Usable AC power from Grid-Tied Systems [RE-wrenches]

[Michael Gullo]

Jeremy,

Output power = array power x irradiance x module tolerance and  
mismatch x array temperature x wiring efficiency x inverter efficiency

irradiance at peak sun is 1000 W/m2 although instantaneous measurement requires the use of a pyranometer to determine watts/m2. If on that clear day the  
irradiance was 900W/m2, your factor is 90%.

module tolerances between the modules vary between 5-10%. Let's use 7%

array temperature is critical. Here in South Jersey (where Tony Soprano dumps the bodies in the pinelands), temps are in the 80s which means that the module  
temperature on the roof is about 45 degrees C. Since modules are  
rated at 25 degrees C, there is a negative temperature coefficient  
of -.5%/C, which translates to a 10% reduction in  
power due to temp.

wiring efficiency is 98%

inverter efficiency is 94%

Therefore:

  Output power = 2880 x 1 x .93 x .9 x .98 x .94 = 2221 W
  Daily power  = 2221 x 6 = 13.326 kWh

This is around 77% which agrees with the NJ State PVWatts estimator.

Mike
Michael Gullo
Solar Solutions LLC
Marlton, NJ

----------------------------------------------------------------------------------------
Wrenches, 
Can those experienced in grid tie system installation and monitoring 
give some input? How much power can you expect to get out of a system 
daily? Example: 2880wpv, 6 peak annual sun hours per day, Fronius IG 
3000 inverter. Is 80% a realistic conversion efficiency?

Thanks!

Jeremy
All Solar
CO, USA


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