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

On Sun, 23 Jul 2017 00:46:22 -0400, Richard Pieri wrote:
>> OK, so here you're saying that instead of a <10% charge/discharge
>> efficiency, batteries actually have a 75%-80% charge/discharge efficiency?
> No. I'm saying that chemical batteries have *at best* a charge
> efficiency of around 75-80% in the real world.

There's a long way from 10% to 75-80%, and you're the one who cited 10%.

>> Agreed!  And Utah, and Arizona, and New Mexico, and large parts of
>> Colorado, Wyoming, Idaho, Oregon, and Washington by your map.  And don't
>> forget Great Plains states like Texas, Montana, North Dakota, South
>> Dakota... hey, I think we're over 0.15%!
> There are three problems that I would consider breakers for these regions:
> First, you just described the heart of Tornado Alley.

I'm more worried about big hail than tornadoes to be honest, but
really big hail (and tornadoes) are actually extremely rare at any
given point (I believe I've read that the return period for tornadoes
at any given point is 2000 years; I don't know what the return period
for, say, 3" hail is).

> Second, you can't charge Li-ion batteries when they are below freezing
> (0C) which makes much of these areas useless for Musk's storage systems
> for significant portions of the year.

Are you saying Tesla cars are useless (can't be recharged) when the
temperature's below freezing?  I see plenty of Teslas here in
Massachusetts all winter, so I guess they find a way.  Use some of
that charge to keep the battery warm, of course.

> And third, high temperatures (above about 25C) reduces efficiency, and
> it causes batteries to wear out faster than their published ratings
> which means you'll be replacing them that much more frequently if you
> set up your stations in the non-freezing areas.

That's harder to solve, of course, but again, there are Tesla owners
in hot climates who don't keep their cars in air conditioned garages.
So I guess it does actually work Well Enough.

>> FWIW, on that last non-technical bit, I and I wager many others on this
>> mailing list see very many places in all the named locales which have good
>> potential for solar.  And that's one of the great things about solar power:
> Maybe good on small scales like homes and offices. Not so good for large
> scale like replacing global dependence on fossil fuels.

Actually, it scales both up and down pretty nicely.
Robert Krawitz                                     <rlk at>

***  MIT Engineers   A Proud Tradition  ***
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