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Storing wind energy

Storing wind energy

(OP)
http://www.globalnewenergynetwork.org/news.php?new...

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

RE: Storing wind energy

Sounds great, until you point out the losses involved in storing energy (typically 50% for several different storage methods).

If you really want to store energy, try consumer site ice storage.

RE: Storing wind energy

I would guess a breather hose to allow atmospheric pressure air into the chamber. Basically you have pumped storage, pumping seawater from the bottom to the surface. Boiling and re-condensing seawater seems like it would be extremely inefficient.

RE: Storing wind energy

There are vacuum breaker valves for vessels that are supposed to remain closed when in service, however for water you'd just need any ole vent somewhere at the top.

Why store anything. Make ice and sell it. Well ... if you're not at the North Pole.

Independent events are seldomly independent.

RE: Storing wind energy

If I was at the N.P. I'd probably make hot water.

Independent events are seldomly independent.

RE: Storing wind energy

Seems like this would work well in Washington DC.

Mike McCann
MMC Engineering

RE: Storing wind energy

I would be willing to bet that the vessel is vented to the surface atmosphere. Then as you pump it out the interior will always be at surface pressure as opposed to depth pressure and the pumping head almost constant (ignoring the height of the vessel). As you let the water back in, it is the same as releasing water held at a height equivalent to the vessel depth. Pumping water uphill for energy storage is a very common method to store energy, i.e. a dam and reservoir. Plus, the vessel will always be loaded with external pressure, placing it in compression, ideal for a low cost concrete vessel. Neat idea!

Timelord

RE: Storing wind energy

The tank will be in tension as soon as it gets some water. Inside pressure is the same as atmospheric, but you've got water inside too.

Independent events are seldomly independent.

RE: Storing wind energy

Quote (article)

One such 25-meter sphere in 400-meter-deep water could store up to 6 megawatt-hours of power, the MIT researchers have calculated

Does this seem just a tad optimistic? I think we've got some wandering decimal points in the equations.

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.

RE: Storing wind energy

I get about 8.9 MWh at 100% efficiency.

RE: Storing wind energy

They themselves admit it's going to be probably more like 60-65% and I expect the scaled up system will probably come in at 55-60% tops, if that, but it's a nice idea.

Independent events are seldomly independent.

RE: Storing wind energy

(OP)
So the potential energy of the water is 4/3*pi*12.5^3 * 1000 * 9.81 * 400 = 32e9 (Joules) = 8.9MWh

Using the quoted 70% round-trip conversion efficiency, gives 6.2MWh.

Maybe I've done something wrong, but I get the same kind of answer they quote.

- Steve

RE: Storing wind energy

The Dinorwig pumped water storage facility in the UK has a claimed round trip efficiency of 74%, not bad for 40 year old technology. That means the turbines themselves must be up around 90%, which is news to me.

Cheers

Greg Locock


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RE: Storing wind energy

Or...?

Independent events are seldomly independent.

RE: Storing wind energy

Unfortunately, there is a strong tendency for the underlying idealizations and assumptions behind the wonderful claimed performance capabilities of any system to not be very clearly stated along with the advertising or marketing literature. These idealizations and assumptions are seldom well matched to the realistic operating duty of the system. As a result, the actual performance rarely matches the lofty expectations for the system, but the system may be able to perform near its expected characteristics under testing set to fairly well match the ideal circumstances.

I'm sure that I am not alone in observing this well established tradition.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

RE: Storing wind energy

(OP)
Negative, ccfowler. Greg has a good point. That energy storage thing in Wales is the dog's danglies.

- Steve

RE: Storing wind energy

At first glance all seems so nice--then one needs to contemplate some significant considerations.

Economies and efficiencies influenced by scale: hundreds of MW vs. single digit MW

Access for maintenance and repair at atmospheric conditions vs. hundreds of feet below the sea surface (the pump/turbine must be below the bottom of the reservoir)

Relative burden of resources required vs. the magnitude of energy storage and recovery available (staggering amounts of concrete, steel, ...) for proportionately minuscule amounts of energy. Cost vs. resources required vs. benefits are unlikely to get into a "happy" range.

The amount of wind energy that can actually be recovered from the wind vs. the nameplate rating. Most wind turbines recover somewhere around 15%. "Traditional" pumped storage works with adequate power available to operate the pump(s) at near BEP conditions. Given the variability of winds, the proportion if time when the pump can get near BEP conditions will usually be a very small percentage.

As wind turbines become more and more plentiful, a time will probably come when serious attention will be turned to the number of birds killed per MWHr, per year, ....

I've spent very much time and effort with "alternative energy" concepts that have looked so very promising until their troublesome little quirks get in the way. The phrase "reality is" has much value. I confess to being a hopeful but many-times-disappointed fan of alternative energy.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

RE: Storing wind energy

(OP)
... a uni study. Some say they are a waste. Some don't. I veer towards the don't team.

- Steve

RE: Storing wind energy

Can I ask my usual question: After 30+ years, and the thing is worn out, how do you decomission it? Or do we just leave them there to become an eyesore.

I.m tot trying to be a pessimest with this question, but a realist, from the experence of the concrete structures from oil production. Or is the answer, someone will figgure it out at the time (It's not my problem).

Most nucular plants are required to have a decomissioning fund, so why shoulden't alternitive energy.

RE: Storing wind energy

Turn them into artificial reefs?

Independent events are seldomly independent.

RE: Storing wind energy

I think that underground compressed air storage would work best during times of low elec demand and high wind power production. The compressed air could be used later during times of high power demand/ low wind production by a gas turbine, whose output and efficiency would be greatly increased if it had access to a reservoir of compressed air.

Another concept proposed by some engineers from holland about 10 yrs ago was to construct an artifical offshore island ,with a deep basin in the middle, with wind turbines around the circumference of the island. During times of low wind power but high demand the ocean would be permitted to rush into the empty basin and produce power thur hydro turbines, and during times of excess wind power and low demand the water would be pumped out of the basin.

Yet another concept would be to have a high energy consuming industry operate only during times of excess wind power- examples may be re-melt of recycled metal, or production of some chemicals.

"Nobody expects the Spanish Inquisition! "

RE: Storing wind energy

Now you are talking smart grid. However the orignal concept of smart grid is to reduce residentual demand for industry uses. AKA, shut off your home airconditioner during the hotest part of the day so some industry can make cheep plastic (humm, chairs, bottles, or smart phones).

Why not just make electricity pricing follow the availibilty. The price can convey the value, or difficulty to generate. Wind power at night should be priced lower than other power during the day. But I guess that is why they are trying to store it.

How about ice storage. If it melts, it cools the building it was intended to cool anyway.

RE: Storing wind energy

Seems like a Rube Goldberg operation to me. My opinion only. I think fuel cells (thinking of Bloom boxes) hold much more commercial potential in the future, especially that methane can be produced from bio sources. Getting creative with energy conservation, as opposed to greater alternative capacity, as others have mentioned, will give a far greater return-on-investment. This is an area that is lagging behind R&D, even though it's far easier to implement (perhaps not in changing people's habits, though)

Or we could always go back to coal fired steam plants. banghead

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.

RE: Storing wind energy

What ever happend with coal gassification, followed by burning it in a combined cycle plant?

Don't get me wrong, we do need power at night. You know for the street light that shines in my window, and the cell phone chargers left plugged in, and the kids night light.
But that energy should be priced to the demand.

Yea, I know electric cars will change all of that, just look at the numbers of units sold.

My point is if you are going to store energy, do it in a way that some of the waste losses can also be used.

Why not just use the wind machine to compress air directly, and get rid of the generator/motor losses. You can then create a distribution system for the compressed air to all the service stations in a large town.

RE: Storing wind energy

cranky 108:
coal gasification makes sense if the energy price of coal is less than half the energy price of natural gas- that may be true in europe , but certainly will not be true in the USA for the next 100 yrs. The combination of very high investment cost plus lower overal availability plus low shale gas cost implies that it will not be viable in the US. There is now being built in Odessa texas a trigeneration gasifier, where hydrogen and pure CO2 are also sold as a product together with the electricity from the IGGG.

Also, integrating the gas fired combined cycle plant with the gasifier should only be considered if you also provide a backup connection to the interstate natural gas pipeline- an IGCC without such an interconnect is doomed to very plant low availability.It only takes one piece of critical equipment to shut the entire plant down, including gasifier, CTG, STG, cryogenic air separation plant,material handling system.

"Nobody expects the Spanish Inquisition! "

RE: Storing wind energy

I understand the hydrogen with nitrogen usage to make NH4, so the hydrogen generation makes since, although I might not have thought about it.

The CO2 is probally used for well injection to increase oil production, which also makes since.

CO2 can also be used for feeding some aquitic plants for oil harvesting to make bio-jet fuel.

However on wind machines, if you are including compressed air as a storage medium, it might be better to have part of the energy extracting capacity for electricty, and part as compressed air, thus limiting the sizing of both. It is doubtful the units will run at full capacity, and having the ability of both allows switching production for the grid, or storage. And if you ever have full wind, you can do both.

My recollections of some wind machines is they have four generators placed around the inside of the hub, so just replace two of them with air compressors, and use clutches select which ones are operating.


RE: Storing wind energy

cranky - don't think about it on a per-nacelle basis, think about it on a per-farm basis. You only connect the [storage technology] to some fraction of the turbines. Simpler that way.

RE: Storing wind energy

Well it would be easer to replace two of the generators with compressors, and use the large volume of the tower as a compressed air tank. It would intergrate the storage into each tower.

RE: Storing wind energy

CAES compressed air energy storage is best applied in conjunction with gas turbines and an underground salt cavern ( for compressed air storage). During times of excess free electricity the compressor part of the gas tubine would be used store air at high pressure in the underground cavern. During times of electricity shortage the stored compressed air would be bled into the combustor of the gas turbine and the power produced by a gas turbine which does not need to use its compressor is 2-3 times the electrical output that would result if it did need to use its compressor.

Storage of compressed air abovegorund in a large tank is extraordinarily dangerous. Also, the only way to manufacture such a large tank onsite would be using the chinese style spiral wound ligaments, multile layers in thickness.

Other strategies to construcitvely use excess free electricity include hydrogen production ( from electrolysis of H2O), batch operation of smelters, batch operation of chemical plants ( eg, sodium hydroxide, otehr energy intensive chemicals). The dutch have proposed builiding a hollow island with wind turbines at teh circumference and pumped hydro storage at the island interior.

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

RE: Storing wind energy

Maybe so, but I seem to recall the auto shop using air tools to remove my tires, so I know it is possible without a GT.

So explain to me why it won't work?

RE: Storing wind energy

Does anyone have any idea as to the pressures needed to store compressed air. It's way more than a gas tubing can generate

RE: Storing wind energy

The domain name for the link expired, I hate when that happens.
So you are looking at pumped storage. The only reason for that, is to keep the value of the generated product up, instead of letting it go to waste.
It does not matter what the efficiency is, because if you are successful at storing, anything, you can resell it.
The primary issue is capital cost.
B.E.

You are judged not by what you know, but by what you can do.

RE: Storing wind energy

The value of stored energy, if assuming 50% loss in storage, is 150% of the orginal cost to generate it. My point is you would have to increase the size of the wind farm to accomidate the losses, and bear the added cost of the added capital. This may come out as energy costing about 150 to 200+% of the energy from a simple no storage system.

So my question is, why wants to pay that much for windless wind stored energy?

However in the case of hydrogen storage, the fuel can be used for transportation, which electricty is more difficult to use.

RE: Storing wind energy

In the limit case where the underground UG reservoir is very large and is leak tight, then the optimum pressure for air storage is the same as the design outplet pressure of the CTG's compressor. If the CTG has a 10:1 pressure ratio for its compressor, then the UG reservoir should be held at 9-10 bar. There may be a 3% pressure drop from the compressor to UG reservoir, and another 3% pressure loss when flowing the air back to the turbine. Those assumptions allow the use of standard CTG components, except for the electrical generator and shaft bearings, since the net electric power generated with the compressor uncoupled may be 2-3 times the net electric power generated with the compressor coupled to the turbine.

In real life the UG reservoir is not of infinite volume, and some leakage is expected.

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

RE: Storing wind energy

I am located in Michigan, and we have a large hydrostatic (pumped -hydro) energy storage facilities in Ludington. You can read more about it here: http://www.consumersenergy.com/content.aspx?id=698...

If you'd like, I can put you in contact with someone who may direct you to the appropriate person at consumers energy who can provide further information.

I am from the power industry, and from where I sit, these ponds seem to work extremely well. The trouble is, there are environmental concerns, and they are hard to get built these days as a result.

RE: Storing wind energy

Use the excess windpower to compress and/or liquefy NG.

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.

RE: Storing wind energy

pumped energy storage using hydro from mountain top reservoirs is currently used on a schedule deteremined by the hedge meisters based on the low cost of electricity ( due to low demand or excess wind capacity) and released thru the hydroelectic turbine generators at a time when the bid price for power is at a maximum. This is an example classic monetary feedback being used to optimize the distribution of resources, and the same model can be used for other means of equalizing demand vs generation.

If sufficient pricing signals are provided to the congnizant consumer, then the consumers will modify their behavior to also equalize demand vs generation. Large industrial consumers of power can be considered as cognizant , and the previously suggested concepts of liquifying gas to LNG, or batch production of energy intensive chemicals ( sodium hydroxide, H2 , etc) will likely follow.

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

RE: Storing wind energy

Studies show that time of day rates don't have a big impact on residentual. Some business might.

RE: Storing wind energy

"This is an example classic monetary feedback being used to optimize the distribution of resources, and the same model can be used for other means of equalizing demand vs generation."

I think people neglect just how much inertia there is, particularly for power bills. To wit, until my coworker's electricity bill hit $300, he hadn't done anything to curtail usage. But, even with that curtailed usage, which was driven by A/C, the usage time remains unchanged, since it's sort of moot to run the A/C in the wee hours, when the heat load is at its greatest 12 hrs earlier.

I think "monetary feedback" simply optimizes the distribution of money into the bank vaults of the power companies. The peak demand period is basically fixed to the couple of hours before noon to after 6pm, due to heat load driving A/C usage. And, unless forced to, companies are loathe to up the ambient temperatures because grumpy, hot, employees are more likely to crash profits than the cost of electricity.

TTFN
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RE: Storing wind energy

In some locations the peak is midnight to 6 am for Winter peaking utilities. And it is because of heating.

What I see is the weather, here, in the summer is typically mild, but with the advent of AC the usage is 24/7.
The issue is the conditioning systems tend to condition, rather then equilize the inside and outside. So maybe a different kind of system needs to be developed.

RE: Storing wind energy

I think the whole point of an A/C is NOT to equalize, given that the comfort zone for people top out below 80F, but the outside temperature can easily be > 90F, even in relatively temperate regions. One common approach is evaporative coolers, but given that we're in a drought in the LA area, that's not going be particularly viable. Moreover, such coolers dump a truckload of moisture into the cooled air, and the higher humidity might be uncomfortable.

TTFN
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RE: Storing wind energy

Mass, intrinsic (already moving) velocity of that mass or potential energy (pressure and temperature) of a static mass, efficiency of that mechanical-energy-by-converting-it-to-useful-continuous-torque, and ability to restore that original stored energy, right?

So, exactly what is the "stored energy" they are (1) going to release to convert to continuous torque?
(2) going to use off-peak available electric power to re-compress/restore to serve at the next cycle?

Pumped storage as at Niagara is near-ideal. A safe, very heavy stable liquid already delivered to the base of the suction of the safe, reliable, easily-controlled suction of the pumps at a continuous rate from a inexhaustible supply upriver that will be well above the minimum NPSH of the pumps. Immediately available, cheap, reliable hydro power from the plant just yards away to re-pump up the water to a stable stored elevation a few feet higher in the (very expensive! VERY controversial pond) above the pumped storage facility under near-unique conditions where that hydro power is NOT needed at night and so can be used to power the pumps to move the water, but the hydro flow IS available due to the Canadian-US early water conservation agreements.

Now, what fluid is being compressed at what efficiency of (original electric) power to stored energy many feet underground/underwater to vented energy (back at the surface) back to power?

If air, you have much less efficiency than with water pumps. Much lower final pressure unless you use positive-displacement compressor-style designs rather than fans - at great change in complexity! Now, if they assume that the compressed gas is "stored" underwater but pressurized by the height of the water column above the gas, then the continuous pressure relies on the collapsing "piston" of a tank with its bubble maintained by a flexible membrane or piston. If the underwater concrete tank is merely the pressure vessel for the stored HP gas, and the underwater location is merely a nearby storage location for holding the HP gas until vented back topside, then you can claim very little "pressure credit" for the outside water pressure holding the internal gasses at bay, since the inside air pressure varies. An externally-pressurized spherical concrete tank can resist external pressures, but they would need to balance the need for greater stored pressure against tremendously higher construction and installation and connection costs.



Now, I grant of course that the buoyancy problems can be solved by the simple application of "more concrete" on the base of the tank. Leakage could be solved and the ever-moving air pipeline from underwater to the topside power plant can be solved - as indeed it has been in the oil industry.

Nothing comes free except college-level "studies" by physicts who DON'T have to justify their assumptions and approximations to ANYBODY. Who are responsible for nothing to nobody for accuracy or reality except writing the application to get their next grant!

What has somewhat been successful is compressing air under ground in salt deposits, then re-venting that air into the burners of a combustion turbine topside to reduce the losses of using the CT compressor. Not a large savings, but enough to pay the design and construction costs.

But offshore? Just how much are they claiming the tanks will cost installed and hookeup?

RE: Storing wind energy

If size is a concern, then grid size may not be possible. Maybe you should aim for something smaller.

RE: Storing wind energy

Well, the daytime peak for A/C usage exactly coincides with PV output, so there should be provided more encouragement to install PV, maybe even require it in new homes .Other passive techniques to reduce solar insolation into the home should be applied as well ( solar screens on south and west windows).

The bigger issue is addressing the random nature of wind energy. We are reasonably sure that tomorrow's forecast is increasing brightness during the early mornging hours, followed by complete daylight, and later in the day less brightness followed by night.Complete darkness expected all night. Not as sure about tomorrow's wind speed.

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

RE: Storing wind energy

Here's an idea for discussion. For southern and tropical climes;
Use a VFD to drive an A/C compressor. Use solar power to add energy to the DC bus.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Storing wind energy

Quote (davefitz)

Well, the daytime peak for A/C usage exactly coincides with PV output, so there should be provided more encouragement to install PV, maybe even require it in new homes .Other passive techniques to reduce solar insolation into the home should be applied as well ( solar screens on south and west windows).

Going to disagree with you there.

PV solar power only matches demand in an idealized government study promoting solar power.

Actual electrical power demand peaks early in the morning as people wake up and start things, then drops off considerably between 9:00 and 2:00 to 3:00 oclock. Afternoon peak is 3:00 through about 7:30 to 8:00. A/C needs drop off after dark, but more lights are needed and home entertainment and the like also increases slightly.

Solar PV is only available from 9:00 AM to 3:00 pm local solar time. So, it begins to generate power just as demand actually lowers - forcing the conventional generators to be cut back even MORE than they would no-solar "assist" and causing even more cyclical strains and cracks in the metal. Then, as the afternoon real peak begins to increase at 4:00 and 5:00 in the afternoon, solar PV drops off to near-zero levels.

RE: Storing wind energy

Theres another problem with PV, in that many fire departments will not attempt to put out a fire on homes with PV because of the concern of being elecuted.
With this fact it is likely homes with PV will be rated in a higher fire risk catagory, and thus higher preminums (and lower home values).

Another issue is clouds should be increasing according to the thread on global warming, which will deminish the PV energy generated.

So PV is becoming nothing more than an expencive toy.

Some studies show that with increasing wind pentration there is increasing grid instability. This is also showing up in fault recovery voltage recordings. There will soon be a push to require wind producers to continue producing energy into lower and lower voltage dips to help stablize fault recovery voltages. This will likely be followed by requirments for non-static var support requirments like what is being required of other energy types.

So it might be better to look at regional or local solutions for storage, rather than grid sized storage solutions.

RE: Storing wind energy

Cranky108,

First responders cocerns are valid and resulted in changes to NEC 2014- see pars 690.12 and 690.13 for remote disconnect requirements

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

RE: Storing wind energy

racooke - The demand curve sometimes looks like that. Have a look at the predicted demand in Texas today for an example: http://www.ercot.com/ - pretty good match to your description for a relatively cool day in Texas when there is little AC demand.

However, summer demand (when our biggest peaks happen) looks totally different, and is much closer to the PV production curve, though lagging somewhat. Peak demand warnings from 2-6PM (CDT, so 1-5 CST) are most common. Fortunately for demand matching, most of the good solar sites are far to the west and most of the demand is weighted east. This shifts us closer to PV output matching the demand curve. Obviously that means some potential transmission issues.

RE: Storing wind energy

Unfortunately, no other states straddle the time zones like TX does.

RE: Storing wind energy

Other (lower 48) states are part of grids (Eastern Interconnect, Western Interconnect) considerably larger than Texas and can use the same effect by siting PV in good sites toward the West of the grid. Works better for the Eastern grid, as the population is also weighted East.

These other grids are considerably larger than the Texas grid and can actually leverage a larger effect.

Also, the absolute best solar sites in Texas (El Paso and Hudspeth counties) are actually part of the Western Interconnect. Located on the wrong edge for time-shaving, unfortunately.

RE: Storing wind energy

Good point. Put all the solar panels on the Eastern grid. However that's not where many of them are going. All that sand in the west looks so inviting.

RE: Storing wind energy

This one probably more palatable for technicals:
http://arstechnica.com/science/2014/04/new-solar-t...

This article points out to me a couple of caveats:
> Lead acid batteries are not particularly energy dense, but net charging efficiency is probably higher
> There's a phrase "given UV" suggesting that the azobenzene only does its deal with UV light, which, coupled with its 14% efficiency, makes it less efficient than batteries, and with more moving parts

TTFN
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RE: Storing wind energy

EPRI had a number of articles some years ago about storing energy is salt ponds. The sun would heat the lower layer of the pond, and be insulated from the air by the upper layer (with the middle layed acting as a buffer). The energy could be extracted with an ammonia steam cycle plant. It seemed to be somewhat pie in the sky.

It wasen't a storage system per say, but more of a energy production facility that could store energy.

I doubt any of these facilities were ever built. However it is possible to use an ammonia cycle plant off any current power plant to increase efficency. But for the cost and risk, I don't see any being built.

RE: Storing wind energy

Anyone here well-read on Tesla? Perhaps the subject of another forum.

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.

RE: Storing wind energy

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 "

RE: Storing wind energy

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.

RE: Storing wind energy

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.

RE: Storing wind energy

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!

RE: Storing wind energy

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

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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RE: Storing wind energy

(OP)
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

RE: Storing wind energy

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.

RE: Storing wind energy

(OP)
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

RE: Storing wind energy

Quote (IRstuff)

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.

RE: Storing wind energy

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.

TTFN
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RE: Storing wind energy

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.

RE: Storing wind energy

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

- Steve

RE: Storing wind energy

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

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.

RE: Storing wind energy

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.

TTFN
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RE: Storing wind energy

(OP)
Exactly.

- Steve

RE: Storing wind energy

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.

RE: Storing wind energy

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

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