[RE-wrenches] Inverter oversizing

[drake.chamberlin at redwoodalliance.org]

> I have REC 215 on Enphase 190.  I see a lot of clipping.  Every sunny
> day in the
> winter and spring.

What angle is your array?  Where is it located?

What I am seeing may be regionally specific.  I have seen some clipping,
but usually the inverters have some overhead left from the 199 W limit.

With the 30 degree angle, even on sunny days with snow on the ground the
inverters max out it the high 180s.  On another system in the area (with a
string inverter)the roof pitch is 45 degrees.  The array can peg the
inverter on those days.  The inverter and the STC rating of the modules
are a perfect match.




>
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>
>
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> ________________________________
> From: Drake <drake.chamberlin at redwoodalliance.org>
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> Sent: Thu, January 20, 2011 8:23:55 AM
> Subject: Re: [RE-wrenches] Inverter oversizing
>
> On a couple of Enphase systems I monitor regularly, the modules are
> oversized
> compared to the inverters.  One system has Sharp 224 W modules and M-190s
> (capable of producing 199 W).  The array is a ground mount at a 30 degree
> tilt
> at 39+ degrees latitude. 
>
>
> When the system was new in the autumn, I noticed two days of some
> clipping. 
> Since then, none.  In the summer, when the sun angle is better, the heat
> will
> keep the wattage down so clipping will very seldom occur.  The modules
> will not
> be close to STC, so the inverters should not be pushed to their maximum.
>
> The same is true of string inverters.  Since real power of the modules in
> generally significantly below the nameplate, inverters will generally not
> run at
> maximum power.   When we take in all the factors affecting the actual
> array
> power, I think that 120% over sizing from nameplate wattage is generally
> safe.
>
>
> Drake
>
>
> At 09:14 PM 1/19/2011, you wrote:
>
> 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.
>>Â 
>>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 â„¢
>>>david.brearley at solarprofessional.com
>>>Direct: 541.261.6545
>>>
>>>On 1/19/11 12:29 PM, "Bill Brooks" <billbrooks7 at yahoo.com> wrote:
>>>
>>>
>>>Kent,
>>>
>>>
>>>Â 
>>>
>>>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.
>>>
>>>Â 
>>>
>>>This is also a deficiency in modeling software since most models are
>>> using
>>>hourly data.
>>>
>>>Â 
>>>
>>>Bill.
>>>
>>>Â 
>>>
>>>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&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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