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David,<br>
<br>
Take a close look at the upper and lowers portions of the graphs of the
10-second data and the 1-minute data for Freiburg. <br>
<br>
To make it easier to see, attached is reproduction of their graphs on
one page. Just as fleeting peaks in irradiance (edge of cloud effect)
should be fewer in the 1 minute averages than in the 10 second raw
data; fleeting lows (caused by passing clouds) should be fewer in the 1
minute averages than in the 10-second data. Inspect the graph and label
which you think is 10-second data and which you think is 1-minute data.
Then compare to the original. The two graphs appear to be mislabeled.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
<br>
David Brearley wrote:
<blockquote
cite="mid:C95DB1B9.B552%25david.brearley@solarprofessional.com"
type="cite">
<title>Re: [RE-wrenches] Inverter oversizing</title>
<font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;">Kent, <br>
<br>
The graphs aren’t mislabeled. The one-minute average data has more
granularity, which shows up at the upper limits of the data. It reveals
more peaks over 1,000 W/m2, even in excess of 1,200 W/m2. These values
get compressed into the lower bins in the hourly data.<br>
<br>
The results from the Florianopolis site in Brazil, gives a pretty good
idea of how significantly different the results can be based on
monitoring frequency:<br>
<br>
“Considerable differences emerge when looking at the high end of the
radiation level<br>
Distribution, which shows for the one-minute averages that some 9% of
the daytime <br>
hours present radiation levels ≥ 1000W/m2, with a corresponding energy
content of<br>
some 23%; hourly averages for the same range correspond to around 6% of
daytime <br>
hours, and below 11% of the total energy content. Radiation levels
above 900W/m2 <br>
occur some 16% of the time when looking at one-minute averages, and
below 13% <br>
of daytime hours when using hourly averages, with corresponding energy
fractions <br>
respectively above 38% and 25%.”<br>
<br>
>From the conclusion:<br>
<br>
“we have demonstrated that the estimation of the actual losses due to
inverter<br>
undersizing increases with increased time resolution of the radiation
measurements, <br>
revealing that hourly averages hide important irradiation peaks. In
fact, results with <br>
hourly averages are an experimental artifact, and lead to an estimation
of the solar <br>
energy resource distribution that does not correspond to reality.
Hourly averages of<br>
irradiation values lead to inverter undersizing and the associated
energy losses.”<br>
<br>
Figures 8 & 9 are interesting. You could imagine what these results
would look like if overlaid onto your charts. <br>
<br>
Best, david<br>
<br>
On 1/19/11 8:14 PM, "Kent Osterberg" <<a moz-do-not-send="true"
href="kent@coveoregon.com">kent@coveoregon.com</a>> wrote:<br>
<br>
</span></font>
<blockquote><font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;">David,<br>
<br>
Thanks for sharing that paper. The labeling the graphs for the
10-second and 1-minute data in Freiburg appears to be reversed - the
one minute averaging seems to have more data in all of the bins above
1000 W/sq m. Basically, these graphs show that irradiance observations
above 1100 watts per square meter are fleeting and disappear in hourly
averages. Such occurrences are also masked to a small extent by
1-minute averages.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
<br>
David Brearley wrote: <br>
</span></font>
<blockquote><font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;"> Re: [RE-wrenches] Inverter oversizing This
reminds me of a scholarly article I came across about a year ago while
doing some research. Here’s a link to it if anyone is interested:<br>
<br>
<a class="moz-txt-link-abbreviated" href="http://www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf">www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf</a>
<<a moz-do-not-send="true"
href="http://www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf">http://www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf</a>>
<br>
<br>
David Brearley, Senior Technical Editor<br>
<i>SolarPro</i> magazine <br>
NABCEP Certified PV Installer ™<br>
<a moz-do-not-send="true" href="david.brearley@solarprofessional.com">david.brearley@solarprofessional.com</a><br>
Direct: 541.261.6545<br>
<br>
On 1/19/11 12:29 PM, "Bill Brooks" <<a moz-do-not-send="true"
href="billbrooks7@yahoo.com">billbrooks7@yahoo.com</a>> wrote:<br>
<br>
<br>
</span></font>
<blockquote><font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;"><font color="#1f497d">Kent,<br>
<br>
How often were your data records? To capture edge of cloud effects, you
need one-second data. Not many people gather that fast or that much
data on inverters. I don’t think there is that much energy in these
spikes, but they are real and make some difference. 15-minute average
data will completely wash out this data.<br>
<br>
This is also a deficiency in modeling software since most models are
using hourly data.<br>
<br>
Bill.<br>
<br>
<br>
</font> </span></font><font size="2"><font
face="Tahoma, Verdana, Helvetica, Arial"><span style="font-size: 10pt;"><b>From:</b>
<a moz-do-not-send="true"
href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a moz-do-not-send="true"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Kent Osterberg<br>
<b>Sent:</b> Tuesday, January 18, 2011 1:18 PM<br>
<b>To:</b> Wrenches; Marco Mangelsdorf<br>
<b>Subject:</b> [RE-wrenches] Inverter oversizing<br>
</span></font></font><font face="Times New Roman"><span
style="font-size: 12pt;"> <br>
<br>
Attached is a graph that I produced to document the effect of various
ratios between the PV array size and the inverter size. I extracted
output power data for a 1020-watt system located in NE Oregon that is
on the Sunny Portal <<a moz-do-not-send="true"
href="http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US">http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US</a>>
. The data are publicly accessible so feel free to run your own
analysis. Better yet, analyze the data for a system near you. <br>
<br>
Using 2009 data, I looked at how much energy would have been lost if
the output was clipped at 800W, 810W, .... 1020W. I used 2009 data
because there was a period in 2010 when the Sunny Webbox didn't have
internet access. At 800 watts, power clipping would have happened on
about 25% of the days. Yet the energy that would have been lost was
only 0.38% of the annual total. <br>
<br>
The results shown on this graph aren't universal, results would be a
little different in 2010, it would be different in some other climate,
it would have been different at another elevation, it would be
different with a different array angle, ..., and the module tolerance
and inverter efficiency also effect the results. Modules in this
system are Suntech 170-watt +/-3%. The inverter is Sunnyboy 1800 that
should be operating at close to 93% efficiency.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar. Inc.<br>
<br>
<br>
</span></font></blockquote>
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style="font-size: 10pt;"><br>
</span></font></font><font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;">David Brearley, Senior Technical Editor<br>
<i>SolarPro</i> magazine <br>
NABCEP Certified PV Installer ™<br>
<a moz-do-not-send="true" href="david.brearley@solarprofessional.com">david.brearley@solarprofessional.com</a><br>
Direct: 541.261.6545<br>
Fax: 541.512.0343<br>
<b><br>
</b>Visit our Web site at solarprofessional.com<br>
<br>
(Sample copy available for download at: solarprofessional.com/sample)<br>
<br>
<br>
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