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This is an intriguing idea (using PV output as a surrogate for
irradiance), but there are a number of complications that need to be
investigated:<br>
1. PV efficiency degrades with temperature; therefore, you have to
have some way to adjust the output by the temperature of the PV (not
the air temperature)<br>
2. you also need to adjust for the tilt and azimuth of the PV panels
to derive the equivalent global horizontal radiation.<br>
3. you also need to split the global horizontal into direct and
diffuse radiation, which could be done using a number of
direct/diffuse split models, which is what's done for 99% of the
weather files anyway because I've yet to find any measured direct
normal radiation outside of strictly research applications.<br>
<br>
When I look at this list, all three could be done using a building
energy simulation program, provided that you know the absorptivity
of the PV and its conversion efficiency as a function of
temperature, but at this point it's getting more hairy than
calculating the solar radiation from standard weather station data
or, beginning in Sept 2015 for US locations, downloading the solar
radiation from NREL. <br>
<br>
I'm not being critical, and actually I am quite intrigued by this
technique, and would be happy to help evaluate how well it works.<br>
<br>
Joe<br>
<br>
<pre class="moz-signature" cols="72">Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
<a class="moz-txt-link-abbreviated" href="mailto:yjhuang@whiteboxtechnologies.com">yjhuang@whiteboxtechnologies.com</a>
<a class="moz-txt-link-freetext" href="http://weather.whiteboxtechnologies.com">http://weather.whiteboxtechnologies.com</a> for simulation-ready weather data
<a class="moz-txt-link-freetext" href="http://www.whiteboxtechnologies.com">http://www.whiteboxtechnologies.com</a>
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
</pre>
<div class="moz-cite-prefix">On 7/21/2015 2:21 AM, Justin Spencer
wrote:<br>
</div>
<blockquote
cite="mid:CAB+zL_=fgoJVJqK3H=M6XewfewtR+D-+38Smhy0eKq_wd2ywMA@mail.gmail.com"
type="cite">
<div dir="ltr">You can use anything you want as a surrogate, as
long as you have some way of proving it works. In this case, if
you could somehow get real time PV data for a set of sites that
also had actual insolation and then looked at your results, I
think you could derive a typical relationship that wouldn't lead
you too far astray. The problem will come when there are passing
clouds and the PV system is "hunting" all the time trying to
catch up with the changing insolation. I bet you could find
those and apply a bias correction that could then be used in
multiple sites with real time PV data. </div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Jul 20, 2015 at 10:55 AM, Chris
Yates <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:chris.malcolm.yates@gmail.com"
target="_blank">chris.malcolm.yates@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<p dir="ltr">Ok, so there's no substitute for doing weather
data right.</p>
<p dir="ltr">However, in the absence of such data, could
real-time pv yield be used as a surrogate?</p>
<p dir="ltr">Chris </p>
<p dir="ltr">Sent from my Android device. Please excuse
typos, etc.</p>
<br>
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