alt.energy.renewable

>In article ,
> Gordon Richmond wrote:
>
>> >In article ,
>> > "Vaughn Simon" wrote:
>> >
>> >> "Anthony Matonak" wrote in message
>> >> news:47dcc2da$0$16655$4c368faf@roadrunner.com...
>> >>
>> >> > You could think of the reversible multi-stage compressor and
>> >> > air motor combined with the x-thousand psi storage tanks as a
>> >> > form of electrical battery. You can charge it by running the
>> >> > motor as a compressor and get the energy back by running the
>> >> > compressor as a motor.
>> >> >
>> >> Yet again, you are ignoring the physics. Storing energy by compressing
>> >> gasses is thermodynamically a very lossy process. Almost anything else
>> >> would
>> >> be
>> >> better.
>> >>
>> >> Vaughn
>> >
>> >LG&E has a 200 MW capacity - high pressure air storage facility to allow
>> >them to take off peak electricity generation and store the energy (with
>> >large losses) in caves as high pressure air. Given the environmental
>> >issues of many other storage methods, this one is better than most. They
>> >release the air when they need peak power. In their part of the US,
>> >off-peak electricity can be bought for as little as 2 cents/kwh and on
>> >critical peak days the price has risen (on a few occasions) to more than
>> >$8/kwh - more normal peak prices on the spot market are in the range of
>> >$1/kwh.
>> >
>> >Like Oil more than 90% of the electric energy is not subject to peak
>> >spot price (it is was your electric bill would be sky high) but when you
>> >are short even a few Megawatts at a critical peak it can be very
>> >expensive.
>> >
>> >I am not advocating air pressure for cars, but please do not sell it
>> >short for shifting electric generation from off peak to peak and for
>> >shifting wind and solar energy from the time of generation to when it is
>> >needed more.
>> >
>> >Doug
>>
>> Doug, without going to the source, I think what's being done in this case is
>> to store
>> "moderately" compressed air in caves, which then serves to bypass or supplant
>> air from the
>> compressor section on gas turbine generators. If the compressor does not have
>> to absorb as
>> much horsepower from the shaft, then more current can be pulled from the
>> generator.
>>
>> You could not use caves to store at a pressure of hundreds of atmospheres
>> needed to run a
>> piston-type air motor as proposed for the MDI car. The rock formation would
>> simply
>> fracture, and the air would bleed off.
>>
>> Gordon Richmond
>
>Vaughn & Gordon -
>
>The plant is active - it is not listed, since it is considered by FERC
>as "Storage" and not a peaking plant. There are no Gas Turbines involved
>in the output. It is purely air turbine. I visited the site last summer
>on a day when it was expected to operate.
>
>Here is an article on one in New Mexico...
>
>http://www.sandia.gov/media/NewsRel/NR2001/norton.htm
>
>and several more...
>
>http://www.energypulse.net/centers/article/article_display.cfm?a_id=436
>
>I do not have the articles on LG&E stashed on the new machine (I crashed
>it and destroyed the hard disk a couple of weeks ago).
>
>In several of these, there is some natural gas (about 10% of the usual
>amount) added to the mix as it runs thru the air turbines, to heat the
>air and gain added push out of the mix.
>
>In most cases it is wind turbines that allow the air to be compressed.
>
>I just was at a project in Scotland where they are looking at having
>100% of the wind turbine output converted to high pressure air
>(approximately 1500psi) and stored - using the result as a baseload
>plant - avoiding the issues with wind power and its variable output.
>
>Doug

Thanks for the links. In the Norton project, they are projecting working pressures of 800
to 1600 psi. Certainly moderate compared to the MDI air car's working pressure.

It's probably worth noting that, being as it's a very large storage volume, the air
compressed into the mine will lose its heat less rapidly than air compressed into small
tanks. The thermal mass of the rock surrounding the chambers will eventually be warmed to
a point that subsequent air charges will lose little of their contained heat energy to the
ground. That answers, at least in part, one of the biggest objections to the use of
compressed air for energy storage, that it's thermodynamically lossy. This is a case where
size matters. The fuel they do burn is likely used to make up for the thermal loss that
does occur.

Also worth noting is that in the case of storage in underground caverns, they are
exploiting an existing resource, a great big hole in the ground, surrounded on all sides
by dense, impermeable rock. This would be a very costly structure to build, if it was not
already in existence. I note from the links that other compressed-air energy storage
facilities also make use of "found" reservoirs.

Sounds like a promising technology, which could be useful wherever you have a potential
reservoir that's reasonably close to the electrical grid. Not all mines are in rock that
is "tight" enough to serve as a reservoir, but perhaps some could be upgraded by spraying
a polymer membrane on all interior surfaces.

This new use for abandoned mine cavities also suggests that it may be possible to work the
"storage potential" of a proposed mine cavity into the feasibility study for a new mine.
Perhaps the added value of the cavity for air storage could tip the scales in favor of
developing a new mine that would otherwise not be started because of marginal grades.

Gordon Richmond