
How Cheap Can Energy Storage Get? Pretty Darn Cheap - ph0rque
http://rameznaam.com/2015/10/14/how-cheap-can-energy-storage-get/
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infogulch
I'm surprised Nickel-iron batteries[0] aren't used for this type of grid-scale
storage. They are _extremely_ time and cycle-durable: 20- _50 years_ , almost
immune to repeated deep discharges, relatively cheap and simple to produce.
Cons: they need a bit of maintenance (not a big deal at grid scale), and have
a less-than-stellar efficiency.

The problem with compressed air is that the Ideal-gas law [1] actively works
against you to reduce efficiency, assuming it will be kept at ambient
temperature. Inserting energy by compressing gas heats it up, which increases
the pressure of the gas in the tank, which makes you work harder to put more
gas in. Extracting energy cools the gas down, which reduces the pressure of
the gas, which reduces the amount of energy you can extract from it. You can
mitigate these issues by carefully controlling the temperature of the gas
(more energy) or having a much much bigger tank so a single cycle only
thermally cycles by a small amount (more $$).

Another option I hadn't considered until now is to let it heat up -- and
insulate it to let it stay hot. It will cycle in both pressure _and_
temperature on a nearly daily basis so you may not lose all that much energy
in heat. But I doubt this is an original idea.

[0]:
[https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery](https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery)

[1]:
[https://en.wikipedia.org/wiki/Ideal_gas_law](https://en.wikipedia.org/wiki/Ideal_gas_law)

~~~
ph0rque
Regarding the compressed-air problem you mentioned, have you seen LightSail
Energy's ([http://lightsailenergy.com](http://lightsailenergy.com)) solution
to it?

"Our innovation: an elegant method of capturing this heat energy and
regenerating useful energy from it. We inject a fine, dense mist of water
spray which rapidly absorbs the heat energy of compression and provides it
during expansion."

Maybe one of the founders, @DaniFong
([https://news.ycombinator.com/user?id=DaniFong](https://news.ycombinator.com/user?id=DaniFong)),
can chime in.

~~~
DaniFong
You've pretty much got it. The author mentions us actually.

The parent commenter does accurately locate the challenge to date with
compressed air energy storage, but we've directly and successfully targeted
that loss channel :-)

~~~
infogulch
Thanks for replying.

Most compressed air systems attempt to pull as much moisture out of the air as
possible to prevent corrosion, but your solution to the heat problem means
actively making the air and interior even more wet. This wouldn't be a problem
in the short term, but your product is meant to be used over a very long
period (~20 years); how are you approaching the issue with corrosion?

