Are Microinverters Reliable?

[lkstaack]

When I was researching PV systems last year, I recall a few sites warning that microinverters were still new to the market and not yet as reliable as string inverters. The consensus seemed to be that microinverters provided many benefits over string, but that they tended to fail after 5 years. Is that still the case?

[russ]

When I was researching PV systems last year, I recall a few sites warning that microinverters were still new to the market and not yet as reliable as string inverters. The consensus seemed to be that microinverters provided many benefits over string, but that they tended to fail after 5 years. Is that still the case?

Now - more or less -
1) micros are good where shade is a problem
2) string inverters are good otherwise
3) micro life? the jury is still out

[subdriver97]

When I was researching PV systems last year, I recall a few sites warning that microinverters were still new to the market and not yet as reliable as string inverters. The consensus seemed to be that microinverters provided many benefits over string, but that they tended to fail after 5 years. Is that still the case?

The majority of problems initially encountered by micros seem to have been overcome by micros as very few are failing as compared to when they first came to market. Note that this statement really only applies to Enphase micros as they have 97+ % of the micro market so there is very little data on other brands. Russ is absolutely correct though, micros have not been around nearly as long as traditional string inverters so there is no case of them been installed for more than several years for the lifespan to be known empirically. The counter point is that Enphase offers a 25 year warranty. Caveat Emptor though, the company Enphase is relatively young and it remains to be seen if Enphase will even be around to back the warranty 25 years from now.

A hybrid solution is gaining popularity involves power optimizers (on the roof) and a power inverter. Personally, I favor this solution as it removes the primary downfall of micro inverters, which is having the heat-sensitive inverter on the roof (in the sun). http://www.solaredge.us

[jimqpublic]

Some other considerations:

Climate under the panels. My flat roof with 15 degrees tilt the microinverter would have 18" airspace under it, so good ventilation. Where I live the summer temps are usually under 90 degrees. In a hotter climate and/or less ideal ventilation the inverter would be subject to more extremes.

Accessibility of inverters. A well spaced array on the ground or a flat roof means that one person can safely access the microinverter by loosening only 1 panel. A big array on a steeply pitched roof over a multi-story building is another matter entirely.

Cost of service call. If you live in a city as I do with several Enphase installers within a 5 mile radius, the cost of a service call is much lower than if you need to pay for a longer drive. Especially important if the company that installed the system goes away.

Risk of total outage vs. partial outage. Some friends had their inverter go out while they were on vacation. By the time they got back, figured there was a problem, called for service, and got a new inverter installed it was 5 weeks. It didn't cost them anything out of pocket but they lost about $300 worth of production towards their annual net-metering bill.


(All based on reading up on the different options. I have decided to go with microinverters but don't have the system designed or installed yet.)

[J.P.M.]

Some other considerations:

Climate under the panels. My flat roof with 15 degrees tilt the microinverter would have 18" airspace under it, so good ventilation. Where I live the summer temps are usually under 90 degrees. In a hotter climate and/or less ideal ventilation the inverter would be subject to more extremes.

Accessibility of inverters. A well spaced array on the ground or a flat roof means that one person can safely access the microinverter by loosening only 1 panel. A big array on a steeply pitched roof over a multi-story building is another matter entirely.

Cost of service call. If you live in a city as I do with several Enphase installers within a 5 mile radius, the cost of a service call is much lower than if you need to pay for a longer drive. Especially important if the company that installed the system goes away.

Risk of total outage vs. partial outage. Some friends had their inverter go out while they were on vacation. By the time they got back, figured there was a problem, called for service, and got a new inverter installed it was 5 weeks. It didn't cost them anything out of pocket but they lost about $300 worth of production towards their annual net-metering bill.


(All based on reading up on the different options. I have decided to go with microinverters but don't have the system designed or installed yet.)

To the temp. issue. My array (18.75 deg. tilt, 195.75 deg. az.) has ~~ 10-12" clearance to the roof deck (which I can get under to meas. temps w/infrared ther.). After about 9 months of measuring panel temps at min. solar incidence angles, in "full" sun, my array temps generally run 20-25 deg. C. above the ambient air temp. on the roof, depending on wind speed/direction and irradiance.

The ambient roof temp. generally runs ~~ 5-8 deg. C. above the ambient air temp. at ground level around the house and neighborhood.

So, FWIW, I'd SWAG the panel temp. run at something like 45 to 60 deg F. (or so) above ground level ambient as a first cut when it's sunny. That's my sit. only, but I'd not be surprised if it was close to others as well.

More FWIW, my measured temps are somewhat in agreement with the calculated temps. used in the SAM temp. algorithm after accounting for roof ambient temp. Wind speed and direction seem to be the biggest source of variability and uncertainty.

[DanS26]

When I was researching PV systems last year, I recall a few sites warning that microinverters were still new to the market and not yet as reliable as string inverters. The consensus seemed to be that microinverters provided many benefits over string, but that they tended to fail after 5 years. Is that still the case?

For a fairly unbiased view of this issue....just look to the financial statements. Audited financial statements are available for Enphase. See here:

http://investor.enphase.com/secfiling.cfm?filingID=1463101-14-7&CIK=1463101

The warranty accruals are one measure the Company's estimation of failure rates. A red flag in this area is if warranty accruals are exceeding the sales growth rate. From 2011 to 2013 Enphase sales increased by 55.7% compared to the increase of warranty accruals of 248%, same period.

It is a metric worth watching to see how it is trending in the longer term.

[Mike90250]

My opinions
Avoid shade on the roof, route the panes around the shade.
Avoid electronics on the roof, optimizers and inverters are about the same thing, they manage about 200w of power, regardless of if it's AC or DC, still a pain to replace

And I've heard that one of the micro inverter companies now only covers the inverter, not the replacement labor. And their "privacy" rules are stifling the reporting of failures.

[sdold]

And their "privacy" rules are stifling the reporting of failures.

Mike, could you tell us more about that? I'm trying to learn how the M215's have been holding up.

[MGE]

Installed 34 Suniva 260w panels with M215 micros back on May 2013 and have generated 22.5Mwh's to date. No issues with micro's working or communicating with Envoy. So far so good.

[Alisobob]

And I've heard that one of the micro inverter companies now only covers the inverter, not the replacement labor.

I had my solar supplier give me paperwork on everything going into my system before I signed the contract, and saw this same info from Enphase.

I had the quote changed to read that...... " All labor to correct any warranty item is included for the life or the warranty, regardless if its provided by the original manufacturer or not".

Hope my inverters hold up...

[Mike90250]

Mike, could you tell us more about that? I'm trying to learn how the M215's have been holding up.

Enphase growth reduced because of warranty losses
http://seekingalpha.com/article/1888...igation-growth
The stock market review is telling:

From the table we can see that in the last 12 months the total warranty obligation has increased from $15.5 million to $29.4 million. A few items of note from the table: accruals for warranties issued during the quarter were down 45% from a year ago on a 1% decrease in unit sales. This must mean that the company expects much lower failure rates of third- and fourth-generation products versus second-generation inverters, which is interesting given that the third- and fourth-generation inverters have a 25 year warranty versus a 15 year warranty for second-generation inverters. We can also see that settlements have increased 97% versus last year, so the company is definitely seeing more failures.

They are screwing with the numbers !

[MGE]

Since I installed my system I will be the fix-it guy if that time comes along. Pretty much plug and play. All of my panels are accessible from my upstairs balcony mostly flat rooftop mounts with a little angle to the south for water to drain. So if I need to isolate a micro and panel I'll just unplug from trunk cable and swap out. Probably have to update Enphase Enlighten with Serial # but that's not an issue.

[wantons0up]

I spoke with a local PV installer yesterday who said that over the last 3 years they've done warranty replacements on lots of micro systems. He says it hasn't cost him or the customer anything, but it's bordering on a 50% failure rate in the last 2-3 years. Lately he's going back to recommending central inverters unless you have a major shade problem.

He also offered the hybrid optimizer system but said it is basically the labor of the micro inverters to install, should be reliable because it still has a central inverter, but too soon to tell thus far.

[ating]

this might seem like a rather pedestrian tidbit, but while we like to think of a non-single point of failure to be a good thing, the flip side of that means that there are many points of failure.

just some food for thought that, i'm sure, has been chewed on many times here.

[Mike90250]

This was a lesson I learned many years ago in the space industry, instead of building backups to the backup circuits, was to design a better, robust circuit with fewer parts to go bad.

If a gadget has a 1% failure rate, having 2 gadgets gives you a 2% failure rate.