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Thursday, August 23, 2007 Harvesting Power from the OceanA new technology could generate electricity from waves. By Kevin Bullis
Researchers from SRI International, based in Menlo Park, CA, recently completed the first ocean tests of a system that uses a so-called artificial muscle to generate power from the motion of a buoy riding up and down on the waves. Although the prototype produces very little electricity, the researchers say that wave farms based on the technology could eventually rival wind turbines in power output, providing a significant source of clean energy. Technology for harnessing the ocean's energy already exists, but it has not been widely adopted, largely because it has trouble withstanding the pounding of the waves. The new system could prove both cheaper and more reliable, the researchers say. Earlier systems used more-conventional electromagnetic devices, such as dynamos with complex transmissions, hydraulic pistons, and turbines. The gears of a transmission, in particular, are vulnerable to wear and tear from the erratic surging of ocean waves. In contrast, the SRI system is not much more than a sheet of rubber attached to a weight. It has "the mechanical complexity of a rubber band," says SRI senior researcher Roy Kornbluh. As a consequence, it is better able to absorb the shock of waves, says Yoseph Bar-Cohen, a senior research scientist at NASA's Jet Propulsion Laboratory, in Pasadena, CA. What's more, Bar-Cohen adds, the materials that the system is made from are cheap, which could help it compete in price with other sources of electricity. The polymer-based system at the heart of the new generator is a variation on an artificial muscle--a device developed as an alternative to electric motors in applications such as robots. An artificial muscle will expand or contract when a voltage is applied to it, but the same process can work in reverse: if the muscle is stretched by an outside force, it can generate electricity. A few years ago, SRI developed a small device that, embedded in the heel of a shoe, enabled the wearer to charge a cell phone simply by walking. The wave-harvesting system is basically a larger version of the same technology. The SRI researchers built their generator by sandwiching a commercially available rubbery material between two electrodes, which are themselves made of a greasy polymer containing conductive materials. The rubber sheet and electrodes are then rolled up, like a scroll, to form a hollow tube. When the tube is pulled by an outside force, the rubber layer is stretched thin, narrowing the gap between the electrodes. Initially, a small battery applies a voltage across the electrodes; when the rubber springs back into its original shape, it forces the electrodes apart, increasing the voltage between them. This excess energy can be siphoned off to generate a current. Part of that current feeds back into the system, so the battery is used only for the first cycle. The researchers recently tested the system off the coast of Florida. A couple of square meters of rubber rolled into the shape of a hollow tube were attached to a weight and mounted at the center of a buoy. As the buoy bobs in the water, it causes the weight to rise and fall, repeatedly stretching the rubber and allowing it to rebound, generating electricity. |
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Energy from Waves
07/14/2008
Comments
SVE on 08/23/2007 at 1:31 AM
41
Compare this to a conventional kilowatt alternator which is about the size of half a shoebox.
<<SRI system produces high voltages, in the range of a kilovolt ... high voltage is an advantage, since it makes it more efficient to transmit electricity>>
By this argument you should rub balloons against carpet and harvest the static electricity. That is high voltage also. Don't fool yourself. If you plan on using semiconductor electronics, kilovolts are terrible.
<<The main challenge moving forward, the researchers say, is to develop a reliable manufacturing process>>
Hah! That's the least of their problems. A couple of square meters to produce 5 watts is like 0.25 milliwatts/cm2. Compare this to a crappy fuel cell that is 25 milliwatts/cm2 and this is 100 times worse.
Move along folks. Nothing to see here.
Elroch on 08/23/2007 at 6:36 AM
28
<< <<SRI system produces high voltages, in the range of a kilovolt ... high voltage is an advantage, since it makes it more efficient to transmit electricity >> >>
<< By this argument you should rub balloons against carpet and harvest the static electricity. That is high voltage also. Don't fool yourself. If you plan on using semiconductor electronics, kilovolts are terrible.>>
The comparison with static electricity is spurious. Static electricity provides very little energy. And if they can manage to deal with the high voltages in a device in a shoe, there may be hope in bouys as well.
<< <<The main challenge moving forward, the researchers say, is to develop a reliable manufacturing process>> >>
<< Hah! That's the least of their problems. A couple of square meters to produce 5 watts is like 0.25 milliwatts/cm2. Compare this to a crappy fuel cell that is 25 milliwatts/cm2 and this is 100 times worse.>>
Fuel cells will be an important power source as time goes by, and the hydrogen economy takes off, but they have an entirely different role: they consume hydrogen and generate electricity. The device in this article is for renewable power generation.
<< Move along folks. Nothing to see here. >>
I can't be as sure, and remain open-minded.
kearns on 08/23/2007 at 9:26 AM
23
SVE on 08/23/2007 at 11:24 AM
41
I have no doubts that energy from the ocean will be viable and play a big part. I just doubt that any piezo-like material, which this is, will play any role. Traditional floats, pumps, turbines, and dynamos just work too well.
As far as OTEC, wind, solar goes they will do well. They will take their place along with other local energy sources like hydro and geothermal as our electric grid decentralizes and becomes radically distributed with many more, smaller suppliers.
By the way, this trend of energy industry decentralization is also what is in store for other industries: the voice/data communications industry, the software industry, mass media, the automobile industry, agribusiness, etc. The world of our children will be much more self-sufficient and self-sustaining.
alrefaee on 08/23/2007 at 7:31 PM
2
Can you see the tipping point? We've been inadvertently, as a human race, trying to cripple one "branch" so far by polluting it, and the earth is still trying to recover by attempting to heal. If we attack other "organs", at some point, the earth will change focus and attempt to cut those "branches" off instead of trying to heal them, all in the attempt to restore balance - it's evolution in its purest form!
I hope it fights back sufficiently to destroy our ability to transform/force it to adapt...
paulkoola on 08/23/2007 at 11:48 AM
1
Later as the technology matures it can be scaled up and used for islands communities where importing fuel to run power plants is exorbitant.
The other option for wave power is to build the structure as self absorbing breakwaters for harbor protection thereby sharing the costs of energy production and harbor protection, which makes them more attractive. Japan, UK and India have already tested prototypes in the range of 100kW.
OTEC however is one source where the oceans act as the storage medium. However unlike wave power where individual devices could be small, the cost of transferring water between bottom depth of the ocean and the surface dictates larger power plants in the MW range to supply the parasitic power required for pumping. The cold nutrient rich water at the bottom of the ocean might have more value than the OTEC energy we can produce. A self sustaining aquaculture environment with OTEC energy for sustaining this environment would be ideal.
mkogrady on 08/23/2007 at 1:30 PM
83
zippo on 08/25/2007 at 11:06 AM
24
I know these devices are designed to harvest kinetic energy, but that energy comes from a temperature gradient, so you are removing heat from the system. Wave farms on a small scale certainly wouldn't have a large impact, but since when do humans ever like to do things on a small scale, especially when they have the promise of cheap clean energy? Part of the reason we are in this whole global warming catastrophe is because of the scale of the industrial revolution. Nobody had a clue that we should also be scaling up the envirnment's ability to process those extra emissions or be searching for was to reduce such emissions. Now the damage has been done and it's all because we burned one to many gallons of fuel, or one to many tons of coal, etc.
I'm not a physics expert or anything, but I think I remember that if you remove energy from a system, in this case by transforming it into electricity, then it has to come form somewhere, almost like an energy vaccuum. Even for buoys, I would expect that would result in a decrease in oceanic thermal energy.
jdm on 08/27/2007 at 11:51 PM
1
barcus1 on 09/05/2007 at 1:34 AM
1
mbloore on 08/27/2007 at 3:19 PM
18
> Compare this to a conventional kilowatt alternator which is about the size of half a shoebox.
no, compare this to the alternator and the engine that drives it and the tank that holds the fuel supply.
cobraphx on 08/23/2007 at 10:50 AM
13
Maybe it works in other scenarios. How about to power self contained signal buoys, or generate electricity for small remote islands? Maybe... But I'm not sure that solar isn't just easier and more reliable in those applications. Unless it's at the extreme north and south. Maybe it would be great to power a remote station in the Bearing Sea. Or to power something in the North Sea.
-Matt
vanjulio on 08/23/2007 at 12:24 PM
1
Maintenance of ocean observatory platforms is extremely expensive and prohibitive to deployment. If very cheap green power such as this were available then it opens the door for many interesting projects.
hosro@comcast.net on 08/27/2007 at 8:52 AM
1
Life cycle costing and maintenance are costs that should be incorporated into all energy sources and we know that current major systems do not. The cost the customer pays at the pump have no means, yet of incorporating all of the costs associated with providing a gallon of gas to any customer. History is a good source of comparing technologies and problems of development overtime; whether they were considered feasible or not how long into their development it was required to meet needs of cost and
suitability.
darjleendale on 09/11/2007 at 12:36 PM
1