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From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: Solar Insolation Levels
Organization: The Armory
Date: Tue, 16 Aug 1994 11:21:39 GMT
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References: <ykgcqc4w165w@sfrsa.com> <Cu1v1p.JqB@armory.com> <Cu2Es6.I48@news.cis.umn.edu> <jonkCuFu25.GBM@netcom.com>
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In article <jonkCuFu25.GBM@netcom.com>,
Jonathan Dale Kirwan <jonk@netcom.com> wrote:
>Brynn Rogers (roger034@gold.tc.umn.edu) wrote:
>: In article <Cu1v1p.JqB@armory.com>,
>: Richard Steven Walz <rstevew@armory.com> wrote:
>
>: >Even in Death Valley, according to my passive solar technology instructor,
>: >you cannot get over about 150 Watt's per meter squared at noon in the
>: >summer on a clear day. I don't know why you think the atmosphere passes
>: >that amount of flux so well. We'd all be par-boiled!! The reflectance is
>: >much higher than that. I was instructed that orbit has, as a rule of thumb,
>: >11 times more solar flux for conversion to heat, such as for smelting, etc.
>: >We could melt steel in a pot with a 1' square Fresnel lens if that were
>: >true, at its focus! We can only melt lead with a 1 footer.
>: >
>: >The 100 to 150 Watt figure was the one used very successfully to predict
>: >the hot water ouput of all the old turn of the century hot water heaters on
>: >roofs in Los Angeles and much of southern California till the natural gas
>: >and petroleum got cheap!!! Few people know that the passive solar water
>: >heater was well on its way to over 50% usage till cheap petrochemicals!
>: >-Steve Walz 
>: >
>
>: 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.
>
>I wonder...  Is the apparent disagreement here simply a matter of 
>confusion, instead?  rstevew argues that 150 watts/m^2 is in the ball 
>park of reality.  roger argues that it is nearer 1000.  But notice that 
>roger says they were using (8) meter^2 panels.  With that much area and 
>with rstevew's figures they'd both be pretty close to an agreement.
>
>So, does the 1000 watt figure come from a single meter^2, roger?  Or did 
>their 8 meter^2 panels develop 1000 watts per meter^2, yielding about 
>8000 watts for the whole panel?  Is there a disagreement or not?
>
>Jon
-----------------------------
I appreciate the support, Jon, and I will follow through: George O. Abell's
book on astronomy has the solar insolation at 1 AU to average 1.37 x 10^3 
W/m^2. Now figuring from the earth's reflectivity, which is also stated by
Abell at .385 to .40 reflectance, then we have only 822 W/m^2 at the
equator. Since they were NOT near the equator and then had both more
atmosphere to shoot through and more of a typically non-zenith oriented
angle on a race track which meandered and was not orthogonal to the rays, I
will, at best, allow them an average of a 30 degree off angle from the
perpendicular to their photovoltaics. This leaves them with 713 W/m^2.
Then they had to contend with efficiency, and this was stated at 15%, and
so we have them down to 107 W/m^2. Perhaps the figure I recall was taken
from the inefficiency of photovoltaics, we shall see. Next the total area
of their panels, which was stated at 8 sqare yards. This brings them to a
max of 856 Watts from their panels. I have to admit that they are closer
to their statement than I am to mine, and so, I must be off about the
insolation (incoming energy from the sun) at sea level by a factor of ten.
This would explain my confusion. And after all, their car did work! It is
likely then that death valley may have a perpendicular insolation of less
than 1000 W/m^2, and that it is 40% greater outside the atmosphere. I had
said no more than 100 W/m^2 in the desert, and clearly, I must have dropped
a zero somewhere in my memory bank! Either that or I recall that figure for
the typical output of photovoltaics at sea level. In either case, I was
incorrect, and their figures were, in fact, more correct.
And so it goes...
-Steve Walz   rstevew@armory.com

