I read about that about four days ago in a Swiss online newspaper [1] (German). The Lake Constance is a large lake (length 64km / 39mi) carved by the Ice Age Rhine glacier shared by Germany, Switzerland and Austria.
Since November last year a hollow concrete sphere with the weight of 20 metric tons has been sitting on the lake bed at a depth of 100m / 300ft. In times of excess power water is pumped out of the sphere and power is regenerated by inflowing water powering a turbine.
Now they are going to experiment with an even bigger sphere in the sea. Perhaps there will be some differences because of the salt water environment.
These sorts of design would generally cover short term demand as they can be started and stopped very quickly.
Really I think if we were developing an energy mix now, and we had a blank piece of paper, it would read as:
- Modern nuclear for base load
- PV/Wind as much as possible
- A mix of things like this article, vehicle to grid, utility battery etc to cover peak demand
- Back up of gas turbines to be used as last resort
The main problem IMO is that nuclear power was extremely badly managed historically:
- Countries used it as a cover to generate weapons grade fissile material
- Modern designs were not invested in and developed sufficiently
- People have irrational fear of nuclear disasters when, actually, coal kills way more people than nuclear power ever has
As an aside, I went to visit the Dungeness nuclear reactor a couple of years ago, and I strongly recommend going if you live in the UK. It cost nothing and was incredibly interesting/a great experience.
I would also add a note on the bottom of the page to time-shift industrial electricity use to take advantage of new peak energy availability.
If you're going to use a great deal of electricity from the grid but don't particularly care about when, right now it makes sense to shift your use to the night-time, when electricity is cheaper. Solar power inverts this, and encourages more daytime use, and even waiting for sunny days if you have enough flexibility in your schedules. There is an inflection point in the difference between daytime and night-time cost (which we might not ever reach) where it stops being worthwhile to run a third shift at a factory, because the difference in energy costs is more than the cost of just building another factory, in the long term.
So if we rebuilt our civilization to take advantage of renewable energy and solar power in particular, we might find ourselves needing less base load power than we do now.
For storage, PSH[1] while obviously not lossless can deal with excess peak capacity -> cyclical demand in a fairly scalable way and unlike lead-acid, LiCO2/LiFePO4/etc, don't suffer from anode dendrite formation.
I have extreme reverence for Bill Nye as a voice of rationality[0], so when I heard him on a talk show nay-saying nuclear power with his prime argument of 3 failures against ~400 I poked to see what sorts of impact it had. At first glance, a failure rate of of almost 1% is absolutely insanity. Things have significantly changed, however, since the design of Chernobyl. Control technologies had progressed in modern (3rd and 4th generation) nuclear power plants, which are safer and cleaner by quite a bit compared to what the 60s hippies were riled up against. (In fact, there are 3rd generation plants that can be powered solely off of the waste-materials of ~7 older plants, providing an auxiliary benefit of consuming spent-fuel rather than having to can->seal->bury). The important thing to consider is that as technology progresses, we (humanity as a collective) should revise our expectations. After all, we don't factor the failure rates of Wright brother era endeavors into Boeing numbers.
Either way, seeing that segment got my curiosity fired up enough to begin some inquiry. (Standard caveat of "everything that follows is armchair"; this isn't even close to the field of study I'm well-versed in. The closest I get to energy professionally is low-voltage/low-amperage li-ion power control, spun such that units pass UL/CSA.) Were his fears founded/relevant to modern nuclear power sources? Were his fears a product of him living through the Cold War as well as living through all 3 of the major disasters that made his fears more emotional than my own? (I.e., he's in his early 60s and lived through the media coverage of 3 mile, Chernobyl and Fukushima[2] which would have impacted his opinion; I'm about to hit 30 and only Fukushima impacted my perception so my fears might be assuaged easier than his.)
I turned to full-cost accounting (from drawing board to decommission; factoring materials sourcing and the ecological impact (e.g. Aluminum takes a lot of power to produce); factoring in transport of sourced materials; maintenance (operational/preventive and modeled failure red-tag fixes); waste disposal) makes nuclear look somewhat appealing, even compared to PV/wind (typically deemed it's closest competitor). As one would expect PV/wind/hydro/thermal/nuclear all score about the same (give or take 50% for all of those technologies), while conventional non-renewable hydrocarbons operate within the next order of magnitude up.
So where does this leave us? Well, certainly there's agreement that fossil fuels/hydrocarbons should be phased out sooner rather than later[4,5,6]. From the damage done to the coal miners lungs, to the carbon impact they're about an order of magnitude less efficient (half-an-order with newer processes to reclaim heat excess and spool up turbines, not unlike using your cars' exhaust volumetric flow to spool up turbos as a form of auxiliary power).
Similarly, those super-tankers that get our iPhones from Foxconn to California off of diesel are doing quite a bit of damage[7] as well. Russia is still using nuclear power for their ice-breakers in the Arctic without incident. I'm not sure how close to catastrophe those units are, but all of the active US Navy combatant submarines are nuclear powered. I'm sure those sailors are thankful they don't have to drink water tainted with diesel as they did in years-yore. I wonder if anyone has conducted viability studies re: utilizing the same power mechanisms that fuel the sub props for those super-tankers (genuinely not sure - if anyone has more information, hit Reply).
Apples to apples (e.g. they both happened within a few years of each other) - the Deepwater Horizon had a catastrophic impact on our ecology. I'm not sure how bad the long-term ecological impact was compared to Fukushima, but I know after a "BP cares" PR campaign, we got right back to business as usual -- we're still pumpin' that black-gold - no one shutdown any hydrocarbon based operations as a result of the catastrophe. The only reason I can think of Fukushima having such a large impact is the historical weight "nuclear power" is burdened with. Someone needs to bring in a PR firm and come up with nuclear's equivalent of "clean coal".
==
[0] Shills on Fox News show up as guests frequently and try to attribute climate change to 'natural cycles in the world' using cherrypicked data (say: CO2 statistics from a selected 7 year period). Nye elegantly anticipates these arguments (not too hard, I suppose, since there are a finite number of them) and then contextualizes them (e.g., bringing out a graph showing a 100 year period). Go watch it on youtube, it's quite entertaining and a very elegant way of argumentation that's accessible to the "Glen Beck" demographic [using pretty charts instead of a chalk board].
[6] https://www.brookings.edu/blog/planetpolicy/2014/05/20/why-t... (Standard full disclosure any time I cite a source that's not purely academic/where conflicting interests may exist: Brookings is a "liberal" think-tank. Even though I agree with most of their publications, I don't think they should have an .edu any more than the Cato Institute should.)
[7] https://www.quora.com/Is-it-true-that-the-15-biggest-ships-i... This question was posed in response to a Daily Mail (UK) article that was sensationalist-journalism. The Quora response is of far better quality and addresses the nuances with significantly more insight than the original article.
>I wonder if anyone has conducted viability studies re: utilizing the same power mechanisms that fuel the sub props for those super-tankers (genuinely not sure - if anyone has more information, hit Reply).
They didn't just do a study, they actually built a nuclear-powered cargo/passenger ship many years ago, called the NS Savannah. It was a commercial failure. That's not the only nuclear-powered merchant ship built; Germany built an ore-carrying ship, and it only ran for 9 years. Japan built one too, and it was a failure on its first voyage.
The second article here thinks the Savannah was doomed by other factors, and tries to argue that maybe nuclear-powered merchant ships should be tried again, but there's a lot of problems with the idea. Past ships had problems with radioactive waste being dumped into the sea (which caused fishermen to refuse to allow the Japanese ship to even dock). It takes a lot more crew to staff a nuclear ship, and they have to be highly trained. They'd probably be a terrorist target. The shipping industry (maintenance, etc.) isn't set up to handle nuclear commercial ships. The insurance would be prohibitive. Overall, it's really questionable whether it'd make economic sense to have nuclear-powered commercial ships.
Base load in Germany is about 50GW, around 10GW of which is handled by wind and water. That leaves approximately 40GW to be handled by other means.
At 20MW per sphere, you need 2000 spheres to cover the entire base load. (Not sure where the article gets its 80 spheres number from, did I make a mistake? There's an order of magnitude difference..)
These spheres don't generate electricity, so you still need other (less constant) means of electricity generation. Germany generates solar electricity peaks of 50GW, so perhaps tripling that capacity could get them close.
Wind energy is around 20GW, but way much more constant, so tripling that could also get them close, and you could possibly do with a lot less spheres, perhaps closer to the 80 in that article.
So with a triple investment in green energy and the building of hundreds of these spheres, Germany might be able to make themselves a 100% renewable energy country. (Assuming my assumptions are close to reality)
Don't mix MWh and MW (it's commonly used to mislead, but not here). The article is declaring 20MHh of storage while using 5MW power turbine. 5MW output from 20MWh storage gives you 4h output.
Edit to add: If you want to make proper calculations, don't forget that these types of storages are very inefficient. You can't compare them with pumped hydro.
Ah thanks, I misread that. I get that these types of storages are inefficient, that's the point I was trying to emphasize, a solution like this looks interesting, but it's not a serious competitor to nuclear power, or even pumped hydro (it's basically pumped hydro, but with a human made reservoir).
How can you say that off-hand without knowing what the costs are? It's not at all obvious to me that building 3000 concrete spheres with turbines and a bunch of PV panels is any harder or more expensive than building giant nuclear power plants.
Each sphere is only worth 5 MW (for 4 hours, totalling 20 MW·h worth of electricity). 80 spheres were not meant to cover the entire base load, but just to make them a relevant factor in the grid.
I saw a talk from MIT professor who came up with a similar idea[0]. Using spheres seemed like a pretty good idea on paper, but when they started doing the cost analysis they found that it would be cheaper to use cylindrical pipe.
Even though one uses more concrete, it's cheaper because we already have the infrastructure in place to produce and lay long concrete pipes.
In both cases he also recommended using such energy storage systems as anchors to hold offshore wind turbines in place, because the concrete is more than heavy enough to do so.
The reinforcement cage in concrete weight coating used on subsea pipelines is relatively ordinary steel. The steel is protected from corrosion by the concrete itself and a system of sacrificial anodes that are easy to survey and replace. (I help design pipelines)
> The steel is protected from corrosion by the concrete itself
I guess that the steel is protected by something else because, as the pre-1970 builders ignored and as it dawned on everyone else 20 years ago, concrete is not waterproof.
Would a cylinder be strong enough? The Germans are talking about operating at a depth of 700m, which is more than twice the maximum depth (300m) of the example analyzed in the paper you cited.
These pipelines have some inner pressure. The idea is here however that a pressure differential is used to drive a turbine. The greater the differential the more energy. The engineering challenges are not really comparable.
The US Navy's DSRV's you referenced do not have cylindrical pressure vessels. The cylindrical external hull encloses 3 linked spheres that are the actual pressure vessel. BTW, the DSRV's were retired several years ago.
Seems to me that if you use compressed air to displace water within the sphere, you could actually store more energy this way... That would require the air to drive electric generators when the sphere is being filled with water though.
Once you start compressing and decompressing air you get a lot of heat loss though, that I would imagine isn't as much of an issue when you're just pumping plain water back and forth
They're testing a concept here that's basically under-water balloons to store potential energy: http://hydrostor.ca
It's a pretty small-scale experiment, but everything has to start somewhere. The Deep Lake Cooling Project was prototyped at some point and that's well into production now, providing inexpensive cold water for chillers through the downtown core: http://www.canadianconsultingengineer.com/features/toronto-w...
The Hydrostor project is roughly located in the same area as the Deep Lake intake pipe comes ashore.
You are referring to the threat of trawling nets yes? So the idea presented in the paper is to use these things as anchors for wind turbines, it would not be a very good idea to go trawling through an offshore wind farm. Of course in either case, it is more likely that such structures will damage the trawling net rather than being damaged by the trawling net.
This is amazing. To store temporary energy, you don't need a mountain range anymore. Instead, you can use nearby offshore trenches and continental shelves.
Open Google Earth. Look at the Philippines, the Arabian Peninsula, Hawaii, and eastern North Carolina. It's a perfect complement to solar energy in certain parts of the world.
Some good ideas are simple. This may be one of them.
I'm seeing more quality research from Fraunhofer in recent years that is also useful for practical purposes. They're preeminent with all things related to energy in Europe: smart meters, protocols, renewable energy data collection, dual-licensed GPL/commercial code in ths domain, e.g. openmuc.org. Applied science done right.
And both are the reason why German universities rank so badly in international rankings. They are attached to the universities, forming clusters, but their accomplishments are not measured anywhere.
This suggests that: a) German universities don't care that much about international rankings, and b) organizations doing the international rankings don't care about their accuracy - otherwise, they would have adjusted their rankings to compensate for the idiosyncrasies of German universities.
More precisely on (a), the unis care about rankings, but the politicians who'd have the power to change the structure of research don't. Indeed for the majority of German politicans, the word "elite" is toxic, even and especially in the context of having a few world-class centres of excellence rather than 50 merely adequate universities.
Global Uni rankings have a big bias toward research. What the poster is saying is that Germans do more of their research at these institutes than at their Universities so German Universities rate poorly on global lists.
As you can see, in Germany and France, research institutes take the place of what in the US and the UK would be universities like Harvard, MIT, Oxford, and Cambridge. Fraunhofer doesn't even show up, because while they do a lot of amazing stuff, they aren't under publish-or-perish constraints (they instead have contracts to fulfill) and so they publish comparatively little.
This has a number of reasons, some of which are pragmatic. For example, if a French or German university wants to hire a professor, that professor usually has to be able to speak French or German, respectively, at least at a near-native level to be an effective teacher (there are exceptions, but it's still a frequent requirement). Research institutes aren't constrained in this fashion, even though they closely interoperate with universities.
There are a lot of Frauenhofer's and the quality varies quite a bit (anecdotally, anything involving physical engineering is usually solid). They also tend to mass apply for all sorts of grants and build research proposals around trends. They are well connected and politically it's never a bad idea to have a Frauenhofer in your consortium if you apply for a national grant (imo).
I'm a bit torn on the overall concept since it seems zero-sum-ish and I'd rather see more research directly at the universities.
> I'm seeing more quality research from Fraunhofer in recent years that is also useful for practical purposes.
This is their intended mission. Only about 30% of Fraunhofer is financed through public funding, the remaining 70% or so have to be earned through doing contract work for the industry. This has a number of goals:
1. It makes advanced R&D accessible for small and medium enterprises that cannot afford their own R&D department.
2. It is a fairly effective way for the government to subsidize private R&D. It's effective, because businesses still have to pay the majority of the cost, so they aren't going to waste money.
3. Less research is hidden behind corporate walls, but can be more easily shared and reused, as Fraunhofer retains intellectual property to some of it (or even straight-out opens it up, such as GPI-2/GASPI [1]).
dunno this seems quite impractical. there's no suggestion on how to build such a sphere that big 700mt underwater and they kinda cheated using a freshwater basin because most of the turbine issues come from saltwater
I don't like being cynical, but this is a lot of concrete for not much storage. Also, building a salt water turbine that can last more than about 15 years is next to impossible.
Still, it's nice to see people trying to solve the storage problem.
I suppose you could start with existing underwater caves, lava tubes, or abandoned mine tunnels. In fact, the tech used to dig the Channel Tunnel could be used to make enormous tunnels for this.
The biggest issue I see is that the scientists specify a depth of 700 meters for the 30 meter sphere to hold 20 MWh. No where near Germany the sea is 700 meters deep. You will likely have to go all the way to Norway to find a suitable sea - with all cable losses and maintenance issues with it.
Ah - and that's another thing: how do you maintain a generator on a depth of 700 meters?
Isn't pumped storage on land a more feasible alternative?
The ingenuity of their invention is that it makes the energy storage of a given m^3 of higher more easily. The problem with pumped storage on land is that the work done is V * rho * g * h with h the height you pump the water, V the volume of water, rho the density of water and g the gravitational constant. Storing 1m^3 of water (1Mg) at 1m gives 10MJ or 10/3600MWh, so you need to store 3600 tons of water or store 1 ton 3.6km above ground to get 10MW or some combination of both.
When you go under water the pressure increases and you have to pump against this pressure. The formula is (if I recall correctly) (P0 + rho * g * D) * V with D the depth under water and P0 atmospheric pressure. Ignoring P0, you would need a reservoir 700 meters above ground to store the same amount of energy in the same amount of water. A 700 meter water tower is harder to build than an underground reservoir.
But the tower solution doesn't need a concrete/steel pressure vessel capable of withstanding whatever the pressure is at 700 meters. Just a bladder would do.
They're in the Alps. Why not just put a bag of water uphill. Fill it using excess energy. Drain it to run a turbine.
There's a patch between Denmark and Norway which is ~700m deep. This a few hundred kms north of Germany. This is actually closer to most of Germany's wind generation than Bavaria, which is much further south.
I'm not very bullish on the technology however, maintaining anything in the ocean is a difficult challenge. My guess is a mixture of batteries and power to gas would probably wind up being easier to scale up, and cheaper in the long run.
The tech used to dig the channel tunnel would not exactly be a zero concrete solution either. I would not be surprised if free-standing underwater tubes could be built with less per storage volume, e.g. due to very different safety requirements.
Opportunistic use of caves and the like could hardly ever be worthwhile because it does not scale.
Can't you just pour liquid concrete into moulds, and wait a few weeks? Maybe I've just been in South East Asia too long, but there seem to be few problems where pouring large quantities of concrete isn't considered the go-to solution.
This reminds me of another "pumped storage" type solution, but using rail cars of basically rocks. This of course has the advantage of working in areas where there's lots of solar and no water, like the desert.
A dude on the Danish engineering society worked through the math, and indeed, rail cars don't seem feasible. Just too expensive.
I don't have too high hopes for the sphere idea either - operating turbines in seawater 700 m down seems too complicated compared to transporting the energy to land and storing it there, somehow.
No mention of how efficient a storage method, but certainly a simple solution and potentially cheap.
One interesting aspect that is not mentioned, as wind is a shift in air pressures, then if there is a low to high shift, the efficiency will be slightly lower than a high to low shift. Presuming the air is pumped down during the former air pressure. Not sure of the effect upon storage capacity and maybe negligible or balances out. But still a factor.
No air is pumped down. The diagram shows "Strom" going down. In German Strom means energy or in this case electricity. Remember air is quite compressible but water is not.
Strom does not mean Energy. It means stream, as in a stream of water, which could be a river, or as in a stream of electrons, which would be electricity. Strom most often refers to Elektronenstrom.
In English energy is a loose synonym of current. My point was that in this case Strom means electricity which you agree with so I'm not sure why you are arguing about semantics.
Aha thank you, though they do say "The underlying studies and calculations concerning the storage capacity assume a charge-discharge efficiency of 80-85 %" So will be interesting how results corelate towards that calculation.
In such depth underwater, difference created by atmospheric pressure is negligible. If they pumped air in, energy would be lost by compressing the air to necessary high pressure.
So I think they just pump out the water and create vacuum.
Pumping air is more "springy" than pumping water. But "springy" isn't exactly the worst thing when it comes to energy storage. Pressurized air storage exists, even though it comes with certain disadvantages, namely thermal losses. Ideally you would want to somehow harvest at least some of the "cold" created during decompression. At least with the "diving bell" variation of compressed air storage, you would store some of the energy not as gas pressure but as lifted water, avoiding the thermal penalty for this part of total capacity.
But you are right, FhG are working with a permanently contained gas bubble that is compressed/expanded as needed. Many of the experiments done with the prototype where about the effect of different amounts of air and about the efficiency difference between a local bubble and a passive air connection to the surface. I am sure that FhG have put more thought into the pneumatic link idea than I could ever do and they seem to have come to the conclusion that a pneumatic connection just isn't feasible, or maybe that losses along the connection would be too big. From what I could gather from other sites (e.g. http://forschung-energiespeicher.info/en/news/aktuelles-einz... ) they seem to have a strong focus on practicality, e.g. having all the electric and mechanic components concentrated in a module that is slotted into the sphere from the top, which might make it a candidate for removal/replacement.
In traditional pumped storage, you use the pressure of water pumped up some elevation to generate electricity by spinning a turbine as it falls back down. In this instance, you use the pressure of the bottom of the ocean and pump the water out, so that when it is allowed to flow back in, it spins a turbine and you generate electricity.
It's necessary to the design for them to be underwater.
Sorry to nitpick, but the concept works just as well above water. It also has the benefit of not requiring the pressure vessel.
Building a swimming pool of the same volume 700m up the side of a mountain, pumping water up and using it to drive a turbine on the way down is the same concept (and would give the same energy storage capacity [Pi * 4/3 * (30/2)^3 * 700 * 1000 * 9.81 / 3600 / 1e6] = ~27 MWh (assuming 100% efficiency).
I would imagine the benefit of doing this in the ocean is that the plumbing is simpler (don't need to lay the pipes) and you don't need to find a 700m mountain and available land for the pool, pipes and base station.
In the undersea version, what you're really doing when you pump the water out of the vessel is lifting the entire ocean level by a minuscule amount and then generating power when you allow it to fall back down.
Right, you're just describing traditional pumped storage. I suppose I should clarify because I didn't actually say what the advantage was, just the ways that the two designs are similar, but different.
In short, the advantage is that it exploits the same concept but in a very different way that avoids the pitfalls of traditional pumped storage.
The (dis)advantages:
- Safety. Dam failure is pretty catastrophic (see Vajont Dam disaster.) Although it's yet to be seen what failure of this device would look like, it's likely to be much less threat to human life. It would probably kill or deafen nearby marine life.
- Ecological concerns: a dam flooding a mountain valley destroys possibly unique ecosystems, and causes uncontrolled greenhouse gas emission as all the vegetation now underwater rots
- Land availability: land is at a premium, but seabed is abundant
Also, mountains for pumped storage are not always near population centers, and are often not near sources of renewable production that need the pumped storage. In that case, you have to transmit power from its point of generation to its point of storage to its point of use. In this scenario, with these spheres potentially being used as anchor points, the transmission distance between generation and storage is ~700m, and then you just need to transmit to your nearest coastal city of choice.
The advantage is having it built out of concrete. But because concrete has compression strength, not so much tensile strength, you need to store negative pressure not positive pressure.
The available pressure at 700m underwater is considerable. There's no equivalent reservoir of high-pressure fluid on the surface (the atmosphere is at a much lower pressure, obviously).
(The pressure difference in submarines is notably much bigger and more troublesome than the pressure difference spacecraft in a vacuum need to resist.)
So surely it's the high pressure at depth that's the attractive resource here? Pumping a gas into a cavern could offer a positive pressure solution, and I'm pretty sure that's been proposed already.
You get exactly the same pressure from traditional pumped storage of the same height. (Well, ignoring the tiny density difference between salt and fresh water)
That's not an advantage to having it underwater. In an above water version using a 700m mountain, the vessel to hold the water would use far less concrete. It's basically a swimming pool.
Not a swimming pool, but a reservoir, and there are already many used for pumped storage. The problem is that you can only do that where the local conditions allow it: you need space for the higher and lower reservoirs, space for laying down the pipes, and enough cheap water to refill the reservoirs (because of evaporation).
The possible big advantage of this solution is that it could be built wherever the sea is deep enough and partially use the existing infrastructure of offshore wind farms.
The energy is stored when all the water is pumped out of the sphere. To use the stored energy you let the water into the sphere, the surrounding water pressure pushes the water in and spins a turbine which generates the energy.
I agree but it is likely that the amount of concrete used to build those spheres is limited compared to say building a highway or a city. This is to be normalized by the amount of used energy storage / traveled roadway / inhabited building by year and by person for the comparison to make any sense.
If the spheres stays in operation for 50+ year, that's a lot of renewable power enabled by this technology.
On those scales equipment could be more of an issue. I shudder to think of the cost of repairing a turbine (or pump), submerged in water at the depth of several hundred meters. This is a little bit equivalent to running several small-scale hydro electric plants under water (where everything gets more complicated and expensive). Maybe the engineering is straight-forward. 50 years without maintenance is impossible.
Was thinking along the same lines with the underwater datacenter Microsoft has been toying around with.
Would you even have to put technology down there? I have absolutely no idea how good or bad humanity is at making very long pneumatic connections, but I would intuitively expect that the pumps and turbines involved would work on air, above the surface.
Is that good or bad? The amount of infinitesimal sea level rise that determines capacity would be the same either way.
One advantage of remote pneumatic pumping would be that power (W) could be scaled independently from capacity (Wh): you either add more spheres or you build bigger pipes/pumps/turbines. Conventional pumped storage installations frequently add more throughput to existing, unchanged reservoirs.
Any specific reasons why you think it should be very expensive? When the water is pumped out of the sphere, I think that the energy needed to bring it up should be very low. With a maintenance boat built purposefully to haul these things up, do the maintenance on the surface, and then let them sink again, I wouldn't expect the costs to be very high.
Volume of a sphere enclosure with radius 15.5 meters and a hollow center sphere 15 meter radius is around 1100 cubic meters. Specific weight of concrete is 2.4 g/cm^3. This monstrosity will weight between 2500 and 3000 tons. It will gain buoyancy when filled with air but the need for maintenance might be due to not being able to move water into and out of the sphere in which case you can add 10^5 more tons to what you need to lift out of the water (in which case I think making repairs at depth might look favorable).
It's probably doable. But it's going to cost a pretty penny.
> This monstrosity will weight between 2500 and 3000 tons
Even if filled with water, you should subtract 1100 tons to the actual weigh as long as the thing is in the water, and I guess that doing repairs with the thing just underwater below/near your ship would be much easier than doing them 700m below the sea. Unless it was possible to do everything with a remotely controlled diving robot, that is :)
This would be great for somewhere like the Pacific Islands, which are often surrounded by water.
Could the structures themselves be used to create artificial reefs? ~80 of these could serve as energy storage as well as creating a new surf break/protection for an island community.
"The Fraunhofer Institute for Wind Energy and Energy Systems Engineering envisions spheres with inner diameters of 30m, placed 700m (or about 2,300 ft) underwater."
I am just not sold. 100m/200m is nothing compared to 700m. Besides the mass increase needed for a concrete anything to survive that depth they want a turbine there too? Do you float these things when they need service? What if you can't? Like it fills up but cannot be pumped out? You are going to lay cable how far out into the ocean and across land, installation will be expensive and maintenance not much better.
there are just too many things that are expensive with this type of solution. Just like movies, when you thrown in scads of water things go wrong and they go expensive.
Just build carbon fiber spheres, bury them, and pump them full of air or other compressible.
I don't see the economics working for very long (10s of months) given the scaling of li-ion battery storage (Gigafactory, Et al) and the economies of scale that are necessarily going to follow.
Like, it -might- be sensible in the near future. But then the costs of battery tech will fall below the cost curve of this tech really fast. So why bother?
Also, I'm not too optimistic about this making it past the proof-of-concept stage due to some hard to solve and hard to scale isuess with the design but I'm perfectly ok with research institutions doing research that attempts to push the envelope. What other point would there be to their existence?
I don't mind research for research sake. But I'm just saying let's not all get over-excited about this being the next way to store energy. In practical terms battery technology makes so much more economic sense so guess where the money will be spent in production deployments at scale? Where it's economic.
Superconducting loops and hydro seem to be the most realistic options at the moment. Hydro is limited by geography, superconducting loops by technology, though there has been some real progress on the latter the last couple of years.
A combination of wind + superconducting load levelers already works quite well in that grid load fluctuations are dealt with efficiently (and in a very compact package) allowing windfarms to feed old and fickle electrical grids.
The knowledge gained there can be applied to longer load shifts but it still is a real challenge.
Sea based renewables (wave/wind technology) usually need anchoring to the floor. If the anchor is also a battery that can be recharged indefinitely, you have yourself a rather good system. The only issue I can see is sediment build up in the device.
When it is full of water, pressures are equal and drain could open from the bottom to eject water and sediment. The pressure differential could keep the valve closed when empty.
The marine environment is the harshest, most corrosive environment for machines. It seems to me underwater would be the last place I would place an energy storage device, if there were viable alternatives. The article does not say what the benefit of using this system is over existing gravity systems.
I hate to be a naysayer, but this is by no means a viable option to store energy.
Let's see how much energy can be stored in this sphere with a diameter of 3m.
E = VP
where E is the energy stored, V is the volume and P the pressure.
V = (1.5m)^3 * 4 * PI / 3 = 14m3
P = 100 * 1e4 N/m2 = 1e6 N/m2
thus E = 14*1e6J = 3.9kWh
Imagine that, the capacity of 4 big car batteries that I can buy for 100€ each! It uses 20 tons of concrete and is a highly delicate and sophisticated machinery.
Luckily, the energy stored scales with the cube of the diameter, right? So a 30m sphere will have a 1000 times higher capacity! 4MWh! However, it will be almost impossible to construct such a sphere out of concrete. Also, 700m depth? That is the limit for saturation divers and current nuclear submarines can't go deeper than 500m before getting crushed!
I have no idea who reviewed the application to this fund. It must have cost millions to build a storage system that stores as much energy as 400€ worth of car batteries.
Although your first-principles approach is admirable, it's also an order of magnitude out from what the original researchers are presenting (for a 30m sphere):
> Assuming the spheres would be fitted with existing 5 MW turbines that could function at that depth, the researchers estimate that each sphere would offer 20 MWh of storage with four hours discharge time.
Looks like you are assuming a 1.5m wall thickness, and then scaling that linearly to the 30m version, neither of which are correct.
> Also, 700m depth? That is the limit for saturation divers and current nuclear submarines can't go deeper than 500m before getting crushed!
I'd be surprised if they were making a claim like this without some justification that they can build at that depth. As a counter-anecdotal number, oil pipelines can be constructed at 2km depth [1]. These spheres are neither pipes nor submarines; I'm guessing they know (at least roughly) what pressure their spheres can tolerate. FWIW, the depth was chosen based on the depth limits of the turbines[2].
> The Fraunhofer Institute for Wind Energy and Energy Systems Engineering envisions spheres with inner diameters of 30m, placed 700m (or about 2,300 ft) underwater.
That would be 5600 times more energy, or the 20 MWh from the article. That's 2 million USD worth of car batteries...
Well, the energy scales with the diameter to the third power (we go from 3m to 30m, so x1000) and linearly with the depth (we go from 100m to 700m, so x7). So in total, a factor of 7000 if everything is ideal.
What I mentioned in the post above (4MWh) is a 30m sphere at 100m.
I agree with your point, but am unconvinced that the system is scalable.
>current nuclear submarines can't go deeper than 500m before getting crushed!
How exactly do you know that? The maximum depths of nuclear submarines are classified information, just like the top speeds of any military ships. The numbers they put on Wikipedia aren't real, those are the "public" numbers just so you can have an idea of how they perform in normal peacetime operation.
I thought the idea was to use the difference in potential energy between the surface level and the sphere as the storage. ie, you'd store energy by emptying the sphere, and release energy by dumping water into it through a turbine. If that's the case, I don't get where the pressure comes into it.
You are right, this is basically a gravity energy storage. It's the same idea as moving a 14m3 blob of water 100m up and down. Unfortunately, gravity storages have really bad energy densities.
Let's see.
E = mgh
E is the energy, m the mass, g the gravitational acceleration, h the difference in height.
m = 14e3kg
g = 10m/s2
h = 100m
E = 14e6J = 3.9kWh
The only gravity storages that have been proved to be scalable so far are hydroelectric. And they have huge lakes behind them.
There are two forms of longevity. One is, how long will it hold a charge? And the other is, How many times can it be charged and discharged before losing capacity or failing?
The uncharged state is at pressure equivalence to the outside environment, so there's no reason not to think that it can last as long as concrete structures in water can last: decades to centuries. The generator parts will need more maintenance.
The charged state is empty, with the interior water pumped out, and holding it will be a mechanical and materials engineering problem. However, the normal call will be for a daily cycle to replace energy that would otherwise come from solar. Reasonable management should prevent any particular cell from being held at charge for more than a few days at a time.
Lithium chemistry cells have a limited lifespan in number of charge cycles; 600-1000 or so for full discharge, up to 10-15,000 for very light discharge cycles. The water storage system won't exhibit those problems unless they fail to filter the water adequately.
Tests have been performed for the the durability of concrete spheres underwater over ten year period and found that concrete under the sea behaves the same way as concrete on the land in same pressure.
In other words, very durable if you make it durable.
But how does one 'place' a sphere of any diameter on such depths? I feel like I lack an enormous amount of knowledge concerning subterranean construction/engineering
If you fill it up with water ~90% (percentage depending on concrete thickness and sphere radius), it should have a similar density to water, which means you can lower it with the same sort of winch used in underwater construction.
In terms of energy, I would expect this to be equivalent to pumping the same volume of water up a mountain of the same height.
How strong does the sphere need to be? The air and water will be at roughly the same pressure, but air is less dense, so it at least needs to be strong and heavy enough to counteract the buoyant force.
Not quite the same thing. When you pump water up hill it comes all the way back down the hill, gaining speed as it falls, and then goes through a turbine. In this case, the water is being pumped out of the sphere against the pressure at that depth. When the water is let back in it only travels a short distance but at a high pressure due to the weight of the water above. So you see, the physical systems are actually quite different. In some ways this is more similar to compressing a spring.
If we assume that the mountain-tank is connected to a pipe of constant diameter, and that water has a constant density, then the speed at the top has to match the speed at the bottom.
If the water could not gain speed on the way down it would stand still at the top of the mountain. Put gravity into the equation and the water gains speed.
Thanks to pipes, the potential energy is not converted into speed on an open ramp along the slope of the mountain, it is converted from pressure to speed right at the turbine station. Any inertia within the pipes is just a medium for the pressure transfer, much like the inertia of a spinning axle in a mechanical transfer of torque. It is there, but it is not the driving force.
It's similar to storing energy by inflating a balloon.
When you inflate a balloon, you are opposed by the tension in the skin of the balloon. You could then use that stored energy to do work if you wanted. E.g. you could make the inflated balloon blow air into a little wind turbine that would, in turn, light a small LED.
With the underwater system, you are inflating a bubble that is held captive in a concrete chamber. The force that opposes you is water pressure. The deeper underwater, the greater the water pressure, so the more power you can store with the same concrete vessel.
EDIT: Energy would also be stored through air compression.
Since November last year a hollow concrete sphere with the weight of 20 metric tons has been sitting on the lake bed at a depth of 100m / 300ft. In times of excess power water is pumped out of the sphere and power is regenerated by inflowing water powering a turbine.
Now they are going to experiment with an even bigger sphere in the sea. Perhaps there will be some differences because of the salt water environment.
[1]: http://www.tagblatt.ch/ostschweiz/Forscher-speichern-Strom-i...