Storing wind energy 1

[SomptingGuy]

http://www.globalnewenergynetwork.org/news.php?news_id=2190696

Can anyone shine more light on this?

It looks quite simple the way it's described: excess power created by the turbine is used to pump out the vessel against (big) hydrostatic pressure. Power is returned by reversing the process.

But what's left in the vessel as it's pumped out? A vacuum (which would boil off the remaining sea water), air from some breather pipe? Other?

- Steve

 

[davefitz]

I recall an asme tech paper from about 15 yrs ago, written by a japanese author, that outlined economic advantages of storing excess electric power in chemical energy, although I forgot which chemical he recommended for this purpose.Certainly one could use the excess energy to de-salinate salt water, or disaccociate H2O to form O2 and H2, but these plant would be operated in batch mode.

"Whom the gods would destroy, they first make mad "

 

[cranky108]

If you had the communications method, you could schedule intermitent loads that would store the energy in a usualable format. Such as water pumping, or ice production in a cooling plant.
Or instead of storing electrical energy, store it as something closer to it's final product.

The signal for these devices to turn on would be something like a reduced price for using the excess energy (i.e. real time pricing). Then let consumer decide if they want to use it at an inconvient time or pay a premium to use energy when they want it.

 

[PZC]

Answer to the original question. The pump is pumping IN water into the sphere container on a higher pressure during the energy storage cycle. Upon taking back the stored energy, the pressurized water inside the chamber is made to flow into the ocean through the turbine ( pump does not run during this phase ) . The water flow stops naturally when the pressure of water inside and outside spherical chamber equalizes. Therefore, there is no vacuum being created, rather only water remains ( at equal pressure ) inside and outside the spherical chamber. The cycle is repeated.

 

[racookpe1978]

If so, it is not practical to store enough "salt water" to a high enough pressure to matter: Water stores potential energy by compression of course.

But water is not "elastic" enough to store much energy. Rather, increasing water expands the pressure vessel HOLDING the pressurized water, the water itself does not "compress" sufficiently to hold much energy. (Some of course, but not much.) Compressed air, on the other hand, DOES gradually and predictably increase in pressure as energy is added, and - more importantly - slowly releases that energy as it "breathes" back out. Compressed water "pops" or spurts out its stored energy.

To illustrate: Two 5 gallon tanks are pressurized to 200 psig - one holding water, one holds gas, Both tanks are vented through a 1/4 inch line 50 feet long. The water-filled tank is fully vented almost before the vent line is even filled! The air tank takes 30 minutes to empty, releasing energy continuously and usefully the whole time.

So, the submerged tank's internal pressure goes up rapidly, AND goes goes down very, very rapidly. It will go down even more quickly in the shallow waters where wind turbines are practically mounted to the subsea surface, quickly turn the submerged concrete tank from resisting external pressure to holding internal pressure - which concrete is poor in resisting with it low tensile strength and low fatigue resistance. Go deeper underwater? Construction and piping costs go up quickly the deeper the sea floor you go, and you face near insurmountable problems in securing your loose wind turbine to the sea floor

... Never mind that pesky electric power transmission thing about getting energy back to the coastline to customers on-shore. High transmission losses, constructions losses, sea floor erosion and connection and leakage/grounding problems, and the impossibly high costs of copper or aluminum conductors! That deep off of US or European or Atlantic shores? You need to go hundreds of miles out!

 

[IRstuff]

btw, the link in the OP appears to have deceased; so much for that great idea ;-)

I would have expected that the idea was to not to compress the water, per se, but rather, compress the air inside the tank using the water. This is the way RO filter systems store their water. The storage tank has a diaphragm that separates the water from the air, which is usually set to ~7 psig with no water. As the treated water is pumped into the tank by the RO system, the pressure on the air side increases until it matches the inlet pressure, at which time you can no longer add any more water, and the RO system stops filtering. When the tap is opened, the pressure side of the tank pushes the water up to the counter top tap and your clean water comes out. Once the pressure is dropped, the RO system can again filter water and store into the tank. Since the RO system's fill rate is extremely slow, it's possible to drain the tank back to nearly its initial pressure, and the water flow trickles down to the production rate of the RO system.

In a similar fashion, then, you are pumping water into a tank filled with air at ambient pressure, so that when the tank is filled, the air pressure is substantially higher than the ambient water pressure. This then allows the tank to pump most of its water back into the ambient, since the pumpback only ceases when the air pressure is the same as the ambient water's.

TTFN
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[SomptingGuy]

Amusing that this thread has restarted. I thought it was done. Nothing more than a pumped storage system. The difference being that the lower reservoir has a finite capacity rather than the usual method, where the upper reservoir is finite. And of course the oddity that the lower reservoir is below sea level. My question was only really about the potential venting issues. The discussion has gone somewhat off at a tangent.

- Steve

 

[stevenal]

There is no compression of air or water needed to make the system work. It is simply a pumped storage system much like any other, relying on gravity.

 

[IRstuff]

If the tank is fully submerged, the ambient water pressure will be higher than the weight of the water inside the tank.

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[SomptingGuy]

The tank doesn't need to be submerged in anything specific. It's just handy if there is a head of water available. You could equally well dig a hole next to a river. It's just more practical this way, especially if the power source (the turbine) is at sea.

- Steve

 

[stevenal]

If the tank is fully submerged, the ambient water pressure will be higher than the weight of the water inside the tank.

I agree that pressure differential is involved, just stating that compression is not required. The air is freely vented to the surface so it is at atmospheric pressure. Internal water pressure will vary with head, but the water can be assumed to be incompressible. The energy storage is gravity based, and not based on a compressible fluid. Ndiaphragmsms, bladders, or compressible fluids are required.

 

[stevenal]

I meant to say No diaphragms, bladders... So much for ieSpell.

Since the original link is gone, try

http://www.sciencedaily.com/releases/2013/05/130515085343.htm

 

[IRstuff]

OK, if that's the case, I don't see it as practical. If the tank is vented, then there is no pressure other than gravity, which would be insufficient to push against the water pressure at the outlet of the turbine. Assuming that the tank is submerged at 400 m, per the article, that puts the water pressure at 4MPa at the outlet of the turbine. That's a lot of back pressure to fight against.

In fact, with the vent open, water is going to want to flow into the tank, even without a pump, as the article describes. But once inside, it's a bear to get the water back out.

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[ornerynorsk]

A vented tank would serve far more usefulness at 50 meters above terra-firma rather than in Davy Jones' locker.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[SomptingGuy]

A gravity-based system doesn't really know or care where someone has chosen to put the datum.

- Steve

 

[ornerynorsk]

Unless the turbine outlets are deeper underwater than the atmospherically vented storage tank

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[IRstuff]

Upon re-reading the article, it's actually going the opposite direction. The "storage" phase is where water is pumped out of the tank. The turbines are turned by water going into the empty tank, pushed by the water pressure. That makes more sense, and that makes it being submerged 400 m more sense.

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[SomptingGuy]

Exactly.

- Steve

 

[ornerynorsk]

That makes much more sense!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Timelord]

IRstuff,

I agree, just like I said back in August (the 7th post). It would appear that most of the replies were by people who didn't read the article in the OP.

Timelord