PV power tolerance [RE-wrenches]

[Bill Brooks]

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Graham,

Not sure where the number 76% came from (maybe in the UK this is common),
but I think that would be for a VERY poorly designed system in the U.S. Not
to say that we don't have a plethora of them in the field, but a
well-designed system should have an Average Annual Efficiency of between
85-90%. It is very difficult to break the 90% barrier with 94% peak
efficient inverters. There is lots of U.S. data to back up these numbers.

Bill.

-----Original Message-----
From: Graham Owen [mailto:graham at solarexpert.com]
Sent: Monday, October 11, 2004 11:08 AM
To: RE-wrenches at topica.com
Subject: RE: PV power tolerance [RE-wrenches]

Hi Dan,

Peak PV inverter efficiencies from various manufacturers run in the low
to mid 90% range for inverter loads between 30% and 100%.  But this is
not the entire picture of inverter efficiency.  There is an overall
inverter efficiency which is calculated as the average inverter output /
average PV output; overall inverter efficiency varies over time from a
high of around 76% to, of course, a low of near zero (night-time).  This
web site research from a University in Glasgow, England, may be of
interest; 4-pages in length:

http://www.esru.strath.ac.uk/EandE/Web_sites/98-9/grid_connected_pv/s_op
tim.htm

Note the suggestion that undersizing inverters as well as multiple
inverters may be the most economical approach when designing PV systems.

Best regards,
Graham

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