Wind power is pretty great: One doesn't need to do much but build turbines and capture the energy from a passing breeze. But, like what happened to the Ancient Mariner, still air means trouble. Intermittent energy is not useful for a grid that requires a continuous supply.
To get over this problem, engineers have devised a number of ways to store energy generated when it's windy for disbursement during the times when it is not. Ideas include giant flywheels, carbon-neutral natural gas and giant batteries made from gravel and argon gas. Now Alexander Slocum, Brian Hodder and their colleagues at MIT have demonstrated a new way to store that energy -- giant hollow concrete balls. They published their results this month in Proceedings of the IEEE.
The concept is pretty simple: As floating offshore wind turbines churn, they send most of the generated power to the grid. Some of the power, though, goes to pumping seawater out from 25-meter-wide hollow spheres which sit on the seafloor. As soon as the wind dies down, the pumps turn off, and the seawater rushes back into the spheres through a turbine; the water turns the turbine, which then generates electricity. The researchers calculated that one such sphere, moored in 400-meter-deep water, could store up to six megawatt-hours of power. A few hundred of those would be enough to offset an hour of energy from a typical nuclear power plant.
According to the researchers, initial estimates indicate that one sphere would cost $12 million to build and deploy, which is three or four times the cost of a typical onshore wind turbine. But worrying about the cost is still a bit premature, as only a 30-inch-diameter proof-of-concept has thus far been built. The MIT team has plans to build a sphere with a diameter of three meters, but further funding will be required to build a 10-meter sphere intended for undersea testing. Still, it could be worth the investment -- the researchers estimate that floating offshore wind farms with energy storage capacity could satisfy more than 20 percent of our energy needs.
1) How efficient is this? How many megawatt-hours do you have to put into one to get the six megawatt-hours of power out?
2) If the interior is supposed to be a near vacuum, isn't it counterproductive to build it underwater where the external pressure is higher?
3) Given that the energy comes from anywhere in the form of electricity, this doesn't really have anything to do with wind power. You could have a coal plant filling them up for high demand times later.
I wonder what they could do with a set of giant wookie balls?
"...excess wind energy..." Yeah, right...
So they are coming up with this concept while the US has no offshore windmills. Perhaps they can work on getting that of the ground first? So this would only be useful in Europe for now which has many offshore windmills and is expanding rapidly. In Belgium they are planning to build an artificial island of the coast that will pump out sea water and let it back in for energy generation when there is less or no wind.
In Norway they apparently have large fiords already that are used as energy storage devises. In the Netherlands they want to use large "polders" for energy storage. Germans have a lot of concepts as well. Also with the supergrid Europe is building wind energy is easily shared across large distances reducing some of the need for energy storage. If some have less wind others can take over. The more alternatives the better of course.
Energy independence and green renewable energy is paramount for a healthier future for not only our planet but our own health as well.
I seem to recall a proposal to use underwater rubber bladders anchored to the seabed that would be pumped full of air,and when power was needed,the air would be forced out by the surrounding water pressure,powering turbines.No doubt rubber bladders would cost a hell of a lot less than concrete balls.
I'd have thought there would be a pretty huge loss using water as medium.
1). Can't say for sure with out knowing more about the system but a good electric motor/genny can be upwards of 90% efficient. Factor in mechanical losses and 70%-60% efficiency (at generator terminals) should be doable.
2). The greater the differential pressure the greater the energy storage and efficiency. Basically this is a hydraulic accumulator.
3). Yes the energy could come from anywhere, but it would be most useful for this application because if the intermittent nature of wind power and the fact you are already building there.
@jefro; why would yo think that?
The higher the differential pressure the more energy required to empty it. Nothing is free here. Nice idea but severely uneconomical....Next.
It's the underwater pressure that drives the turbine when the sphere is in power generating mode. They store energy by pumping out the water and letting in air from above. Flooding the chamber drives the turbine.
A rubber bladder will deteriorate over time. It would not last long. A concrete sphere would last 50+ years. How long do you think a rubber bladder will last? And under water at that.
This sounds like a well thought out concept. Considering the cost of other energy storage concepts, possibly a cheap one at that.
For offshore wind turbines, they could use the same generator for both the wind powered and water powered modes. Just use a transmission and drive shaft to connect the two types of turbines.
"So they are coming up with this concept while the US has no offshore windmills. Perhaps they can work on getting that of the ground first?"
It's politics that is holding back the construction of offshore windmills in the US. An issue with salesmen and politicians. This design is an engineering issue. "They" are not a monolithic entity, but individuals doing different things.
"initial estimates indicate that one sphere would cost $12 million to build and deploy"
"A few hundred of those would be enough to offset an hour of energy from a typical nuclear power plant."
$12,000,000 times 200 = $2,400,000,000 for 1 hours worth of energy from a typical nuclear power plant not including the cost of the wind turbines to pump them up because it is unlikely that one wind turbine will pump up all 200.
Interesting idea but doesn't make any kind of financial sense.
They will likely fail in the big earth changes. You-tube is spreading a rumor that a pyramid in Alaska is functional and producing or converting massive power.
<i>"According to the researchers, initial estimates indicate that one sphere would cost $12 million to build and deploy, which is three or four times the cost of a typical onshore wind turbine."</i>
The more complexity is added to any system, the greater grows the operational "friction" involved in keeping it running.
I'd expect to see something like this speculative effort on the part of the electrical engineers. What sort of input might we expect from the <b>mechanical</b> engineers, I wonder?
<i>"This sounds like a well thought out concept. Considering the cost of other energy storage concepts, possibly a cheap one at that."</i>
Consider that this concept relies upon pressurization, and therefore the integrity of connections that have to function - by design - in the face of constant physical stress changes which will inevitably result in breaches, particularly in those interfaces between the dissimilar materials composing these systems. Factor in the effects of chemical degradation (for which seawater exposure is notorious) and the influences of heat, cold, and the physical poundings imposed by wind and wave, and you've got a failure tree suitable for the attentions of a Paul Bunyan.
Why use pressurization when it might be more feasible to pump water <i><b>up</b></i> into a columnar reservoir instead, and then rely on gravity to induce flow turning an impeller to generate electricity?
A gravity-fed system would be susceptible to failures as well, but the stressors (on both the macro- and the micro- levels) wouldn't be as failure-critical, meaning that materials and manufacturing methods need not be as exacting or costly.
Keep it simple - or, at least, simpl<i><b>er</b></i>.
Using a column with little or no back pressure would require a much larger volume of material and the bottom of the column would still be subject to great stress variations. I suspect they went with a sphere because of the inherent strength of a sphere and minimizing material. Also concrete is very strong in compression so as long as the net pressure is inward the pressure vessel would be very strong.
Over all an interesting idea, but as others point out the money numbers do not work very well. And we need to get over the "I want off shore wind power, but I don't want to look out the window of my 10 million dollar beach home and see a bunch of ugly dot on the horizon"
Why the need to store the energy at the source? You are going to need to move the energy to land to use it any way. Why not store the energy on a flywheel on land? More efficient, easier to install, maintain and monitor.
Here's the website for the people building the flexible underwater energy storage system: www.http://hydrostor.ca/home/
This concept would not make offshore wind power more efficient. Nor would it even make offshore wind power any more cost competitive with onshore wind power.
Using expensive, giant concrete spheres to store the power produced from expensive offshore wind turbines, in the form of compressed air, makes absolutely no economic sense. CAES concepts based on using existing underground storage capacity and cheaper onshore turbines does not even make economic sense.
Automatically starts thinking me of adding a shaped tube underneath, set for tidal flow and compression. Try to get past some of the limitations of both systems by combining them.
The word "floating" in the article makes no sense to me. They can't be floating, right?
Couldn't you store just as much energy using hollow (buoyant) balls and just raise and lower them? This would avoid many of the mechanical problems (though introduce some new ones). ON balance (pun intended) it would be easier.
I always said the wind power sector needed more balls to become a major player in energy production but that wasn't what I was thinking....
Here is one issue nobody has discussed: As you pump water out of the sphere, vacuum created will draw water vapor out of the seawater (which could possibly even boil because the vapor pressure is so low.) The water vapor will dilute the vacuum. When water rushes back in, the water vapor will warm up and therefore will not immediately condense out fully. I.e., there will be a gas bubble inside the chamber that will take a while to disappear. So some of the stored energy is wasted. In effect, some of the energy used to pump out the water will be used to vaporize the water, and that energy is not recovered.