[RE-wrenches] PVWatts Module Temperature Coefficient (was Enphase derate)

[Joel Davidson]

Wrenches,
PVWatts does not accurately predicate Unisolar and Sunpower module performance because it uses a generic single crystal silicon solar module power temperature coefficient (I think -0.4% per degree C). Does someone have the technical paper that specifies PVWatts module temperature coefficient? Thank you.
Joel Davidson

  ----- Original Message ----- 
  From: Kirk Herander, VSE 
  To: 'RE-wrenches' 
  Sent: Sunday, April 18, 2010 4:32 AM
  Subject: [RE-wrenches] Enphase derate (was Tilt biased....)


  Enphase has a tech note pdf for download that recommends and rationalizes a PV watts derate of .819 instead of the standard .77 (which IMO is a little conservative to begin with). 

   

  http://www.enphaseenergy.com/downloads/EnphaseAppNote_PVWatts.pdf

   

   

   

  Kirk Herander

  Vermont Solar Engineering

  802.863.1202  fax 802.863.7908

  VT RE Incentive Program  Partner

  NYSERDA Incentive-eligible Partner

  NABCEPTM    Certified Installer

   

  From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
  Sent: Sunday, April 18, 2010 3:18 AM
  To: RE-wrenches
  Subject: Re: [RE-wrenches] Tilt biased....

   

  Holt,
  Feedback re the low tilt angle: Go for it, you're good.

  Re wind loading: check out UniRac's Code Compliant Installation Manual, http://www.unirac.com/pdf/ii227.pdf, especially pages 3-9.

  Less wind loading is one of the main reasons for going with a lower tilt angle. Another is closer module row spacing (at 3X height RoT) without inter-row shading.

  No experience with Enphase.
  Allan

  Allan Sindelar
  Allan at positiveenergysolar.com
  NABCEP Certified Photovoltaic Installer
  EE98J Journeyman Electrician
  Positive Energy, Inc.
  3201 Calle Marie
  Santa Fe, New Mexico 87507
  505 424-1112
  www.positiveenergysolar.com



  holtek at sbcglobal.net wrote: 

  Searching for opinions.....is this "over design"?

  Designing small system (2.35kW). Customer uses gas for heating. Typical A/C unit. I was thinking of biasing the tilt to summer production for greater offset of summer demand (lat 31.6, proposing 18). No net metering in this part of the world. PVwatts shows a drop of 2% /yr. in production , 5% higher production for A/C months. Feedback?

   

   Also, this array will go on a carport. I understand that windloading is actually greater for an open structure than one with walls (another reason for lower tilt) - is there any one that can direct me to data on finding out how much more? 

   

  Lastly, what is a good avg. target derate factor for Enphase inverters (real world)?

   

  Holt E. Kelly
  Holtek Fireplace & Solar Products
  500 Jewell Dr.
  Waco TX. 76712
  254-751-9111
  www.holteksolar.com

 
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