[RE-wrenches] Inverter oversizing

[Bill Brooks]

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-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at 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&splan
g=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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