Re: [RE-wrenches] calculating low string voltage
At an SMA training last year they recommended the following temperature adders: Open field: +22°C Rooftop, lots of ventilation: +28°C Rooftop, some ventilation: +29°C Rooftop, little ventilation: +32°C Rooftop BIPV, no ventilation: +43°C Façade, some ventilation: +35°C Façade, little ventilation: +39°C Façade BIPV, no ventilation: +55°C For your Sanyo project, I'd agree that the pole mount would be a good fit and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter with a 300V+ tracking window wouldn't work very well during the summers for very long. My own rooftop system has a design VMP of around 294 at 70C module temperature and I've seen it a bit lower than that on a sunny day-- I think it's because in irradiances below 1000Wm/2, the modules can still get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. So all told, maybe plan for an array minimum of: Inverter Tracking Minimum /0.85 (degradation and voltage tolerance) /0.95 (effect I just described) /0.825 (60C operating temp) = minimum string VMP at STC (similar to what Bill said) On 2011/11/30 11:04, Kirk Herander wrote: Thanks for all the good response. Speaking of monkey wrenches, these are Sanyo HIT Double panels, mounted on a rack which is 5 ½ feet above the roof surface. They will absorb reflected light on the backside, so I assume the cells will operate at a higher temp. But they are elevated enough to simulate a pole-mount, thus lowering operating cell temp. So what operating temp to use? If I use 25 C as the operating temp, the low voltage calc comes out to 301 vdc (inverter min is 300 – using SMA US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel string. Unfortunately I really don’t want to use 7 panel strings due to the layout. If I used a US7000 it would work since min vdc in is 250. However the inverters are part of a SunnyTower and I can’t swap a 7000 for an 8000 without voiding the Tower UL listing. Kirk Herander VT Solar, LLC dba Vermont Solar Engineering NABCEP^TM Certified installer Charter Member NYSERDA-eligible Installer VT RE Incentive Program Partner *From:*re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *b...@midnitesolar.com *Sent:* Wednesday, November 30, 2011 1:03 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] calculating low string voltage If you really want to throw a monkey wrench into the mix, bring up partial shading... Or, maybe that's just not allowed in that debate ?? Just a thought. boB On 11/29/2011 8:39 PM, Kent Osterberg wrote: Kirk, You've got some good feedback on this from Ray and Bill. I'll try to add a little more. Most module datasheets show a normal operating cell temperature, NOCT, value that's typically 47.5°C. That's 20°C ambient temperature, 800 W/sq m, and calm wind and nothing blocking the airflow on the back of the module. That 27.5°C temperature rise should be pretty close to the temperature rise that occurs for a pole-top mount. It's common to see people use 25°C for modules on a pole and 30°C or 35°C on a roof and there are data that support these typical values. With 1000 W/sq irradiance, the temperature rise can obviously be more too. Between the intensity of the sun, the direction of the sun, the color of the roof, the spacing off the roof, and the wind speed there is a lot that is different from one system to the next or even one day to the next. Most PV module spec sheets don't give you a temperature coefficient for Vmp. I've seen people use the the Voc coefficient, usually expressed as a percentage, for both Voc and Vmp. Big mistake. Data from NREL indicates as Bill said, the temperature coefficient for Vmp is higher than that the temperature coefficient for Voc. That's particularly true when the coefficient is expressed as a percentage per °C. Since there are very few manufacturer's that give both temperature coefficients, I'll use a value from an old Evergreen module for an example. The Evergreen ES-195 datasheet shows Voc = 30.5 volts with a coefficient of -0.34%/°C and Vmp = 27.1 volts with a coefficient of -0.47%/°C. Since one shouldn't add volts and percents, I'll put the temperature coefficients in volts/°C: Voc = 30.5 V - 0.10 V/°C and Vmp = 27.1 V - 0.13V/°C. So Vmp is moving faster than Voc, but not a lot faster. That's generically true for c-Si or poly-Si. Kent Osterberg Blue Mountain Solar, Inc. www.bluemountainsolar.com http://www.bluemountainsolar.com t: 541-568-4882 On 11/29/2011 11:48 AM, Kirk Herander wrote: I am in debate with a PE over calculation of low voltage of a series string on a hot day. He insists that an arbitrary high cell temp is factored in, not just ambient temperature. Could someone please give an accepted formula for this calculation? Thanks. I cannot find a clear reference to low voltage calculation on a hot day (but every reference material is clear on how to calculate high voltage on a cold
Re: [RE-wrenches] Diversion load for AC coupled system
At 12:16 -0700 30/11/11, Larry Crutcher, Here's a scenario: Sun is up and voltage rises slowly to the diversion controller set point. PWM starts and maintains the voltage. Current continues to increase but the load is keeping the voltage constant until the controller is overloaded. I think the point that most people don't get is that you can't overload the controller if you choose the correct dump load. You can get to the point where the dump load is fully turned on (100% duty cycle) and then it is 'overloaded' in the sense that it has not further ability to limit the rise in voltage. However it will not be damaged. Then the voltage will rise further and hopefully another controller will start dumping or something good will happen to protect the batteries from damage. If you have 2 controllers with dump loads that can handle 150% of the incoming PV current between them then you can be sure of never 'overloading' them. But it will not matter if you 'overload' one before the other comes on because it will never draw more current than the dump load takes at the prevailing voltage. Here is a calculation: 3.8 kW at float voltage 54 volts gives 3800/54 = 70.4 amps. According to NEC you multiply this by 1.5 to get 106 amps. Now you need to choose dump loads that will each dump at least 53 amps at 54 volts. (1.02 ohms, maybe one ohm plus resistance of leads.) These will be the same loads as will do 60 amps at 61 volts and they are the lowest resistance you can safely use with the TS60. If you plan to EQ at voltages higher than 61 then you need to use higher resistance and you cannot meet the NEC target of 150% of incoming current at float voltages. That's how I see it anyway. It's possible that the NEC thing does not required you to look at float voltage. all the best, -- Hugh Piggott Scoraig http://www.scoraigwind.co.uk ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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
[RE-wrenches] OutBack Radian
Hi all, We are looking at a busy winter season and there are several systems I'd like to size using OutBack's Radian. These are all out of the country jobs and I would be interested in any experiences anyone has had so far installing and/or using these seemingly great inverters. I would likely be using them in HBX mode, so secondary inquiries would be around susing the Mate3. Is it any more intuitive than the Mate? Similar in programming? Any thoughts from anyone with experience with Radian systems would be greatly appreciated. Thanks, Daryl DeJoy NABCEP Certified PV installer Penobscot Solar Design ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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
Re: [RE-wrenches] OutBack Radian
Daryl, We have not had any hands on experience yet with the Radian series inverters, and only minimal interaction with the MATE3. But since you mentioned that your systems would be out of country I thought I would bring up the fact that the Radian inverters only come in 60Hz models, no 50Hz output available. Orion Thornton Project Manager Independent Power Systems NABCEP Certified PV Installer (Office) 406.587.5295 (Mobile) 406.249.9912 www.solarips.com -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of penobscotso...@midmaine.com Sent: Thursday, December 01, 2011 12:25 PM To: RE-wrenches Subject: [RE-wrenches] OutBack Radian Hi all, We are looking at a busy winter season and there are several systems I'd like to size using OutBack's Radian. These are all out of the country jobs and I would be interested in any experiences anyone has had so far installing and/or using these seemingly great inverters. I would likely be using them in HBX mode, so secondary inquiries would be around susing the Mate3. Is it any more intuitive than the Mate? Similar in programming? Any thoughts from anyone with experience with Radian systems would be greatly appreciated. Thanks, Daryl DeJoy NABCEP Certified PV installer Penobscot Solar Design ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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: RE-wrenches@lists.re-wrenches.org 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
Re: [RE-wrenches] calculating low string voltage
That's more detailed info, but I still am wondering what ambient temp to apply (which AHSRAE #) with the temp adder. Daryl suggested using a 2% high temp. Also, where are you all getting your weather data? I found the NEC suggested ASHRAE manual to be close to $200. That's a bit much just to get a couple of numbers for our design. It seems this calculation of low voltage is far from being entirely codified, and I'm trying to standardize it somewhat for my PV class. Non of the design manuals I have currently are even close to this level of complexity, yet this is obviously an important calculation. Should I suggest that my students just use the inverter manufacturers' online tools, and forget about trying to run this voltage calc themselves? Thanks, Ray On 12/1/2011 6:30 AM, Dave Click wrote: At an SMA training last year they recommended the following temperature adders: Open field: +22°C Rooftop, lots of ventilation: +28°C Rooftop, some ventilation: +29°C Rooftop, little ventilation: +32°C Rooftop BIPV, no ventilation: +43°C Façade, some ventilation: +35°C Façade, little ventilation: +39°C Façade BIPV, no ventilation: +55°C For your Sanyo project, I'd agree that the pole mount would be a good fit and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter with a 300V+ tracking window wouldn't work very well during the summers for very long. My own rooftop system has a design VMP of around 294 at 70C module temperature and I've seen it a bit lower than that on a sunny day-- I think it's because in irradiances below 1000Wm/2, the modules can still get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. So all told, maybe plan for an array minimum of: Inverter Tracking Minimum /0.85 (degradation and voltage tolerance) /0.95 (effect I just described) /0.825 (60C operating temp) = minimum string VMP at STC (similar to what Bill said) On 2011/11/30 11:04, Kirk Herander wrote: Thanks for all the good response. Speaking of monkey wrenches, these are Sanyo HIT Double panels, mounted on a rack which is 5 ½ feet above the roof surface. They will absorb reflected light on the backside, so I assume the cells will operate at a higher temp. But they are elevated enough to simulate a pole-mount, thus lowering operating cell temp. So what operating temp to use? If I use 25 C as the operating temp, the low voltage calc comes out to 301 vdc (inverter min is 300 – using SMA US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel string. Unfortunately I really don’t want to use 7 panel strings due to the layout. If I used a US7000 it would work since min vdc in is 250. However the inverters are part of a SunnyTower and I can’t swap a 7000 for an 8000 without voiding the Tower UL listing. Kirk Herander VT Solar, LLC dba Vermont Solar Engineering NABCEP^TM Certified installer Charter Member NYSERDA-eligible Installer VT RE Incentive Program Partner *From:*re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *b...@midnitesolar.com *Sent:* Wednesday, November 30, 2011 1:03 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] calculating low string voltage If you really want to throw a monkey wrench into the mix, bring up partial shading... Or, maybe that's just not allowed in that debate ?? Just a thought. boB On 11/29/2011 8:39 PM, Kent Osterberg wrote: Kirk, You've got some good feedback on this from Ray and Bill. I'll try to add a little more. Most module datasheets show a normal operating cell temperature, NOCT, value that's typically 47.5°C. That's 20°C ambient temperature, 800 W/sq m, and calm wind and nothing blocking the airflow on the back of the module. That 27.5°C temperature rise should be pretty close to the temperature rise that occurs for a pole-top mount. It's common to see people use 25°C for modules on a pole and 30°C or 35°C on a roof and there are data that support these typical values. With 1000 W/sq irradiance, the temperature rise can obviously be more too. Between the intensity of the sun, the direction of the sun, the color of the roof, the spacing off the roof, and the wind speed there is a lot that is different from one system to the next or even one day to the next. Most PV module spec sheets don't give you a temperature coefficient for Vmp. I've seen people use the the Voc coefficient, usually expressed as a percentage, for both Voc and Vmp. Big mistake. Data from NREL indicates as Bill said, the temperature coefficient for Vmp is higher than that the temperature coefficient for Voc. That's particularly true when the coefficient is expressed as a percentage per °C. Since there are very few manufacturer's that give both temperature coefficients, I'll use a value from an old Evergreen module for an example. The Evergreen ES-195 datasheet shows Voc = 30.5 volts with a coefficient of -0.34%/°C and Vmp = 27.1 volts with a coefficient of -0.47%/°C. Since one
Re: [RE-wrenches] calculating low string voltage
Ray: Look at Appendix F in the Expedited Permit Process for PV Systems - A Standardized Process for the Review of Small-Scale PV Systems Prepared by Bill Brooks, P.E. Brooks Engineering This document provides the ASHRE temperatures for a lot of locations around the USA. http://www.solarabcs.org/about/publications/reports/expedited-permit/pdfs/Expermitprocess.pdf Regards, Gary Willett, PE On 12/1/2011 14:48, Ray Walters wrote: That's more detailed info, but I still am wondering what ambient temp to apply (which AHSRAE #) with the temp adder. Daryl suggested using a 2% high temp. Also, where are you all getting your weather data? I found the NEC suggested ASHRAE manual to be close to $200. That's a bit much just to get a couple of numbers for our design. It seems this calculation of low voltage is far from being entirely codified, and I'm trying to standardize it somewhat for my PV class. Non of the design manuals I have currently are even close to this level of complexity, yet this is obviously an important calculation. Should I suggest that my students just use the inverter manufacturers' online tools, and forget about trying to run this voltage calc themselves? Thanks, Ray On 12/1/2011 6:30 AM, Dave Click wrote: At an SMA training last year they recommended the following temperature adders: Open field: +22°C Rooftop, lots of ventilation: +28°C Rooftop, some ventilation: +29°C Rooftop, little ventilation: +32°C Rooftop BIPV, no ventilation: +43°C Façade, some ventilation: +35°C Façade, little ventilation: +39°C Façade BIPV, no ventilation: +55°C For your Sanyo project, I'd agree that the pole mount would be a good fit and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter with a 300V+ tracking window wouldn't work very well during the summers for very long. My own rooftop system has a design VMP of around 294 at 70C module temperature and I've seen it a bit lower than that on a sunny day-- I think it's because in irradiances below 1000Wm/2, the modules can still get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. So all told, maybe plan for an array minimum of: Inverter Tracking Minimum /0.85 (degradation and voltage tolerance) /0.95 (effect I just described) /0.825 (60C operating temp) = minimum string VMP at STC (similar to what Bill said) On 2011/11/30 11:04, Kirk Herander wrote: Thanks for all the good response. Speaking of monkey wrenches, these are Sanyo HIT Double panels, mounted on a rack which is 5 ½ feet above the roof surface. They will absorb reflected light on the backside, so I assume the cells will operate at a higher temp. But they are elevated enough to simulate a pole-mount, thus lowering operating cell temp. So what operating temp to use? If I use 25 C as the operating temp, the low voltage calc comes out to 301 vdc (inverter min is 300 – using SMA US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel string. Unfortunately I really don’t want to use 7 panel strings due to the layout. If I used a US7000 it would work since min vdc in is 250. However the inverters are part of a SunnyTower and I can’t swap a 7000 for an 8000 without voiding the Tower UL listing. Kirk Herander VT Solar, LLC dba Vermont Solar Engineering NABCEP^TM Certified installer Charter Member NYSERDA-eligible Installer VT RE Incentive Program Partner *From:*re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *b...@midnitesolar.com *Sent:* Wednesday, November 30, 2011 1:03 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] calculating low string voltage If you really want to throw a monkey wrench into the mix, bring up partial shading... Or, maybe that's just not allowed in that debate ?? Just a thought. boB On 11/29/2011 8:39 PM, Kent Osterberg wrote: Kirk, You've got some good feedback on this from Ray and Bill. I'll try to add a little more. Most module datasheets show a normal operating cell temperature, NOCT, value that's typically 47.5°C. That's 20°C ambient temperature, 800 W/sq m, and calm wind and nothing blocking the airflow on the back of the module. That 27.5°C temperature rise should be pretty close to the temperature rise that occurs for a pole-top mount. It's common to see people use 25°C for modules on a pole and 30°C or 35°C on a roof and there are data that support these typical values. With 1000 W/sq irradiance, the temperature rise can obviously be more too. Between the intensity of the sun, the direction of the sun, the color of the roof, the spacing off the roof, and the wind speed there is a lot that is different from one system to the next or even one day to the next. Most PV module spec sheets don't give you a temperature coefficient for Vmp. I've seen people use the the Voc coefficient, usually expressed as a percentage, for both Voc and Vmp. Big mistake. Data from NREL indicates as Bill said, the
Re: [RE-wrenches] calculating low string voltage
ASHRAE temp data as applicable to PV can be found (with some digging) on the Solar ABCs website. http://solarabcs.org/about/publications/reports/expedited-permit/map/map_int ro.html -Glenn -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Thursday, December 01, 2011 3:49 PM To: RE-wrenches Subject: Re: [RE-wrenches] calculating low string voltage That's more detailed info, but I still am wondering what ambient temp to apply (which AHSRAE #) with the temp adder. Daryl suggested using a 2% high temp. Also, where are you all getting your weather data? I found the NEC suggested ASHRAE manual to be close to $200. That's a bit much just to get a couple of numbers for our design. It seems this calculation of low voltage is far from being entirely codified, and I'm trying to standardize it somewhat for my PV class. Non of the design manuals I have currently are even close to this level of complexity, yet this is obviously an important calculation. Should I suggest that my students just use the inverter manufacturers' online tools, and forget about trying to run this voltage calc themselves? Thanks, Ray On 12/1/2011 6:30 AM, Dave Click wrote: At an SMA training last year they recommended the following temperature adders: Open field: +22°C Rooftop, lots of ventilation: +28°C Rooftop, some ventilation: +29°C Rooftop, little ventilation: +32°C Rooftop BIPV, no ventilation: +43°C Façade, some ventilation: +35°C Façade, little ventilation: +39°C Façade BIPV, no ventilation: +55°C For your Sanyo project, I'd agree that the pole mount would be a good fit and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter with a 300V+ tracking window wouldn't work very well during the summers for very long. My own rooftop system has a design VMP of around 294 at 70C module temperature and I've seen it a bit lower than that on a sunny day-- I think it's because in irradiances below 1000Wm/2, the modules can still get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. So all told, maybe plan for an array minimum of: Inverter Tracking Minimum /0.85 (degradation and voltage tolerance) /0.95 (effect I just described) /0.825 (60C operating temp) = minimum string VMP at STC (similar to what Bill said) On 2011/11/30 11:04, Kirk Herander wrote: Thanks for all the good response. Speaking of monkey wrenches, these are Sanyo HIT Double panels, mounted on a rack which is 5 ½ feet above the roof surface. They will absorb reflected light on the backside, so I assume the cells will operate at a higher temp. But they are elevated enough to simulate a pole-mount, thus lowering operating cell temp. So what operating temp to use? If I use 25 C as the operating temp, the low voltage calc comes out to 301 vdc (inverter min is 300 using SMA US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel string. Unfortunately I really dont want to use 7 panel strings due to the layout. If I used a US7000 it would work since min vdc in is 250. However the inverters are part of a SunnyTower and I cant swap a 7000 for an 8000 without voiding the Tower UL listing. Kirk Herander VT Solar, LLC dba Vermont Solar Engineering NABCEP^TM Certified installer Charter Member NYSERDA-eligible Installer VT RE Incentive Program Partner *From:*re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *b...@midnitesolar.com *Sent:* Wednesday, November 30, 2011 1:03 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] calculating low string voltage If you really want to throw a monkey wrench into the mix, bring up partial shading... Or, maybe that's just not allowed in that debate ?? Just a thought. boB On 11/29/2011 8:39 PM, Kent Osterberg wrote: Kirk, You've got some good feedback on this from Ray and Bill. I'll try to add a little more. Most module datasheets show a normal operating cell temperature, NOCT, value that's typically 47.5°C. That's 20°C ambient temperature, 800 W/sq m, and calm wind and nothing blocking the airflow on the back of the module. That 27.5°C temperature rise should be pretty close to the temperature rise that occurs for a pole-top mount. It's common to see people use 25°C for modules on a pole and 30°C or 35°C on a roof and there are data that support these typical values. With 1000 W/sq irradiance, the temperature rise can obviously be more too. Between the intensity of the sun, the direction of the sun, the color of the roof, the spacing off the roof, and the wind speed there is a lot that is different from one system to the next or even one day to the next. Most PV module spec sheets don't give you a temperature coefficient for Vmp. I've seen people use the the Voc coefficient, usually expressed as a percentage,
Re: [RE-wrenches] OutBack Radian
Thanks Orion, Most of our work in the winter is in the Caribbean and Mexico and they all use 60 hz. I appreciate it, though. Daryl Daryl, We have not had any hands on experience yet with the Radian series inverters, and only minimal interaction with the MATE3. But since you mentioned that your systems would be out of country I thought I would bring up the fact that the Radian inverters only come in 60Hz models, no 50Hz output available. Orion Thornton Project Manager Independent Power Systems NABCEP Certified PV Installer (Office) 406.587.5295 (Mobile) 406.249.9912 www.solarips.com -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of penobscotso...@midmaine.com Sent: Thursday, December 01, 2011 12:25 PM To: RE-wrenches Subject: [RE-wrenches] OutBack Radian Hi all, We are looking at a busy winter season and there are several systems I'd like to size using OutBack's Radian. These are all out of the country jobs and I would be interested in any experiences anyone has had so far installing and/or using these seemingly great inverters. I would likely be using them in HBX mode, so secondary inquiries would be around susing the Mate3. Is it any more intuitive than the Mate? Similar in programming? Any thoughts from anyone with experience with Radian systems would be greatly appreciated. Thanks, Daryl DeJoy NABCEP Certified PV installer Penobscot Solar Design ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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: RE-wrenches@lists.re-wrenches.org 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: RE-wrenches@lists.re-wrenches.org 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
Re: [RE-wrenches] calculating low string voltage
Ray, I'd use the 2% high temp. The 0.4% high temp would only be reached a few hours out of the year. However, the 0.4% high is only a few degC warmer than the 2% high, so that would change my fudge factor below by a max of 1.8-2.0%. On 2011/12/1 15:48, Ray Walters wrote: That's more detailed info, but I still am wondering what ambient temp to apply (which AHSRAE #) with the temp adder. Daryl suggested using a 2% high temp. Also, where are you all getting your weather data? I found the NEC suggested ASHRAE manual to be close to $200. That's a bit much just to get a couple of numbers for our design. It seems this calculation of low voltage is far from being entirely codified, and I'm trying to standardize it somewhat for my PV class. Non of the design manuals I have currently are even close to this level of complexity, yet this is obviously an important calculation. Should I suggest that my students just use the inverter manufacturers' online tools, and forget about trying to run this voltage calc themselves? Thanks, Ray On 12/1/2011 6:30 AM, Dave Click wrote: At an SMA training last year they recommended the following temperature adders: Open field: +22°C Rooftop, lots of ventilation: +28°C Rooftop, some ventilation: +29°C Rooftop, little ventilation: +32°C Rooftop BIPV, no ventilation: +43°C Façade, some ventilation: +35°C Façade, little ventilation: +39°C Façade BIPV, no ventilation: +55°C For your Sanyo project, I'd agree that the pole mount would be a good fit and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter with a 300V+ tracking window wouldn't work very well during the summers for very long. My own rooftop system has a design VMP of around 294 at 70C module temperature and I've seen it a bit lower than that on a sunny day-- I think it's because in irradiances below 1000Wm/2, the modules can still get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. So all told, maybe plan for an array minimum of: Inverter Tracking Minimum /0.85 (degradation and voltage tolerance) /0.95 (effect I just described) /0.825 (60C operating temp) = minimum string VMP at STC (similar to what Bill said) On 2011/11/30 11:04, Kirk Herander wrote: Thanks for all the good response. Speaking of monkey wrenches, these are Sanyo HIT Double panels, mounted on a rack which is 5 ½ feet above the roof surface. They will absorb reflected light on the backside, so I assume the cells will operate at a higher temp. But they are elevated enough to simulate a pole-mount, thus lowering operating cell temp. So what operating temp to use? If I use 25 C as the operating temp, the low voltage calc comes out to 301 vdc (inverter min is 300 – using SMA US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel string. Unfortunately I really don’t want to use 7 panel strings due to the layout. If I used a US7000 it would work since min vdc in is 250. However the inverters are part of a SunnyTower and I can’t swap a 7000 for an 8000 without voiding the Tower UL listing. Kirk Herander VT Solar, LLC dba Vermont Solar Engineering NABCEP^TM Certified installer Charter Member NYSERDA-eligible Installer VT RE Incentive Program Partner *From:*re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *b...@midnitesolar.com *Sent:* Wednesday, November 30, 2011 1:03 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] calculating low string voltage If you really want to throw a monkey wrench into the mix, bring up partial shading... Or, maybe that's just not allowed in that debate ?? Just a thought. boB On 11/29/2011 8:39 PM, Kent Osterberg wrote: Kirk, You've got some good feedback on this from Ray and Bill. I'll try to add a little more. Most module datasheets show a normal operating cell temperature, NOCT, value that's typically 47.5°C. That's 20°C ambient temperature, 800 W/sq m, and calm wind and nothing blocking the airflow on the back of the module. That 27.5°C temperature rise should be pretty close to the temperature rise that occurs for a pole-top mount. It's common to see people use 25°C for modules on a pole and 30°C or 35°C on a roof and there are data that support these typical values. With 1000 W/sq irradiance, the temperature rise can obviously be more too. Between the intensity of the sun, the direction of the sun, the color of the roof, the spacing off the roof, and the wind speed there is a lot that is different from one system to the next or even one day to the next. Most PV module spec sheets don't give you a temperature coefficient for Vmp. I've seen people use the the Voc coefficient, usually expressed as a percentage, for both Voc and Vmp. Big mistake. Data from NREL indicates as Bill said, the temperature coefficient for Vmp is higher than that the temperature coefficient for Voc. That's particularly true when the coefficient is expressed as a percentage per °C. Since there are very few manufacturer's
Re: [RE-wrenches] calculating low string voltage
Ray, There is an explanation on the www.solarabcs.org/permitting webpage for the interactive solar map. The 2% ASHRAE data represents 14 hours in a month-meaning temperature will be at or above that value for 14 hours in a typical month. This is likely to correspond to at least one 3-hour timeframe which is considered continuous in the NEC. The Copper Development Association has chosen this number for ambient temperature calculations in the NEC. The NEC Handbook (not the NEC) uses this number in their example problems. The 0.4% ASHRAE date represents 3 hours in a month. It is much more conservative number. I put it in the data to provide a context for the 2% number and it allows engineers to consider a more conservative number. Of course, the mean extreme minimum drybulb temperature is also on that website for 690.7 max system voltage calculations. Enjoy-its free thanks to SolarABCs. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Thursday, December 01, 2011 3:58 PM To: RE-wrenches Subject: Re: [RE-wrenches] calculating low string voltage Fantastic Info everyone, I think I've got a full grasp on this topic now, from using the correct coefficient to the correct weather data, to the adders for installation type, and a nice link to the applicable data without spending $180 for the ASHRAE book. I'm guessing the 2% number is 2% of the time year round 24/7, not 2% of the time the sun is shining, so losses could be higher than 2% of production? Sorry to keep asking questions, but I know my class will probably ask the same thing. Ray On 12/1/2011 2:57 PM, Gary Willett wrote: RAY: This Solar Reference Guide Map web site is also linked to on the SolarABCs site and provides the ASHRAE 0.4% 2% high temperatures, as well as the PV module max temp based on distance above the roof (0.5, 3.5, and 12). http://www.solarabcs.org/about/publications/reports/expedited-permit/map/ind ex.html Regards, Gary Willett, PE On 12/1/2011 14:56, Gary Willett wrote: Ray: Look at Appendix F in the Expedited Permit Process for PV Systems - A Standardized Process for the Review of Small-Scale PV Systems Prepared by Bill Brooks, P.E. Brooks Engineering This document provides the ASHRE temperatures for a lot of locations around the USA. http://www.solarabcs.org/about/publications/reports/expedited-permit/pdfs/Ex permitprocess.pdf Regards, Gary Willett, PE ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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
Re: [RE-wrenches] calculating low string voltage
http://www.copper.org/applications/electrical/building/pdf/rooftop.pdf ³ASHRAE bases its ³warm-season temperature conditions² for each city on annual percentiles of 0.4%, 2 %, 5% and 10%. As an example, the June 2.0% dry-bulb design temperature for Atlanta is 91.7°F. Therefore, based on a 30-day month (i.e., 720 hours), the actual temperatures can be expected to exceed 91.7°F for total of 14 hours a month. The corresponding 5.0% design temperature (89.3°F) can be expected to be exceeded for 36 hours a month; while the 0.4% design temperature (94.7°F) can be expected to be exceeded for 3 hours a month.² On 12/1/11 5:57 PM, Ray Walters r...@solarray.com wrote: Fantastic Info everyone, I think I've got a full grasp on this topic now, from using the correct coefficient to the correct weather data, to the adders for installation type, and a nice link to the applicable data without spending $180 for the ASHRAE book. I'm guessing the 2% number is 2% of the time year round 24/7, not 2% of the time the sun is shining, so losses could be higher than 2% of production? Sorry to keep asking questions, but I know my class will probably ask the same thing. Ray On 12/1/2011 2:57 PM, Gary Willett wrote: RAY: This Solar Reference Guide Map web site is also linked to on the SolarABCs site and provides the ASHRAE 0.4% 2% high temperatures, as well as the PV module max temp based on distance above the roof (0.5, 3.5, and 12). http://www.solarabcs.org/about/publications/reports/expedited-permit/map/inde x.html Regards, Gary Willett, PE On 12/1/2011 14:56, Gary Willett wrote: Ray: Look at Appendix F in the Expedited Permit Process for PV Systems - A Standardized Process for the Review of Small-Scale PV Systems Prepared by Bill Brooks, P.E. Brooks Engineering This document provides the ASHRE temperatures for a lot of locations around the USA. http://www.solarabcs.org/about/publications/reports/expedited-permit/pdfs/Ex permitprocess.pdf Regards, Gary Willett, PE On 12/1/2011 14:48, Ray Walters wrote: That's more detailed info, but I still am wondering what ambient temp to apply (which AHSRAE #) with the temp adder. Daryl suggested using a 2% high temp. Also, where are you all getting your weather data? I found the NEC suggested ASHRAE manual to be close to $200. That's a bit much just to get a couple of numbers for our design. It seems this calculation of low voltage is far from being entirely codified, and I'm trying to standardize it somewhat for my PV class. Non of the design manuals I have currently are even close to this level of complexity, yet this is obviously an important calculation. Should I suggest that my students just use the inverter manufacturers' online tools, and forget about trying to run this voltage calc themselves? Thanks, Ray On 12/1/2011 6:30 AM, Dave Click wrote: At an SMA training last year they recommended the following temperature adders: Open field: +22°C Rooftop, lots of ventilation: +28°C Rooftop, some ventilation: +29°C Rooftop, little ventilation: +32°C Rooftop BIPV, no ventilation: +43°C Façade, some ventilation: +35°C Façade, little ventilation: +39°C Façade BIPV, no ventilation: +55°C For your Sanyo project, I'd agree that the pole mount would be a good fit and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter with a 300V+ tracking window wouldn't work very well during the summers for very long. My own rooftop system has a design VMP of around 294 at 70C module temperature and I've seen it a bit lower than that on a sunny day-- I think it's because in irradiances below 1000Wm/2, the modules can still get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. So all told, maybe plan for an array minimum of: Inverter Tracking Minimum /0.85 (degradation and voltage tolerance) /0.95 (effect I just described) /0.825 (60C operating temp) = minimum string VMP at STC (similar to what Bill said) On 2011/11/30 11:04, Kirk Herander wrote: Thanks for all the good response. Speaking of monkey wrenches, these are Sanyo HIT Double panels, mounted on a rack which is 5 12 feet above the roof surface. They will absorb reflected light on the backside, so I assume the cells will operate at a higher temp. But they are elevated enough to simulate a pole-mount, thus lowering operating cell temp. So what operating temp to use? If I use 25 C as the operating temp, the low voltage calc comes out to 301 vdc (inverter min is 300 using SMA US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel string. Unfortunately I really don¹t want to use 7 panel strings due to the layout. If I used a US7000 it would work since min vdc in is 250. However the inverters are part of a SunnyTower and I can¹t
Re: [RE-wrenches] calculating low string voltage
Again Thanks Bill and David; Continued excellent information. I just jumped on Solectria'a string sizing online tool, and what are they using for the Vmpp coefficent? just a tiny bit higher than the Voc coefficient. SMAs new design tool just lists the Voc coeff. I think some manus might need to be following this thread as well, and tweak their sizing tools appropriately. Ray On 12/1/2011 5:54 PM, Bill Brooks wrote: Ray, There is an explanation on the www.solarabcs.org/permitting http://www.solarabcs.org/permitting webpage for the interactive solar map. The 2% ASHRAE data represents 14 hours in a month---meaning temperature will be at or above that value for 14 hours in a typical month. This is likely to correspond to at least one 3-hour timeframe which is considered continuous in the NEC. The Copper Development Association has chosen this number for ambient temperature calculations in the NEC. The NEC Handbook (not the NEC) uses this number in their example problems. The 0.4% ASHRAE date represents 3 hours in a month. It is much more conservative number. I put it in the data to provide a context for the 2% number and it allows engineers to consider a more conservative number. Of course, the mean extreme minimum drybulb temperature is also on that website for 690.7 max system voltage calculations. Enjoy---its free thanks to SolarABCs. Bill. *From:*re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Ray Walters *Sent:* Thursday, December 01, 2011 3:58 PM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] calculating low string voltage Fantastic Info everyone, I think I've got a full grasp on this topic now, from using the correct coefficient to the correct weather data, to the adders for installation type, and a nice link to the applicable data without spending $180 for the ASHRAE book. I'm guessing the 2% number is 2% of the time year round 24/7, not 2% of the time the sun is shining, so losses could be higher than 2% of production? Sorry to keep asking questions, but I know my class will probably ask the same thing. Ray On 12/1/2011 2:57 PM, Gary Willett wrote: RAY: This Solar Reference Guide Map web site is also linked to on the SolarABCs site and provides the ASHRAE 0.4% 2% high temperatures, as well as the PV module max temp based on distance above the roof (0.5, 3.5, and 12). http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html Regards, Gary Willett, PE On 12/1/2011 14:56, Gary Willett wrote: Ray: Look at Appendix F in the Expedited Permit Process for PV Systems - A Standardized Process for the Review of Small-Scale PV Systems Prepared by Bill Brooks, P.E. Brooks Engineering This document provides the ASHRE temperatures for a lot of locations around the USA. http://www.solarabcs.org/about/publications/reports/expedited-permit/pdfs/Expermitprocess.pdf Regards, Gary Willett, PE ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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: RE-wrenches@lists.re-wrenches.org 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
[RE-wrenches] old trace manual
Hi All, Does anyone know of a link to the old Trace 2624 inverter/Charger (the one with the plexiglass front. I believe the model number was U2624, but I'm not positive. I'm trying to remember what the maximum bulk voltage setting was on it. Also wondering how sensitive to lower gennie voltage output (113 vAC) the charger was. How much would that cut down on the current output capacity? Thanks, Howie -- Howie Michaelson NABCEP Certified Solar PV Installer Catamount Solar, LLC Renewable Energy Systems Sales and Service VT Solar Electric Hot Water Incentive Partner http://www.CatamountSolar.com 802-272-0004 ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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
[RE-wrenches] SMA Sunny Design temperature/voltage calculations
Apropos to the great discussion about temperature voltage calculations, has anyone else been frustrated by the removal of output information on the Sunny Design tool compared to the old on-line string sizing calculator? It was very useful to me to have the string sizer show the temperature voltage calculations for low and high temperature - as far as I know the only string sizing application that showed this info. The defunct online sizer allowed me to quickly look at a variety stringing options, see the impact on voltage, narrow down the possibilities and then run my own voltage calculations to verify. Sunny Design makes quickly scanning various string options not so easy, and it buries the results behind more obscure output info. It is quite a sophisticated program, but I wish they gave a way to see the calculations behind the choices it makes. Or am I just missing something? Howie -- Howie Michaelson NABCEP Certified Solar PV Installer Catamount Solar, LLC Renewable Energy Systems Sales and Service VT Solar Electric Hot Water Incentive Partner http://www.CatamountSolar.com 802-272-0004 ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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
