Are microinverters really more reliable than large single inverters?

[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.