[RE-wrenches] P1 micro performance
Nick, Is Enphase going to be introducing to market any time in the near-term a new micro with a higher output? It seems very likely that the trend toward higher output mods will continue. The M215 will surely be left behind to a greater degree as this trend continues if there are higher and reliable and comparably priced, on a dollar/watt basis, micros available. Thanks, marco Hi Carl, Marco, and Wrenches, As a longtime installer, I understand your point of view. Historically, I designed my string and microinverter systems with the same consideration for maintaining conservative DC to AC ratios. That being said, the costs of modules have decreased significantly and the dynamics have changed. Solar companies should be focused on selling systems that offers a great rate of return. Maximizing the customer's investment is most important. Isn't that what your customer wants? What Enphase is encouraging is the development of cost effective PV systems that will generate a healthy return. Considering that the modules are only 20% of the total system costs today, it is smart to give up 0.2% or more of the module production to lower the overall system costs by 5-10%. The NEC requires that the AC panel boards, conductors, and circuit breakers are sized to the inverter continuous output current rating. We should be maximizing this infrastructure. The data available indicates that when a system is installed with a 1.2 to 1.25 DC to AC ratio, it will rarely operate at peak output. Installing a PV system with a 1.25 DC to AC ratio is not driving the equipment to the maximum. In the case of the Enphase M215s; they are designed to operate continuously at peak output, so reaching that level a few hours in the first years is not problematic. To be clear, this limiting will occur the most during the spring months, because you have a combination of both cool weather and high irradiance levels. As Dan mentioned, this applies to string inverters as well as microinverters. One of the most common system designs of the early US grid-tied market was installing 18- 165 watt modules on an SWR-2500. I designed hundreds of projects like that. That was a ~1.2 multiplier, and was at a time when the modules cost $5 per watt; not $1 per watt. Why be more conservative now? ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Friends, Keeping the record straight. I need to say that I have had correspondence 'off list' from a development engineer from a prominent manufacturer who assures me that his product is designed to run 'flat out' 24/7. The unit in fact is just coasting at it's maximum power rating. This allows for a projected life matching that of the PV. In this case power clipping will not shorten the products life. I am unable to confirm if all manufacturers are taking this approach, buyer beware. Regards Carl Emerson Nick, Is Enphase going to be introducing to market any time in the near-term a new micro with a higher output? It seems very likely that the trend toward higher output mods will continue. The M215 will surely be left behind to a greater degree as this trend continues if there are higher and reliable and comparably priced, on a dollar/watt basis, micros available. Thanks, marco Hi Carl, Marco, and Wrenches, As a longtime installer, I understand your point of view. Historically, I designed my string and microinverter systems with the same consideration for maintaining conservative DC to AC ratios. That being said, the costs of modules have decreased significantly and the dynamics have changed. Solar companies should be focused on selling systems that offers a great rate of return. Maximizing the customer's investment is most important. Isn't that what your customer wants? What Enphase is encouraging is the development of cost effective PV systems that will generate a healthy return. Considering that the modules are only 20% of the total system costs today, it is smart to give up 0.2% or more of the module production to lower the overall system costs by 5-10%. The NEC requires that the AC panel boards, conductors, and circuit breakers are sized to the inverter continuous output current rating. We should be maximizing this infrastructure. The data available indicates that when a system is installed with a 1.2 to 1.25 DC to AC ratio, it will rarely operate at peak output. Installing a PV system with a 1.25 DC to AC ratio is not driving the equipment to the maximum. In the case of the Enphase M215s; they are designed to operate continuously at peak output, so reaching that level a few hours in the first years is not problematic. To be clear, this limiting will occur the most during the spring months, because you have a combination of both cool weather and high irradiance levels. As Dan mentioned, this applies to string inverters as well as microinverters. One of the most common system designs of the early US grid-tied market was installing 18- 165 watt modules on an SWR-2500. I designed hundreds of projects like that. That was a ~1.2 multiplier, and was at a time when the modules cost $5 per watt; not $1 per watt. Why be more conservative now? ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Fellow Wrenches, No stones from this Missouri P.E. Perhaps if more Greybeards gave such candid comments it might influence others toward something other than a race to the bottom. Bill Loesch Solar 1 - Saint Louis Solar 314 631 1094 On 24-Mar-13 12:07 PM, Ray Walters wrote: Hear, Hear, Carl. That has also always been my experience as well. In my off grid work, reliability trumps budget, and I almost always over size charge controllers, relays, inverters, fuse holders, etc. Most failures seem to be related to pushing the design limits of the equipment. I spent the past year working on multi MW systems, where they saved every penny possible. The inverters were undersized by 20 to 25% but sitting in unairconditioned enclosures. Even better that the projected 30 year life of the system did not even include inverter replacements. I'm sure I shall be stoned to death for saying this, but basically the grid tie solar community just doesn't have enough experience under its belt yet to have seen what we learned a decade ago in the off grid world. When they start putting call backs, down time, inverter replacements, and the related loss of respect and business into their spread sheets; they'll start oversizing the inverters more, like you, Marco, and many of us already know. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 3/23/2013 7:19 PM, Carl Emerson wrote: Friends, I am a little puzzled by this topic. What has happened to the good engineering practice of sizing electronic equipment so that it is not driven to the maximum. My understanding is that the MTBF increases significantly the harder you drive the unit. This seems to be a case of overdriving the units for short term gain. *Carl Emerson* *Free Power Co. * *Auckland N.Z.*** What I *can't* answer is the long-term effect this may have on the overall life of the inverter. THAT depends on various intricate design considerations that went into creating the inverter in the first place. Dan Lepinski, Senior Engineer Exeltech / Exeltech Solar Products With 41 years experience as a design engineer in solar energy. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 No virus found in this message. Checked by AVG - www.avg.com http://www.avg.com Version: 2013.0.2904 / Virus Database: 2641/6187 - Release Date: 03/18/13 - No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2904 / Virus Database: 2641/6187 - Release Date: 03/18/13___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Marco, I still challenge those who believe that “some clipping is good” to make their case. Well, the way you've phrased it, you've made my job pretty easy-- though it seems to me that several folks have already done this for you. Some power limiting at some point over the 25-year life of a system is definitely a good thing. A 25-year life corresponds to about 110,000 hours of daylight. Let's say that you can expect one total hour of those 110,000 in which a Montana system sees 1600 W/m2 (high slope, snow reflection, edge-of-cloud) while simultaneously experiencing a record low temperature and 50 mph winds. Would you put a 9kW inverter on your 5kW array to avoid any power limiting ever? Of course not-- you're substantially increasing system cost for a $0.15 gain. It comes down to figuring out probabilities and doing some complicated and annoying math to figure out the best size for an inverter. Or more realistically, attempting to get high-sample-rate weather data to simulate array performance at your target location. When you oversize an inverter, your system will be operating at a lower efficiency, on average. It increases the cost to the customer not just from the base cost of the larger unit, but also the larger output conductor and raceway sizes, the output disconnect, the interconnection breakers/fuses... and maybe even upsized panelboards that didn't actually need to be upgraded had you correctly sized the inverters. So you have to figure out whether the additional production is worth the increased cost of installation. Oversizing an inverter may extend its life but I don't know that we'll ever have those numbers from manufacturers to better quantify that impact. More current causes more heat, which is bad, but increasing an inverter size to the next higher power rating available doesn't guarantee that the larger inverter will be more reliable. So that's a general response. As for your Power-One 250 vs Enphase 224 conundrum, if all else is equal but the power rating, then I'd probably join you in choosing the Power-One. But as you know, there are other factors to take into account-- [perceived] reliability, BOS cost (e.g. more Enphase units fitting on a 20A breaker may save you a circuit), DAS usefulness, resistance to corrosion, and the fact that Enphase operates at a higher conversion efficiency in the lower half of its operating range (where it spends most of its operating time). I am not saying that Enphase is better than Power-One in anything but low-range efficiency-- I don't know one way or the other. Efficiency Curves: http://gosolarcalifornia.com/equipment/inverter_tests/summaries/Enphase%20M215%20IG-240V.pdf http://gosolarcalifornia.com/equipment/inverter_tests/summaries/Power-One%20MICRO-0.25-I-OUTD-US-240.pdf After all this discussion, it's pretty funny that the peak conversion efficiency of the 250W Power-One micro occurs at... a 250W output. So even though the marketing guys tell you you should only plug in a 265W module, the engineers are clearly asking you to turn it up to 11. Do you, Mr./Mrs./Ms. Homeowner, want a PV system that produces as much solar kWhs for your investment as possible? isn't the right question to ask. Try, Do you, Mr./Mrs./Ms. Homeowner, want a PV system that produces the best value for your investment? Then show your super impressive calculations, based on your years of experience, that your recommended inverter is the best fit for them. Allowing for maximum kWh harvesting, within reason, is the best design strategy. Dave 5.376kWdc on a 5.000kWac, and loving it On 2013/3/23 19:31, Marco Mangelsdorf wrote: From Dan at Exeltech: Trying to explain in depth the how and why slightly larger PV is of benefit to a customer is like trying to explain photovoltaic equipment to the general public. I still challenge those who believe that “some clipping is good” to make their case. And as far as the general buying public, I’m find that people do in fact understand when you ask them the following questions: Do you, Mr./Mrs./Ms. Homeowner, want a PV system that produces as much solar kWhs for your investment as possible? Usual response: absolutely. If I give you the choice of PV system using a 250-watt module paired with a COMPARABLY priced 250-watt micro inverter OR that same 250-watt module with a max output ~ 224-watt micro inverter that will never under any circumstances allow that 250-watt module to put out its max rated power output, which option do you think they’ll choose? They get that. It doesn’t take someone with an engineering degree or 10-40 years in the field to get that simple premise. For what it’s worth, being here in the tropics in the Hawaiian islands we don’t get those bright and sunny and cold late fall/winter/early spring days that will allow for an array to put out its STC-rated power. But seeing regular times during the day—any time of year—where the irradiance is more than 1,000
Re: [RE-wrenches] P1 micro performance
Hi Carl, Marco, and Wrenches, As a longtime installer, I understand your point of view. Historically, I designed my string and microinverter systems with the same consideration for maintaining conservative DC to AC ratios. That being said, the costs of modules have decreased significantly and the dynamics have changed. Solar companies should be focused on selling systems that offers a great rate of return. Maximizing the customer's investment is most important. Isn't that what your customer wants? What Enphase is encouraging is the development of cost effective PV systems that will generate a healthy return. Considering that the modules are only 20% of the total system costs today, it is smart to give up 0.2% or more of the module production to lower the overall system costs by 5-10%. The NEC requires that the AC panel boards, conductors, and circuit breakers are sized to the inverter continuous output current rating. We should be maximizing this infrastructure. The data available indicates that when a system is installed with a 1.2 to 1.25 DC to AC ratio, it will rarely operate at peak output. Installing a PV system with a 1.25 DC to AC ratio is not driving the equipment to the maximum. In the case of the Enphase M215s; they are designed to operate continuously at peak output, so reaching that level a few hours in the first years is not problematic. To be clear, this limiting will occur the most during the spring months, because you have a combination of both cool weather and high irradiance levels. As Dan mentioned, this applies to string inverters as well as microinverters. One of the most common system designs of the early US grid-tied market was installing 18- 165 watt modules on an SWR-2500. I designed hundreds of projects like that. That was a ~1.2 multiplier, and was at a time when the modules cost $5 per watt; not $1 per watt. Why be more conservative now? On Sat, Mar 23, 2013 at 6:19 PM, Carl Emerson c...@solarking.net.nz wrote: Friends, ** ** I am a little puzzled by this topic. ** ** What has happened to the good engineering practice of sizing electronic equipment so that it is not driven to the maximum. ** ** My understanding is that the MTBF increases significantly the harder you drive the unit. ** ** This seems to be a case of overdriving the units for short term gain. *** * ** ** *Carl Emerson* *Free Power Co. * *Auckland N.Z.*** ** ** *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto: re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Exeltech *Sent:* 24 March 2013 5:50 a.m. *To:* RE-wrenches *Subject:* Re: [RE-wrenches] P1 micro performance ** ** Marco .. and Wrenches .. I'm going to take a run at this -- just once. First ... Without proper and *accurate* data acquisition equipment, there's no way to know what the actual available PV wattage is compared to the inverter's output wattage when its output is being *LIMITED*. This limiting action occurs in an inverter when there's more available power at the input than the inverter can produce at its output. Subsequently, you don't know how much potential energy wasn't harvested. Now then ... Let's say the inverter is producing 216 watts, and the PV *could* produce 227.3 watts at max power point under those specific conditions if every PV-generated milliwatt were used. Next, and presuming the inverter is 95% efficient, that's a limited loss of ONE WATT. 227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt). Under what conditions (and since you're in Hawaii, I'll use 70F) would this occur, and with what size PV? I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I could find. NESL DJ-270P,. YOU think it's producing 270 watts. It's not. At 77F (25C), and under the conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day, light wind, that particular PV will produce 227 watts +/- its tolerance. (Let's say the tolerance is dead on.) Now, consider the benefit of increased energy output due to more rapid output wattage rise experienced during early morning, and the higher output later in the afternoon, AS WELL AS the increased power output realized during periods of less than 100% irradiance one derives from using larger PV compared to PV you might consider perfectly matched to the inverter. ALL of this adds up to more kilowatt-hours produced annually than had the inverter been connected to your perfect PV that doesn't produce enough wattage to have the inverter begin limiting its output. The shoulders of the output wattage curve are steeper than with lower-wattage PV. Granted you *could* connect the inverter to [say] a 450 watt PV module, and that would truly be a waste of the PV wattage. There *is* a broad sweet spot for AC Module inverters and microinverters alike, and it's actually on the higher side of the PV's rated output wattage versus
Re: [RE-wrenches] P1 micro performance
Hear, Hear, Carl. That has also always been my experience as well. In my off grid work, reliability trumps budget, and I almost always over size charge controllers, relays, inverters, fuse holders, etc. Most failures seem to be related to pushing the design limits of the equipment. I spent the past year working on multi MW systems, where they saved every penny possible. The inverters were undersized by 20 to 25% but sitting in unairconditioned enclosures. Even better that the projected 30 year life of the system did not even include inverter replacements. I'm sure I shall be stoned to death for saying this, but basically the grid tie solar community just doesn't have enough experience under its belt yet to have seen what we learned a decade ago in the off grid world. When they start putting call backs, down time, inverter replacements, and the related loss of respect and business into their spread sheets; they'll start oversizing the inverters more, like you, Marco, and many of us already know. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 3/23/2013 7:19 PM, Carl Emerson wrote: Friends, I am a little puzzled by this topic. What has happened to the good engineering practice of sizing electronic equipment so that it is not driven to the maximum. My understanding is that the MTBF increases significantly the harder you drive the unit. This seems to be a case of overdriving the units for short term gain. *Carl Emerson* *Free Power Co. * *Auckland N.Z.*** What I *can't* answer is the long-term effect this may have on the overall life of the inverter. THAT depends on various intricate design considerations that went into creating the inverter in the first place. Dan Lepinski, Senior Engineer Exeltech / Exeltech Solar Products With 41 years experience as a design engineer in solar energy. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Yes, I know that that screen shot was only a moment in time. Here it's only March and clipping is already taking place. Imagine what kind of clipping is going to take place at higher irradiance levels later in the year. Yes, the monitoring program cannot as of now quantify what kind of harvesting losses would take place over time compared to an identical array using Enphase micros. But the principle remains unchallengeable: not allowing for maximum kWh harvesting is plain and simple NOT the best design strategy. Some clipping is good? You've got to be joking. Not being able to harvest usable solar energy is good? What kind of optimal design philosophy is that? As module outputs have been going up, Enphase has a vested interest in continuing to move product with little regard for the harvestable energy being essentially lost. Using larger micros that reduce or eliminate that clipping is prima facie a good thing if one cares about maximizing kWh harvest. As more micro products come on the product with higher outputs than the venerable and solid M215, Enphase risks being left behind and losing market share. I for one find that white paper overly self-serving. marco From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Nick Soleil Sent: Thursday, March 21, 2013 8:04 PM To: RE-wrenches Subject: Re: [RE-wrenches] P1 micro performance Good points David, we are in peak season for inverters to be limiting power. Marco, your diagram shows that the modules are only overproducing the Enphase M215's output of 225 watts for a single 15 minute period during the day. That would only equate to about 3 watt-hours of lost power on a day when the modules are producing more than 1000 watt-hours. That tends to be in agreement with our study, which can be viewed at; http://enphase.com/wp-uploads/enphase.com/2011/12/Enphase_White_Paper_Module _Rightsizing.pdf. Averaged across the entire year, this loss of power would total less than 0.1%, and would be less than 0.2% for a 265 watt module. Keep in mind that with degradation accounted for, you will see even less limiting in future years. I'd encourage Wrenches to look closely at the attached document. It is based upon real system production data from Enlighten compared against actual irradiance data. Most analysts would agree that some clipping is good. You will have a better return on your investment when your DC to AC ratio is greater than one. In this case, bigger is better. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Marco .. and Wrenches .. I'm going to take a run at this -- just once. First ... Without proper and *accurate* data acquisition equipment, there's no way to know what the actual available PV wattage is compared to the inverter's output wattage when its output is being *LIMITED*. This limiting action occurs in an inverter when there's more available power at the input than the inverter can produce at its output. Subsequently, you don't know how much potential energy wasn't harvested. Now then ... Let's say the inverter is producing 216 watts, and the PV *could* produce 227.3 watts at max power point under those specific conditions if every PV-generated milliwatt were used. Next, and presuming the inverter is 95% efficient, that's a limited loss of ONE WATT. 227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt). Under what conditions (and since you're in Hawaii, I'll use 70F) would this occur, and with what size PV? I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I could find. NESL DJ-270P,. YOU think it's producing 270 watts. It's not. At 77F (25C), and under the conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day, light wind, that particular PV will produce 227 watts +/- its tolerance. (Let's say the tolerance is dead on.) Now, consider the benefit of increased energy output due to more rapid output wattage rise experienced during early morning, and the higher output later in the afternoon, AS WELL AS the increased power output realized during periods of less than 100% irradiance one derives from using larger PV compared to PV you might consider perfectly matched to the inverter. ALL of this adds up to more kilowatt-hours produced annually than had the inverter been connected to your perfect PV that doesn't produce enough wattage to have the inverter begin limiting its output. The shoulders of the output wattage curve are steeper than with lower-wattage PV. Granted you *could* connect the inverter to [say] a 450 watt PV module, and that would truly be a waste of the PV wattage. There *is* a broad sweet spot for AC Module inverters and microinverters alike, and it's actually on the higher side of the PV's rated output wattage versus the inverter's wattage rating. So, can you over-do it? Sure. But there IS an overall kilowatt-hours-produced benefit for *modest* over-sizing the PV. What I *can't* answer is the long-term effect this may have on the overall life of the inverter. THAT depends on various intricate design considerations that went into creating the inverter in the first place. This isn't an Enphase issue, nor are they trying to mislead you on this topic. It's an industry-wide issue. Wrenches face it every time you designed a string system, especially those being installed in regions with wide temperature swings. Trying to explain in depth the how and why slightly larger PV is of benefit to a customer is like trying to explain photovoltaic equipment to the general public. As a competitor to Enphase .. I'm not coming to their defense. However, what Nick said (below) IS fact. Whether you elect to believe this or not is up to you. Regards to all, Dan Lepinski, Senior Engineer Exeltech / Exeltech Solar Products With 41 years experience as a design engineer in solar energy. --- On Sat, 3/23/13, Marco Mangelsdorf ma...@pvthawaii.com wrote: From: Marco Mangelsdorf ma...@pvthawaii.com Subject: [RE-wrenches] P1 micro performance To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org Date: Saturday, March 23, 2013, 4:04 AM Yes, I know that that screen shot was only a moment in time. Here it’s only March and clipping is already taking place. Imagine what kind of clipping is going to take place at higher irradiance levels later in the year. Yes, the monitoring program cannot as of now quantify what kind of harvesting losses would take place over time compared to an identical array using Enphase micros. But the principle remains unchallengeable: not allowing for maximum kWh harvesting is plain and simple NOT the best design strategy. “Some clipping is good”? You’ve got to be joking. Not being able to harvest usable solar energy is good? What kind of optimal design philosophy is that? As module outputs have been going up, Enphase has a vested interest in continuing to move product with little regard for the harvestable energy being essentially lost. Using larger micros that reduce or eliminate that clipping is prima facie a good thing if one cares about maximizing kWh harvest. As more micro products come on the product with higher outputs than the venerable and solid M215, Enphase risks being left behind and losing market share. I for one find that “white paper” overly self-serving. marco From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Nick Soleil Sent: Thursday, March 21, 2013 8:04 PM To: RE-wrenches Subject: Re: [RE-wrenches] P1 micro
Re: [RE-wrenches] P1 micro performance
Friends, I am a little puzzled by this topic. What has happened to the good engineering practice of sizing electronic equipment so that it is not driven to the maximum. My understanding is that the MTBF increases significantly the harder you drive the unit. This seems to be a case of overdriving the units for short term gain. Carl Emerson Free Power Co. Auckland N.Z. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Exeltech Sent: 24 March 2013 5:50 a.m. To: RE-wrenches Subject: Re: [RE-wrenches] P1 micro performance Marco .. and Wrenches .. I'm going to take a run at this -- just once. First ... Without proper and *accurate* data acquisition equipment, there's no way to know what the actual available PV wattage is compared to the inverter's output wattage when its output is being *LIMITED*. This limiting action occurs in an inverter when there's more available power at the input than the inverter can produce at its output. Subsequently, you don't know how much potential energy wasn't harvested. Now then ... Let's say the inverter is producing 216 watts, and the PV *could* produce 227.3 watts at max power point under those specific conditions if every PV-generated milliwatt were used. Next, and presuming the inverter is 95% efficient, that's a limited loss of ONE WATT. 227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt). Under what conditions (and since you're in Hawaii, I'll use 70F) would this occur, and with what size PV? I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I could find. NESL DJ-270P,. YOU think it's producing 270 watts. It's not. At 77F (25C), and under the conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day, light wind, that particular PV will produce 227 watts +/- its tolerance. (Let's say the tolerance is dead on.) Now, consider the benefit of increased energy output due to more rapid output wattage rise experienced during early morning, and the higher output later in the afternoon, AS WELL AS the increased power output realized during periods of less than 100% irradiance one derives from using larger PV compared to PV you might consider perfectly matched to the inverter. ALL of this adds up to more kilowatt-hours produced annually than had the inverter been connected to your perfect PV that doesn't produce enough wattage to have the inverter begin limiting its output. The shoulders of the output wattage curve are steeper than with lower-wattage PV. Granted you *could* connect the inverter to [say] a 450 watt PV module, and that would truly be a waste of the PV wattage. There *is* a broad sweet spot for AC Module inverters and microinverters alike, and it's actually on the higher side of the PV's rated output wattage versus the inverter's wattage rating. So, can you over-do it? Sure. But there IS an overall kilowatt-hours-produced benefit for *modest* over-sizing the PV. What I *can't* answer is the long-term effect this may have on the overall life of the inverter. THAT depends on various intricate design considerations that went into creating the inverter in the first place. This isn't an Enphase issue, nor are they trying to mislead you on this topic. It's an industry-wide issue. Wrenches face it every time you designed a string system, especially those being installed in regions with wide temperature swings. Trying to explain in depth the how and why slightly larger PV is of benefit to a customer is like trying to explain photovoltaic equipment to the general public. As a competitor to Enphase .. I'm not coming to their defense. However, what Nick said (below) IS fact. Whether you elect to believe this or not is up to you. Regards to all, Dan Lepinski, Senior Engineer Exeltech / Exeltech Solar Products With 41 years experience as a design engineer in solar energy. --- On Sat, 3/23/13, Marco Mangelsdorf ma...@pvthawaii.com wrote: From: Marco Mangelsdorf ma...@pvthawaii.com Subject: [RE-wrenches] P1 micro performance To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org Date: Saturday, March 23, 2013, 4:04 AM Yes, I know that that screen shot was only a moment in time. Here it's only March and clipping is already taking place. Imagine what kind of clipping is going to take place at higher irradiance levels later in the year. Yes, the monitoring program cannot as of now quantify what kind of harvesting losses would take place over time compared to an identical array using Enphase micros. But the principle remains unchallengeable: not allowing for maximum kWh harvesting is plain and simple NOT the best design strategy. Some clipping is good? You've got to be joking. Not being able to harvest usable solar energy is good? What kind of optimal design philosophy is that? As module outputs have been going up, Enphase has a vested interest in continuing to move product with little regard
[RE-wrenches] P1 micro performance
From Dan at Exeltech: Trying to explain in depth the how and why slightly larger PV is of benefit to a customer is like trying to explain photovoltaic equipment to the general public. I still challenge those who believe that “some clipping is good” to make their case. And as far as the general buying public, I’m find that people do in fact understand when you ask them the following questions: Do you, Mr./Mrs./Ms. Homeowner, want a PV system that produces as much solar kWhs for your investment as possible? Usual response: absolutely. If I give you the choice of PV system using a 250-watt module paired with a COMPARABLY priced 250-watt micro inverter OR that same 250-watt module with a max output ~ 224-watt micro inverter that will never under any circumstances allow that 250-watt module to put out its max rated power output, which option do you think they’ll choose? They get that. It doesn’t take someone with an engineering degree or 10-40 years in the field to get that simple premise. For what it’s worth, being here in the tropics in the Hawaiian islands we don’t get those bright and sunny and cold late fall/winter/early spring days that will allow for an array to put out its STC-rated power. But seeing regular times during the day—any time of year—where the irradiance is more than 1,000 watts/sq. meter is not at all common. marco Yes, I know that that screen shot was only a moment in time. Here it’s only March and clipping is already taking place. Imagine what kind of clipping is going to take place at higher irradiance levels later in the year. Yes, the monitoring program cannot as of now quantify what kind of harvesting losses would take place over time compared to an identical array using Enphase micros. But the principle remains unchallengeable: not allowing for maximum kWh harvesting is plain and simple NOT the best design strategy. “Some clipping is good”? You’ve got to be joking. Not being able to harvest usable solar energy is good? What kind of optimal design philosophy is that? As module outputs have been going up, Enphase has a vested interest in continuing to move product with little regard for the harvestable energy being essentially lost. Using larger micros that reduce or eliminate that clipping is prima facie a good thing if one cares about maximizing kWh harvest. As more micro products come on the product with higher outputs than the venerable and solid M215, Enphase risks being left behind and losing market share. I for one find that “white paper” overly self-serving. marco ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
On 3/21/2013 9:59 PM, Exeltech wrote: Wrenches, I'm probably a lone voice on this .. and not intending to get overly picky. No, two lonely voices, Dan. I associate clipping with audio waveforms which stops the negative or positive voltage peaks flat. Also called flat-topping. Limiting is like turning down the volume. The waveform stays the same and does not distort as it would if it were being flat topped (and flat bottomed) Thanks ! boB Could we call power limiting what it is .. limiting, and not clipping? Clipping implies distortion, which isn't the case here. Limiting is just that. The inverter output is limited to some maximum value -- not clipped. The output power curve flattens when integrated over time, but this still isn't distortion in the waveform. It's simply a point in the output where the derivative is zero. Not increasing, not decreasing. Just .. zero. No additional increase in the output for an increase in available energy at the input. Think governor on an engine Thanks. Dan Lepinski, Sr. Engineer Exeltech / Exeltech Solar Products --- On *Thu, 3/21/13, David Brearley /david.brear...@solarprofessional.com/* wrote: From: David Brearley david.brear...@solarprofessional.com Subject: Re: [RE-wrenches] P1 micro performance To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Thursday, March 21, 2013, 11:37 PM Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module---like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often---I wouldn't try that here in Texas. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Hi Dan, A very heartfelt thanks for the education. It is exactly this kind of attention to detail that separate the professional from the practitioner. Moreover, at least in this case, the proper terminology is hopefully better and more widely understood. Thanks again, Bill Loesch Solar 1 - Saint Louis Solar 314 631 1094 On 21-Mar-13 11:59 PM, Exeltech wrote: Wrenches, I'm probably a lone voice on this .. and not intending to get overly picky. Could we call power limiting what it is .. limiting, and not clipping? Clipping implies distortion, which isn't the case here. Limiting is just that. The inverter output is limited to some maximum value -- not clipped. The output power curve flattens when integrated over time, but this still isn't distortion in the waveform. It's simply a point in the output where the derivative is zero. Not increasing, not decreasing. Just .. zero. No additional increase in the output for an increase in available energy at the input. Think governor on an engine Thanks. Dan Lepinski, Sr. Engineer Exeltech / Exeltech Solar Products --- On *Thu, 3/21/13, David Brearley /david.brear...@solarprofessional.com/* wrote: From: David Brearley david.brear...@solarprofessional.com Subject: Re: [RE-wrenches] P1 micro performance To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Thursday, March 21, 2013, 11:37 PM Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often—I wouldn't try that here in Texas. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 No virus found in this message. Checked by AVG - www.avg.com http://www.avg.com Version: 2013.0.2904 / Virus Database: 2641/6187 - Release Date: 03/18/13 - No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2904 / Virus Database: 2641/6187 - Release Date: 03/18/13___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
Hi boB, Kudos to you, too. Flat-topping (bottoming) is so very descriptive and hopefully universally understandable. Excellent analogies. Technical education/expertise sharing is one of the most prized benefits of belonging/participating on the RE-wrenches list. Thanks, Bill Loesch Solar 1 - Saint Louis Solar 314 631 1094 On 22-Mar-13 1:07 AM, boB wrote: On 3/21/2013 9:59 PM, Exeltech wrote: Wrenches, I'm probably a lone voice on this .. and not intending to get overly picky. No, two lonely voices, Dan. I associate clipping with audio waveforms which stops the negative or positive voltage peaks flat. Also called flat-topping. Limiting is like turning down the volume. The waveform stays the same and does not distort as it would if it were being flat topped (and flat bottomed) Thanks ! boB Could we call power limiting what it is .. limiting, and not clipping? Clipping implies distortion, which isn't the case here. Limiting is just that. The inverter output is limited to some maximum value -- not clipped. The output power curve flattens when integrated over time, but this still isn't distortion in the waveform. It's simply a point in the output where the derivative is zero. Not increasing, not decreasing. Just .. zero. No additional increase in the output for an increase in available energy at the input. Think governor on an engine Thanks. Dan Lepinski, Sr. Engineer Exeltech / Exeltech Solar Products --- On *Thu, 3/21/13, David Brearley /david.brear...@solarprofessional.com/* wrote: From: David Brearley david.brear...@solarprofessional.com Subject: Re: [RE-wrenches] P1 micro performance To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Thursday, March 21, 2013, 11:37 PM Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module---like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often---I wouldn't try that here in Texas. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 No virus found in this message. Checked by AVG - www.avg.com http://www.avg.com Version: 2013.0.2904 / Virus Database: 2641/6187 - Release Date: 03/18/13 - No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2904 / Virus Database: 2641/6187 - Release Date: 03/18/13___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
It would be good to quantify the amount of peak energy that is lost through power limiting. We have a 2160 Watt array on a 40 degree pitched roof with a SB 2500HF US inverter. The other day I watched the meter hover over 2000 W and peak at 2490 W. It was a clear, cold day. It runs in the STC range and higher many days in the spring. I have one Enphase customer with a ground mount with Sharp 224s and Enphase 190s. The inverters can stay pegged for 4 hours at a time in the spring. Emacs! The graph above was from a day with some clouds, but still power limited much of the day. It would be good to get a better understanding of the annual percentage effect. Enphase claims an overall power increase, even with this effect. Undersized string inverters are clearly an issue. Drake At 12:37 AM 3/22/2013, you wrote: Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W modulelike a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very oftenI wouldn't try that here in Texas. On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote: Check out the output of the modules below at 1PM on this Spring equinox for this system here in Hilo, Hawaii. These mods are SunPower 245s with the Power-One micro 250s. Notice that the AC outputs below are 223 watts and higher. If we had installed Enphase M215s instead, the max output possible would be ~ 224 watts. If theres clipping this early in the year, imagine the degree to which the clipping will be increasing in the months to come as the solar insolation increases. And these mods were only 245s. Enphase states that their M215s are fine with modules up to 265 watts! Imagine the amount of clipping taking place when that kind of pairing takes place. marco image005.png image006.png ___ List sponsored by Home Power magazine List Address: mailto:RE-wrenches@lists.re-wrenches.orgRE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orghttp://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orghttp://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: http://www.re-wrenches.org/etiquette.htmwww.re-wrenches.org/etiquette.htm Check out participant bios: http://www.members.re-wrenches.orgwww.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 inline: 6aa851.jpg___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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] P1 micro performance
The power quality should not be adversely affected. While I'm sure different manufacturers may limit power in different ways, in theory all the inverter is doing is moving the array off its MPP. Here's a description from AE: If the power available from the array exceeds the nameplate rating of the inverter, the inverter will limit the power and current coming from the array to the inverter’s maximum nameplate power and current rating. The inverter does this by reducing the DC input current, which causes the DC operating voltage to rise above the maximum power point of the array, thereby ‘clipping’ the array output. This effectively limits the output of the array without stressing the inverter. http://solarenergy.advanced-energy.com/upload/File/Application%20Notes/DCLoadingOfPVPinverters.55-600100-75-A.pdf On Mar 22, 2013, at 9:52 AM, William Dorsett wrote: OK, if the upper limit if the curve is “flat topped” do we get increased problems with harmonic noise at the knee as you would in modified “square” wave? Bill Dorsett Manhattan, KS From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of David Brearley Sent: Friday, March 22, 2013 8:43 AM To: RE-wrenches Subject: Re: [RE-wrenches] P1 micro performance Thanks for the clarification. FWIW: Flat topping is exactly what occurs. Inverter limiting clips the inverter output power curve (not the voltage or current wave forms). The chart below has one data point for every hour of the year. The clipped/flat-top area is the result of the 225 kW inverter limiting the power output of a 385 kW array: image001.jpg On Mar 22, 2013, at 1:07 AM, boB wrote: On 3/21/2013 9:59 PM, Exeltech wrote: Wrenches, I'm probably a lone voice on this .. and not intending to get overly picky. No, two lonely voices, Dan. I associate clipping with audio waveforms which stops the negative or positive voltage peaks flat. Also called flat-topping. Limiting is like turning down the volume. The waveform stays the same and does not distort as it would if it were being flat topped (and flat bottomed) Thanks ! boB Could we call power limiting what it is .. limiting, and not clipping? Clipping implies distortion, which isn't the case here. Limiting is just that. The inverter output is limited to some maximum value -- not clipped. The output power curve flattens when integrated over time, but this still isn't distortion in the waveform. It's simply a point in the output where the derivative is zero. Not increasing, not decreasing. Just .. zero. No additional increase in the output for an increase in available energy at the input. Think governor on an engine Thanks. Dan Lepinski, Sr. Engineer Exeltech / Exeltech Solar Products --- On Thu, 3/21/13, David Brearley david.brear...@solarprofessional.com wrote: From: David Brearley david.brear...@solarprofessional.com Subject: Re: [RE-wrenches] P1 micro performance To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Thursday, March 21, 2013, 11:37 PM Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often—I wouldn't try that here in Texas. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 Change email address 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] P1 micro performance
Good points David, we are in peak season for inverters to be limiting power. Marco, your diagram shows that the modules are only overproducing the Enphase M215's output of 225 watts for a single 15 minute period during the day. That would only equate to about 3 watt-hours of lost power on a day when the modules are producing more than 1000 watt-hours. That tends to be in agreement with our study, which can be viewed at; http://enphase.com/wp-uploads/enphase.com/2011/12/Enphase_White_Paper_Module_Rightsizing.pdf. Averaged across the entire year, this loss of power would total less than 0.1%, and would be less than 0.2% for a 265 watt module. Keep in mind that with degradation accounted for, you will see even less limiting in future years. I'd encourage Wrenches to look closely at the attached document. It is based upon real system production data from Enlighten compared against actual irradiance data. Most analysts would agree that some clipping is good. You will have a better return on your investment when your DC to AC ratio is greater than one. In this case, bigger is better. On Thu, Mar 21, 2013 at 9:37 PM, David Brearley david.brear...@solarprofessional.com wrote: Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often—I wouldn't try that here in Texas. On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote: Check out the output of the modules below at 1PM on this Spring equinox for this system here in Hilo, Hawaii. ** ** These mods are SunPower 245s with the Power-One micro 250s. Notice that the AC outputs below are 223 watts and higher. ** ** If we had installed Enphase M215s instead, the max output possible would be ~ 224 watts. ** ** If there’s clipping this early in the year, imagine the degree to which the clipping will be increasing in the months to come as the solar insolation increases. ** ** And these mods were “only” 245s. Enphase states that their M215s are fine with modules up to 265 watts! Imagine the amount of clipping taking place when that kind of pairing takes place. ** ** marco ** ** image005.png image006.png ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 Change email address 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 -- Cordially, *Nick Soleil* *Field Applications Engineer * *Enphase Energy* Mobile: (707) 321-2937 ** *Enphase Commercial Solar.* *Limitless.*http://www.enphase.com/commercial?utm_source=emailutm_medium=sigutm_campaign=Comm2012 * *http://www.enphase.com/commercial?utm_source=emailutm_medium=sigutm_campaign=Comm2012 1420 North McDowell Petaluma, CA 94954 www.enphase.com http://www.enphaseenergy.com/ P: (707) 763-4784 x7267 F: (707) 763-0784 E: nsol...@enphaseenergy.com [image: nabcep logo] Certified Solar PV Installer #03262011-300 “Don’t get me wrong: I love nuclear energy! It’s just that I prefer fusion to fission. And it just so happens that there’s an enormous fusion reactor safely banked a few million miles from us. It delivers more than we could ever use in just about 8 minutes. And it’s wireless! .” - William McDonough This email message is for the sole use of the intended recipient(s) and may contain confidential and/or privileged information. If you are not an intended recipient, you may not review, use, copy, disclose or distribute this message. If you received this message in error, please contact the sender by reply email and destroy
Re: [RE-wrenches] P1 micro performance
Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often—I wouldn't try that here in Texas. On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote: Check out the output of the modules below at 1PM on this Spring equinox for this system here in Hilo, Hawaii. These mods are SunPower 245s with the Power-One micro 250s. Notice that the AC outputs below are 223 watts and higher. If we had installed Enphase M215s instead, the max output possible would be ~ 224 watts. If there’s clipping this early in the year, imagine the degree to which the clipping will be increasing in the months to come as the solar insolation increases. And these mods were “only” 245s. Enphase states that their M215s are fine with modules up to 265 watts! Imagine the amount of clipping taking place when that kind of pairing takes place. marco image005.png image006.png ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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 Change email address 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] P1 micro performance
Wrenches, I'm probably a lone voice on this .. and not intending to get overly picky. Could we call power limiting what it is .. limiting, and not clipping? Clipping implies distortion, which isn't the case here. Limiting is just that. The inverter output is limited to some maximum value -- not clipped. The output power curve flattens when integrated over time, but this still isn't distortion in the waveform. It's simply a point in the output where the derivative is zero. Not increasing, not decreasing. Just .. zero. No additional increase in the output for an increase in available energy at the input. Think governor on an engine Thanks. Dan Lepinski, Sr. Engineer Exeltech / Exeltech Solar Products --- On Thu, 3/21/13, David Brearley david.brear...@solarprofessional.com wrote: From: David Brearley david.brear...@solarprofessional.com Subject: Re: [RE-wrenches] P1 micro performance To: RE-wrenches re-wrenches@lists.re-wrenches.org Date: Thursday, March 21, 2013, 11:37 PM Thanks for sharing the screen capture, Marco. Interesting issues to think about here. This is actually prime clipping season in many places (not sure about Hawaii) due to the cool weather. While there are more sun-hours in the summer, the cell temperatures are often high enough that you won't tend to see rated power out of the modules. While I'm not running performance models for work, the people who do are routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said that, most inverters aren't installed on a roof. (Not yet anyway.) I'd probably lean to a more conservative sizing ratio for micros. While I can imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 W/m^2 very often—I wouldn't try that here in Texas. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address 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
