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

[Richard Pieri]

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.


> 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.

> 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.

-- 
Rich P.