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

[Bill Brooks]

Mike,

You must be using June average irradiation for your estimate of 6 sun hours
(kwh/m^2-day). New Jersey averages about 4.5 sun hours a day. Also, the 77%
that you quote from PVWATTS is not correcting for irradiance as you have in
your estimate. If you look at the rundown on the PVWATTS standard
reductions, you have only included a few of the factors. 77% is a little on
the conservative side for typical PV systems, but only slightly. It is a
good conservative estimate.

Output Power = STC module ratings x 0.77 x irradiance adjustment x temp
adjustment (if more than 45C). PV modules can get up to 70C on hot days even
in New Jersey.

Bill.



-----Original Message-----
From: Michael Gullo [mailto:mgullo3 at comcast.net] 
Sent: Friday, July 07, 2006 6:54 PM
To: RE-wrenches at topica.com
Subject: Re: Usable AC power from Grid-Tied Systems [RE-wrenches]



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


- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address:
www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com


- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------