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From: roger034@gold.tc.umn.edu (Brynn Rogers)
Subject: Re: Solar Insolation Levels
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References: <ykgcqc4w165w@sfrsa.com> <Cu1v1p.JqB@armory.com> <Cu2Es6.I48@news.cis.umn.edu> <Cu5rGv.CFB@armory.com>
Date: Mon, 8 Aug 1994 06:20:51 GMT
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In article <Cu5rGv.CFB@armory.com>,
Richard Steven Walz <rstevew@armory.com> wrote:
>In article <Cu2Es6.I48@news.cis.umn.edu>,
>Brynn Rogers <roger034@gold.tc.umn.edu> wrote:
>>In article <Cu1v1p.JqB@armory.com>,
>>Richard Steven Walz <rstevew@armory.com> wrote:
>>
>>>   [stuff deleted]
>>
>>This 150 W per square meter, is that what you can get out of the cells
>>or what you think the total solar flux is?
>>
>>My source worked on Mankato States SunRaycer solar car and with the
>>8 square meter panel they would get 900W in bright sun, maybe even 
>>1000W occasionally.  Either their cells were way better than they
>>paid for (%15 is what they had) or your number is what a solar cell
>>can convert to power, NOT the total solar flux.
>>--
>>Brynn Rogers     roger034@gold.tc.umn.edu
>----------------------------------
>Brynn, I am puzzled. I have a book for the passive solar course I took as
>well as a figure for the Sun's intrinsic brightness in Watts and the simple
>formula for the area the earth subtends and the area of a sphere,
>(4*pi*r^2), and a figure for the earth's albedo that indicates we are quite
>bright, perhaps not so much as Venus, but very reflective. The insolation
>here in orbit and at ground is of necessity quite different, as even with
>rotisserie mode, spacecraft have to radiate quite a bit of heat, and they
>have a major job of cooling their occupants even if they do only absorb for
>45 out of 90 minutes per orbit. Interestingly, the book for the course
>agrees perfectly with a astronomy book by Abell.

Don't believe everything you read.  Sounds like you went through a lot of
calculations to get a number that solar car racers use every day.

>                                                Could it be that the cars
>were allowed to charge batteries at night so that their contribution comes
>into play? 

Sure they could charge the batteries at night, but they could only use the
solar panel.  Starlight and Moonlight are not bright enough sources for
practical use.  :)

Actually they do have limits on when they can charge the batteries, something
like not before 7:00 AM and not after 8:00 PM. Every car had an observer riding
with each car's support team to make sure there were no rule infractions.

Of course the 900 to 1000Watts from an 8 square meter panel using %15
efficiency cells I quoted is Solar panel alone.  The %15 is what the
manufacture rates the cells at, in practice they are covered with a clear coat
of laquer to protect from the elements, plus when they get warm (and they do
get very warm in the sun, U Mich had liquid cooling under their panel) the
efficiency suffers more.  Figure %15 as very best case.  Also Mankato State's
panel was not flat, so when pointed at the sun there was a loss because all of
the cells were not perpindicular to the sun.  They would take the top off the
car and put it in a rack that held it at a 90 degree angle to the sun.
  They can get a lot more out of the batteries when they use them, but this
discussion was about solar cells, and I am only talking about the output of
the solar cells.


>        I believe that I saw that mentioned in a science show about that
>race.

  I have spent hours discussing all aspects of solar and electric cars with a
member of a solar race team.  Since he built the solar panel (two of them,
actually) and was responsible for its operation, I believe his figures.

>    Do you have a figure for the terrestrial albedo different from about
>66% reflectance of total insolation? And on top of that is the atmospheric
>absorption of infrared as well.
>-Steve Walz   rstevew@armory.com

   As I understand it the solar cells are working on a fairly narrow band of
visible light.  I don't have any book numbers for you.

   I don't want to have this thread continue til everyone is annoyed, can't
you just admit you don't know everything, Steve?

Brynn

--
Brynn Rogers     roger034@gold.tc.umn.edu

