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RE: starship-design: Preliminary Design for a Solar Laser Power Station


>[L. Parker]  Typical high power lasers are currently running between 1 
>percent and 2 percent efficiency. A solar pumped carbon dioxide laser 
>has been run at 2 percent efficiency. The reason I was speculating on 
>the "solar laser" had to do with removing intervening conversion steps 
>and thereby removing possible sources of additional inefficiency.

I know, but some of these intervening steps may increase efficiency.
In theory we could just bundle the sunlight with big mirrors. I guess that
if you would collect sunlight from a particular direction of the sun's
surface, you might be able to make at as straight as a laser beam. Actually
you might even make it straigther since its easier to use big apertures.

>Using photovoltaic panels to convert sunlight to electricity will require 
>between 100 and 1,000 times much surface area of panels as a simple

PV's (photovoltaic) may be combined with concentrators too. If the added
complexity of using a concentrator is cheaper, they will likely use it.

>Any sail that we design to reflect a particular 
>frequency of visible light is going to reflect ALL frequencies of 
>visible light.

You've to explain that, as far as I know no material can reflect all
frequencies just as well. I know we can do extremely well for a single
frequency, but don't have numbers for a certain bandwith.

>Solar panels combined with the right electrical lasers do quite well too.
>And if you're talking about single frequencies, their efficiency is probably
>10 times higher.
>[L. Parker]  I happen to be partial to free electron lasers (I assume 
>that is what you mean when you say electrical lasers) but in order to 
>offset conversion inefficiencies you will need to increase their 
>output/input power ratios enormously.

Sorry, with electrical I meant those that you can just plug into your
wall-contact. If I understand correctly, they are just stimulated by a
bright lamp.

>To be fair, I have not seen ANY efficiency ratios for this "solar 
>laser" so it is all speculation.

One of the reports tells about 5 Watt/m^2. I guess those square meters are
at Earth surface. So assuming 50% of the solar radiation will penetrate the
atmosphere, it will give 700 Watt/m^2. This would mean an efficiency of
5/700 = 0.7%

I read that CO2 lasers can be 30% efficient. Together with PV's, that would
be about 8% efficiency. I must admit though that most other lasers have much
lower efficiencies (less than 2%). The drawback of CO2 laser is that it
produces far infrared light, which may make reflectivity harder.