
To Store Renewable Energy, Try Freezing Air - fortran77
https://www.scientificamerican.com/article/to-store-renewable-energy-try-freezing-air/
======
ChuckMcM
It is a fun idea, I tried to convince a large internet company to do something
similar outside their data centers at one time, they chose not to bite.

A much better solution is this one: [https://www.heindl-energy.com/wp-
content/uploads/2017/10/Bro...](https://www.heindl-energy.com/wp-
content/uploads/2017/10/Brochure_Gravity_Storage_2017.pdf) it stores energy by
pumping water into a tank to lift up a giant concrete piston. When you want
the energy back you just let it down by running the turbo pumps.

The nice thing about gravity storage like this are that it doesn't need
anything but a hole in the ground and existing hydroelectric technology. The
down side is that it can freeze at low temperatures, you get some back because
at the depth these cylinders would be dug there is significant below ground
heating but there would be days when it would be too cold to run these things
without warming them (and thus impacting your efficiency)

~~~
japanuspus
Except recouping the CO2-expenditure of the concrete piston will take a long
time. A simpler solution is to use the gravitational potential energy of the
water directly. Pumped hydro, as this is known, is super simple if you have a
mountain and maybe even an existing hydro-power plant to take the energy back
out.

I have never checked this, but a Swiss friend of mine once explained the Swiss
energy system as being centered around pumped hydro using free surplus power
from the French nuclear power plants.

~~~
imtringued
The entire point of hydraulic hydro is that energy capacity scales by r^4
(dimensions of the piston + height within the hole). It is possible to just
carve out the piston head from existing rock with wire saws. Systems with
1.6TWh storage capacity are not impossible.

~~~
eliaspro
There's a local company which has developed exactly this concept:
[https://heindl-energy.com/technical-concept](https://heindl-
energy.com/technical-concept)

Efficiency of around 80% (comparable to pumped hydro), capacity of 8GWh for a
250m diameter piston.

------
meatmanek
This Low-Tech Magazine article[1] does a much better job of explaining the
complexities of compressed-air energy storage, including different ways to
minimize or harness adiabatic heating, though with a focus on home-scale
installations rather than grid-scale.

1\. [https://solar.lowtechmagazine.com/2018/05/ditch-the-
batterie...](https://solar.lowtechmagazine.com/2018/05/ditch-the-batteries-
off-grid-compressed-air-energy-storage.html)

------
8bitsrule
From what I've read, winter heating consumes 40% of American households'
energy budget. (A seldom-mentioned part of the big picture.) The heat
extracted from liquifying air might be used for home-heating in a place like
Vermont.

I recall walking by a city telecom building getting rid of excess heat, _in
the winter_ , by opening big vents in the wall. Meanwhile, apartment buildings
around it were burning fuel to keep warm. There are many ways we can do this
stuff better.

~~~
dredmorbius
District heating and cooling, and seasonal energy storage, are both approaches
to an integrated energy system which distributes needs over space (district)
and/or time (seasonal).

District heating distributes heating (or cooling) from sites with an excess to
sites with a need. Industrial processes are frequently utilised, though in
sufficiently dense construction, office cooling can be a source of heating
elsewhere. Many office towers have a net _cooling_ load at all times of year,
even under cold ambient conditions.

Seasonal energy storage banks heat from warm periods of year for use in cold
periods. This may be completely adequate for general space heat, and
sufficient for a large portion of higher-intensity heating (e.g., water).
Storage may be in geological structures, if those are sufficiently stable
(ground-water migration will also migrate out your stored heat), or
constructed energy storage facilities, often little more than well-insulated
water tanks with vertical thermal stratification.

Thorstein Chlupp of Rienna LLC designs zero-net-energy homes in Fairbanks, AK,
utilising seasonal thermal energy storage. His videos run long, but are
exceedingly comprehensive and explain in detail design and construction
decisions.

Seasonal storage is covered here beginning at about 1h18m, to about 1h30m:

[https://invidio.us/watch?v=AtHkvpRI6fc](https://invidio.us/watch?v=AtHkvpRI6fc)

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

~~~
kardos
Storing heat in a big water tank is certainly an option but it has drawbacks.
I'm looking forward to developments in thermal storage in phase change
materials and also storage via endothermic reactions.

~~~
undreren
We do this in Denmark for storage of district heating water. They are called
"varmeakkumulatortanke" in Danish, roughly translated to "heat accumulator
tanks".

They are insulated like a thermos (but more efficiently), and since they are
really big, they have small surface area compared to their volume.

It is a VERY efficient way to store heat over shorter periods, like a week or
so, and it helps making power plants more cost efficient.

The best way to make it efficient for long term storage (like seasonal
storage) is to

1\. Make them huge

2\. Make them ball shaped

3\. Put them underground

There has been talk of tryibg this out in Denmark. Almost all our powerplants
(i.e. the not-really-old ones) are combined heat and power plants, and because
we use district heating water to create a vacuum behind the power producing
turbines turbines (instead of sea water) we go from a theoretical limit on the
energy efficiency of around 60% to 98%, as we do not pump out the excess heat
into the sea.

Newer combined heat and power plants have an energy efficiency of around 95%
to 96%. The trade of is a slightly lower vacuum, meaning less production of
power. However, we can scale up heat production to reduce costs of running
power plants when energy prices are low (or even negative).

~~~
kardos
> 1\. Make them huge

That more or less puts it out of reach for homeowners, condo dwellers, etc.
You need a big expensive coordinated project to get that built.

Meanwhile, as an analogy, solar panels are within reach for a homeowner.
Seasonal thermal storage will need to be more modular / modest sized for it to
be widely applied. The potential for storing heat by forcing endothermic
reactions (where you later extract it by running the reaction in reverse) has
a lot more potential to be "homeowner sized".

~~~
dredmorbius
Many though not all passive energy designs do require a substantial ground-up
redesign. The notion that single standardised designs can be spread across
continents without consideration for local conditions will likely pass.

Retrofits are possible, though with compromises to both extant structures and
building envelope and passive energy systems.

Since efficiency of storage scales with size, community-based (neighbourhood-
scale) thermal storage is an option. This allocates storage across a number of
local structures, at the scale of tens to hundreds of structures per storage
structure.

Similar notions apply to electrical storage, e.g., neighbourhood battery
facilities. This works well for battery designs (e.g., liquid metal, molten
salt), which are too technical and risky for safe household deployments, but
could be deployed in clustered units with dedicated technical expertise.

------
gwbas1c
No mention of efficiency...

Anyone know the efficiency? Batteries are in the high 90s, but are so
expensive that they don't make sense for stockpiling. (Charge in the summer
when days are long, discharge in the winter when everyone needs to turn on the
heat.)

~~~
philipkglass
They claim 60% in the basic configuration, or 70% if coupled with a low grade
heat source:

[https://www.highviewpower.com/benefits/](https://www.highviewpower.com/benefits/)

When I searched Google Scholar, I found this 2016 report from their first 350
kilowatt pilot plant at the University of Birmingham:

[https://www.researchgate.net/profile/Adriano_Sciacovelli/pub...](https://www.researchgate.net/profile/Adriano_Sciacovelli/publication/303814262_Liquid_air_energy_storage_-
_Operation_and_performance_of_the_first_pilot_plant_in_the_world/links/5757c6aa08aef6cbe35f5ad9.pdf)

That pilot project claimed less than 25% efficiency, but the authors seemed
confident efficiency could be raised. A 5 megawatt demonstration plant has
been running in the UK since 2018:

[https://www.greentechmedia.com/articles/read/highview-
power-...](https://www.greentechmedia.com/articles/read/highview-power-
completes-uk-liquid-air-storage-plant)

I presume that the 0.35 MW and 5 MW projects worked reasonably well if they
are now trying to develop a 50 MW project.

~~~
oever
There's some recent videos about the Highview system.

Animation
[https://www.youtube.com/watch?v=Nu9zLOBi0-E](https://www.youtube.com/watch?v=Nu9zLOBi0-E)

Interview
[https://www.youtube.com/watch?v=4hbyzuES5J0](https://www.youtube.com/watch?v=4hbyzuES5J0)

Recent article [https://www.theguardian.com/environment/2019/oct/21/uk-
firm-...](https://www.theguardian.com/environment/2019/oct/21/uk-firm-
highview-power-announces-plans-for-first-liquid-to-gas-cryogenic-battery)

------
hedora
They should be able to pull liquid CO2 or dry ice out at some point during the
cooling process. That could be fed into a carbon recapture system.

I wonder if using this system for both carbon capture and energy storage is
more efficient than using wind or solar to power carbon capture and charge
batteries directly.

The energy to crack the CO2 into carbon and oxygen is probably the same either
way, but concentrating atmospheric CO2 is energy intensive, and direct carbon
capture would have to do that anyway — probably by cooling down a bunch of
air, then releasing it. Perhaps another way to think about it is that carbon
capture will create a large “waste” stream of cooled CO2-free air; perhaps
converting that air to liquid is better than wasting the energy it took to
cool it in the first place.

Either way, as the price of renewables drops, the problem of stranded/excess
capacity will only grow. The atmosphere is way past the point where we need to
use that capacity to pull CO2 out of the air.

------
aurizon
You might get away with pissing on Carnot's grave once - but twice - never. By
that I mean the energy of compression is lost. A compressor is an analog to an
internal combustion engine - in reverse. You put in energy via amotor and
compress the air. Unless you can use that heat of compression it is lost. Then
you run another analog to an internal combustion engine - in reverse.
[https://www.google.com/search?ei=jFgWXoCkI474-gTJspPoDQ&q=en...](https://www.google.com/search?ei=jFgWXoCkI474-gTJspPoDQ&q=energy+efficiency+of+an+air+compressor&oq=energy+efficiency+of+an+air+compressor&gs_l=psy-
ab.12...4691.7128..9727...0.2..0.100.661.5j2......0....1..gws-
wiz.......0i71j0i13j0i13i5i30.PGxHy-
B_CRo&ved=0ahUKEwiAmpzFh_XmAhUOvJ4KHUnZBN0Q4dUDCAs) Extract:- • Is compressed
air free? No, compressed air is not free. Although "it's only air," compressed
air is actually very expensive because only 10 to 20 percent of the electric
energy input reaches the point of end-use. The remaining input energy converts
to wasted heat or is lost through leakage. For example, to generate 5 CFM it
takes 1 HP.

So 10-20% for the compressor.

Then the expansion:-
[https://en.wikipedia.org/wiki/Pneumatic_motor](https://en.wikipedia.org/wiki/Pneumatic_motor)

sir motors are in the 60-65% efficiency range. Then the electric motor to
drive the generator is about 93% efficient (some as high as 95%)

This string of 10-20% plus 60-65% plus 93.95%

Gives a net range of 5.58% efficient all at low end of range to about 12.35%
at the high end. At best you lose 87% and at worst you lose 94.5%

But this is wasted energy anyway, but it has to pay for manitanance and staff
etc, so in the worst case it is terrible and the best case is sub-marinal.
Looks like a free energy racket to me?

~~~
p1necone
Are there many downsides to just lifting weights/pumping water up hills? What
if you connected a lot of very large weights and electric motors to the grid
and intelligently wound them up/let them down based on demand?

Maybe a two tiered approach combined with capacitors for fine tuning?

~~~
opencl
Pumped hydro is by far the most commonly used utility-scale energy storage in
use today. Efficiency is in the range of 70-80% so it's a lot better than
compressed air in that regard, the main downside is that you just need a
really large amount of water and a place to put all of it.

Lifting weights for energy storage is not really very conceptually different
from pumped hydro (both store gravitational potential energy), water just
happens to be vastly cheaper per ton than pretty much anything else. Concrete
is something like $50 per ton and water is more like $0.50.

~~~
twic
How about instead of pushing water up into the air, you pulled air down into
the water. Build a big floating object at sea and drag it down into the water
with a cable attached to a motor/generator.

~~~
qqqwerty
I think you would have to use a vessel that could withstand underwater
pressures. I imagine that would be on the expensive side, probably more
expensive than the concrete blocks. And if the the vessel compresses at all, I
think you loose efficiency due to the loss of buoyancy.

On a more general note, I think the issue with these novel storage methods is
that even their more optimistic $/kWh targets are barely competitive with
existing battery prices. And due to manufacturing scale, battery prices are
expected to continue to decline. A similar thing happened in the solar market.
Prices were really high, which led to a bunch of startups attempting to bring
novel technologies to market (Solyndra was one of them), but once China
started flexing its manufacturing muscle, PV prices dropped and the novel
technologies had no hope of competing.

------
syllable_studio
This is a smart solution - it's great that stories like this are getting
attention. I'd like to share a similar project that I'm working on called
Terrament. [https://www.terramenthq.com/](https://www.terramenthq.com/)

Terrament is building underground pumped hydro energy storage (UPHS). Just
like other pumped storage solutions, UPHS is extremely cost competitive
(measured by LCOE, levelized cost of energy). It's extremely efficient (80-90%
round trip). But unlike most pumped hydro, you can build UPHS anywhere. Just
like this liquid air solution, you only need a couple acres of land. Many
people assume this would use lots of water, but it doesn't because it's a
closed-loop system.

I see that Heindl energy's solution was also mentioned above -- I love that
design. Though, our analysis suggests that our design will give us better
capacity.

Thanks everyone for your interest in this important field! This is not just a
booming business, it's also critical for supporting the sustained growth
renewable energy.

~~~
rwmj
Isn't the classic problem with pumped hydro that you can't really store very
much energy unless you have a huge amount of water or a large drop?

~~~
syllable_studio
Yup, though we don't consider it a problem, that's just the simple math. Our
solution tunnels down 1 mile deep and excavates an underground reservoir.
While this may sound extreme, it's entirely feasible and cost-effective. We
can say that with confidence because we're basing our analysis on research
from the U.S. Department of energy. We link to that research on our website if
you're interested.

------
im3w1l
Maybe in the future we could use desalination/resalination for power storage.
There is a lot of sea out there.

~~~
thaumasiotes
In desalination, you're taking a substance that is literally worthless and
turning it into something valuable (though cheap).

It seems unlikely that once you've got the water, the best available use for
it would be dumping it back into the sea. (Which would be the easiest way to
resalinate it -- since you're already desalinating, we can safely assume
you're next to the sea.)

~~~
adrianN
Perhaps they want to use
[https://news.ycombinator.com/item?id=21721049](https://news.ycombinator.com/item?id=21721049)

------
aaron695
> Such energy storage technology could help relieve congested transmission
> lines in places like Vermont

Normal garbage form Scientific American.

It's either a good battery or it isn't.

What does Vermont have to do with it?

If anything it's an awful test, they obviously will have to update the
congested transmission lines, then you have a expensive plant that's useless,
if the congested transmission lines don't factor in then why are we talking
about them?

CRYOBattery is being sold as a long term payoff battery that has a small
footprint. Land is cheap around power stations, creating a dam and turbine is
simple tech that works, I can't see why this is better and SA is not helping.

