down movement of the tide - it captures the horizontal flow of water as it flows from point A to point B. This means that your entire calculation is completely useless. It isn't captured twice a day, it is captured constantly with an oscillating efficiency. The energy captured is only marginally related to a mass of water falling the height of the tide - the falling is translated into horizontal speed, where g is completely overwhelmed by local geometry. And lets not even get into real and apparent water flow, turbine construction, efficiencies, etc...
Really, you could have saved yourself a lot of time and just said "I don't know how this works".
Re:What's wrong with it (Score:3, Informative)
where does that subsidy come from? Why, yes, from economic activity derived from burning fossil fuels.
I dunno. When Northern Europe is reporting that wind energy significantly cuts the cost of power [wsj.com] I'd guess that the "subsidies" issue is fast disappearing...