
Ideas on how to store energy - robin_reala
https://arstechnica.com/information-technology/2017/10/a-world-tour-of-some-of-the-biggest-energy-storage-schemes/
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chris_va
This is basically just a summary of the Wikipedia page:

[https://en.m.wikipedia.org/wiki/Grid_energy_storage](https://en.m.wikipedia.org/wiki/Grid_energy_storage)

... And really misses the important aspects, notably round trip efficiency,
cost per kWh, and cost per KW capacity.

~~~
enraged_camel
Yeah, Ars Technica used to have great science and technology coverage. For the
past few years though, it has just been... sad. Articles either have gross,
embarrassing inaccuracies, or are very shallow.

They do have decent coverage of the space and telecommunications industries
though. So they aren't _completely_ hopeless.

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splittingTimes
I would add gravity storage [1].

"The fundamental principle is based on the hydraulic lifting of a large rock
mass. [...] Water is pumped beneath a movable rock piston, thereby lifting the
rock mass. [Later] the water which is under high pressure from the rock mass,
is routed to a turbine [...] and generates electricity using a generator."

"[For certain pistons] the storage capacity increases with the fourth power of
the radius, r^4. The construction costs however only increase with the square
of the radius, r². [...] Strictly speaking, the price per kilowatt hour of
storage capacity decreases with 1/r². This is the outstanding competitive
advantage of this storage concept."

===

[1] [http://www.heindl-energy.com/gravity-storage/gravity-
storage...](http://www.heindl-energy.com/gravity-storage/gravity-storage-
overview.html)

~~~
semi-extrinsic
Interesting concept, but lifting rock "only" gives you a ~3x advantage over
lifting water, which can be lifted much higher.

~~~
splittingTimes
I saw a talk of the inventor a couple of years back. The test site they where
exploring they wanted to build a rock piston with a diameter of 250 and a
height of 500-1000m (cannot remember exactly, but it was in this order). Since
they can lift the piston to half its height that would be 250-500m altitude
difference. Not sure what the limiting factor of the height of the piston is,
so it might be even bigger.

For comparison the Three Gorges damn has an altitude difference of ~100m [1].

Also, it is much more compact then a traditional dam [2].

===

[1]
[https://en.wikipedia.org/wiki/Three_Gorges_Dam#Composition_a...](https://en.wikipedia.org/wiki/Three_Gorges_Dam#Composition_and_dimensions)

[2] For anybody wondering why ~3x: density of water 1 g/cm^3, density of rock
~ 3 g/cm^3

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leggomylibro
So...what is that in Megawatt-hours?

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oh_sigh
potential energy = HAM = __H __eight * __A __cceleration(due to gravity) * __M
__ass.

Height = 250m

Acceleration(on earth) = 9.8 m/s/s

Mass = pi * r^2 * __h = pi * 125m * 125m * 500m * 3 g /cm^3 = 7.36e13

HAM = 250 * 9.8 * 7.36e13 = 1.8e17

~~~
splittingTimes
Compared to the potential energy of lifted water mass in a dam, isn't the
water also highly pressurized under that rock mass? Would that not need to be
taken into account as well?

~~~
semi-extrinsic
Water is very incompressible, so you don't really get anything in addition to
the potential energy. If you decompress water from 300 bar (equivalent to 1
kilometer height of rock above it) to 1 bar (atmospheric pressure) it only
expands by 1.5%.

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Tossrock
I hadn't heard of / thought of the thermal storage idea (freezing ice at night
- when it's more efficient both cost wise due to cheaper power, and
thermodynamically due to lower outside temperature - and then using that to
reduce the need for daytime cooling), and it's so obvious in retrospect that
it seems like it should be everywhere. Given what a huge amount of electricity
is used on air conditioning (~6% of all electricity generated in the US,
apparently), this seems like it could be pretty big.

~~~
microcolonel
Thermal is also useful at the utility level, if you're trying to make
concentrated solar work (though it can only really work _okay_ , ultimately).
The usual medium is molten salt.

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jjcm
The flywheels are interesting to me, especially for their use in vehicles. I
wonder what the tests for catastrophic failure looked like though, especially
since that Volvo engine spun theirs at 60,000rpm max. That is a _lot_ of
energy in a small package.

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Theodores
Williams F1 did the most recent relevant work on flywheel energy storage for
F1 KERS Kinetic Energy Recovery Systems.

They dropped it from the original F1 application in preference to the
batteries that the other F1 teams were using. A few Porache 911 GT3 cars were
modified to use the flywheel. These track only cars didn't have a passenger
seat, instead the flywheel was there, spinning round at tens of thousands of
revolutions per minute, just next to your 'privates'.

More recently Le Mans cars have had the flywheel although nowadays the
business is owned by GKN. Williams sold the business after it was not found to
be what they needed for F1. Lots of London busses have the flywheel, it has
found its application in stopping busses and getting them back up to speed
quickly.

How much power does the flywheel give out? The peak power is about 3/5 of a
Nissan Leaf. It is designed to be used in series with the main engine or in
parallel. In this way the vehicle can be designed to have a much smaller
engine with the flywheel taking care of all acceleration. Multiple flywheels
can be used.

The applications the flywheel is sold into are specialist where things get
serviced properly. I don't think it will ever be in mainstream automotive
because we are giving up on ICE cars and if you have got batteries on the car
anyway then you might as well use them for the regen.

Now where I think Williams went wrong was in not making a flywheel that
happened to be made from some lithium-ion batteries. So that metric tonne of
batteries lugged around on a Tesla, imagine how much potential energy you
could store if you flew that around at 36k RPM. You could spin the thing up
before leaving the house and not have to use the battery for your first few
miles.

I would like to see a purely mechanical version of flywheel, so just gears and
a clutch to transfer energy to the flywheel when braking and accelerating
away.

~~~
slilo
Reminds me on gyrobus

[https://en.wikipedia.org/wiki/Gyrobus](https://en.wikipedia.org/wiki/Gyrobus)

"A gyrobus is an electric bus that uses flywheel energy storage, not overhead
wires like a trolleybus."

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robotresearcher
Reminds you? It is completely explicit!

> Lots of London busses have the flywheel, it has found its application in
> stopping busses and getting them back up to speed quickly.

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tfolbrecht
First we need excess energy to have a storage problem. Ignoring that, I think
some market based mechanisms on the consumption side could gobble that
capacity up.

If energy is a big enough input to some process like metallurgy, recycling,
computation, etc in times of excess you could drop the price to the base mwh
rate minus the cost of a theoretical amortized storage solution + transmission
inefficiencies and give incentive to burn that capacity off.

Since we've already invented the economy, we can pass around excess money to
use for on demand/scaling consumption instead of building big energy network
storage and transportation and eating the cost.

In theory subsidizing scalable supplies with the fixed supplies.

~~~
llukas
We already need to deal with this problem every day as generation sources do
not follow daily demand curve.

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anotheryou
I really like this idea: [http://www.heindl-energy.com/media-and-
newsletter/videos.htm...](http://www.heindl-energy.com/media-and-
newsletter/videos.html)

A gravity storage in form of a piston carved from rock. It's lifted with water
that's pumped underneath. The seal is a rolling "sleeve": [http://www.heindl-
energy.com/gravity-storage/idea-function/s...](http://www.heindl-
energy.com/gravity-storage/idea-function/sealing-the-rock-piston.html)

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michaelmwangi
I am a huge fan of the Donald Sadoway team at Ambri.
[http://www.ambri.com/technology/](http://www.ambri.com/technology/) Liquid
Metal Batteries

~~~
philipkglass
I'd really like Ambri to succeed. It's not clear if the use of low cost
materials for the storage chemistry will produce low system costs. The
inexpensive chemistry appears to have led to expensive problems with
seals/separators. Similar materials problems have kept sodium-sulfur battery
costs high, even though the active storage materials are cheap, abundant, and
offer good energy density.

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jaggederest
I always thought it was interesting that more of these systems didn't exploit
phase changes and the cold side of the Carnot cycle. For example, instead of
compressing air, you can liquify it, and then when you want to recover the
energy you use it as a heat sink for a heat engine (for example, solar
thermal) - in theory, this is just as efficient as adding energy to the 'hot'
side of the cycle, and you can expand it out through an engine as well.

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baron816
I'm curious if there could be any advantages/disadvantages to using a
different, heavier liquid for pumped storage other than water. My physics
knowledge is quite poor, but intuitively, wouldn't using something like
mercury or iodine create more pressure going down, thus generating more energy
by volume, thus requiring less volume, thus making it more practical to use a
tower? Surely someone's looked into this.

~~~
samsari
I think that would work, but the challenge would be in finding a denser liquid
than water in quantities that would make it useful - and cost effective.

~~~
thmsths
And safe. Imagine the disaster if that mercury tower started leaking.

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nradov
Is there any prospect of making superconducting magnetic energy storage more
cost effective?
[https://en.wikipedia.org/wiki/Superconducting_magnetic_energ...](https://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage)

~~~
goldenkey
The main point of these systems is to store energy for months without much
loss. Considering the cooling costs of the mechanism you mentioned, it only
seems viable for more rapid usage situations ie. the middle ground between
fast discharging batteries and slow discharging hydro gravity storage.

The beautiful thing about gravitational storage is that it is reversable. So
the same pump that used energy to pump the water into a tank 20 stories up can
also spin down as water pours through the turbines, acting as a hydroelectric
generator as the water is released. Having a single reversable mechanism makes
these systems pretty easy to maintain and the only places energy is lost is
through friction during conversion and through leaks. They are pretty hard to
beat.

The idea of deep ocean pods is similar in execution but instead of working
solely against and with gravitys energy potential, the water pressure is used
as well...its just more compact..but the orbs will need to be well built to
withstand insane pressures.

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amelius
It's missing the supercapacitor.

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jcoffland
I think you mean Superconducting Magnetic Energy Storage (SMES).
Supercapacitors are a different thing.

[https://en.m.wikipedia.org/wiki/Superconducting_magnetic_ene...](https://en.m.wikipedia.org/wiki/Superconducting_magnetic_energy_storage)

[https://en.m.wikipedia.org/wiki/Supercapacitor](https://en.m.wikipedia.org/wiki/Supercapacitor)

~~~
jakeogh
Rather unlikely that parent confused the two. Supercaps are nice if you don't
mind trading their ~<1/5 energy density (mass, volume) of batteries for their
excellent cycle count. Clearly not grid scale since batteries barely are.

~~~
Dylan16807
1/5 takes quite a stretch, or comparing to especially low-density batteries.
Maybe in a couple decades they'll be there, but my understanding is that high-
end supercaps are currently 25x less energy dense than a lithium ion battery.

~~~
jakeogh
~9Wh/kg for the best supercaps, compared to the old (and still standard) lead-
acid maxing out around 42Wh/kg. Li-ion maxes out at amazing 265Wh/kg but they
are always? small and scaled up by putting many in parallel... and if you
damage one it's emergency fire preparedness time.

~~~
Dylan16807
But if you have just about _any_ concern for density, you're not using lead-
acid. Not when that's another 5x worse than other batteries.

I'm willing to bet that most lead-acid users would happily switch to cheaper
supercaps if they existed.

~~~
jakeogh
Agreed. When supercap J/$ hits lead-acid levels the J/kg difference wont
matter and most people using lead-acid will happily trade 1/4th the energy
density for near infinite recharges.

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timb07
Aluminum has also been considered as an energy storage material, specifically
one that is easily transported:
[http://evworld.com/article.cfm?storyid=765](http://evworld.com/article.cfm?storyid=765)

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agumonkey
practical engineering youtube channels talked about swell pressure under
buildings, I find this kind of "osmotic" work interesting. Extremely
interesting.

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jakeogh
The
[https://en.wikipedia.org/wiki/Trompe](https://en.wikipedia.org/wiki/Trompe)
is an interesting device for the compressed air category.

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randyrand
What about storing it in fat cells? Bio chemistry storage. Is this
possible/advantageous?

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andrewflnr
Not sure about fat cells, but IIRC there has been some work in using algae to
generate hydrocarbons from the air. I can't really see "fat in fat cells"
being better than alternatives that skip some steps, though.

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m3kw9
How about a system that loads springs as mechanical energy, do that have
those?

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dhimes
paging dani fong to weigh in on this....

