AndyH
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 2:04 pm

RegGuheert wrote:
AndyH wrote:No, stop reading into the statement. I didn't say a THING about microinverters - only temperatures.
This thread is about microinverters, not roofs. Please start a separate thread if you want to discuss roofs.
The thread appears to be about the negative effects of high temperature environments on microinverter life. It seems to me that some awareness of where we might have high temperature environments might be germane.

I'm expecting dead canaries from the SW through Florida.
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RegGuheert
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 2:35 pm

AndyH wrote:The thread appears to be about the negative effects of high temperature environments on microinverter life. It seems to me that some awareness of where we might have high temperature environments might be germane.
It is. I think we agree that very high temperatures will reduce both MTBF and product life. But the absolute value of the temperature is very important in the discussion. In other words, just saying the South is hotter than the North does not condemn microinverters. But if it gets TOO hot in the South then the microinverters will not live long enough to serve their owners as expected.

I've given some details about the internal temperatures of my inverters at their very hottest point as well as some details about my array. Can we determine what the deck temperature of my shingles would have been that day had the PV system NOT been installed? Would it be higher , lower, or about the same? How much? If not, then we cannot make the opposite calculation of microinverter temperature from roof temperature. My point is that this correlation depends heavily on many factors which I previously detailed.
AndyH wrote:I'm expecting dead canaries from the SW through Florida.
You may very well be correct.

One thing I would like to know is whether we are in the bottom of the bathtub curve in Phoenix with the M190s or are we starting to rise the end-of-life portion of the curve. If it is the former, then my MTBF calculations are meaningful, and a version focused on Phoenix systems would be even more interesting. Particularly if we compare it with the MTBF in other areas. To be quite frank, I'm alarmed to notice that the currently-calculated MTBF for my local geographical area is higher than what I think is given for AZ. I will try to greatly increase the sample size for both areas to try to get more accurate data and therefore see if this is anomalous or perhaps real.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

LEAFfan
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 2:43 pm

RegGuheert wrote:
AndyH wrote:Exactly! That's what I tried to show in another thread. The problem isn't limited to Arizona - the sun is pretty intense 'down here' across the south. Those 170-180°F roof deck temps run through Texas and Florida as well.
But do roof deck temperatures correllate well with microinverter temperatures? It seems there are many factors involved so it would be very hard to know if the climate for the inverter would be hotter, cooler or about the same as the bare roof deck had been. Here are some factors:

- Original color of the roof deck. Of course if the roof is a lite color it will reflect a significant amount of sunlight and will therefore run cooler. A black roof will attain the highest temperatures.
- A producing PV panel (such as one with a microinverter attached) should never attain as high a surface temperature as a black roof would. This is because the PV panel will convert 12 to 18% of the light into electricity rather than heat. OTOH, the PV panel may attain higher surface temperatures than a white roof would.
- The microinverter lives in an environment beneath the PV panel. In cases where the air is mostly trapped around the inverter that environment might resemble a solar cooker, resulting in a large temperature rise in the air around the inverter. In other cases, there will be easy movement of ambient air around around the microinverter perhaps aided by a chimney effect caused by the heating of the panels themselves.

By looking at the peak temperatures in the microinverters on our roof, I can see that there is a fairly wide range of environments found there. Both the hottest and the coldest inverter are found on the garage. The hottest is in the top row, third from the right end while the coolest is in the bottom left corner. The former is at the top of the "chimney" and in and oven, of sorts and the latter is at the bottom of the "chimney" and is very open to ambient air. I will say that the thermal environment would have been significantly better had I run the mounting rails up and down the roof rather than side-to-side. (Of course, the panels would not have fit very well that way!)

In any case, it seems that the M215s should manage to live in an environment for which they are designed in all but the very worst installations/inverter locations. But I'll agree that if the term "Operating temperature range" on the M190 datasheet means the INTERNAL temperature like it does on the M215 datasheet (and I think it does), then those electrolytic capacitors might be spending a few hours during some summer days close to 85C. Is that a problem for the capacitors? I doubt it. According to Nichicon, they should be able to live for 32,000 hours (3.6 years) operating at that temperature. Since they spend the vast majority of their life significantly cooler than that, they should be good for well over a decade. So my conclusion is that none of these capacitors must be worn out yet.

But the high temperatures and daily thermal cycling stress everything, including solder joints. So are we seeing a wide range of random failures with the rate increased by the heat or is there a consistent failure mode in the M190s. While I'm sure Enphase knows the answer since they replace all the failures and pay for return shipping, it's really hard for us to say.

Perhaps someone with microinverters also has a roof sensor. LEAFfan, do you have access to internal temperature data from your inverters? It would be interesting to compare that to your roof sensor.
No, but the highest operating temp for them is 70C/158F and of the seven needing replaced, six of those are at the top of the array. There's a fairly big gap between the MI and the roof, but it doesn't seem to help that much. One thing about my MIs is that along with the PV panels, they are guaranteed for 25 years. I just hope Exeltech stays in the MI production for at least 25 years.
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RegGuheert
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 3:01 pm

LEAFfan wrote:No, but the highest operating temp for them is 70C/158F and of the seven needing replaced, six of those are at the top of the array.
O.K. Thanks! That agrees with the temperature gradients that drees and I are seeing in our arrays.
LEAFfan wrote:There's a fairly big gap between the MI and the roof, but it doesn't seem to help that much.
Yeah, the bottom of our microinverters are four or more inches above the surface of the shingles, but the peak temperatures of some of them in the top row are about 25F higher than those of the coolest units. That's a pretty big difference!
LEAFfan wrote:One thing about my MIs is that along with the PV panels, they are guaranteed for 25 years. I just hope Exeltech stays in the MI production for at least 25 years.
But replacing microinverters can be quite a job depending where they are located in the array. Hopefully Exeltech has been able to identify and fix a root cause for your failures so that your replacements will live a much longer life.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

LEAFfan
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 3:08 pm

Yeah, the replacements (14) that arrived today were made in March, 2013. Hopefully, they are more robust. Usually, they send one replacement at a time which takes at least two weeks, sometimes longer until installed, but this time I asked if they would send a few extra and they sent me 14! :mrgreen:
The installer is coming Monday morning and I'm going to watch the installation. Last time it took about 5 minutes to switch one out. Only four screws hold them in place underneath the panel. The MIs are located at the top of each panel, so the top ones are much easier to replace. Labor is for only 5 years, then I'll have to replace them myself.
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RegGuheert
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Re: AZ: Canary in the coalmine for microinverters, too?

Sun Apr 21, 2013 3:11 am

LEAFfan wrote:Yeah, the replacements (14) that arrived today were made in March, 2013. Hopefully, they are more robust. Usually, they send one replacement at a time which takes at least two weeks, sometimes longer until installed, but this time I asked if they would send a few extra and they sent me 14! :mrgreen:
That's awesome! I guess Exeltech has realized that labor is, by far, the most expensive part of the warranty calls.
LEAFfan wrote:The installer is coming Monday morning and I'm going to watch the installation. Last time it took about 5 minutes to switch one out. Only four screws hold them in place underneath the panel. The MIs are located at the top of each panel, so the top ones are much easier to replace. Labor is for only 5 years, then I'll have to replace them myself.
Yeah, those look quite a bit easier to install than our microinverters, at least for the top row. The rest will take some more effort. Watch carefully to see how the installer deals with "healing the wound" on the drop cable when he removes the old inverter cable which stabs through the insulation.
LEAFfan wrote:There's a fairly big gap between the MI and the roof, but it doesn't seem to help that much.
O.K. I had a look at Exeltech's website and I see that their "AC Modules" are actually integrated into the back of the PV panel in place of the junction box. While this might be convenient for installers, it is almost certainly a much worse thermal environment than the one Enphase inverters live in since the panel is heated directly by sunlight.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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RegGuheert
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Re: AZ: Canary in the coalmine for microinverters, too?

Sun Apr 21, 2013 8:56 am

drees wrote:Anecdotally, it seems that if a site has one failure, it appears that it is more likely to experience additional failures. It seems that there may have been some bad batches here and there resulting in premature failure. Specifically with the M380.
Well, I'm seeing this in spades now! I've added all of the systems within about a 35-mile radius that have a public website and there are a total of about 15 M190-based publicly-visible systems. Of those, two of the installations look particularly bad: one with five out of 21 inverters failed, one with 11 of of 33 inverters failed. And there is a third local system with three inverters underperforming, but not yet replaced.

If I calculate the local M190 MTBF with those two systems included, I come up with only 61 years, and that does not include the last three failures listed above. (That calculation includes about 1350 device-years of operation.)

So what about these systems that are failing? I don't think heat is a real issue around here. As I've shown, none of our inverters have ever exceeded their maximum specified operating temperature, although a couple have come close. Perhaps cycling both very hot and very cold could be an issue, but who knows? I suppose it could be bad batches of inverters, but it could also be something site-specific, such as the failure to properly ground the equipment or perhaps problems with lightning. I think my one failure occurred during a period of time when the array was not grounded.

So far I see no indication of any failures of M215s anywhere.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

QueenBee
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Re: AZ: Canary in the coalmine for microinverters, too?

Sun Apr 21, 2013 10:52 am

RegGuheert wrote:
LEAFfan wrote:The installer is coming Monday morning and I'm going to watch the installation. Last time it took about 5 minutes to switch one out. Only four screws hold them in place underneath the panel. The MIs are located at the top of each panel, so the top ones are much easier to replace. Labor is for only 5 years, then I'll have to replace them myself.
Yeah, those look quite a bit easier to install than our microinverters, at least for the top row. The rest will take some more effort. Watch carefully to see how the installer deals with "healing the wound" on the drop cable when he removes the old inverter cable which stabs through the insulation.
LEAFfan wrote:There's a fairly big gap between the MI and the roof, but it doesn't seem to help that much.
O.K. I had a look at Exeltech's website and I see that their "AC Modules" are actually integrated into the back of the PV panel in place of the junction box. While this might be convenient for installers, it is almost certainly a much worse thermal environment than the one Enphase inverters live in since the panel is heated directly by sunlight.
I've never liked the idea of AC modules. The amount of time it saves installing them just doesn't seem worth it. Sure it saves a WEEB and a 1 mount bolt in the case of the M215s but again the materials saving just doesn't seem worth it.

To add to the data. Originally had about a half dozen M215s that got mounted upside down before I realized. Initially I left them because Enphase said it would not be an issue. To better describe this. The M215 has a solid piece of metal as it's top. This is mounted to the top of the rail. So when mounted like that the M215 is actually below the top of the rail. It would seem that the metal plate would also shield the M215 assume the PV panel was hotter than the roof deck. Additionally if we assume that is true then the upside down mounting also made the M215 closer to the PV panel. Anyway, I decided to redo the mounting when I saw that during the summer the M215s mounted this way in the middle of the array were hotter.

I wish I would have recorded the temperatures :( Basically it was something close to this. The hottest normally mounted in the middle of the array M215s were seeing internal temperatures of about 45 degrees C. The ones that were upside down were in the low 50s.

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DaveEV
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Re: AZ: Canary in the coalmine for microinverters, too?

Sun Apr 21, 2013 1:33 pm

RegGuheert wrote:
LEAFfan wrote:There's a fairly big gap between the MI and the roof, but it doesn't seem to help that much.
Yeah, the bottom of our microinverters are four or more inches above the surface of the shingles, but the peak temperatures of some of them in the top row are about 25F higher than those of the coolest units. That's a pretty big difference!
Yeah, that's huge - how many rows of panels are in your array?

My 2-row array (portrait, nearly flat install, ~6" above pretty white asphalt roof) showed about a 10F difference between the coolest/hottest inverter.

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RegGuheert
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Re: AZ: Canary in the coalmine for microinverters, too?

Sun Apr 21, 2013 3:57 pm

drees wrote:Yeah, that's huge - how many rows of panels are in your array?
Three. In portrait format.
drees wrote:My 2-row array (portrait, nearly flat install, ~6" above pretty white asphalt roof) showed about a 10F difference between the coolest/hottest inverter.
You can see my array in the link in my signature, including photographs.

The hottest inverter is under a panel in the top row of the garage, third from the right. Here is the data again from the week containing the hottest day last year: July 6, 2012:
Hottest Inverter 6 July 2012.png
(The new Enlighten website refuses to put Y-axis information on their graphs for anything other than power. But by poking around, I have figured out that the scale for temperature in Fahrenheit is one-half that shown for Power Produced (W). In other words, if you see 250 on the scale, you read the temperature curve as 125F.)

The coolest inverter is under a panel at the bottom-left of the array on the garage. Here is the data again from the same week as shown for the other inverter above:
Coolest Inverter 6 July 2012.png
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RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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