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

On 7/23/2017 9:58 AM, Robert Krawitz wrote:
> "As low as" 50% is a whole lot more than 10%.

As low as 50% when new. Efficiency drops off as batteries age. If you've
ever replaced a phone or notebook battery because the battery was worn
out then you've experienced this first hand.

> Supercaps have their own problems...not very dense compared to
> batteries, for example.  And a lot more expensive for the same
> storage.

You don't need the same storage. That is, you don't need 14+ hours of
storage with geostationary solar stations like you do with ground
stations. You only need ~70 minutes of storage which obviates the
self-discharge problem that makes supercapacitors less than ideal for
long term storage.

This assumes one station. With 2 or more stations you will never be
without exposure, further reducing the need for eclipse storage.

> The pinnacle at present, maybe.  While it's true we can't count on
> particular breakthroughs, it's pretty clear we can count on
> breakthroughs of some kind happening.  There may be improvements in
> Li-ion that improve lifetime, charge density, etc.  Hopefully we'll

You mean like Li-air and other metal-air concepts, which haven't had the
several necessary breakthroughs in the past almost 50 years since the
concept was introduced? Breakthroughs are rare, and when you need
several for something to be viable? I wouldn't bet on it.

> find something based on non-lithium chemistry, since lithium's
The only element better than lithium is hydrogen. Nothing else is
capable of higher charge densities. Since we can't have metallic
hydrogen at room temperature and pressure we use lithium.

As previously noted, Li-sulfur shows promise but it has serious problems
that need to be overcome before it can be commercially viable.

> scarce.  And not renewable?  Since when?  Extract the lithium and use
> it to fabricate new batteries.

Recycling Li-ion batteries costs more than mining the metals and
refining the plastics from fossil fuels. Until this changes they cannot
be considered sustainable. And, of course, the elimination of the
petrol-based plastics is necessary as well.

> Interesting that we can't count on breakthroughs in battery
> technology but we can in space...

We don't need breakthroughs in space for SBSP. All of the technologies
exist today.  What we don't have is launch capacity to put 10+ kilotons
(CAST's estimate for their proposed 1GW station) into orbit. Doing this
doesn't require any breakthroughs, just a lot of brute force and enough
nations or corporations willing to foot the bills.

That said, there are advances which could significantly reduce those
costs. CAST's proposal includes lunar manufacture. With no atmosphere
and 1/6th the gravity, launching from the Moon is quite a lot easier
than terrestrial launch. Then again, with no atmosphere and 1/6 the
gravity, lunar manufacture has it's own problems to overcome.

Rich P.

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