[RE-wrenches] Inverter oversizing

[David Brearley]

This reminds me of a scholarly article I came across about a year ago while
doing some research. Here¹s 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.brearley at solarprofessional.com
Direct: 541.261.6545

On 1/19/11 12:29 PM, "Bill Brooks" <billbrooks7 at 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 don¹t 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-a3
> 47-48fb-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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