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Underwater Ocean Kites To Harvest Tidal Energy
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."
At first I read "Ocean Kitties" and wanted to see pictures of those...
Because of the tides, the Earth's rotational energy is being stolen by the moon, which is using that energy to slowly escape from orbit. (This is a diminishing effect over time, that will eventually reach equilibrium.) But when we leach this energy for our own purposes, we are changing the delicate balance of that equation. ...Siphon off too much energy from the tides, and we could either increase the rate at which the Earth is slowing, bring the moon crashing down upon us, or both!
Won't somebody think of the children? We owe future generations a planet fit to live on and capable of sustaining the future.
HSJ$$*&#^!#+++ATH0
NO CARRIER
now whales can enjoy the "renewable revolution" like migratory birds and bats do with windmills.
THL phish sticks
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.)
Seems this would be relatively high maintenance. Anyone who owns a boat knows that stuff can and will grow on it, which will have to be cleaned off eventually, no? Setting aside the initial cost, which isn't mentioned, wouldn't the maintenance be costly?
If they're anything like my kites, they'll just end up nose-first in the silt.
Great minds think alike; fools seldom differ.
short answers: No, there is. The sun. No.
Like windmills, PV solar (and arguably, thermal solar), this will use a ton of capital (in multiple dimensions -- energetic, costs, and materials) to harvest very diffuse energy. The cries to subsidize installation -- and possibly operational -- costs will start almost immediately.
Dog is my co-pilot.
Tidal forces are from the moon, and over time the moon is getting farther away. Clearly, if we harvest tidal energy we will force the moon away faster as it makes up for the difference. If NASA times it just right, we could put people on the moon, launch the moon at Mars and have people walking on Mars just months later. Melt the polar icecaps on Mars, use tidal kites there, and repeat as needed to keep using the moon as our Earth/Mars space shuttle. Add Phobos and Deimos into the mix and space tourism can take off.
Next, we use the tide from the sun to travel to Alpha Centauri.
My webcomic
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. :/
The enemies of Democracy are
The solution is obvious. I am selling gravity credits to absolve you of your moon-doom guilt. Each credit you purchase represents energy gathered from sources not directly linked to the moon's potential energy plus some of the profits will be used to fund missions that will increase the moon's potential energy. This gravity offset program will save the earth for our posterity. As the administrator of this program, I will, of course, take a percentage of the sales as compensation. My motives are, however, purely in the interest of the future.
One last thing: Sometimes I wonder; "Is that someone's signature? Or do they type that at the end of each post?"
Yeah, it'd be great if they could try to make some sort of proof of concept, or trial version to test it out before investing in it whole-hog....
Well ok. Anything wrong with that?
I was having difficulty visualizing this technology, from the text description. Here is a YouTube video that sheds more light. Spoiler: essentially the tethered kite does figure-8 patterns to continually move the turbine through the water.
http://www.youtube.com/watch?v=1qCDRj8TE9Y
Pretend I said something meaningful or insightful here.
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.
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
fava
You've got it all wrong. I don't even think you read TFA, because you said "assume... it's moving out with the tide" - you don't get it.
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.
Wind farms are unlikely to stop the wind. Wind is a byproduct of temperature differentials, and as such, as long as the earth isn't exactly the same temperature everywhere all the time, there will be wind.
Tidal farms, on the other hand, I don't know. Tides are due to the difference in gravitational fields at different points on the earth. As such, the tidal energy comes from the Sun's and the moon's gravitational field. Since neither the sun nor the moon are losing mass through the use of tide turbines, what has to change is the distance between the sun, moon and earth. Somehow, I think the time scales on which this becomes a problem are large enough that we'll have entirely different problems then.
The only real problem I can see with tidal turbines is that if they are large enough, they will restrict the flow of the tides, and tides will become less pronounced - which will have an immediate impact on any tidal areas. And since tidal areas and shallow bays are pretty much where the food chains for a lot of marine animals reside, this could be a real problem. But again, it would have to be something on the scale of putting turbines across the entire straight of Gibraltar, and reducing the flow to near zero. Unlikely to happen, but not impossible.
Those who can, do. Those who can't, sue.
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
2. Sunlight; there's plenty to spare: http://en.wikipedia.org/wiki/Solar_energy "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
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.
There is a problem with your reasoning. The 60 cubic meters of water is not the total amount of water that would run by this device. The 60 cubic meters figure you quote would be the amount of water acting upon the device *at a single point in time*. As the water flows and the kite moves, much, much more than 60 cubic meters of water will flow by this device.
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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.
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
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".
Those who can, do. Those who can't, sue.
Why, yes, from economic activity derived from burning fossil fuels.
Yes, like essentially everything we do today, no matter if it is something that is trying to get us off of fossil fuels or not. Our economy is based on burning fossil fuels, ergo all economic activity is based on burning fossil fuels.
Spending some of that activity to stop using fossil fuels is, if you consider using fossil fuels bad, what we would call "intelligent".
We should be looking at truly sustainable energy solutions, not scams.
If they produce more energy in their lifetimes than they take to produce -- which, if the system works, they almost certainly will -- then it's not a scam, it's a viable energy source. The more of these we build, the less of our economic activity will be based on fossil fuels, and the problem in the first part of this post will be resolved.
Up-front costs can prevent the development of new technologies, even if in the longer term they are a net positive. Something can be economically viable (which is what it means to have a net positive return on investment) without necessarily being economically practical for a particular entity at a particular time. Subsidies offset this, and get us to the point where we are using fewer fossil fuels faster. This is a good thing.
The enemies of Democracy are
A follow-up question- would it be possible to build so many solar panels that all the energy from the sun gets sucked up and the planet freezes over?
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 I'd guess that the "subsidies" issue is fast disappearing...
I have no problem with your religion until you decide it's reason to deprive others of the truth.
Different energy sources make sense for different reasons. Windmills for instance have a very small unit size, but that also means that if one is down for maintainance there is little difference to the total energy generated. Distribution and peaks also drive the use of technologies other than pure base load ideas. Some technologies are actually complementary in ways I doubt you have considered, for instance solar thermal providing preheating at a coal thermal power station (Liddell NSW, Australia). I can also see a strong argument for wind driven pump storage to supply water for hydro at peak loads.
Then there is the obvious niche filled since the 1970s of small installations off the grid where PV solar etc is competing against internal combustion engines. Then there's things like google's solar in datacentres - effectively just a giant UPS which makes perfect sense if California's electrity supply is as poor as it used to be.
Like windmills, PV solar (and arguably, thermal solar), this will use a ton of capital (in multiple dimensions -- energetic, costs, and materials) to harvest very diffuse energy.
Kites use two orders of magnitude less material than a turbine of equivalent swept area. Water is two orders of magnitude denser than air.
This is starting to add up to something that doesn't sound so diffuse any more.
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.