
Ditch the Batteries: Off-Grid Compressed Air Energy Storage - helb
http://www.lowtechmagazine.com/2018/05/ditch-the-batteries-off-the-grid-compressed-air-energy-storage.html
======
drizzle87
I was quite excited by compressed air storage when Lightsail came into the
picture almost 5-7 years ago. Sadly, they could not make the economics work
and ended up pivoting into a company that sells carbon fibre tanks for high-
pressure storage.

As someone who follows the energy space closely, Lithium ion batteries now
have so much momentum and $$$ pumped into them via R&D work, it's going to be
hard for competing energy storage technologies to catch up. Flywheel and
hydrogen fuel-cell also often come up but I think we're at a point now where
batteries are going to take off simply because of their wide area of
applicability. With that economy of scale costs will drive down and even more
research and $$$ will flow.

~~~
joncrane
Aren't flywheels used in datacenters to cover the split second between when
the power goes out and the generators kick on?

~~~
chrisa
I toured a datacenter 5 years ago or so - and yes, they had a big flywheel for
temporary power loses (until they could get the generators running)

~~~
walshemj
That's only if they don't /cant run the entire DC of battery -whilst the
gensets come online this is how telco exchanges / central offices work and
important ones may have power supplied via different routes.

------
mabbo
> However, to store 360 Wh of potential electrical energy, the system requires
> a storage reservoir of 18 m3, the size of a small room measuring 3x3x2
> metres. The authors note that “although the tank size appears very large, it
> still makes sense for applications in rural areas”.

This would light a home for an hour, with LED bulbs and careful usage. And all
it requires is a room-sized storage tank.

So if I wanted something that ran my house all night, I'd need a storage tank
larger than said house.

~~~
jandrese
For home use you also have to consider that you're basically making a bomb
every time you store energy in the thing.

~~~
ajuc
Any kind of high-density energy storage is basically a bomb.

If you charge or discharge Lithium polymer or lithuium ion batteries "wrong"
they explode too.

I wouldn't want to be near a flywheel that stores 360 Wh of energy when it
breaks.

~~~
beat
On the other hand, flywheels can be easily buried underground, and easily
contained. The max power of a flywheel is known, so it's just a matter of
putting enough concrete between humans and flywheel, a straightforward and
inexpensive engineering problem. And unlike compressed air, the containment
isn't under constant, wearing pressure.

~~~
jandrese
You can bury the air tanks too and avoid most of the danger, but that's
expensive and makes them harder to maintain. The big advantage of flywheels is
that when they fail you know the energy will be discharged in a particular
plane. You can orient them such that nothing vital is in that plane (like your
house!). With compressed air all bets are off.

~~~
thebluehawk
SCUBA tanks have a "burst-disk" or a weaker part of the tank that is designed
to fail first, rather than the whole thing exploding and launching shrapnel.
It's still violent and can throw some shrapnel, but it's much less. Also when
SCUBA shops fill tanks they usually put them into a container that would
somewhat contain that.

I imagine something similar could be done. It's not like there are zero safety
mechanisms with compressed air.

------
newman8r
An added benefit is you could power your air-tools with something like this
without having to convert to electrical energy. As a former off-gridder,
that's actually a really big plus.

Another non conventional way to store energy is using gravity power modules
(example: [http://www.gravitypower.net/](http://www.gravitypower.net/))

Storing hydrogen from electrolysis via solar panels also sounds interesting.
Basically once your batteries are charged you start making hydrogen.

~~~
brittohalloran
Similar to those gravity power modules: a company called Ares
([https://www.aresnorthamerica.com/](https://www.aresnorthamerica.com/)) is
trying to use much smaller concrete 'cars' on rails to store energy. Not sure
of the status of it but it looked promising to me.

The direct use of compressed air is interesting. Taking it to the extreme, you
could have compressed air as your primary utility piped through your home, and
have appliances that run off compressed air. Refrigeration cycle is
compression based anyway for example. You would still need some electricity
for control circuits for example, but you might be able to keep the heavy
lifting air-based.

~~~
sandworm101
In the midwest, running compressed air through a home is called amish
electricity. They do use it for many things. Ive seen air-powered blenders.
(Air power is a big thing for woodworking and so its use in the home too is no
suprise.)

~~~
newman8r
I had no idea these existed, I want these when I move back off-grid.
[https://www.cottagecraftworks.com/kitchen-food-prep/non-
elec...](https://www.cottagecraftworks.com/kitchen-food-prep/non-electric-
kitchen-appliances/air-powered-appliances)

~~~
sandworm101
It is functional but has many issues. Water/condensation in the lines is a big
deal in winter. Running pipes in walls makes leak detection difficult. They
are all also very very loud.

------
donquichotte
At ETH Zurich, there is a project aiming at scaling compressed air storage to
MWhs. [1]

The interesting part is that they are trying to make the storage adiabatic,
i.e., they store the heat that is generated while compressing the air in a
phase change material (i.e., a material that will become liquid when hot,
since a lot of energy can be stored in phase transitions) and get the heat
back to warm up the cold expanding gas on decompression.

The issue is that even with the phase change storage, heat will dissipate into
the rock within a couple of days, making the whole process inefficient for
long-term storage.

[1] [https://www.ethz.ch/content/specialinterest/mavt/energy-
tech...](https://www.ethz.ch/content/specialinterest/mavt/energy-
technology/renewable-energy-carriers/en/research/energy-storage/elecstor.html)

~~~
jononor
Sounds like a promosing solution for averaging out daily fluctuations though.

------
Uhrheber
When compressing air, a lot of heat is generated, and in most cases wasted.
When the air is released, it cools down, and has to take heat from the
surroundings. Which doesn't work very fast without additional heat exchangers,
and especially not in cold environments. Compressed air storage is only
efficient with additional heat storage, which is something that promoters of
compressed air storage often "forget" to tell you.

~~~
josefresco
They didn't forget - it's addressed in detail. They are advocating "small
scale"

 _The low efficiency is mainly since air heats up during compression. This
waste heat, which holds a large share of the energy input, is dumped into the
atmosphere. A related problem is that air cools down when it is decompressed,
lowering electricity production and possibly freezing the water vapour in the
air. To avoid this, large-scale CAES plants heat the air prior to expansion
using natural gas fuel, which further deteriorates the system efficiency and
makes renewable energy storage dependent on fossil fuels._

~~~
davidhyde
Going "small scale" does not solve the heat problem unfortunately. If it does
then the authors did not mention it. All they mentioned is how large scale
plants deal with the problem.

~~~
josefresco
Come on dude...

 _Small-scale compressed air energy storage systems with high air pressures
turn the inefficiency of compression and expansion into an advantage. While
large-scale AA-CAES aims to recover the heat of compression with the aim of
maximizing electricity production, these small-scale systems take advantage of
the temperature differences to allow trigeneration of electrical, heating and
cooling power._

~~~
Neeek
And then also goes in to detail about small scale iso-thermal setups that have
negligible thermal losses. Apparently "author did not mention" actually means
"I did not read the article".

------
fleetside72
I worked for a company that had old underground mines and a power company used
them to fill with compressed air when energy was cheap and then release and
generate electricity when it is more expensive. My company got a cut.

~~~
reaperducer
I used to have friends in the oil industry in the 90's, and I remember them
talking about the industry maybe using dried up wells the same way.

I don't know if it ever became anything, though.

As much as people consider the oil industry a bunch of evildoers, it is always
at the forefront of the absolute latest in tech. Hard problems + money does
that.

------
tomhoward
Reminds me of this project from a few years ago: a two-person hot-rod driven
at up to 20mph by a 256-cylinder compressed-air engine, constructed out of
Lego...

[https://www.youtube.com/watch?v=_ObE4_nMCjE](https://www.youtube.com/watch?v=_ObE4_nMCjE)

------
penetrarthur
Volvo diesel cars avoid turbo lag by storing compressed air. Not very relevant
but interesting nevertheless [https://www.roadandtrack.com/new-cars/car-
technology/news/a2...](https://www.roadandtrack.com/new-cars/car-
technology/news/a27515/volvos-diesel-turbo-lag-solution-is-compressed-air/)

~~~
imeron
And Bosch uses compressed air to keep motorcycles on track (experimental tech)
[https://www.youtube.com/watch?v=3ERowrZJyfw](https://www.youtube.com/watch?v=3ERowrZJyfw)

~~~
tonyedgecombe
If you could point them backwards for a little extra thrust ...

~~~
johnbrodie
Modern supersports are pushing ~200hp, no need for the extra weight that would
generate the thrust.

~~~
stcredzero
The Spitfire actually used the jet propulsion of the rearward facing exhaust
for an extra few horsepower. Many piston engine aircraft do this.

------
rossdavidh
So, I seem to recall that the Amish sometimes use something like this to power
their tools. Source: my own unreliable memory of an article I read somewhere.
Anybody more knowledgeable out there able to confirm or disfirm?

~~~
manveru
There's an article about it at
[http://www.amishnews.com/amisharticles/amish_tech.htm](http://www.amishnews.com/amisharticles/amish_tech.htm)
which references some books that might describe it in more detail.

> Almost any electrical appliance can be adapted to work off of alternate
> power, such as compressed air. Some Amish women have been using compressed
> air to power blenders in the kitchen for years. In one house, compressed air
> powers a water pump, sewing and washing machines, and drills and saws in the
> shop. Some Amish businesses have as their specialty adapting such appliances
> so they can be powered by compressed air.

------
JohnJamesRambo
I'm surprised no one is talking about how scary it is that you are basically
making a high powered bomb at your house any time you have one of these.
Anyone that has watched Mystbusters understands the incredible destructive
power stored in compressed air. I'll stick with batteries, thanks.

~~~
beat
You probably keep multiple gallons of gasoline nearby, tho.

~~~
evan_
Not to mention the giant propane tanks that many houses in rural areas already
have

~~~
JoeAltmaier
Not the same? Shoot a propane tank, it leaks. No oxygen in the tank.

There is very little outside compressed gas that can explode disastrously
without oxygen. A tank of compressed gas is probably high up on the 'bomb in
the house' category. Just under the water heater I suppose.

------
jakecrouch
Lightsail Energy tried and failed to bring this to market - not sure whether
this can ultimately outperform Lithium Ion Batteries, which have all the
pressure of the electronics industry behind them.

~~~
newman8r
I feel like they have different applications so they're not necessarily
competing. Obviously compressed air systems will never have the energy density
of a battery, but they could be much more reliable. It also scales up really
easily, and I think that's where the sweet spot is - I've heard of people
sealing off caves to make giant air storage tanks for these projects.

~~~
oori
"sealing off caves" \- would love to see, or hear the facts. Specifically,
about safety of the pressure "chamber".

~~~
jandrese
I think it is more typically done with old mines. Natural caves are far more
complex systems and there are environmental concerns.

~~~
newman8r
you're right - it looks like the caverns being used for experimentation are
the result of solution mining for salt.

------
andyidsinga
Its really interesting that they can get up to the efficiency of led acid
batteries in applications for rural areas. I wonder if maintaining that large
air tank is more difficult / costly than maintaining the batteries.

Its also interesting that we're only talking about 116 PSI - I'm guessing CFM
is more important.

> A simulation for a stand-alone CAES aimed at unpowered rural areas, and
> which is connected to a solar PV system and used for lighting only, operates
> at a relatively low air pressure of 8 bar and obtains a round-trip
> efficiency of 60% -- comparable to the efficiency of lead-acid batteries.
> [7] However, to store 360 Wh of potential electrical energy, the system
> requires a storage reservoir of 18 m3, the size of a small room measuring
> 3x3x2 metres. The authors note that “although the tank size appears very
> large, it still makes sense for applications in rural areas”.

------
simonebrunozzi
> "they do not require rare or toxic materials"

This benefit alone would make me hope for compressed air energy batteries to
receive tons of funding, and become cost-competitive with other forms of
batteries.

Also, consider that there are three important elements in a battery
"economics":

1) Weight / energy density - how much energy can you store, per weight of the
battery? Important for cars.

2) Volume / energy density - how much energy can you store, per volume of the
battery? Important for cars as well.

3) Cost / energy stored - how much does it cost to store a unit of energy?
This can also be divided into two elements: setup (e.g. the cost of producing
the battery and deploying it) vs maintenance (how much does it cost to keep
the battery alive, over the years?)

There are also other minor factors, such as reaction to environmental changes
(e.g. temperatures, etc).

------
theyinwhy
Peugeot is working on this for years but it got frozen last year:
[https://www.groupe-psa.com/en/newsroom/automotive-
innovation...](https://www.groupe-psa.com/en/newsroom/automotive-
innovation/hybrid-air/)

------
corey_moncure
An early design for the automobile ran on compressed (liquid!) air.

[http://www.didik.com/ev_hist.htm](http://www.didik.com/ev_hist.htm)

It might work for some applications, but in 120 years we haven't been able to
make it work for cars, at least.

~~~
JustSomeNobody
> ... but in 120 years we haven't been able to make it work for cars...

Ok, but has anyone _worked_ on the problem in the past 120 years?

~~~
brohee
[https://www.mdi.lu](https://www.mdi.lu) tried to make compressed air two
person urban cars (Air Pod) but with the main inventor and visionary now dead
I don't know if there is much momentum left...

------
ChuckMcM
I have argued unsuccessfully in the past that this technique would be an
excellent data center strategy. That is especially true if you had your data
center near the Columbia river and its near constant winds.

Using wind power to compress into high pressure tanks, then when you need
extra energy you pull it out and pipe the air expansion pipes _through_ heat
exchanges in the data center. That way heat from the data center goes to
warming up the air (better efficiency when you feed it to the turbines) and it
cools the data center which is part of what one might use the energy for in
the first place.

If you put the air expansion pipes in a conveniently located source of water
you could chill that water to freezing.

~~~
cwkoss
If the entire contents of the data center were pressurized, would it increase
the efficiency of air cooling? (Denser air -> more heat capacity?)

~~~
ChuckMcM
It would certainly increase the heat capacity of the air.

Compressing air into the data center however would not be a win. During
compression the air gets hot. In the system that I was pushing the compressed
air tanks were outside in the wind so that they were benefiting from the
cooling effects of the same wind that was pumping air into them.

~~~
cwkoss
Good point. Could allow for low power cooling (once pressurized, venting
pressure would drop temperature of the contents without added energy), but
probably not worth the trouble.

------
Timothycquinn
Seems like a technology that has narrow usecases like where cogeneration is
possible. I guess large city's and industrial applications which can use the
waste products of the thermal cycle.

For alternatives, my money in the long run is on molten salt batteries [1] for
large scale. Technology also has benefit of increased industry knowledge of
how to utilize molten salts safely which will benefit LFTR research.

(1) [http://news.mit.edu/2018/metal-mesh-membrane-rechargeable-
ba...](http://news.mit.edu/2018/metal-mesh-membrane-rechargeable-batteries-
renewable-energy-0122)

------
awful
I would just love a couple of small vertical turbines slowly pumping up my
underground storage. I live in a sometimes violent wind location, often just
when I could use the energy to run the furnace. I could see easily augering
10-15ft holes , dropping in vertically buried, used, composite tanks bought
off Ebay, run at a fraction of their max pressure. Easily adding more to
increase capacity, as needed. Yes a little pock-pock noise of the pistons and
check valves, but it would only happen when wind blows. Though, a tank failure
may mean retrieving it off the roof.

------
jacknews
This makes some sense in poor tropical nations, where rigging a mechanical
system like this is quite feasible locally (instead of having to import
advanced lithium batteries, along with usually exorbitant import duties etc),
and some of the "inefficiency" can be used to heat, and particularly, cool
spaces.

It also makes sense for oceanic wind turbines, which can use periods of high
wind vs low demand to pump air into large under-sea air storage bags, using
the sea as free cooling/heating towards isothermal operation.

------
natch
Or, don’t ditch the batteries. They work fine.

The title of the article strikes me as one of those marketing titles possibly
planted by a press release. Position the competing product as if it’s somehow
bad. “Protein-free!”

I’m not buying it.

------
tomohawk
Also works for vehicles. Hydraulic hybrids capture 3x more of the braking
energy.

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

There's a retrofit for garbage trucks that pays for itself in 2 years, or you
can buy them new.

[http://www.govtech.com/transportation/Hybrid-Garbage-
Miami-D...](http://www.govtech.com/transportation/Hybrid-Garbage-Miami-
Dade-040511.html)

------
dpcx
Joey Hess has been using his fridge for off-grid energy storage... With lots
of data around what he's seeing. It's really interesting, and he still gets to
keep his food cold.

EDIT: Not really used as a battery, but probably could be.

[http://joeyh.name/blog/entry/fridge_0.1/](http://joeyh.name/blog/entry/fridge_0.1/)

------
1024core
Isn't there a loss in efficiency due to heat? Compressing air heats it up,
which is lost (this is the basic principle behind refrigeration, though it
doesn't use air). And then there's the loss in converting this PE back into
electricity. Are these losses less than what's lost in LiON cells?

~~~
contravariant
Read the article they go into this in detail.

------
jeena
This reminds me of perri air from spaceballs

[https://4.bp.blogspot.com/-prQEijRsbNk/Vnq-6GVfO-I/AAAAAAAAB...](https://4.bp.blogspot.com/-prQEijRsbNk/Vnq-6GVfO-I/AAAAAAAABjA/GSEn_ij3AzE/s1600/spaceballs-
scrocco-perri-air.png)

------
g8oz
Also interesting is hydraulic energy storage. Any entrepreneurs want to take a
shot with this system?

[http://license.umn.edu/technologies/z07054_hydraulic-
energy-...](http://license.umn.edu/technologies/z07054_hydraulic-energy-
storage-systems)

~~~
leblancfg
>Hydraulic energy storage systems store energy by compressing air similar to a
battery storing energy in an electric circuit.

Wait, did you read the article? :)

~~~
g8oz
Hydraulic systems and compressed air systems are usually regarded as separate
things. Maybe the distinction is a bit arbitrary and the former can be
regarded as a subset of the latter but there you go. edit: Google says
hydraulic transmits power through fluid, compressed air through air/gas.

~~~
blattimwind
Pneumatic vs hydraulic is about compressible vs incompressible fluids.
(Naturally, hydraulic oil is also a much better lubricator and an exceedingly
superior sealant than oiled air).

------
sangnoir
Off-topic: one of my favourite Ted Chiang short stories - Exhalation[1] - is
about compressed-air-based lifeforms.

1\.
[http://www.lightspeedmagazine.com/fiction/exhalation/](http://www.lightspeedmagazine.com/fiction/exhalation/)

------
KirinDave
> The low efficiency is mainly since air heats up during compression. This
> waste heat, which holds a large share of the energy input, is dumped into
> the atmosphere.

Wait... wait... I'm... not sure I believe the extend of this statement. If
this isn't wrong it's certainly awkwardly worded.

------
driverdan
It's interesting to see research done in this space but it's not even remotely
practical yet. Their 410Wh system is more complex, five times larger, and has
a much higher up front cost than an equivalent amount of lithium battery
storage.

------
gleglegle
Highview claims to be able to do this at prices competitive with Lithium
batteries.
[https://www.highviewpower.com/technology/](https://www.highviewpower.com/technology/)

------
dylanz
I'm not knowledgeable about any of this, but how does this compare to a
Trompe?
[https://en.wikipedia.org/wiki/Trompe](https://en.wikipedia.org/wiki/Trompe)

------
stmw
When compressed air energy storage comes up, it is always worth remembering PV
= nRT, the ideal gas law. And then remembering that things are not ideal.

~~~
btrettel
Mechanical engineer here. The ideal gas approximation is plenty reasonable for
the pressures and temperatures of interest here.

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

------
sgt101
Silly question - could tires be used to do this? I mean, could one improvise a
storage system via a stack of car tires?

------
leowoo91
Afaik, compressed air energy startups come and go since long time, this should
be ok for use in enterprise though.

------
newnewpdro
I always wanted to have an air compressor running every day on my otherwise
quiet property.

------
kazinator
How about steel springs? Rubber bands? Weights hoisted on cables?

------
trumped
I'd love to go nuclear ... charge your phone once a year?

------
toolslive
Hold on... So if you take a Tesla, remove the batteries, remove the electro
engine, and replace that with a trivial compressed air based pneumatic motor
it would be more eco friendly, more powerful and have a higher autonomy ?

~~~
balfirevic
From
[https://en.wikipedia.org/wiki/Compressed_air_car#Disadvantag...](https://en.wikipedia.org/wiki/Compressed_air_car#Disadvantages)

\- A 2005 study demonstrated that cars running on lithium-ion batteries out-
perform both compressed air and fuel cell vehicles more than threefold at the
same speeds.

\- A 2009 University of Berkeley Research Letter found that "Even under highly
optimistic assumptions the compressed-air car is significantly less efficient
than a battery electric vehicle and produces more greenhouse gas emissions
than a conventional gas-powered car with a coal intensive power mix."

