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

[rlk at alum.mit.edu (Robert Krawitz)]

On Sat, 22 Jul 2017 20:08:24 -0400, Richard Pieri wrote:
> On 7/22/2017 12:22 PM, Robert Krawitz wrote:
>> 10x?  Battery charging isn't that inefficient -- 85% for lead-acid
>> batteries, for example
>> (http://www.solar-facts.com/batteries/battery-charging.php).
>
> "Overall, an efficiency level of 85% is often *assumed*."
>
> Emphasis mine. The rest of that paragraph goes on to explain some of the
> reasons why you can and will get less than this. Also, these are lead
> acid batteries which have longer lifespans than the Li-ion batteries
> Musk is selling, and they will hold to their higher efficiencies for longer.

But it's considerably more than 10% in practice, right?

>> That's the least of the problems.  You have to keep it in orbit, the
>> beam has to keep station (that kind of concentrated beam had better
>> not leak), and a geosync orbit is still eclipsed part of the time.
>
> At geostationary altitude a station is eclipsed from the sun for only 70
> minutes per day, and this is only when the sun is near the equatorial
> plane. In practice, a geostationary PV station would have ~99.3%
> exposure over the course of a year vs. a ground station which has at
> best ~33% exposure, and that ~99.3% exposure is always "noon" vs. the
> ground station's noon being a fraction of its exposure time.

You still need storage for those blackouts (albeit less), right?

>> Care to discuss what you see as the problems and how to go about
>> addressing them?
>
> https://dothemath.ucsd.edu/2012/03/space-based-solar-power/
> covers them pretty well, and I do agree with the conclusion that SBSP
> isn't worth it in the short term. Putting that much mass into orbit is
> too expensive right now.

The author is quite clear that he simply doesn't see this as being
plausible any time soon.  And no doubt batteries will improve along
the way.
-- 
Robert Krawitz                                     <rlk at alum.mit.edu>

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