[ExI] gravel batteries

[Adrian Tymes]

> The battery consists of two large silos filled with crushed
> rock. Electricity generated by the turbine heats and
> pressurizes argon gas and feeds it into the first silo.

> The argon is then fed into the second silo where it returns
> to normal atmospheric pressure, initiating a cooling effect
> that chills the gas and rock to -256 degrees. Thus, the
> electricity is stored as a temperature difference between
> the two chambers.

Alternately, just take two large lake basins - possibly
artificial - one lower than the other.  When you have energy,
pump from lower to higher.  When you need energy, drain from
higher to lower and use the flow to spin turbines.  Might be
even cheaper, unless you get protesters worried about the
environmental results of moving that much dihydrogen
monoxide around.