Are microinverters really more reliable than large single inverters?

[jayk]

I talked to a solar installation contractor today and he swore microinverters (an inverter per panel) are more reliable than a single big inverter.  This doesn't make sense to me, since there are dramatically more parts in a microinverter system (though the peak currents are a lot lower) and, in general, the inverters will be running hotter than a single inverter would (which is typically located inside). 

What is people's experience?  This guy claims large solar inverters tend to fail around 10 years, but how many microinverters are even 10 years old at this point to make a meaningful comparison?

[Berni]

It all depends on the quality of the inverter and how hard of a life it has.

An inverter that is running under the roof on a nice shaded side running at half the rated power will have an easier as an inverter that is run to full power on an exposed sunny wall that is pointing towards the sea side where the salty mist covers it. These microinverters having to live up on the roof can't be nice to them either.

But in general well made inverters should be very reliable. The first thing that would go are likely the cooling fans.

Lots of microinverters are indeed more likely to experience a failure because there are more of them. But if 1 inverter fails then say the other 9 keep running so the whole setup is still running at 90% capacity. But if your big single inverter fails you have 0% capacity. So id say they are more reliable in the sense that it takes a lot of failures to seriously degrade the solar array performance.

I think a single big inverter is more sensible. You need to run cables down from the roof anyway. It is in a easier to service spot down there..etc If you are worried about partial shading problems then you can get inverters with multiple MPPT inputs to slice the array up into sections, or use optimizer modules on the panels that contain a small DC/DC converter to balance the shaded panels with the sunny ones.

[Faringdon]

Yes good points, i cant see microinverters being more reliable, since they will run hot on the roof, their electrolytic capacitors will get boiled off quicker.
Also, if you have a  battery storeage, than you want a single inverter so that you can control it not to export power when your house is not using much electricity.....if you have microinverters, they will just shovel power into the grid when your house isnt using much elec.

[Kjelt]

They probably have polymer capacitors or extra high temp electrolytes calculated at their expected lifetime.

[nctnico]

Personally I would go for the cheapest, most servicable option. One big inverter is likely to be cheaper and easier to replace. How do you get to a failed microinverter tucked away between the panels? Over the lifetime of an array of solar panels, the chance that at least one inverter fails is 1.

[rteodor]

There is this open source microinverter project here on eevblog: https://www.eevblog.com/forum/projects/opensource-hwsw-grid-solar-microinverter-450w-97-efficiency-25yrs-lifespan/msg4165114/#msg4165114 (I am no involved, but I would very much like to see it succeed).

They aim for 25 years lifespan by not using large electrolitics and using inductors as much as possible.

The best might be both type of inverters: baterry system with a central inverter plus microinverters. There is offgrid backup (for upcoming rolling blackouts here in Europe) and flexibility to freely expand the system.

[Marco]

Still have to add groups in the fuse box to significantly expand,  flexibility doesn't seem worth the losses with battery storage to me.

[Siwastaja]

Regarding "are microinverters really more reliable", the general consensus pretty much is they are LESS reliable, so the relevant question is the opposite: are they really less reliable, and if yes, by how much?

The bright side is that failure of one microinverter only brings that one panel down. If you talk to owners of microinverter systems, about every other has one failed microinverter, but it is not a disaster of course. Much more rarely you hear about string inverter failures, but when it happens, it's worse.

The often attributed cause for microinverter failure is the combination of worse efficiency (so more heat), fanless design, and exposure to elements, especially heat behind the hot panels, easily exceeding Ta=60degC, so it is harder to design them to be reliable. Yet, it is entirely possible to design super-reliable microinverters, just harder. String inverters tend to sit indoors in heated/air conditioned room temperatures.

The problem with getting information from contractors / installers is, everybody is selling their favorite systems, so information is always biased. IMHO, it's best to compare $/kWh and ignore technology differences, unless you have a system where every panel faces different direction with lot of shading, in which case you want microinverters.

[Marco]

How about a compromise, parallel connected optimizers Can directly charge a battery with the bus voltage, the inverter can be designed for a single voltage which will be maintained regardless of the number of panels.

[jonpaul]

no, more complex, exposure to elements, more connectors, needs management systems eg for shading

Pushed by certain panel mfg and installers.

Experience shows poor reliability vs bulk inv

Of course cheap Chinese junk inverters will be failure prone either micro inverters or bulk.

Check with Daniel at Beyond Oil Solar, a disty for DIYers

Jon

[Berni]

If you do want to have individual panel MPPT and a central inverter you can use optimizer modules:


But doesn't this bring the worst of both worlds? Electronics on the hot roof and a single point of failure. Well... yes and no.

The optimizer modules are indeed power converters that have to live in the harsh roof environment. However the difference is that they now have a lot less work to do. They are just a buck boost DC/DC converter with an input and output range of about 5 to 40V. This means it does not have to deal with mains (high voltage, isolation required, large caps to store between 50Hz cycles, resilience to surges etc..) so it is a lot simpler and produces less waste heat. In a perfectly balanced scenario they can just bypass all of the DC power trough them, making them almost 100% efficient. The more difficult task of turning DC into AC is then done by the classical big central inverter (Where it can have fans, advantage of smoother 3 phase power..etc)

This tech unfortunately looks like it is currently exclusive to SolarEdge because they patented the hell out of it.

[jayk]

Thanks for all the feedback.  Yes I think this particular installer has just decided he likes microinverters.  I talked to the guy again and turns out they've only been installing microinverters for a couple of years, so his thoughts on reliability don't mean much.  They are installing Enphase IQ8 microinverters, which are spec'd to 140F ambient.  Hard to know exactly what this means... it regularly gets over 100F air temp here, so it's not a stretch to think the microinverter running at full power on the back of a panel will get up to at least 140F.  But 'ambient' should mean outside air temp, right?

For sure these will be operating at the high end of their design range for at least part of the year.  Seems much better to have a single big inverter in a garage than all these little inverters cooking up on the roof.

[Ed.Kloonk]

Yes I think this particular installer has just decided he likes microinverters. 

Installers, generally, have pet solutions systems that they hitch their wagon to and then modify the components to suit each application.

Not every installer can know all the ins and outs of every type of system. They usually have a deal with one or two eco system's suppliers and to go outside the square, they don't have much supplier discount, or the funds to handle install problems etc.

I'm over simplifying it, and installer -could- deploy any system but the market is often so tight that the customer often only gets offered the easy, cost effective option.

[Siwastaja]

Installers, generally, have pet solutions systems that they hitch their wagon to and then modify the components to suit each application.

This, and also remember installers often have no freaking clue whatsoever about the technology they install. It's actually pretty sad. They can of course (usually!) follow installation instructions, but that's pretty much it. Otherwise than that, an enthusiast who have spent just a few hours (let alone days!) to read a few technical articles easily surpasses the technical knowledge of a salesman / installer.

There are exceptions to this, of course, but in general, those with high IQ or a lot of interest about technology will rarely take low-level install / marketing jobs, instead they become designers of some kind.

[richard.cs]

Yes good points, i cant see microinverters being more reliable, since they will run hot on the roof, their electrolytic capacitors will get boiled off quicker.
Also, if you have a  battery storeage, than you want a single inverter so that you can control it not to export power when your house is not using much electricity.....if you have microinverters, they will just shovel power into the grid when your house isnt using much elec.

In the UK the default seems to be to put standard inverters in the attic space, which I can certainly believe will be hotter than behind a roof mounted panel. 50-60 C ambient seems pretty plausible on a sunny day, I guess on a roof with solar panels they might lower the inside temperature somewhat.

[David Hess]

What is people's experience?  This guy claims large solar inverters tend to fail around 10 years, but how many microinverters are even 10 years old at this point to make a meaningful comparison?

I do not have any direct experience with them, but here are my thoughts.

I talked to a solar installation contractor today and he swore microinverters (an inverter per panel) are more reliable than a single big inverter.  This doesn't make sense to me, since there are dramatically more parts in a microinverter system (though the peak currents are a lot lower) and, in general, the inverters will be running hotter than a single inverter would (which is typically located inside).

In aggregate micro-inverters should be less reliable because there are more parts to fail and they are more exposed, but they can also afford greater derating and a failure of one micro-inverter is not a catastrophic failure of the system.

What I would like to know is which is more reliable under adverse conditions, like nearly lighting strikes.

[David Hess]

They probably have polymer capacitors or extra high temp electrolytes calculated at their expected lifetime.

In military and aerospace applications they may design aluminum electrolytic capacitors out entirely for greater reliability and operating life.

[EEVblog]

If you do want to have individual panel MPPT and a central inverter you can use optimizer modules:
But doesn't this bring the worst of both worlds? Electronics on the hot roof and a single point of failure. Well... yes and no.

If you are going to have electronics on the roof, then it might as well be microinverters.
Optimisers seem like a bit of a half-arsed solution? But I guess there is a market for half-arsed solutions.

[EEVblog]

I talked to a solar installation contractor today and he swore microinverters (an inverter per panel) are more reliable than a single big inverter.  This doesn't make sense to me, since there are dramatically more parts in a microinverter system (though the peak currents are a lot lower) and, in general, the inverters will be running hotter than a single inverter would (which is typically located inside). 

Most I have seen are mounted outside.
Mine was mounted on the other side of the house (outside) so it was in a shaded spot that wouldn't get the harsh afternoon sun on it.

[EEVblog]

In the UK the default seems to be to put standard inverters in the attic space, which I can certainly believe will be hotter than behind a roof mounted panel. 50-60 C ambient seems pretty plausible on a sunny day, I guess on a roof with solar panels they might lower the inside temperature somewhat.

Mine under the panel is at 100F today on a perfect winter day.
Summer is 141F
There is no way the roof is not hotter than under the panel, as you'd easily have 50C ambient up there in summer.

[Berni]

In the UK the default seems to be to put standard inverters in the attic space, which I can certainly believe will be hotter than behind a roof mounted panel. 50-60 C ambient seems pretty plausible on a sunny day, I guess on a roof with solar panels they might lower the inside temperature somewhat.

Here installers tell you not to use an attic because it gets too hot up there. They usually get installed outside on a wall somewhere near the electrical box so that they don't have to run the AC cables very far(preferably in shade). Sometimes they also get installed inside a garage since electrical panels are often in there.

[EEVblog]

Here installers tell you not to use an attic because it gets too hot up there. They usually get installed outside on a wall somewhere near the electrical box so that they don't have to run the AC cables very far(preferably in shade). Sometimes they also get installed inside a garage since electrical panels are often in there.

As mentioned, mine was deliberately put on the other side of the house which required huge wire runs both ways. When they installed it I was told that it was well worth the extra cable run to keep the inverter cool, and that I'd thank them for it later. 8 years later, still running fine.

[Berni]

As mentioned, mine was deliberately put on the other side of the house which required huge wire runs both ways. When they installed it I was told that it was well worth the extra cable run to keep the inverter cool, and that I'd thank them for it later. 8 years later, still running fine.

Some good installers right there.

The trend i noticed on youtube is that solar installers love to take shortcuts and do things in the easiest way possible. Like having an inverter with 4 MPPT inputs and instead they just hook up 2 inputs because that means they have to run less cables. (And the guy had panels facing in 4 different directions on the roof, so it would definitely help with partial shading) Especially since the average joe wouldn't be able to know the difference.

[EEVblog]

As mentioned, mine was deliberately put on the other side of the house which required huge wire runs both ways. When they installed it I was told that it was well worth the extra cable run to keep the inverter cool, and that I'd thank them for it later. 8 years later, still running fine.

Some good installers right there.
The trend i noticed on youtube is that solar installers love to take shortcuts and do things in the easiest way possible. Like having an inverter with 4 MPPT inputs and instead they just hook up 2 inputs because that means they have to run less cables. (And the guy had panels facing in 4 different directions on the roof, so it would definitely help with partial shading) Especially since the average joe wouldn't be able to know the difference.

Yes. Would have been far easier to put the inverter right next to the power board and the solar panels directly above, only a few meters of cable run required. Opposite shaded side of the house is a good 25m away.

[Ed.Kloonk]

If you do want to have individual panel MPPT and a central inverter you can use optimizer modules:
But doesn't this bring the worst of both worlds? Electronics on the hot roof and a single point of failure. Well... yes and no.

If you are going to have electronics on the roof, then it might as well be microinverters.
Optimisers seem like a bit of a half-arsed solution? But I guess there is a market for half-arsed solutions.

I figured that optimisers suit the niche area where a less than optimum string array has been installed for a while, and the removal of shady trees is infeasible. The panels themselves and the inverter are still pulling their weight, a microinverter system seems overkill, doesn't it? And is the guy fitting the enphase microinvs going to be happy connecting them to old panels?

Or am I missing something?

[Siwastaja]

Or am I missing something?

You are missing the non-technical side, in other words, marketing and lobbying. Whenever there are a few different technological solutions which all are acceptable for the job, the tiny technological details rarely matter at all. For example, it can be seen optimizer systems are a big thing in the USA. Microinverters are niche, but still not insignificant, pretty much everywhere globally. String inverters dominate in global numbers.

And if you want to buy something which everyone buys, and everyone sells on your area, it is probably also the cheapest option (and least risky), even if it has bigger component cost or more complexity.

[EEVblog]

I figured that optimisers suit the niche area where a less than optimum string array has been installed for a while, and the removal of shady trees is infeasible. The panels themselves and the inverter are still pulling their weight, a microinverter system seems overkill, doesn't it?

In that case, sure. There will also be niches for things.

And is the guy fitting the enphase microinvs going to be happy connecting them to old panels?

No because the microinveretsr are worth more than the old panels.
I'm in this situation right now. I have old-ish 8yo string system with 12x250W panels. Still going strong, but I want to add another small string so I new either a new string inverter or go with enphase microinverters that match my existing system.
There is no way I'm going to pay for microinverters for my old 250W panels, so it makes sense to get a new bigger string inverter system.

[Phoenix]

For example, it can be seen optimizer systems are a big thing in the USA.

The US now requires "PV Rapid Shutdown" at the PV module level.
https://www.ul.com/insights/pv-rapid-shutdown-safety-requirements-and-communication

The optimizers (like the Tigo) are providing this function, along side their primary MPPT function.
https://www.tigoenergy.com/post/tigos-newest-rapid-shutdown-solution-reaches-rooftops-across-the-country

[uer166]

The optimizers (like the Tigo) are providing this function, along side their primary MPPT function.
https://www.tigoenergy.com/post/tigos-newest-rapid-shutdown-solution-reaches-rooftops-across-the-country

But surely horses for courses and you'd rather only buy the actual rapid shutdown thing if you need, instead of a full DC/DC converter solution? E.g. https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/6250ca59dd6a56e088f33fad_TS4-A-S%20(700W)%20(Safety)%20Datasheet%20EN%20-%2020220329.pdf

[Phoenix]

The optimizers (like the Tigo) are providing this function, along side their primary MPPT function.
https://www.tigoenergy.com/post/tigos-newest-rapid-shutdown-solution-reaches-rooftops-across-the-country

But surely horses for courses and you'd rather only buy the actual rapid shutdown thing if you need, instead of a full DC/DC converter solution? E.g. https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/6250ca59dd6a56e088f33fad_TS4-A-S%20(700W)%20(Safety)%20Datasheet%20EN%20-%2020220329.pdf

True. In fact the product I linked only does monitoring and rapid shutdown... but they do offer it with optimizer.

https://www.tigoenergy.com/ts4

In any case, I agree that wide spread use of optimisers is unnecessary, and really only make sense in certain cases.

[bdunham7]

I talked to a solar installation contractor today and he swore microinverters (an inverter per panel) are more reliable than a single big inverter.  This doesn't make sense to me, since there are dramatically more parts in a microinverter system (though the peak currents are a lot lower) and, in general, the inverters will be running hotter than a single inverter would (which is typically located inside). 

What is people's experience?  This guy claims large solar inverters tend to fail around 10 years, but how many microinverters are even 10 years old at this point to make a meaningful comparison?

A decade ago, inverter failures were fairly common after the 5 year mark.  I recall some sales materials that actually accounted for one replacement inverter in their 10 or 15 year economic analysis.  Microinverter failures wer also fairly common up until about 10 years ago, after that they've been fairly reliable at least for Enphase.  However, they'll still fail on occasion and 30 microinverters are probably more likely to have at least one failure than one single inverter.  I have a 10 year old system with Enphase M215 inverters and I've just now had one go bad.  It still sort of works but seems to have trouble correctly reading the AC voltage and then shuts off for a while.  Its overall production is off about 40-50%.  Enphase checked the data and sent me a replacement, a kit using the new IQ7 module.  Until I get up on the roof and replace it, my system will have to struggle on at 98% capacity.  And that is the main advantage right there--if a single inverter or string failed, I'd have zero percent until it got fixed.  It sort of depends on what you mean by 'failure'.

[Berni]

Yeah if you have all panels pointing in the same direction and never get partial shading then individual optimizer modules or microinverters won't really make a difference.

As for microinverter versus one big inverter, it also depends on what you want. Microinverters do indeed fail more often and there is more to fail, but they don't knock down the whole array. One big inverter is less likely to die in the first place and there is only one so in total it is much more unlikely the system suffers a fault. It does bring down the whole array if it dies but it is also hanging on a wall, so it is a easy job of just sticking a new one on a wall and honking it up.

In the end the total uptime numbers are probably similar.

The panels themselves cost the most anyway.

[tszaboo]

If you do want to have individual panel MPPT and a central inverter you can use optimizer modules:
But doesn't this bring the worst of both worlds? Electronics on the hot roof and a single point of failure. Well... yes and no.

If you are going to have electronics on the roof, then it might as well be microinverters.
Optimisers seem like a bit of a half-arsed solution? But I guess there is a market for half-arsed solutions.

Optimizers are cheaper than microinverters system wise. They also provide per panel MPPT. The Solaredge ones only have ceramic capacitors in the optimizer, so it will probably survive the panel. And they use 100% the capacity, unlike the Enphase microinverters that max up at 300W or so.

That being said, there are new microinverters with 4 MPPT inputs, which might be the best value now.

The panels themselves cost the most anyway.

Microinverters cost more than the panels.

[Kjelt]

I am looking at this right now for a new installation.
Micro inverter enphase costs around €170 a piece
Optimizer solaredge around €74 per panel plus about €2200 for the single inverter.

So with about 20 panels you have break even
BUT
1) the enphase microinverter is only 25yr guaranteed with 65C max. The thing itself also produces heat so I am pretty sure in the summer temperature will exceed that.
2) you only need the optimizers on those panels that potentially might catch shade.

Question: is there a difference in the output waveform of the microinverter vs the single inverter. I would imagine that perhaps the microinverter has some cheaper trapezium waveform vs sinusoid on the single inverter ?

[tszaboo]

I am looking at this right now for a new installation.
Micro inverter enphase costs around €170 a piece
Optimizer solaredge around €74 per panel plus about €2200 for the single inverter.

Ask around a bit. In 2020 I got a quote for 47 EUR for the P401 and the inverter was 850 EUR. 3500W, but the bigger ones are not that much more expensive. Plus tax, but you get that back.
I got about 5 quotes, and the prices were all over the place for different installers.

[Scrts]

Micro inverter enphase costs around €170 a piece

I understand Enphase is a premium supplier? Any cheaper options?

[Berni]

If microinverters are this expensive then they really don't make sense for large installations indeed (The kind of size that would cover a house with a heatpump as heat).

The SolarEdge optimizer modules are 25 years warranty and rated up to +85°C (With some power de rating above +70°C). They are also all high frequency DC/DC so only ceramic capacitors are required inside. So all this along with being cheaper is the reason why they make sense.

But as it has been said before, if you have all panels in the same plane with no partial shading you don't even need optimizers. Tho they can still come in handy for monitoring individual panels or for providing a safe shutdown as it is mandated in some places.

[Kjelt]

Ask around a bit. In 2020 I got a quote for 47 EUR for the P401 and the inverter was 850 EUR.

Depends on the brand I guess. Also solar hardware has gone up 50+% the last two years due to high demand, and ofcourse chippageddon.

[Kjelt]

So those optimizers are those dc-dc converters that crank up the voltage if one panel gets shade or are they constant current circuits ? Anywhere some good tear down video anout these optimizers vs micro inverters ?

[bdunham7]

1) the enphase microinverter is only 25yr guaranteed with 65C max. The thing itself also produces heat so I am pretty sure in the summer temperature will exceed that.

Question: is there a difference in the output waveform of the microinverter vs the single inverter. I would imagine that perhaps the microinverter has some cheaper trapezium waveform vs sinusoid on the single inverter ?

Mine never get to 60C even on the hottest days.  Does anyone have a warranty longer than 25 years?

The output will be a clean, low-harmonic sinusoid and on modern Enphase they have the capability of adjusting the source PF on external command. 

[Kjelt]

Mine never get to 60C even on the hottest days.  Does anyone have a warranty longer than 25 years?

At what ambient outside temperature ? In other words are you in Florida or Alaska 
My black rooftiles can get to 75 in the summer but the underside of the solarpanels might be isolated from the sun, if there is free air circulation it might not be that bad.

[bdunham7]

At what ambient outside temperature ? In other words are you in Florida or Alaska 
My black rooftiles can get to 75 in the summer but the underside of the solarpanels might be isolated from the sun, if there is free air circulation it might not be that bad.

Southern California inland.  Ambient air temps up to 40C and very intense sun at certain times of the year.  Dark items in direct sunlight may get extremely hot--a few years ago I had a bunch of plants including my avocado tree spontaneously combust.  The microinverters are under panels and about 4" off the roof. 

[Berni]

So those optimizers are those dc-dc converters that crank up the voltage if one panel gets shade or are they constant current circuits ? Anywhere some good tear down video anout these optimizers vs micro inverters ?

Solaredge shows the PCBs for some of there products in there official PDFs

https://www.glavaenergycenter.se/wp-content/uploads/2018/11/solaredge.pdf

They have some MCU smarts inside that can do MPPT tracking and powerline communication back to the inverter.

[Kjelt]

So looks like they are current controlled and don't have any elektrolytes only mlcc, nice.
Although mlcc's are also vulnerable for cracking 

[David Hess]

So looks like they are current controlled and don't have any elektrolytes only mlcc, nice.
Although mlcc's are also vulnerable for cracking 

"Brick" converters are built the same way, but they use leaded MLCCs to provide strain relief.

[tszaboo]

Ask around a bit. In 2020 I got a quote for 47 EUR for the P401 and the inverter was 850 EUR.

Depends on the brand I guess. Also solar hardware has gone up 50+% the last two years due to high demand, and ofcourse chippageddon.

https://www.solar-outlet.nl/solaredge-p401-power-optimizer.html
You might be right that it increased in price. I just don't like companies that overcharge customers.

So looks like they are current controlled and don't have any elektrolytes only mlcc, nice.
Although mlcc's are also vulnerable for cracking 

I think the entire thing is potted inside, which should reduce the stress and help with the thermals.
Also, you don't really find teardowns because of this.

If microinverters are this expensive then they really don't make sense for large installations indeed

For large installations, they make even less sense. Going from a 3.5 KW inverter to a 10 KW inverter is ~50% increase in price, and the largest 25KW one is only 80% more expensive. It's economies of scale.

I think the multiple input microinverters will have a good future though, an example:
https://www.renvu.com/APSystems-QS1-4-Module-Micro-Inverter-for-375W-Modules

This is equivalent to 4x Enphase IP7+, which is about twice the price. Plus you need that Q relay and the communications box which is an extra cost. This could very well make sense for systems up to ~12 panels.

[Siwastaja]

I think the entire thing is potted inside, which should reduce the stress

A weird comment. Potting can only increase mechanical stress on components like MLCCs, there is no physical mechanism I'm aware of that is able to reduce the stress. MLCCs are really sensitive to any forces that touch the actual ceramic body or cause shear.

Very well evaluated potting compounds can end up being neutral on the MLCC stress, i.e., not make the reliability any worse. OTOH, poorly chosen potting is well known to kill MLCCs in short time.

I'm sure SolarEdge has done their homework on this given the product is already quite mature. I would also guess the larger capacitors are soft-terminated plus automotive rated parts, they are not that expensive, and I use them in designs like this. But I avoid potting because I see it as a risk factor due to low volumes and limited resources I usually deal with.

Thermals will be quite manageable because such simple DC/DC converter can be designed to run at very high efficiency. As always, not producing heat is always way easier than removing heat.

[tszaboo]

I think the entire thing is potted inside, which should reduce the stress

A weird comment. Potting can only increase mechanical stress on components like MLCCs, there is no physical mechanism I'm aware of that is able to reduce the stress. MLCCs are really sensitive to any forces that touch the actual ceramic body or cause shear.

You can just apply Occam's razor, and assume that the engineers at a billion dollar hardware company know what they are doing.
They pot it to increase reliability, otherwise they wouldn't spend money on it.

[Marco]

there is no physical mechanism I'm aware of that is able to reduce the stress.

Bending PCBs crack MLCCs, potted PCBs don't bend easily.

[Siwastaja]

You can just apply Occam's razor, and assume that the engineers at a billion dollar hardware company know what they are doing.
They pot it to increase reliability, otherwise they wouldn't spend money on it.

Potting is mainly to protect against moisture, and hence, to increase reliability by reducing moisture damage. Potting also prevents large and heavy parts like inductors from shaking off. The added mechanical firmness helps some components, but components that are fundamentally sensitive to mechanical firmness are then susceptible to a new failure mode.

MLCC cracking is primarily solved by reducing board flex by choosing mounting points appropriately, and using soft terminated MLCCs.

I don't think anyone at that billion dollar hardware company chose to pot to solve MLCC cracking. Potting is for different reasons. As I said, they probably just engineered the potting compound to be MLCC-neutral, i.e., they made sure the MLCCs do not crack, and then made sure potting doesn't make them crack, either - i.e., use a compound which is soft (but not too soft, so it would not help), which does not develop internal tensions when curing, something which thermally expands at the same rate as the PCB so that it does not cause PCB flexing. In other words, something which is known and tested to not cause MLCC cracking.

The problem is, when you assume that others know what they are doing, even if that assumption is true, you don't know why they are doing that. Your Occam's razor completely ignores all technical details, and details matter. The assumption they do it for MLCC cracking prevention is completely your invention and not explained by the billion dollar-ness of the company at all. I'm merely saying I don't share this assumption. I bet the potting is to hold the heavy inductors in place plus protect against moisture, simple as that.

The reason I am posting this is because I have seen reports on this forum and elsewhere, where adding a potting has caused significant levels of MLCC cracking failures. This is why I don't believe anyone tries to use potting to solve MLCC failures.

[Siwastaja]

there is no physical mechanism I'm aware of that is able to reduce the stress.

Bending PCBs crack MLCCs, potted PCBs don't bend easily.

Except when the internal stresses formed during curing, and simply different thermal coeffs of expansion, cause the potted assembly to bend more than a non-potted one.

[Kjelt]

https://www.solar-outlet.nl/solaredge-p401-power-optimizer.html
You might be right that it increased in price. I just don't like companies that overcharge customers.

I read that the P type optimizers from SE caused serious radio interference, the german Veron took action.

[tszaboo]

The problem is, when you assume that others know what they are doing, even if that assumption is true, you don't know why they are doing that. Your Occam's razor completely ignores all technical details, and details matter. The assumption they do it for MLCC cracking prevention is completely your invention and not explained by the billion dollar-ness of the company at all. I'm merely saying I don't share this assumption. I bet the potting is to hold the heavy inductors in place plus protect against moisture, simple as that.

The reason I am posting this is because I have seen reports on this forum and elsewhere, where adding a potting has caused significant levels of MLCC cracking failures. This is why I don't believe anyone tries to use potting to solve MLCC failures.

I talked with some potting compound experts, who actually encountered with the problem in the past. Stuff failing because a metal enclosure was used as the potting base, 100% filled. Then the thermal expansion was directed into the board. That's not how these are made, there is a separate block of potted electronics that is then fitted into the enclosure. If you make the PCB thicker, it will bend less. Similarly, if you pot it in a few cm of resin or urethane, it will bend less, and cracking will be lesser of a problem.
So I'm saying this, because it coincides with the info I get from the experts.

[Marco]

simply different thermal coeffs of expansion

If the potting has strong adhesion a thick rigid layer of it just wins, the PCB will have to expand/contract in thickness cause it isn't going to bend the potting. The tail does not wag the dog.

[Siwastaja]

simply different thermal coeffs of expansion

If the potting has strong adhesion a thick rigid layer of it just wins, the PCB will have to expand/contract in thickness cause it isn't going to bend the potting. The tail does not wag the dog.

Yes, and imagine the forces involved in making the resin "win". FR4 can take this no problem. Now apply this force to the MLCC body. Board did not flex, but MLCC failed anyway. This is why MLCC-compatible potting compounds are not that hard, they need to be somewhat flexible, reducing the forces. But the problem is here: MLCC bodies are surprisingly sensitive, even small forces from soft compounds are risky. This is why this shit is actually designed and evaluated by very experienced people.

I'm no expert on choosing the potting compounds, but I know enough to know it is far from trivial and have read stories of smaller companies wasting years with poor initial assumptions. Personally I just sidestep whenever possible, mounting heavy components using silicone or other types of glue, instructing sealed enclosures, possibly with a silica gel bag strapped inside.

I have also read about using a very soft intermediate layer just on the top of shear sensitive components (MLCCs), around which hard potting compound can be used. For small MLCC sizes, bog standard conformal coating alone might be enough, but small packages are lesser of a problem anyway.

I talked with some potting compound experts, who actually encountered with the problem in the past. Stuff failing because a metal enclosure was used as the potting base, 100% filled. Then the thermal expansion was directed into the board. That's not how these are made, there is a separate block of potted electronics that is then fitted into the enclosure. If you make the PCB thicker, it will bend less. Similarly, if you pot it in a few cm of resin or urethane, it will bend less, and cracking will be lesser of a problem.
So I'm saying this, because it coincides with the info I get from the experts.

Now I totally agree with this. Your story made full 180 degrees from: potting is used to reduce cracking, to: with correct potting, cracking [caused by potting] can be "lesser of a problem", exactly my original point.

[Siwastaja]

I read that the P type optimizers from SE caused serious radio interference, the german Veron took action.

I head from a local installer of SolarEdge that they have been banned in Sweden due to emissions interfering with some radio networks used by authorities. Don't know if this is true, so consider it a rumor.

EDIT: I can use Google! https://www.pv-magazine.com/2021/12/23/solaredge-growatt-found-in-breach-of-swedish-electromagnetic-rules-some-products-banned-from-sale/

[bdunham7]

I'm no expert on choosing the potting compounds, but I know enough to know it is far from trivial and have read stories of smaller companies wasting years with poor initial assumptions. Personally I just sidestep whenever possible, mounting heavy components using silicone or other types of glue, instructing sealed enclosures, possibly with a silica gel bag strapped inside.

I haven't done a study and can't claim causation from correlation, but in the specific field of automotive engine controllers the failure rate of potted types seemed to be much, much higher during the time that they were widely used.