"Real" Sun Hours [RE-wrenches]

[Joel Davidson]

Thanks for jogging my memory about Ron Richmond's 1984 Guidebook on Photovoltaic
Applications in Hawaii. See page 40 for Oahu yearly average peak sun hours per day. A
more recent and excellent source of data is Michael Pelosi's Solar Design Studio
software. Michael's audio tutorial is so good it defies description. Check it out at
http://www.mauisolarsoftware.com/

mmangelsdorf at hei.com wrote:

> My 2 cents.
>
> The NREL red book includes many sites which have less than accurate solar
> data listed.  If the site is designated by NREL as "primary" then you can
> have confidence that the data listed is accurate based on actual long-term
> (XX years) monitoring.  If it's a "secondary site" then the data listed is
> an extrapolation/estimate of the insolation based on computer modeling and
> the actual data recorded at a "nearby" primary site.  For example, here in
> Hawai'i, the only real data listed for our four listed locations (Honolulu,
> Hilo, Kahului and Lihue) is for Honolulu.  The other three sites are
> secondary sites where NREL is using the modeling approach based on estimated
> cloud cover, precipitation, etc.  Mike Pelosi's very useful Maui Solar
> Software design program uses NREL data to estimate system performance.  But
> I have to remind myself that many of the listed cities in the U.S. are
> secondary sites.  But hey, you have to put something into the program if you
> want to get some idea of what the system is going to do.
>
> My 2 cents are up.
>
> marco
>
> Carl and Travis,
> Most insolation data provided by folks like NREL and others is in units
> referred to as "peak sun hours". This is kWh/m2/day. Values are often
> published for monthly or yearly averages as in the NREL "Red Book". Goto
> http://rredc.nrel.gov/solar/pubs/redbook/ and look at this. You can also
> order a copy online.
> Measurements are made with pyranometers and the insolation recorded is
> listed in units of peak sun hours. This is an average daily energy delivered
>
> by the sun (averaged over 30 years in the case of the "Red Book"), not an
> instantaneous irradiance measurement.
> I hope this helps.
> Bill.
>
> > -----Original Message-----
> > From: Carl Emerson [mailto:freepower at freepower.co.nz]
> > Sent: Tuesday, September 25, 2001 2:10 PM
> > To: RE-wrenches at topica.com
> > Subject: Re: "Real" Sun Hours [RE-wrenches]
> >
> >
> > Travis,
> >
> > I'll stick my neck out on this one...
> >
> > Real sun hours is very complicated to measure and requires very
> > sophisticated
> > recorders that can integrate the varying insolation levels during
> > the day and
> > come out with an index for 1000 watts/SqM.
> > Very early recorders used a magnifying glass to burn a track in a
> > paper roll and
> > could therefore only record a threshold.
> > Using a C40 might indicate a threshold and you could relate this
> > to a current
> > reading and an insolation level, but this will not be able to account for
> > integrating the intensity variations.
> > Personally I have gone away from using 'sun hours' in my design
> > calculations and
> > use the irradiance data. I find this much more useful and accurate partly
> > because even today the sun hour recordings in our country are
> > useful only to
> > tourists who might want to calculate the gallons of sun cream
> > required for their
> > holiday...
> >
> > "Travis Creswell, Ozark Solar" wrote:
> >
> > > My second question of the day.
> > >
> > > Noticing the high module temps I am seeing even on cool days I
> > am wondering
> > > about the accuracy of Sun Hour numbers.
> > >
> > > I use the DVM on my C40 to make a crude calculation of the
> > daily sun hours I
> > > am getting.  Of course, it's accuracy is questionable and
> > commonly I have
> > > found the C40 DVM's that I've installed to read amps about 10%
> > low.  Voltage
> > > is usually right on.  Mine is no different.  Simply, I divide
> > the rated amps
> > > of my array into the amp hours for that day and that tells me
> > how Sun Hours
> > > I got.   Currently I have only part of my array installed so I
> > only have 7.1
> > > amps (Four Astro power 120's at 48 volts).
> > >
> > > But what I just realized about this number is that it factors
> > everything in,
> > > including a de-rate for heat and actual insolation.  Are these things
> > > already factored in to the commonly published Sun Hours numbers?
> > >
> > > Travis Creswell
> > > Ozark Solar
> > >
> > > - - - -
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> > >
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> >
> > --
> > Regards,
> >
> >
> > Carl Emerson
> > Manager
> > FREEPOWER LTD.  "Harnessing Natural Energy"
> > P.O. Box 10-1207 N.S.M.C. Auckland, NEW ZEALAND.
> > Ph. 09 4275206 fax 09 4275208  cell 021-633999  web www.freepower.co.nz
> >
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