by AndyH (Posted Mon, 25 Mar 2013 16:01:45 GMT)
I'm sorry to report that I missed your grand summary post on page 2. While I did appreciate reading the report by the gents hired by the venture capitalists, I hope you're not disappointed when I suggest that's not independent. In my experience (such as it is) when an electronics, PV, battery, or other energy-related manufacturer wants independent validation of their products, they send them to a national lab or one of the independent commercial test facilities. I've reports from Sandia on the lithium cells I used to import, for example. I hoped for something that confirms the total performance the devices from a truly independent source. I'd like to see results from accelerated testing on all inverters, but that's not likely to happen.
Note that the #1 criticism about the devices from the balance of the industry is on the capacitors. Note that the VC team didn't want an analysis of semiconductor life or heat dissipation, or optoelectronics, they wanted to know if the caps could survive. I'm not saying that the device is bad, or that the cap choices are bad - I'm only saying that Enphase was forced to provide these papers because they addressed specific criticisms from industry and potential customers. That's also why they had to push the warranty to 25 years - they'd certainly much rather have the warranty tail the industry standard 5 years long. It's a business decision forced on them, not a show of altruism. The engineering was driven by the warranty, not the other way around, because products are engineered to be just good enough and not a penny more. That's basic business.
![;)]( "Wink")
No Reg - this is not correct. What I have said a number of times is that in order to estimate system life I 1. went back to the designers so that I could evaluate their design goals and how well they think they achieved them, and 2. sought folks that are successfully doing what I intend to, in order to learn of their experiences. This is required because some of the equipment is too new - are are no 20+ year field studies available for much of what I've chosen. The only reason I brought that into the conversation was to point out that we are looking at similar problem from different directions.
As for "string inverters" (and central inverters), I agree completely! Apparently utility-scale central inverter manufacturers do as well - that's why many of them do not use electrolytic capacitors at all. There's been a two-pronged push in the inverter industry - one to bring prices down (Sunshot program), and the other to increase reliability. Manufacturers understand that optical devices, e-caps, and IGBTs are wear items.
I asked you about Enphase, not any other product. In order to achieve a long capacitor life, at least some of the electrolyte should stay inside and active. The fact remains, as Enphase has clearly stated, that they do not expect the caps to live beyond 15 years even in their products with a 25 year warranty. As you've already stated, you'll accept an efficiency hit later in the life of the inverter.
That's fine - I'm glad we've gotten here! As we've agreed earlier, no device is perfect and designers must design around the strengths and weaknesses of the parts with which they're working. It appears that, at least as of Feb 2010, the folks at Enphase are also satisfied with a loss of efficiency and solar harvest when a customer uses their inverters:
For grid-scale applications:
Home-scale systems:
Note this comment from a utility-scale central inverter manufacturer from the same interview. It gives insight into their concerns and focus as well as their reliability goals:
Feb 4, 2010, number 54 on the I-Tunes list.
http://www.renewableenergyworld.com/rea/news/podcast/2010/02/micro-inverters-vs-central-inverters-is-there-a-clear-winner
https://itunes.apple.com/us/podcast/ins ... d135363982
This is incorrect, Reg. Neither the paper you linked, nor Enphase's "Proprietary and Confidential" version use live inverter data.
http://enphase.com/wp-uploads/enphase.com/2011/11/EnphaseElectrolyticCapacitorLife092908.pdf
http://enphase.com/downloads/ElectolyticCapacitorLife092908.pdf
Both clearly state that while they did use climactic data for Palm Springs, it came from:
While I'm not suggesting that the calculated result will be statistically insignificant when compared with actual performance data for an array in Palm Springs, it is clear that the capacitor evaluation exercise was nothing more or less than a paperwork exercise. No actual capacitor temperatures were used.
But AndyH, you have come here and claimed the units would last for 20 years if you replace the fans. I see no such statement from Midnite anywhere. i see no discussion of how these capacitors are used and how an insependent reliability expert has done additonal anaylysis and testing to verify a long life. Instead, they provide a 5-year warranty.
Incorrect again, Reg. I NEVER claimed that my charge controller would last for "20 years if I replace the" fan. What I have said a number of times is that I will keep a spare fan and a set of replacement capacitors in a maintenance box in case they should be needed later. I did say, however, that I intend to maintain the device so that it provides a 20 year real-world lifespan. Besides, the Classic can be run in a sealed configuration - fanless - for only a slight loss of power (For a 24 volt battery, max current drops from 94A to 80A). Since I am already derating the entire system to 80% max (45% for the charge controller), the fan is not a factor, dead or alive.
Maybe, as with Enphase, I'll decide in 12 years that there is an acceptable amount of ripple on the PV line and simply leave the device on-line. It's good to have options, yes?![;)]( "Wink")
I didn't say MPPT charge controllers, did I? That's a significant part of the problem here, Reg, because some in the microcontroller camp, likely only those with a marketing bent, feel it's ok to use reliability or warranty information from very old tech in order to make their devices look better. The fact remains that some old tech charge controllers, off-grid inverter/chargers, and grid tied devices - including microinverters - had horrible records! But not all - and this is important! There are plenty of devices that have 30+ years of real-world fault-free service.
Off track again already? Haven't you been telling me it's wrong to bring off-grid inverters into the mix? I'm confused!![:lol:]( "Laughing")
Peak for the VFX3524 is 92% VS the 96.3% peak for an M215. This is a bogus comparison though, Reg, and I suspect you know that.
Firstly, if we want to compare PV harvest efficiency, we'll need to put an array with micros up against an array with a charge controller. But even that's not a great comparison, because while they both perform MPPT and some level of DC/DC conversion, the micro is also inverting.
Secondly, the goals and real-world experience for grid-tied and off-grid folks are different. Many grid-tied operators want to put as much sun on the grid as possible. Others want enough to net-zero every 12 months. Off-grid folks, on the other hand, want full batteries daily. Once the battery is full, any energy not used is wasted. On good sun days when the battery's full, we go hog-wild and run the waffle iron and the washing machine and the welder.![:lol:]( "Laughing")
http://www.homepower.com/articles/toast-pancakes-and-waffles
Third, when I'm pulling power from the inverter when the sun's out, the path is PV-charge controller-inverter-outlet and in that regime, I expect the inverter's 92% efficiency to combine with the charge controller's ~96% to give me about 88%. I completely agree that efficiency is lower when the sun's down. Flooded lead acid is close to 100% when below 80% state of charge, so at best nighttime efficiency is about 87%. Off grid efficiency is not compared with grid-tied, however - it's compared with the grid it's severed from. And an off grid system on a bad day is more efficient than the grid on a perfect day.
Yes, many do use fans. Not all do, however. Outback has VFX...models (vented/fan cooled) as well as FX... (sealed, not fan cooled). They both live long lives in the field. And they both have the same warranty length.They've only been in the field for ten years and they contain the same electrolytic capacitors that you have villified Enphase for using. By Nichicon's definition, they will not live beyond 15 years no matter what. But beyond that, they are on 24/7. Pleas show me the analysis that indicates the many, many electrolytic capacitors in the Outback inverters will last for the 20 years that you have claimed, even though the manufacturer only back you up for five.
They plan to make good money selling parts. It's a poor business model, IMO, which has run its course.
I haven't villified anyone for anything, just trying to find the connection between a 15 year part and the 25 year warranty that you claim is equivalent to service life.![;)]( "Wink")
Off-grid inverters are generally not pushing power 24/7, by the way, Even hard-core homeowners do have to sleep. More efficiency-oriented off-gridders use a small inverter to handle the small 24/7 loads so that the primary unit can be sure to sleep as well. Off-grid inverters get some of the capacitor-extending beauty sleep that grid-tied inverters are reported to get.![:lol:]( "Laughing")
Hang on - they plan to make good money selling parts? Parts for what - their inverters that you say will die soon after their fifth year in operation?![;)]( "Wink")
But - didn't you say that the string/central/off-grid inverter manufacturers don't have any failure visibility after the 5th year? Seems to me it would be a pretty brain-dead corporation that was not tracking owners of their junk if they planned an income stream from parts sales! Seriously - get on the phone - maybe they'll give you a reward for your suggestion! ![:lol:]( "Laughing")
Seriously? Another course change? What I reported is that the ENTIRE INVERTER INDUSTRY is not large enough to sway capacitor manufacturers. It doesn't matter what any single manufacturer does in this instance as it's still a relatively small overall industry.
As far as I'm concerned, Reg, my desired mission is complete. I think we've agreed that off-grid inverters are not performing an equivalent task with any type of grid-tied inverter, whether micro, string, or central. Because of that, I don't think that pulling off-grid stats into a microinverter discussion is useful. By extension, and more to the point, I think it's very useful to understand that it's not useful to point to inverters with fans as there are plenty of devices on the streets that do not use fans and also ship with a 99% uptime guarantee.
Additionally, I think we agree that electrolytic capacitors are a limiting component in power electronics and that devices that do not use them have the potential of being more reliable than equipment that incorporates them - even if they provide redundant parts.
Finally, I think we agree that one should evaluate an entire design - including pros and cons of alternate architectures - before making the final decision about which tech to select.
RegGuheert wrote:
AndyH wrote:
Can (or have?) you provided proof of independent life tests for Enphase's inverters?
I have. The contact information is included in the documentation for verication.I'm sorry to report that I missed your grand summary post on page 2. While I did appreciate reading the report by the gents hired by the venture capitalists, I hope you're not disappointed when I suggest that's not independent. In my experience (such as it is) when an electronics, PV, battery, or other energy-related manufacturer wants independent validation of their products, they send them to a national lab or one of the independent commercial test facilities. I've reports from Sandia on the lithium cells I used to import, for example. I hoped for something that confirms the total performance the devices from a truly independent source. I'd like to see results from accelerated testing on all inverters, but that's not likely to happen.
Note that the #1 criticism about the devices from the balance of the industry is on the capacitors. Note that the VC team didn't want an analysis of semiconductor life or heat dissipation, or optoelectronics, they wanted to know if the caps could survive. I'm not saying that the device is bad, or that the cap choices are bad - I'm only saying that Enphase was forced to provide these papers because they addressed specific criticisms from industry and potential customers. That's also why they had to push the warranty to 25 years - they'd certainly much rather have the warranty tail the industry standard 5 years long. It's a business decision forced on them, not a show of altruism. The engineering was driven by the warranty, not the other way around, because products are engineered to be just good enough and not a penny more. That's basic business.
RegGuheert wrote:
Have you provided ANY evidence or analysis from the manufacturer or anyone else that the Classic Controller or the OutBack inverters can achieve a long life? No, you haven't. All you have done is you have claimed that you met some unnamed people at some unnamed internet location who had good experiences.
I'll answer for me, thanks. 
No Reg - this is not correct. What I have said a number of times is that in order to estimate system life I 1. went back to the designers so that I could evaluate their design goals and how well they think they achieved them, and 2. sought folks that are successfully doing what I intend to, in order to learn of their experiences. This is required because some of the equipment is too new - are are no 20+ year field studies available for much of what I've chosen. The only reason I brought that into the conversation was to point out that we are looking at similar problem from different directions.RegGuheert wrote:
AndyH wrote:
The paper includes plenty of numbers and other info that appears to be backed by cap manufacturers design documents. But there's a subject that's missing - electrolyte. Under the best conditions, electrolyte is consumed in the capacitor. Seal degrade and electrolyte leaks.
Actually, the Nichicon paper that Enphase references covers that subject in some detail. The electrolyte is apparently also consumed in the process of "healing". More healing occurs under high-voltage operation, which is why the string inverters have more difficulty achieving a very long life.As for "string inverters" (and central inverters), I agree completely! Apparently utility-scale central inverter manufacturers do as well - that's why many of them do not use electrolytic capacitors at all. There's been a two-pronged push in the inverter industry - one to bring prices down (Sunshot program), and the other to increase reliability. Manufacturers understand that optical devices, e-caps, and IGBTs are wear items.
I asked you about Enphase, not any other product. In order to achieve a long capacitor life, at least some of the electrolyte should stay inside and active. The fact remains, as Enphase has clearly stated, that they do not expect the caps to live beyond 15 years even in their products with a 25 year warranty. As you've already stated, you'll accept an efficiency hit later in the life of the inverter.
That's fine - I'm glad we've gotten here! As we've agreed earlier, no device is perfect and designers must design around the strengths and weaknesses of the parts with which they're working. It appears that, at least as of Feb 2010, the folks at Enphase are also satisfied with a loss of efficiency and solar harvest when a customer uses their inverters:
For grid-scale applications:
Raghu Balure VP marketing Enphase wrote:
You don't have to go out there and fix a broken module or fix a broken inverter until you're on [the next scheduled service visit...]
Home-scale systems:
Quote:
In the unlikely event you have a failure, you don't have to service it for a year because the loss of energy is so small...you can choose to fix it whenever it's convenient.
Note this comment from a utility-scale central inverter manufacturer from the same interview. It gives insight into their concerns and focus as well as their reliability goals:
Leo Casey SatCon (8KW up commercial and utility-scale) wrote:
Reliability ultimately is about wear-out if things are well made. It's about components, it's not about voltages and it's not semiconductors, it's about components. Satcon has not sold a product in our history that used a single electrolytic capacitor. We've not sold a product in at least 10 years that's used any optical components or optical isolators. It's well known that if you use those sort of components in hot environments and in environments that have temperature cycling that you have a fundamental limit to the lifetime of the product...Satcon is very comfortable giving a 99% up-time guarantees...Extensive studies have shown that inverters today, big inverters, exceed 99% uptimes, this is by independent people.
Feb 4, 2010, number 54 on the I-Tunes list.
http://www.renewableenergyworld.com/rea/news/podcast/2010/02/micro-inverters-vs-central-inverters-is-there-a-clear-winner
https://itunes.apple.com/us/podcast/ins ... d135363982
RegGuheert wrote:
AndyH wrote:
The paper presents a 'paper exercise' that uses climate data from NREL. The numbers in this paper were NOT generated by instrumenting an inverter and putting it on a roof. Why not?
Clearly you didn't read the independent analysis paper. The author clearly stated that Enphase had provided measured data from instrumentation inside inverters in Palm Springs to verify the temperature assumptions.This is incorrect, Reg. Neither the paper you linked, nor Enphase's "Proprietary and Confidential" version use live inverter data.
http://enphase.com/wp-uploads/enphase.com/2011/11/EnphaseElectrolyticCapacitorLife092908.pdf
http://enphase.com/downloads/ElectolyticCapacitorLife092908.pdf
Both clearly state that while they did use climactic data for Palm Springs, it came from:
Quote:
The climatic and irradiance data used in this test was obtained from the National Solar Radiation Data Base (NREL), which provides hourly meteorological data for locations throughout the United States.
While I'm not suggesting that the calculated result will be statistically insignificant when compared with actual performance data for an array in Palm Springs, it is clear that the capacitor evaluation exercise was nothing more or less than a paperwork exercise. No actual capacitor temperatures were used.
RegGuheert wrote:
AndyH wrote:
The equipment that interfaces with the panels in an off-grid system is the charge controller. They 'only' have to do DC-DC.
It's true. But the Classic Controller the you (and I) have bought have fans which I think we both agree need replacement every five years to avoid a catastrophic failure. But they also have electrolytics capacitors inside. I see five of them. If they have been well-designed into the application, they can possibly reach the 15-year design limit that Nichicon sees. If they are not well-designed in the application, they should fail before that point. Since Midnite only warrants five years of operation, not analysis is needed to convince the customer that these will last for five years.But AndyH, you have come here and claimed the units would last for 20 years if you replace the fans. I see no such statement from Midnite anywhere. i see no discussion of how these capacitors are used and how an insependent reliability expert has done additonal anaylysis and testing to verify a long life. Instead, they provide a 5-year warranty.
Incorrect again, Reg. I NEVER claimed that my charge controller would last for "20 years if I replace the" fan. What I have said a number of times is that I will keep a spare fan and a set of replacement capacitors in a maintenance box in case they should be needed later. I did say, however, that I intend to maintain the device so that it provides a 20 year real-world lifespan. Besides, the Classic can be run in a sealed configuration - fanless - for only a slight loss of power (For a 24 volt battery, max current drops from 94A to 80A). Since I am already derating the entire system to 80% max (45% for the charge controller), the fan is not a factor, dead or alive.
Maybe, as with Enphase, I'll decide in 12 years that there is an acceptable amount of ripple on the PV line and simply leave the device on-line. It's good to have options, yes?
RegGuheert wrote:
AndyH wrote:
They're known to last much longer than their warranty as well - like the 30+ year example referenced earlier.
I must have missed the refernce. No matter. There are no thirty-year-old MPPT charge controllers out there. Those didn't start to show up in the market until the 1990s. I have a whole pile of dead ones in my attic from one of the earlier attempts.I didn't say MPPT charge controllers, did I? That's a significant part of the problem here, Reg, because some in the microcontroller camp, likely only those with a marketing bent, feel it's ok to use reliability or warranty information from very old tech in order to make their devices look better. The fact remains that some old tech charge controllers, off-grid inverter/chargers, and grid tied devices - including microinverters - had horrible records! But not all - and this is important! There are plenty of devices that have 30+ years of real-world fault-free service.
RegGuheert wrote:
AndyH wrote:
But this is all a huge red herring. Why? Because the central inverter world, both off-grid and large scale grid tied, sees capacitors as a maintenance item and designs for repairability.
Agreed.AndyH wrote:
Enphase, on the other hand, is willing to accept the loss of efficiency when the caps fail in their non-serviceable assemblies. And, again, it's NOT about warranty, as Enphase's primary customers - folks like us and our parents - are not at ALL likely to notice the efficiency deterioration from years 12 thru 25 either because they're not looking, or because it's lost in the noise of panel and wiring deterioration and is thus deniable by Enphase.
Let's see...Enphase inverters offer an efficiency of around 95% while your Outback inverter peaks around 90%. Considering a grid-tied system harvests well over 90% of the electricity coming from the panels while an off-grid system might achieve 25% to 50%, I don't think a drop of a couple of percent at the end of the life of the inverter is a terrible thing.Off track again already? Haven't you been telling me it's wrong to bring off-grid inverters into the mix? I'm confused!
Peak for the VFX3524 is 92% VS the 96.3% peak for an M215. This is a bogus comparison though, Reg, and I suspect you know that.
Firstly, if we want to compare PV harvest efficiency, we'll need to put an array with micros up against an array with a charge controller. But even that's not a great comparison, because while they both perform MPPT and some level of DC/DC conversion, the micro is also inverting.
Secondly, the goals and real-world experience for grid-tied and off-grid folks are different. Many grid-tied operators want to put as much sun on the grid as possible. Others want enough to net-zero every 12 months. Off-grid folks, on the other hand, want full batteries daily. Once the battery is full, any energy not used is wasted. On good sun days when the battery's full, we go hog-wild and run the waffle iron and the washing machine and the welder.
http://www.homepower.com/articles/toast-pancakes-and-waffles
Third, when I'm pulling power from the inverter when the sun's out, the path is PV-charge controller-inverter-outlet and in that regime, I expect the inverter's 92% efficiency to combine with the charge controller's ~96% to give me about 88%. I completely agree that efficiency is lower when the sun's down. Flooded lead acid is close to 100% when below 80% state of charge, so at best nighttime efficiency is about 87%. Off grid efficiency is not compared with grid-tied, however - it's compared with the grid it's severed from. And an off grid system on a bad day is more efficient than the grid on a perfect day.
RegGuheert wrote:
AndyH wrote:
RegGuheert wrote:
Most off-grid inverters and charge controllers continue to use fans for cooling and that fact is reflected in their short warranty periods.
Yes, many do use fans. Not all do, however. Outback has VFX...models (vented/fan cooled) as well as FX... (sealed, not fan cooled). They both live long lives in the field. And they both have the same warranty length.
They plan to make good money selling parts. It's a poor business model, IMO, which has run its course.
I haven't villified anyone for anything, just trying to find the connection between a 15 year part and the 25 year warranty that you claim is equivalent to service life.
Off-grid inverters are generally not pushing power 24/7, by the way, Even hard-core homeowners do have to sleep. More efficiency-oriented off-gridders use a small inverter to handle the small 24/7 loads so that the primary unit can be sure to sleep as well. Off-grid inverters get some of the capacitor-extending beauty sleep that grid-tied inverters are reported to get.
Hang on - they plan to make good money selling parts? Parts for what - their inverters that you say will die soon after their fifth year in operation?
But - didn't you say that the string/central/off-grid inverter manufacturers don't have any failure visibility after the 5th year? Seems to me it would be a pretty brain-dead corporation that was not tracking owners of their junk if they planned an income stream from parts sales! Seriously - get on the phone - maybe they'll give you a reward for your suggestion! RegGuheert wrote:
AndyH wrote:
While your faith in the company is admirable, there is absolutely no way that Enphase's ~12% of residential generation, has pull with component manufacturers that the companies serving the remaining 88% of residential, plus commercial plus industrial scale plus mobile inverters plus the automotive/hybrid/EV sector has.
You're kidding, right? Enphase sells an inverter for each PV panel. They have literally sold MILLIONS of them, each one with four of the Nichicon capacitors. Yes, anyone who purchases 10 million components within a four-year timeframe will have sway with their suppliers. Can you name any other inverter company who has used 10 million components of a single type in their products? How about 100,000?Seriously? Another course change? What I reported is that the ENTIRE INVERTER INDUSTRY is not large enough to sway capacitor manufacturers. It doesn't matter what any single manufacturer does in this instance as it's still a relatively small overall industry.
As far as I'm concerned, Reg, my desired mission is complete. I think we've agreed that off-grid inverters are not performing an equivalent task with any type of grid-tied inverter, whether micro, string, or central. Because of that, I don't think that pulling off-grid stats into a microinverter discussion is useful. By extension, and more to the point, I think it's very useful to understand that it's not useful to point to inverters with fans as there are plenty of devices on the streets that do not use fans and also ship with a 99% uptime guarantee.
Additionally, I think we agree that electrolytic capacitors are a limiting component in power electronics and that devices that do not use them have the potential of being more reliable than equipment that incorporates them - even if they provide redundant parts.
Finally, I think we agree that one should evaluate an entire design - including pros and cons of alternate architectures - before making the final decision about which tech to select.