
German institute successfully tests underwater energy storage sphere - Tomte
https://arstechnica.com/science/2017/03/german-institute-successfully-tests-underwater-energy-storage-sphere/
======
_nalply
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.

[1]: [http://www.tagblatt.ch/ostschweiz/Forscher-speichern-
Strom-i...](http://www.tagblatt.ch/ostschweiz/Forscher-speichern-Strom-im-
Bodensee-mit-Betonkugel;art120094,4918903)

~~~
danielbln
Would something like that be able to provide base-load? That's usually the
first nuclear-fisson/fossil-fuel argument: can it cover baseload?

~~~
tinco
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)

~~~
vilda
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.

~~~
tinco
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).

~~~
lutorm
_it 's not a serious competitor to nuclear power_

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.

------
gene-h
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.

[0][https://www.naefrontiers.org/File.aspx?id=48498](https://www.naefrontiers.org/File.aspx?id=48498)

~~~
tzs
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.

~~~
chillydawg
Under sea pipelines for a variety of depths, pressures and capacities are a
solved problem, courtesy of the oil and gas industry.

~~~
heisenbit
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 engineering challenge is more comparable to submarine design. Nuclear
submarines go down 500m and even the navy deep submergence rescue vehicle
[http://www.navy.mil/navydata/fact_display.asp?cid=4100&tid=5...](http://www.navy.mil/navydata/fact_display.asp?cid=4100&tid=500&ct=4)
is going 1.5km deep only with its tube design. Compare this with really,
really deep dive designs like
[https://en.wikipedia.org/wiki/File:Trieste_nh96807.svg](https://en.wikipedia.org/wiki/File:Trieste_nh96807.svg)
with a sphere observation gondola.

~~~
Mchl
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.

~~~
skosch
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

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ISL
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.

~~~
hendry
Austria is laughing at Germany for not building reservoirs on top of hills
(mountain range not needed).

I fear water based cells will be as damaging as salmon farms.

~~~
literallycancer
More damaging than flooding a valley? Or hollowing out a hill?

------
rodionos
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.

~~~
jacquesm
> I'm seeing more quality research from Fraunhofer in recent years that is
> also useful for practical purposes.

Did you miss the fact that they are the people that came up with the basis for
MP3 compression?

Fraunhofer has done all kinds of research with real world applications and has
been doing so for decades.

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chris_va
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.

~~~
troymc
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.

~~~
PietdeVries
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?

~~~
BlackFly
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.

~~~
JoeAltmaier
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.

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cbanek
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.

[http://www.aresnorthamerica.com/grid-scale-energy-
storage](http://www.aresnorthamerica.com/grid-scale-energy-storage)

~~~
Faaak
I think ares will never see the light of day. The infrastructure is too
complicated compared to this or to a battery.

~~~
olau
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.

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Zenst
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.

~~~
jcoffland
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.

~~~
madez
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.

~~~
jcoffland
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.

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intrasight
What's the advantage to having these under water? Aesthetics? It's gotta be
way more expensive to have them under water.

~~~
oconnore
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.

~~~
theoh
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.

~~~
snovv_crash
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)

------
Beltiras
I'd like to see a study on the environmental cost of the materials. Concrete
(or rather cement) is one of the dirtiest building material to make.

~~~
ogrisel
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.

~~~
Beltiras
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.

~~~
danmaz74
If the sphere is suspended on a cable, can't you haul it up do to maintenance?

~~~
Beltiras
At great cost, sure.

~~~
danmaz74
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.

~~~
Beltiras
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.

~~~
danmaz74
> 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 :)

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haser_au
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.

~~~
jcoffland
Not at a 2,300 foot depth.

"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."

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Shivetya
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.

~~~
madez
Using compressables lowers the efficiency because compression leads to
heating.

------
vorotato
Also if water levels rise due to global warming it's like a hydroelectric
station :V

~~~
fhood
It's at times like these when silver linings are most important.

------
strig
A Canadian company is doing something similar:
[http://hydrostor.ca/](http://hydrostor.ca/)

------
cottsak
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?

~~~
jacquesm
> So why bother?

Because you're making quite a few assumptions.

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?

~~~
cottsak
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.

~~~
jacquesm
I'm not to bullish on battery technology for grid level storage either.

~~~
andai
Are you optimistic about any technology in particular for grid level storage?

~~~
jacquesm
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.

------
joshuaheard
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.

~~~
andai
I'm curious about these existing solutions, do you have any links or names?

~~~
joshuaheard
There's a link in the article to one.

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donquichotte
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.

~~~
joantune
You're probably missing an important number there, not that I'm sure that it
will make a difference, but:

How about longevity? one of those will probably hold that capacity for much
longer than a Lithium battery, no?

~~~
dsr_
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.

------
maggelo
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

~~~
merraksh
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.

~~~
danmaz74
Yes, and the whole concept is based on filling the sphere with water...

------
p1mrx
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.

~~~
jcoffland
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.

~~~
p1mrx
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.

Thus, water cannot gain speed on the way down.

~~~
larsnystrom
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.

~~~
usrusr
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.

------
mrfusion
I'm really not understanding the physics of this?

~~~
Pitarou
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.

------
hjbkhjbjn1
nm,m

