Title: Re: [RE-wrenches] Inverter oversizing
David,
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.
Kent Osterberg
Blue Mountain Solar, Inc.
David Brearley wrote:
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:
www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf
David Brearley, Senior Technical Editor
SolarPro magazine
NABCEP Certified PV Installer ™
david.brear...@solarprofessional.com
Direct: 541.261.6545
On 1/19/11 12:29 PM, "Bill Brooks" <billbroo...@yahoo.com> wrote:
Kent,
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.
This is also a deficiency in modeling software since most models are
using hourly data.
Bill.
From:
re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org]
On Behalf Of Kent Osterberg
Sent: Tuesday, January 18, 2011 1:18 PM
To: Wrenches; Marco Mangelsdorf
Subject: [RE-wrenches] Inverter oversizing
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 <http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US>
. The data are publicly accessible so feel free to run your own
analysis. Better yet, analyze the data for a system near you.
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.
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.
Kent Osterberg
Blue Mountain Solar. Inc.
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