From: everything-list@googlegroups.com
[mailto:everything-list@googlegroups.com] On Behalf Of meekerdb
Sent: Thursday, November 14, 2013 8:39 PM
To: everything-list@googlegroups.com
Subject: Re: Our Demon-Haunted World
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> 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.
All valid points and with which I agree. PV systems have also been following
cost curves reminiscent of that other silicon technology. Already the other
system costs outweigh the cells themselves. Eventually I hope to see wide
scale distributed solar PV with some benign form of energy storage. I also
hope they can get the mass manufacturing costs down for multijunction cells
that can harvest electrons over a wider spectrum of wavelengths.
CSP systems do have this inherent ability when paired with efficient thermal
reservoirs to time shift their generating capacity and deliver current onto
the grid many hours after the sun has gone down. They can behave in many
regards somewhat like baseload generation; not completely of course for they
are still subject to longer duration periods of bad weather, but they can
both smooth their output (compared to PV, which responds almost instantly to
variations in light levels) and have this inherent ability to store the
energy for a short duration - perhaps even several days if the tanks are
super insulated.
The lower efficiency of thermo-electric conversion I believe is partially
made up by the higher efficiency of thermal harvesting of incident solar
irradiance - I could be wrong about that though, but the best single
junction PV is around 20% so maybe not that hard to beat.
In the end I think large scale CSV is more of a niche supply that makes
sense in some desert areas that can scale in size to the sizes needed in
order to get scales of efficiency.
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.
Other engineering friends of mine have levelled the same criticism of that
idea. I guess the only counter argument could be that the very heavy
piston's weight would be born directly by the compressed water column, and
that for very large masses the cable systems could present serious problems
with stresses from wear - have you ever seen when an elevator cable is
un-torqued; it literally whips around as the stresses are released.
Wondering about the stresses that repeated winding and unwinding of the
support cables would induce.
Chris
Brent
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