Re: [RE-wrenches] Module Degradation - voltage or current?
Thanks for the info everyone. Bill's Solar Pro article notes that min Vmp on inverters is affected by grid voltage. Is that universally true or just for some inverters? Does that mean that models that work on 240VAC and 208VAC have different min Vmp? I rarely see inverter DC input specs listed differently for different AC voltages. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com d...@ecotechenergy.com 360.318.7646 On Wed, Jun 4, 2014 at 3:53 PM, Bill Brooks billbroo...@yahoo.com wrote: Folks, Voc does not degrade as much as Isc, but neither is key. Both Vmp and Imp degrade. We call this a degradation of Fill Factor. This happens with all PV systems and the degradation rates for current and voltage are very similar. Imp and Isc degrade because less light gets to the cell from etching glass, yellowing encapsulant and IR coating on cells changing. Vmp changes because of increased contact resistance of conductors on the cells and other contact points. Voc is unimpacted by contact resistance since there is no current flow. Bill. *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Ray Walters *Sent:* Wednesday, June 04, 2014 11:30 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Module Degradation - voltage or current? I agree that Voc doesn't seem to degrade as much. I've had a chance to measure several modules over 20 years old, and the Voc is only dropping about 1/2 the rate suggested by others here. I think a more appropriate number might be 0.25% V drop/ year. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 6/4/2014 11:36 AM, Nathan Charles wrote: So I read this paper, Smith, R. M., Jordan, D. C., Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. Thoughts from other wrenches? On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer suneng...@gmail.com wrote: Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com d...@ecotechenergy.com 360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 suneng...@gmail.com bhof...@sunergyengineeringservices.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change
Re: [RE-wrenches] Module Degradation - voltage or current?
So I read this paper, Smith, R. M., Jordan, D. C., Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. Thoughts from other wrenches? On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer suneng...@gmail.com wrote: Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com d...@ecotechenergy.com 360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 suneng...@gmail.com bhof...@sunergyengineeringservices.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Module Degradation - voltage or current?
Bill and all, Dana asked for good conservative data for long-term performance. This is not necessarily what you would use when you are trying to make yourself look as good as possible for a financier. The real question is, where did this data come from confirming lower losses? It takes about 7-10 years of data to establish a degradation rate. The newer data is based on an NREL study that was released several years ago. This means that the study was based on modules manufactured in the U.S., Japan, and Germany with very few Chinese or other Asian origins. The numbers may have improved-or they could be worse. Ultimately, if you do not have long term data on any module (which you clearly don't) any assumption about voltage or current degradation is a guess at best. Figures lie and liars figure. Cynicism in this area is a positive character trait. Bill. From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bill Hoffer Sent: Tuesday, June 03, 2014 9:00 PM To: RE-wrenches Subject: Re: [RE-wrenches] Module Degradation - voltage or current? Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com mailto:d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Module Degradation - voltage or current?
If it modules not diodes which will give you different issues, no voc change but a combination with less power at 25c best to use a iv curve tool like the solmetric product very cool and printable On Jun 4, 2014 10:36 AM, Nathan Charles nchar...@paradiseenergysolutions.com wrote: So I read this paper, Smith, R. M., Jordan, D. C., Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. Thoughts from other wrenches? On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer suneng...@gmail.com wrote: Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com d...@ecotechenergy.com 360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 suneng...@gmail.com bhof...@sunergyengineeringservices.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Module Degradation - voltage or current?
I agree that Voc doesn't seem to degrade as much. I've had a chance to measure several modules over 20 years old, and the Voc is only dropping about 1/2 the rate suggested by others here. I think a more appropriate number might be 0.25% V drop/ year. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 6/4/2014 11:36 AM, Nathan Charles wrote: So I read this paper, Smith, R. M., Jordan, D. C., Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. Thoughts from other wrenches? On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer suneng...@gmail.com mailto:suneng...@gmail.com wrote: Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com mailto:d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com http://www.ecotechenergy.com d...@ecotechenergy.com mailto:d...@ecotechenergy.com 360.318.7646 tel:360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org http://www.members.re-wrenches.org -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 suneng...@gmail.com mailto:bhof...@sunergyengineeringservices.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org http://www.members.re-wrenches.org -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette:
Re: [RE-wrenches] Module Degradation - voltage or current?
Folks, Voc does not degrade as much as Isc, but neither is key. Both Vmp and Imp degrade. We call this a degradation of Fill Factor. This happens with all PV systems and the degradation rates for current and voltage are very similar. Imp and Isc degrade because less light gets to the cell from etching glass, yellowing encapsulant and IR coating on cells changing. Vmp changes because of increased contact resistance of conductors on the cells and other contact points. Voc is unimpacted by contact resistance since there is no current flow. Bill. From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Wednesday, June 04, 2014 11:30 AM To: RE-wrenches Subject: Re: [RE-wrenches] Module Degradation - voltage or current? I agree that Voc doesn't seem to degrade as much. I've had a chance to measure several modules over 20 years old, and the Voc is only dropping about 1/2 the rate suggested by others here. I think a more appropriate number might be 0.25% V drop/ year. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 6/4/2014 11:36 AM, Nathan Charles wrote: So I read this paper, Smith, R. M., Jordan, D. C., Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. Thoughts from other wrenches? On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer suneng...@gmail.com mailto:suneng...@gmail.com wrote: Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com mailto:d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com http://www.ecotechenergy.com d...@ecotechenergy.com mailto:d...@ecotechenergy.com 360.318.7646 tel:360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org http://www.members.re-wrenches.org -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 suneng...@gmail.com mailto:bhof...@sunergyengineeringservices.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org http://www.members.re-wrenches.org -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re
Re: [RE-wrenches] Module Degradation - voltage or current?
Read this article from SolarPro: “Array Voltage Considerations”, SolarPro Magazine, October/November 2010, pp 68-78. Bill. From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dana Brandt Sent: Tuesday, June 03, 2014 3:42 PM To: RE-wrenches Subject: [RE-wrenches] Module Degradation - voltage or current? Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com http://www.ecotechenergy.com d...@ecotechenergy.com mailto:d...@ecotechenergy.com 360.318.7646 --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Module Degradation - voltage or current?
Dana, Excellent question. More than 20 years of PV degradation research conducted by NREL and others has shown the dominant loss to be in the Isc and fill-factor aspects of PV performance due to increasing effective series resistance. Voc stays essentially stable over the life of the PV module. Vmp will decrease over time depending on the severity of the impact on fill factor. With 0.5% average annual degradation in PV wattage, and attributing [say] 80% of the wattage reduction to a decrease in current, the balance of the difference would be a reduction in Vmp. A copy of one such study is here. www.nrel.gov Document: Photovoltaic Degradation Rates - An Analytical Review By: Dirk C. Jordan and Sarah R. Kurtz Journal Article NREL/JA-5200-51664, June 2012 Contract No. DE-AC36-08GO28308 Dan Lepinski On Tue, 6/3/14, Dana Brandt d...@ecotechenergy.com wrote: Subject: [RE-wrenches] Module Degradation - voltage or current? To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Tuesday, June 3, 2014, 5:41 PM Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com d...@ecotechenergy.com 360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Module Degradation - voltage or current?
Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt d...@ecotechenergy.com wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com d...@ecotechenergy.com 360.318.7646 ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 suneng...@gmail.com bhof...@sunergyengineeringservices.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
