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: [email protected] [mailto:[email protected]] 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 [email protected] NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com [email protected] 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 ------------------------------------------------------------------------------ _______________________________________________List sponsored by Home Power magazine List Address: [email protected] Options & settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette:www.re-wrenches.org/etiquette.htm Check out participant bios:www.members.re-wrenches.org ------------------------------------------------------------------------------ _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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