[RE-wrenches] Enphase derate (was Tilt biased....)

Sun Apr 18 04:32:10 PDT 2010

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
 <mailto:Allan at positiveenergysolar.com> 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
 <http://www.positiveenergysolar.com/> www.positiveenergysolar.com

 <mailto:holtek at sbcglobal.net> 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
 <http://www.holteksolar.com> www.holteksolar.com

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