MX60 question [RE-wrenches]

Christopher Freitas --- OutBack Power cfreitas at outbackpower.com
Tue Sep 21 17:11:32 PDT 2004


 

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sunwise wrote:
> Can you explain the partial shading a little better?  

Performance of a partially shaded PV array is extremely variable - it 
depends on the specific wiring configuration and even the orientation of 
the modules themselves.  

The paritally shaded condition I was referring to as being improved by 
having a higher than normal PV array voltage being stepped down by a 
MX60 is one in which the multiple sets of series connected panels are 
getting similar shading on each individual panel or series set.  

The situation most of us are familar with is one were you shade 20% or 
so of the PV panel and the output drops 80% - this is caused by the 
panels Vmp (voltage at max power) being lower than the battery's voltage 
it is charging - you "fall" off the power curve due to the shading of a 
few cells.  When you start with a peak power point 2 or three times that 
of the battery voltage and a MPPT type controller which can also do 
step-down, then shading 20% of the PV array reduces the output by around 
20% instead.  

Of course things in the real world are never that simple... We are 
planning to use our matched PV arrays here at OutBack to do some testing 
of different shading conditions to see what the impacts are... stay 
tuned again!  

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  

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