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From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: Solar Insolation Levels
Organization: The Armory
Date: Thu, 11 Aug 1994 07:29:21 GMT
Message-ID: <CuD0sy.CyB@armory.com>
References: <ykgcqc4w165w@sfrsa.com> <Cu2Es6.I48@news.cis.umn.edu> <Cu5rGv.CFB@armory.com> <Cu7DIr.2nA@news.cis.umn.edu>
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In article <Cu7DIr.2nA@news.cis.umn.edu>,
Brynn Rogers <roger034@gold.tc.umn.edu> wrote:
>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 Rogers     roger034@gold.tc.umn.edu
-------------------------------------------
I don't think the sun's insolation at this radius, or the actual albedo of
the earth is really subject to dispute, unlike ANOTHER thread we had on
here recently! So I guess I must simply be wrong! But I assure you that I
came by that state diligently!:-) I want to go through my books again and
see if I read them wrong or if they were simply wrong. It rankles that I
paid good money for them too! But you DO have the superior claim by far,
since obviously the car worked! I must be wrong, I just wish I knew why!
-Steve Walz  rstevew@armory.com

