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

Sat Apr 20, 2013 1:32 am

LEAFfan wrote:I have a roof temp sensor, and I believe it hit 170-180F last summer.
Wow! :shock:
That would explain why we see so many failures in AZ. It doesn't explain why I see two failures out of 41 inverters on a roof near here.
LEAFfan wrote:I don't have Enphase micros (have Honeywell/Exeltec), but Monday will be the seventh one to be replaced out of 20. The one Monday is a replacement for a replacement.
What a pain. At some point this becomes unworkable for both the manufacturer and the customer.

In the case of Enphase, I wonder if they will simply offer an upgrade to M215 if the failure rates get high enough.
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.
THAT may explain why the nearby system has two failures. Or perhaps it just happened.

I suspect that the roof characteristics and the installation may play a key role in operating temperatures. For instance, a roof with a low pitch and with the mounting rails down close to the roof should have lower airflow from chimney effect on a still day and thus should see higher temperatures. It may be possible to estimate roof pitch based upon seasonality of production. I wonder if a correlation might be seen there.

I have also taken the additional step of mounting the microinverters on our roof so that the outer "can" is upside down so that water could not pool in the inverter. While Enphase has said these are NEMA 6 rated enclosures and that the encapsulant would prevent water incursion, I didn't want to risk any moisture getting inside. Frankly, it was a pain to do, but who knows it it will make a difference. Perhaps it was wasted effort.
drees wrote:Specifically with the M380.
I don't think I have any M380 failures showing in my spreadsheet, yet. The signature for that should be two adjacent inverters being replaced simultaneously. That's propably because there weren't as many of those installed. IMO, it wasn't one of Enphase' better ideas.
drees wrote:The M215 should be more reliable than the 190W inverters.
Let's hope so. If not, then Enphase may be in serious trouble.
drees wrote:Either way, heat will speed up the failure rate of electronics, just as it speeds up capacity loss of lithium batteries.
Agreed. And that brings us back to the title of the thread. So we watch as we see what appears to be a lower-than-predicted (by Enphase) MTBF in Phoenix. We also have roofs with multiple failures in more moderate climates like around here, which I find surprising.

So, like with the LEAf, the rest of us wonder what the implications are for our installations. While we have a much better warranty in place than Nissan offers for the LEAF, if the overall failure rate is high enough, then Enphase is doomed and our warranties will not cover us.

I wish I could keep this spreadsheet running long-term, but I suspect Enphase will turn off the old websites within the next few months. After that, we will be limited to anecdotal, self-reported data, which is not usable for calculating MTBF.
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?

Sat Apr 20, 2013 4:42 am

RegGuheert wrote:I'll have to look at the temperatures in our inverters on a hot day.
Well, I dug around and found the hottest inverter in our array as well as the highest temperature it achieved. Interestingly, the highest internal inverter temperature was NOT recorded on the hottest day of the year, but rather it was on a hot day with very little wind: July 6, 2012. Here's a plot of power and temperature data for the week around that date:
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.)

As you can see, the inverter achieved a temperature of 149F, which is 65C, the specified limit for this inverter. It stayed at that temperature for one hour. I'm pretty surprised to find that the internal inverter temperature was 54F higher than the day's high temperature of 95F. Also surprising was the fact that the temperature difference between the hottest and the coolest inverter on our roof that day was 25F.

For reference, our roof has a 7/12 pitch, which is the same as a 30-degree elevation. In other words, it is not overly flat. I would expect a flatter roof to have an even higher temperature rise than ours. Also, if the array were larger or had more restrictive airflow, further rises are conceivable. A 65F rise does not seem unreasonable. In Phoenix where the ambient temperature can reach 118F, that means the internal inverter temperature could reach 183F or 84C. It's interesting that this is roughly the maximum internal operating temperature of 85C specified for the M215.
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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

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

Sat Apr 20, 2013 5:56 am

RegGuheert wrote:
LEAFfan wrote:I have a roof temp sensor, and I believe it hit 170-180F last summer.
Wow! :shock:
That would explain why we see so many failures in AZ. It doesn't explain why I see two failures out of 41 inverters on a roof near here.


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.

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

And then there's Illinois: :shock:
Peak wood sheathing temperatures during summer were also reduced by about 4°F for south facing sections (173° vs. 177°f).
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drees
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 7:40 am

RegGuheert wrote:Interestingly, the highest internal inverter temperature was NOT recorded on the hottest day of the year, but rather it was on a hot day with very little wind: July 6, 2012.
I have found the same correlation. Low wind = hot inverters and the hottest inverters are in the middle of rows and if there are multiple rows the higher rows have higher temps.

I believe the panels themselves are seeing the same temperature differences as production tends to be higher on the edges and bottom row, too.

The higher the rails/panels are off the roof the better and having gaps in between rows is good to let the hot air escape. Best case scenario for keeping panels/inverters cool is probably panels tilted up at a higher angle than the roof.
'11 LEAF SL Powered By 3.24 kW Enphase Solar PV

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

Sat Apr 20, 2013 8:15 am

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.
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?

Sat Apr 20, 2013 8:21 am

drees wrote:I have found the same correlation. Low wind = hot inverters and the hottest inverters are in the middle of rows and if there are multiple rows the higher rows have higher temps.
That's precisely the distribution of temperatures that I see, too.
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

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

Sat Apr 20, 2013 11:15 am

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?

Are we missing something here? Two roofs at latitude angles with the same brown asphalt shingles - one in central Wisconsin and one in Shreveport -- which will have the higher roof deck temperature? Which will have the hotter solar panel? Which will have the hotter air between the roof and panel?
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RegGuheert
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 12:26 pm

AndyH wrote:Are we missing something here? Two roofs at latitude angles with the same brown asphalt shingles - one in central Wisconsin and one in Shreveport -- which will have the higher roof deck temperature? Which will have the hotter solar panel? Which will have the hotter air between the roof and panel?
You are making a non sequitur argument here. Just because a roof deck in Shreveport is hotter than a roof deck in Wisconsin it does not follow that a microinverter-based PV installation on the Shreveport roof will have a high failure rate.
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

AndyH
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Location: San Antonio

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

Sat Apr 20, 2013 1:53 pm

RegGuheert wrote:
AndyH wrote:Are we missing something here? Two roofs at latitude angles with the same brown asphalt shingles - one in central Wisconsin and one in Shreveport -- which will have the higher roof deck temperature? Which will have the hotter solar panel? Which will have the hotter air between the roof and panel?
You are making a non sequitur argument here. Just because a roof deck in Shreveport is hotter than a roof deck in Wisconsin it does not follow that a microinverter-based PV installation on the Shreveport roof will have a high failure rate.

No, stop reading into the statement. I didn't say a THING about microinverters - only temperatures.
"The stupid become extinct."-Bill Mollison
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RegGuheert
Posts: 6332
Joined: Mon Mar 19, 2012 4:12 am
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Re: AZ: Canary in the coalmine for microinverters, too?

Sat Apr 20, 2013 1:59 pm

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.
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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