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Underwater Pumped-Storage Hydroelectric Project Completes Its First Practical Test (forschung-energiespeicher.info)
What if you built massive concrete spheres -- 98 feet in diameter, with 10-foot walls -- under the ocean to help generate electricity during peak periods? Slashdot reader nachtkap reports that German researchers just finished testing their 1:10-scale prototype StEnSEA:
It was retrieved from Lake Constance, where it was submerged at a depth of 100 meters [328-feet] since November. The system was developed by the Fraunhofer-Institut IWES in Kassel, Germany in collaboration with its inventors... The German Trade Department and Department of Education and Research as well as the German construction company Hochtief are also involved with the project.
The system's hollow concrete spheres are intended to be used in conjunction with off-shore wind-farms to serve as energy storage for peak hours. The spheres are ultimately supposed to be submerged near off-shore wind-farms and pumped free of water with excess energy. When additional energy is needed during peak hours the system goes into reverse and water rushes in, driving a turbine... At 700 meters the system has a capacity of 20MWh, with a linear capacity increase as depth increases.
The system's hollow concrete spheres are intended to be used in conjunction with off-shore wind-farms to serve as energy storage for peak hours. The spheres are ultimately supposed to be submerged near off-shore wind-farms and pumped free of water with excess energy. When additional energy is needed during peak hours the system goes into reverse and water rushes in, driving a turbine... At 700 meters the system has a capacity of 20MWh, with a linear capacity increase as depth increases.
When it implodes it goes MOOB!
In what ways is this better than simply pumping water uphill into a holding tank or artificial reservoir? It sounds a hell of a lot more complicated, so must have some offsetting feature that would shift the balance.
Yes, I can see the obvious answer that the increased pressure means a higher energy density, but *so* much higher as to make it worth doing?
Pumps are very inefficient. I wonder why they wouldn't just use the excess energy to drive a motor/generator to pull an empty sphere towards the bottom with a cable and then generate energy in reverse as it rises up?
Sounds like that would create more moving parts in an environment that's not kind to them.
Because (as a first-order approximation) water is incompressible and a solid object's buoyancy will not change as you change its depth. Even then, it's just equivalent to moving a weight up and down. Might as well store energy in a freight elevator*.
However, if you move a compressible fluid (air) into the chamber, it takes exponentially more pressure vs volume for a given depth. I.e. there is a (fairly shallow) point where you can get greater energy density compressing air than you can moving the mass.
*: There is a project (ARES) Advanced Rail Energy Storage that aims to do exactly that; use electric trains to move concrete blocks up and down a hill to store energy.
I have a cottage outside of Marmora, who has a lovely pumped-storage kit in the form of a large mine (see the picture at
http://www.marmoraandlake.ca/w...) that's well above the Crow river. A good modern pump/turbine could do a sparkling job of storing wind-/solar-power until night.
davecb@spamcop.net
Not that many agencies around the world have good satellite technology.
Hang two of them on a pulley and motor set up so when one sphere is full you raise it to the surface while dropping an empty sphere. all you are lifting is the water as the spheres are equal. Once the empty sphere is on the bottom and the full sphere is swinging in the breeze, you drain the full one using gravity...
You have the right to remain sentient. If you give up the right to remain sentient, you will be elected to public office
America didn't vote for him...by 2.9 million votes
The problem is the Slave State compromise called Electoral college
Pumps are very inefficient. I wonder why they wouldn't just use the excess energy to drive a motor/generator to pull an empty sphere towards the bottom with a cable and then generate energy in reverse as it rises up?
My guess would be: fewer moving parts and/or less complexity with a pump.
It must have been something you assimilated. . . .
Err... why would it have to change buoyancy?
1 newton over 1 m == 1 joule. All it has to do is exert force over a distance AFAICS.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
With a hill the water is stored at the top and taken out through a turbine at the bottom. So you have to store water in two places, the top and the bottom. The water is exposed to sunlight so it will grow crap in it. And you battle evaporation. the whole apparatus will take miles of pipe. finally there's friction losses as the water moves down the miles of pipe. And there's the modest potential of flooding if you scale this up. It takes up useful and expensive mountain top land or destroys wilderness.
at the bottom of the lake, the pump just pumps the water out into the immediate vicinity. when it's time for water to go back in, it pumps water in from the immediate vicinity. no pipe, no losses.
Some drink at the fountain of knowledge. Others just gargle.
I always wondered if you couldn't do essentially the same thing on dry land with raised masses. Use excess generation capacity raise a series of masses and when the power is needed let gravity lower the masses, dumping the power into flywheel(s) attached to generators.
The masses could be sized so that rather than raising one very large mass, a series of smaller masses would be raised allowing relatively small excess generation amounts to captured over time.
I thought now the EPA and other government agencies were banned from reporting on climate change and NASA has been essentially told it isn't getting any money to research it that the problem has magically gone away?! It seems odd that Trumps alternative truth wouldn't actually be the truth...
This was research funded by the German Federal Government, not the US Federal Government. We have not, so far, elected Trump or anyone of a similar disposition to a major government position.
Stephan
Perhaps motors and gears and pulleys, oh my would make too much noise? The graphics supplied conveniently omitted the beached cetaceans. How much undersea noise this will generate?
Pumps are very inefficient. I wonder why they wouldn't just use the excess energy to drive a motor/generator to pull an empty sphere towards the bottom with a cable and then generate energy in reverse as it rises up?
Conventional pumped storage systems have about 75-80% round trip efficiency, which is not that bad. One reason for the loss is evaporation from the upper reservoir, which would not be a problem for this system, so round trip efficiency in the 80+% range is realistic. That is not to bad if you have free electricity to begin with.
Stephan
The advantage of the pump system becomes even greater when you scale up the storage capacity, as that only requires adding more empty storage spheres, and not more pumps.
Because gearing is also really inefficient, and you'd need to gear up the motion of the buoys as the rise in the water column so it's fast enough to spin a generator.
In contrast with this scheme you can retrieve the energy using a perfectly conventional (and highly efficient) hydroelectric turbine. The net efficiency is (presumably) greater.
In any case physical efficiency isn't quite as big a deal with renewables as it is with fossil fuels. Renewables capture energy that you're not paying for in the first place: sunshine, wind, tides. It's the cost of operation per unit of energy that matters, especially in a storage scheme like this where you're capturing energy you can't use for various reasons and getting some of it back later when prices are higher.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
It's going to take some pretty big balls to pull something like this off.
Have gnu, will travel.
No bullshit grab-for-the-stars (and never get them) waste of money and time, but practical, pragmatic and addressed at real problems. Of course, this will take another 10 years or so to practical deployment, but it is highly likely to work and be both reliable and cost-effective. Things like these drive progress.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
I think you should learn some German history.
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I don't think that the solid spheres would be very buoyant. They are made of very thick concrete to withstand the pressure, which has a density several times that of water. By my calculation, the shell uses 27% of the total volume, so these things would barely float.
If you made the spheres out of thin material like a balloon instead, the air inside would compress as you pulled it down and you would get thermodynamic losses like a heat engine.
Seriously.... a major death trap.... you're going to pump a giant underwater sphere free of water?
Then when you release it, or if something breaks,
That will be some SERIOUS... Delta-P
Imagine all the potential energy build-up, and the impact of the sudden release on anything living happening to be anywhere near the input pipes.
In what way is a less efficient/more expensive system a "better idea"?
The hydrogen fuel cell approach makes sense if you need to power machines which are not always connected to the grid, such as cars and trucks, but it makes very little sense for grid storage.
I think you should learn some German history.
Yes, I was implicitly assuming "in the context of the FRG".
Stephan
Yes where ever you put the storage site, you need to generate the same amount of electricity, but you can still get away with storing less by putting your storage right by the consumer. Assume total loses in transmission are 50%, and energy storage is 80% efficient (which it isn't) and the consumer needs 80 kilowatt hours of power If storage is at the generator site, you need to send 160 kilowatt hours to give the consumer 80, and you need to generate 200 to store 160. If the storage is by the consumer, you need to receive 100 kilowatt hours in order to store 80 for use by the consumer. which means you need to send 200 from the generating site. So either way, you're generating 200 kilowatt hours to use 80, but in the second scenario you only have to pay for 80 kilowatt hours of energy storage capacity, and in the first you need to pay for 160.
At 700m where they are experiencing ~70 atmospheres of pressure, the story becomes different. I bet that one of the hardest problems they will have is reliably keeping these things anchored to the bottom when they pump the water out.
You're going to get all kinds of sea life growing on all those moving parts, turbine blades and such. Be nasty, expensive work trying to clean it all off. Maybe they can engineer around that??
I was envisioning a system of anchored pulleys with locking brakes below each sphere with cables going all the way back to a floating motor/generation unit on the surface. Nothing would be under water but spheres, pulleys, and cables. The motor generation unit could have many spheres tied to a single shaft with an ability to control whether the shaft is actually engaged with each sphere's cable individually (or the cable is locked at the bottom pulley when the generator is not engaged). A sphere near the bottom with more buoyancy can supply more force. So with all the sphere's on the bottom, only one at a time might actually apply force until it gets to a certain depth. As the depth rises, more spheres at a time would be used to keep the force the same with all spheres applying force as the maximum depth is approached. Gearing is eliminated, the force pulling the floating motor/generator under is always kept to a fraction of the storage farm's capacity thus not forcing some island sized floating unit, and with a little extra thought, you could manage to harness some of the tide's energy as the floating unit goes up and down with the tide.
If you're working with offshore wind farms, this makes a great deal of sense - as part of the construction you add as many of these as appropriate and use them to stabilize the power output from the farm.
Methods of storing power to be delivered when needed have always been the goal, what's changed more in recent years is more focus on the efficiency and cleanliness of the storage and delivery methods. If you change your thinking from "coal/oil/gas is a fuel" to "coal/oil/gas are energy storage mediums" it can change your thinking on a lot of these things.
fencepost
just a little off
Have these people ever lived by the sea? There is no way a pump is going to sit at depth without needing to be taken out and cleaned every few weeks. There is no way the generator turbine is going to sit at depth without getting furred up. There is no way the influx and drain pipes will remain clear. Even the sphere itself will slowly fill.
The sea is not just salty water. It's a soup of animals, plants and minerals in suspension. The test might work in a fresh water lake for a few months but the sea is far more active at destroying machinery. Otherwise we'd just build big turbines and let the tides generate all of our electricity.
I saw that. My initial thoughts were based on pumping the air. It then clicked that they are pumping the water. So, yeh, my bad. Pumping an incompressible liquid is a vastly more favorable problem than the air.
It still falls short of the efficiencies that can be had with mechanical coupling to a modern generator though. And as I've mentioned elsewhere, I think they have more underwater complexity because the pump units / turbines have to be at the same depth as the spheres in their case. I'd envision pulleys at depth and cables mechanically transmitting energy back to motor / generators at the surface.
I don't see how the pressure will affect buoyancy. Since water is almost incompressible, its density will be the nearly the same at 700m as at the surface. The force pulling the empty sphere upwards will be about the same as near the surface; my math says it's about 4700 tons of force either way.
Given that the sphere would already comprise about 10,000 tons of concrete, it wouldn't be too hard to weigh it down a little more so it doesn't even float.
You *do* in fact need to store a *lot* of water up hill if you want to have energy when the weather isn't cooperating for a few days at a time, and power electric cars, etc. To provide for all of our energy needs, replacing petrol, heating oil, etc, we need three times as much electricity as we have now.
I did the geographic modeling for the US. Obviously Germany has different geography, but this will give you a general sense to scale. To have three days of pumped storage sufficient to provide for the energy needs of the US, we'd need to flood 1/3rd of the continental United States. Of course that number goes down significantly if you want only a few hours of storage, running nuclear or traditional power plants when the weather isn't suitable for renewable, and if you continue to use gasoline, heating oil, etc for most of your energy needs.
The prototype was used to test details of the construction, installation, powertrain setup, electrical systems, operation management and regulation, system state monitoring and the dynamic modeling and simulation of the whole system.
The power train part together with the cross section images highly suggests, to me, a pump for each sphere. To me there is also the question of practicality. I'd think it would be easier construct the whole thing on land then having to attach the spheres to the pump on the ocean floor. If that pump where to malfunction it would knock out a whole bank of spheres that would then have to be de- and reconnected.
I share your concerns about violating the articles of the Benthic Treaty.
The system described in the article uses the pressure difference between the inside of the sphere (low pressure to near vacuum) and the water outside. What's interesting is that the deeper you get the higher the pressure difference and thus the more potential energy you get.
In contrast your mechanism only relies on the density difference between your spheres and the water so that no matter what depth they're at the force they exert on the cable is the same. If you place your spheres at a depth of 700m, to extract the same amount of energy as the system in the article you'd have to let them float all the way to the surface. Even staying well under the surface, having the spheres move up and down hundreds of meters seems much more fragile.
The system described in the article relies on the pressure difference between the inside and the outside of the sphere. A sphere is ideal for resisting such pressure differences. If the pump was shared it would have to be connected to the spheres via pipes which are essentially cylinders. Cylinders are fine for containing pressure differences as long as the high pressure is inside. But in this case the high pressure environment is outside so the pipe would just flatten. You could certainly use thick walls to avoid that but I guess it would increase cost too much or be fragile.
A balloon would not work just as well.
Storing energy with compressed air involves significant losses because compressing the air heats it, and most of that energy gets lost. A submerged rigid sphere could store energy without using any compressed air, just water pumped against gravity. When empty, the air inside would be at sea level pressure (no compression), but this requires a pressure-resistant container.
Normal hydro-storage depends on pumping water uphill - and that means you can only use it where there are hills or mountains nearby. But this only requires pressure, which is available in many places where drops aren't. It could certainly add to the options for large-scale storage.
It's big and expensive to build of course - but I'm not sure it's actually bigger and more expensive than a coal or solar plant. So it may still be a win.
Unicode killed the ASCII-art *
Use solar/wind/wave power to make hydrogen. Use the hydrogen to run fuel cells during peak periods. I know this is not new and NREL has looked at it.
$/kWh is going to be higher, but we're taking about peak periods anyway.
It's the storage of the hydrogen that is the issue, it leaks readily.
My ism, it's full of beliefs.
The killer to these projects is you have to recoup your cost before the system wears out while also covering maintenance costs. We do this on land pumping water up hills and doesn't make economic sense. The systems require to much maintenance. In North America the ones that are already build are used as insurance. Utilities pay for the ability to draw several MW from these systems while they wait for a coal system to come on line. Coal takes a while, while hydro is close to instant. The utilities pay for this insurance every month whether they use the electricity or not and when they do use the electricity they pay in the multiple dollars per KWh. The system in the article will be charged with unwanted electricity, cost 0, but will sell the electricity only at peak and shoulder prices. It's not going to viable.
you evidently didn't read it.
But I'm sure some environmentalist will say, "what about the fish?!?" LOL