On Sun, 30 Sep 2018 22:37:42 -0700, 2G wrote:
On Sunday, September 30, 2018 at 4:23:22 AM UTC-7, Martin Gregorie
wrote:
On Sat, 29 Sep 2018 23:07:27 -0700, 2G wrote:
On Saturday, September 29, 2018 at 6:30:20 PM UTC-7, Martin Gregorie
wrote:
On Sat, 29 Sep 2018 16:38:53 -0700, Bill.Daniels wrote:
But, an electric motor is more than three times as efficient as an
internal combustion engine - 98% vs. 33% - so they don't need as
much 'fuel'.
Well, getting on that way - but certainly no better if you include
the generation and charging efficiencies.
Actually, all I was looking to do was to put numbers to the overall
efficiency of electric storage in terms of weight or volume compared
with hydrocarbon fuels. Batteries are much worse here than petrol.
And there's another demerit too: run the tank dry on a turbo or jet
and the empty tank is nice and light for the rest of the flight
home, while a battery that has been run flat is no lighter than when
it was fully charged.
A quick scan for zinc-air battery characteristics suggests they are
only suitable for low power applications, tend to have a high
self-discharge rate and don't like high temperatures or humidity.
Nobody, that I found anyway, is quoting energy density (kWh/kg) or
volumetric efficiency (kWh/
litre).
Bottom line: I like the idea of electric powered vehicles. But in
this application the volume and weight of energy storage systems is
all- important, but electrochemistry is against any large
improvement, at least for rechargeable batteries using currently
proven chemistry. So far nobody has gotten better results from
fuel-cells either, or we'd be seeing them in cars.
--
Martin | martin at Gregorie | gregorie dot org
Here is an interesting 2015 presentation on zinc-air batteries that
indicates the possibility for very high energy densities (1200+
WHr/kg):
https://www.csm.ornl.gov/BLI8/presen...UNIST-BYI8.pdf
Interesting stuff but, unless I totally misunderstood the presentation:
- the theoretical energy density of ZAB is around 170% of what LiFePO4
can do (0.3 kWh/kg vs 0.18 kWh/kg). no comparison with Li-ion made.
(page 4).
- page 18 quotes a measured 1 kWh/kg.
- page 32 quotes 0.0357 kWh/kg (0.41 kWh/litre) for an experimental
ZAB
rig.
- page 36 quotes 1.9 kWh/kg (0.0036 kWh/litre) for a flexible cable
format battery.
... all quite a way short of the 10 kWh/litre (12.5 kWh/kg) of
hydrocarbon energy storage.
The sort of high power performance needed for a car or aircraft motor
wasn't really discussed or apparent in the accompanying numbers, charts
and graphs.
Still, looks to be worth watching and the possibility of almost instant
recharge by replacing the zinc becomes interesting if a cell with high
power output can be designed for easy 'slip out/slip in' zinc
replacement without needing special equipment, e.g to deal with the
(highly alkaline)
potassium hydroxide electrolyte.
The possibility of recycling the 'used' zinc externally sounds good
too.
--
Martin | martin at Gregorie | gregorie dot org
Here is an excellent paper that discusses the current state-of-the-art
in zinc-air batteries:
https://www.researchgate.net/profile...6/publication/
311098275_Electrically_Rechargeable_Zinc-
Air_Batteries_Progress_Challenges_and_Perspectives/links/
59da6e38458515a5bc2b43b1/Electrically-Rechargeable-Zinc-Air-Batteries-
Progress-Challenges-and-Perspectives.pdf
I haven't had time yet to read the full paper, but what I have read so
far is most instructive.
Tom
Thanks for that. Saved for reading later.
--
Martin | martin at
Gregorie | gregorie dot org