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Looking for"integrated" solar spectrum

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Posted by Paul Ciszek on July 3, 2007, 2:27 am
 
I would like a reference for the amount of power contained in
sunlight between two given wavelengths.  Sure, I could get that
information by integrating the raw data, but I don't know where
to get the raw data either.

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Posted by Morris Dovey on July 3, 2007, 8:34 am
 
Paul Ciszek wrote:
| I would like a reference for the amount of power contained in
| sunlight between two given wavelengths.  Sure, I could get that
| information by integrating the raw data, but I don't know where
| to get the raw data either.

Paul...

I think you'll need to work with the raw data. Note that it'll make a
significant difference at some wavelengths whether the data were
collected outside the atmosphere or at the earth's surface - and that
the surface readings may be influenced by locale-specific effects.

A good starting point might be
http://rredc.nrel.gov/solar/spectra/am0/  which contains links to
downloadable data sets.

You might also find it productive to nose around NASA databases.

HTH

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by Erdemal on July 3, 2007, 11:02 am
 Paul Ciszek wrote:

You cant integrate 'raw data' for an electromagnetic spectrum
because 'spectrum' is not a continuous function.

Trying to do that led Max Planck to quantum theory IIRC :)

Erdy

Posted by Morris Dovey on July 3, 2007, 11:48 am
 Erdemal wrote:
| Paul Ciszek wrote:
|| I would like a reference for the amount of power contained in
|| sunlight between two given wavelengths.  Sure, I could get that
|| information by integrating the raw data, but I don't know where
|| to get the raw data either.
|
| You cant integrate 'raw data' for an electromagnetic spectrum
| because 'spectrum' is not a continuous function.
|
| Trying to do that led Max Planck to quantum theory IIRC :)

It is possible, however, to produce approximations that are useful for
many purposes. Given that Sol's exact output varies from one instant
to the next, an approximation is about all one can hope for. The only
issue is whether or not the approximation is useful for a particular
purpose.

I think that for the terrestrial applications normally discussed in
a.s.t, the atmospheric filtering and locale-specific effects will
cause more significant variations than Paul is likely to introduce by
assuming that the data points can be connected by straight lines...

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by nicksanspam on July 3, 2007, 12:07 pm
 

Table 2.6.1 on page 64 of Duffie and Beckman's 2006 3rd edition
of Solar Enineering of Thermal Processes divides an AM1.5 solar
terrestrial beam radiation spectrum into 20 equal-energy bins
with midpoint wavelengths at 0.396, 0.451, 0.490, 0.527, 0.563,
0.599, 0.635, 0.672, 0.710, 0.752, 0.798, 0.846, 0.896, 0.981,
1.044, 1.142, 1.249, 1.510, 1.678 and 2.232 micrometers.

This looks hard to calculate, starting with a black body sun,
since the atmosphere attenuates different wavelengths with
various scattering and molecular absorption modes by dust and
water droplets and water vapor and ozone and CO2 and so on.

Nick


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