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

Dave Click daveclick at fsec.ucf.edu
Mon Apr 19 07:01:32 PDT 2010


It seems to be -0.5%/degC:
http://rredc.nrel.gov/solar/calculators/PVWATTS/moreabout.html


-------- Original Message --------
Subject: [RE-wrenches] PVWatts Module Temperature Coefficient (was 
Enphase derate)
From: Joel  Davidson <joel.davidson at sbcglobal.net>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Date: 2010/4/18 12:23

> 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 <mailto:kirk at vtsolar.com>
>     *To:* 'RE-wrenches' <mailto:re-wrenches at lists.re-wrenches.org>
>     *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
>
>     NABCEP^TM 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_ <mailto: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_ <http://www.positiveenergysolar.com/>
>
>
>
>     _holtek at sbcglobal.net_ <mailto: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_ <http://www.holteksolar.com>
>
>
>
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