On 11/14/2013 6:28 PM, Chris de Morsella wrote:


*From:*everything-list@googlegroups.com [mailto:everything-list@googlegroups.com] *On Behalf Of *meekerdb
*Sent:* Thursday, November 14, 2013 4:29 PM
*To:* everything-list@googlegroups.com
*Subject:* Re: Our Demon-Haunted World

On 11/14/2013 3:39 PM, LizR wrote:

    On 15 November 2013 11:39, John Mikes <jami...@gmail.com 
<mailto:jami...@gmail.com>>
    wrote:

        Telmo and other 'experts':

        why does nobody even mention the geothermic energy app - available in 
huge Q-s
        and so far tapped only in (literalily) 'superficial' usage. The high 
pressure
        ultra-clean steam from a deepened modification of the exhausted oil 
wells may
        provide much much more energy than today's needs, so it could serve as 
driving
        force for more than we think by ongoing technology. (E.g. potable water,
        agri-irrigation, when fresh-water becomes scarce - like now - 
pollution-free
        transportation, keeping politicians in asylum, etc.) .

    I assume you mean geothermal energy. It is used in New Zealand but doesn't 
provide
    as much energy as wind and hydro as far as I know.

    It's an option in some parts of the world, certainly, but I would say solar 
is more
    readily available overall.


>>It might blend well with solar. There have been proposals to store solar energy by heating underground reservoirs.

Large scale CSPs (concentrating solar (thermal) power) such as the new GW complex they have built in southern California use molten salt as their energy carrier. This facility can keep generating electricity well after the sun has gone down because it stores the hot molten salt (saltpeter I believe) in insulated vats. This is one of the advantages of large scale solar thermal has over PV; as soon as the sun is occulted solar PV output drops precipitously (though newer PV cells that also have band-gaps tuned for infrared energy would continue to produce some output even when clouds came overhead, because of the infrared energy.)

There is a lot of money and R&D being thrown at the energy storage problem and a fair number of utility scale battery types are on the R&D pipeline as well as some other interesting ideas for energy storage. CSP is unique in that because it is harvesting heat it can store its energy with the same energy carrier it uses to harvest the solar energy -- i.e. the molten salt. Wind, PV, etc. need to transform the electricity into another medium (unless using supercapacitors) in order to store the energy and this invariably (second law of thermodynamics) entails a process loss -- and in both directions.


I don't think there's any thermodynamic advantage though to a solar/molten-salt system as compared to a PV. When the sun is shining the PV produces electricity (low entropy energy) directly while the solar/salt system has to use a heat engine to get electricity. If there is excess energy the PV systems could also store in molten salt. The disadvantage for the PV system is then that it needs a heat engine too. It then incurs the same thermodynamic inefficiency when the heat engine runs off the molten salt.

Most electricity storage -- and by a huge margin -- is accomplished by pumped storage. Japan, in particular leads in this area. But traditional pumped storage suffers from siting issues. I have looked at some novel pumped storage proposals that instead bore deep cylinders with a moving and very massive (heavy) piston. The system would have a low pressure upper reservoir and a high pressure lower reservoir below the piston. To draw energy down water from the high pressure reservoir is run through a turbine to generate electricity and flows into the spent reservoir above the piston (which descends towards the bottom of the cylinder); to re-charge the "battery" electricity is consumed to run the generator/turbine in reverse and pump the water (or other working fluid) from the low pressure reservoir, back into the high pressure one. Air pressure is also used (Alabama).


So the energy would be stored in the potential energy of the heavy piston and the water would just be a working medium? Why not put the weight on a cable and use a purely mechanical system? I'd think that could be more efficient that a water turbine.

Brent

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