[Discuss] Eclipses Re: Great talks last night, however...

[grg-webvisible+blu at ai.mit.edu (grg)]

On Sun, Jul 23, 2017 at 01:20:05PM -0400, Richard Pieri wrote:
> On 7/23/2017 12:29 PM, grg wrote:
> > OK, so you're saying that instead of single-digit percentages, there are
> > real-world battery installations which get 75%-80% charge/discharge
> > efficiency; meaning that if using them we'd only need to make 20%-25% more
> > solar power, not 1000% more, to compensate for the loss in batteries.
> 
> When new under good conditions. Those numbers drop as conditions change
> (extremes of heat and cold) and batteries wear out.
> 
> > http://www.sandia.gov/ess/docs/pr_conferences/2014/Friday/Session10/04_Vishwanathan_V_Powin_Dispatchable_Battery.pdf
> 
> And what are their numbers after 3, 4 or 5 years?

Actually, the coulombic efficiency (CE, the battery's component of the
overall charge/discharge efficiency) of lithium-ion batteries stays well
above 99% for the full life of the battery, and even improves a bit as the
battery ages.  What drops as batteries age is instead the total capacity of
the battery.

Here's a source - behind a paywall, but the abstract is free and gives the
relevant highlights: "A solid-state high-voltage (5 V) lithium battery is
demonstrated to deliver a cycle life of 10,000 with 90% capacity
retention. The solid electrolyte enables the use of high-voltage cathodes
and Li anodes with minimum side reactions, leading to a high Coulombic
efficiency of 99.98+%."

http://onlinelibrary.wiley.com/doi/10.1002/aenm.201401408/abstract;jsessionid=CBDD74C72BBF0C1C53B7FBB1AC2DB1B5.f04t03

In the paper they show that a conventional li-ion battery holds 90% of the
original charge after 3000 cycles (~9 years of daily cycling); and after
those 9 years it actually has the highest coulombic efficiency (CE) of its
life so far, well over 99%. (That's their baseline; the paper's goal is to
present a battery improvement which has that performance to 10,000 cycles =
30 years instead of just 3,000 cycles = 9 years.)  So actually, in contrast
to your claim, the efficiency goes up a bit as they age and "wear out".

Oh, I found a non-paywalled version of that paper (formatting's not nearly
as nice as the paywalled version, but hey, it's free):
https://www.osti.gov/pages/biblio/1185480-solid-electrolyte-key-high-voltage-lithium-batteries


> > But somehow, 99.99% of people and corn and cows (not counting that
> > unfortunate animal in the movie Twister) have managed to survive there.
> > I'm betting solar panels will have a similar tornado survival rate, unless
> > we decide to install them only at trailer parks.
> 
> That's because people and livestock can seek shelter in foul weather,
> and plants grow and heal or at the least can be plowed under and the
> land replanted. None of these describe thousands of square kilometers of
> solar panels.

Nor do those characteristics describe millions of homes and buildings.  How
many buildings do you think are destroyed in Kansas by tornados each year?
Hundreds, for a survival rate of 99.99%.  So no, it's not because cows are
running away from approaching tornados or because they're sharing Farmer
John's storm cellar, it's actually because 99.99% of the spots in Kansas
don't have a tornado land on them.


> > One standard solution to weather exposure would be to house them below the
> > frost line, which is only 2'-3' deep in Kansas:
> >     https://www.ngs.noaa.gov/PUBS_LIB/GeodeticBMs/#figure13
> > You'll get a moderate temperature all year round.
> 
> Then you're insulating them which means they'll be that much hotter when
> charging during warm months. See previous about heat being bad for
> batteries.

I guess you'll be surprised to learn that the ground is actually an
effective heat sink; see the ground loops in heat pumps, which provide air
conditioning by sinking the removed heat into the ground.  Here's a source
for you:  https://energy.gov/energysaver/geothermal-heat-pumps

Excerpting: "Geothermal heat pumps (GHPs)...have been in use since the late
1940s.  They use the constant temperature of the earth as the exchange
medium instead of the outside air temperature.  Although many parts of the
country experience seasonal temperature extremes -- from scorching heat in
the summer to sub-zero cold in the winter -- a few feet below the earth's
surface the ground remains at a relatively constant temperature...The GHP
takes advantage of this by exchanging heat with the earth through a ground
heat exchanger."


> > Again, if you do the math, it's exactly pi.  The equator is a circle; the
> > sunlight incident on it is its shadow at this point in space, which is a
> > line that is the diameter of Earth - on that line every point is always at
> > "noon", and it would collect all the light the equator sees.  Will ascii
> > art help?
> 
> You're ignoring the atmosphere.

Actually, I already addressed that in previous emails when discussing the
"insolation" issue (instead of the "noon" issue here): 1370 W/m^2 in space,
of which ~1000 W/m^2 makes it to the surface on average.  In case it wasn't
clear (no pun intended), it's the atmosphere which is responsible for that
difference.

--grg