So how bad are string inverters vs microinverters?

[Mike90250]

Yes, and now with Rapid Shutdown codes being applied, you have a choice of micros or optimizers . Optimizers are somewhat simpler, and less likely to fail long term

[Mike 134]

Totally understand embracing the KISS principle and I'm a big subscriber to it, but since 2017 the NEC has eliminated KISS for rooftop solar systems. So now it's just how expensive a dodad do you want to put on the roof.

I'm installing a Solar Edge system I'll keep everyone updated how it works out.

[J.P.M.]

Where your points are valid and everyone’s situation is different I will offer a few a couple thought for you to chew over regarding the optimizer and micro inverters.


Does kiss apply? I understand the theory of keeping it simple but micro inverters and optimizers are pretty plug and play. Yes, they can be hard to access in the panel array but sellers offer 25 year warranty including labor. Picking up the phone and calling the installer seems pretty simple and failures not costing you anything seems pretty cheap when it only effects a single solar panel vs the entire array.

Understood.

Among other reasons, I'm of the opinion KISS applies because:

1.) There are (1- # of panels) more devices than 1 central inverter. If there are, say, 18 panels there are 18 micros/optimizers and 17 more failure points + connections/wiring for possible problems. There's just more stuff to go wrong which only increases the probability of failure.

2.) Access to all 18 of those failure points is nowhere as easy as access to a central inverter in, say, a garage.

3.) With most roof arrays I'm familiar with, including arrays using micros/optimizers, little thought is given to the panel arrangement other than how many can get crammed onto a roof. Scenario: 20 panels in a 5 X 4 array packed tight. How do you get at the panels not on an outside row or column ? How many panels need to be removed and replaced to get at the panel needing service ? Then, if/when another micro/optimizer problem/failure occurs, it's back to the roof removing and reinstalling panels. All that will in itself likely increase failure probability for the moved/fooled with stuff for the simple reason of screwing around with stuff that's not broken. It's a failure probability self generating rathole.

4.) Often or even commonly, micro/optimizer material costs are covered under warranty. Labor is not. By virtue of their location, a non-easy location panel's labor will be more than for array edge panels. Material and labor for incidental damage to otherwise OK panels caused by un/reinstalling them to get at a panel may not be covered under warranty.

5) Not directly part of the KISS principle: I'd guess that folks who post more than, say, 5 - 10 times on this forum are probably more aware of what their array is doing if for no other reason than they look at their monitors and maybe read their electric meters on a regular basis. I'd bet just as much that most residential PV array owners either never look at their array's output or their electric usage and wouldn't know what to look for if they did. As a result, that may well mean that one panel's dropped output from a failed micro/optimize may well go unnoticed by most non or less involved folks because it's a relatively small amount of the total output that's lost and also likely also to be masked by the noise of the variable irradiance in most locations - if noticed or even looked for at all. I'd think a failed string inverter will have a high(er) probability of getting noticed as soon as the next electric bill arrived. A 5% loss on a 20 panel array is easier to not notice than no array output at all.

I see a lot of folks on this forum crying the blues about problems with micros and also/particularly SolarEdge products much more often than I read about problems with string inverters. I believe that disparity in reported problems is at least a partial consequence of the KISS principle.

Take what you want of the above. Scrap the rest.

[Wavelet8]

True enphase isn’t covering the labor. The system installer is covering the cost of the labor and the penetrations of the solar array for a 25 year period. The damage created from the penetrations is not covered.

[SunEagle]

Where your points are valid and everyone’s situation is different I will offer a few a couple thought for you to chew over regarding the optimizer and micro inverters.


Does kiss apply? I understand the theory of keeping it simple but micro inverters and optimizers are pretty plug and play. Yes, they can be hard to access in the panel array but sellers offer 25 year warranty including labor. Picking up the phone and calling the installer seems pretty simple and failures not costing you anything seems pretty cheap when it only effects a single solar panel vs the entire array.

As oregon_phil states warrantees on labor may not be clear or even available. Especially if the company is out of business before the equipment fails. Very few companies last 25 years And if the array is up on a 2 story roof and hard to access you can forget about any free labor needed to replace any equipment.

Unless the array is a ground mount I still think micros will end up costing someone more throughout the system's life.

[oregon_phil]

Enphase doesn't cover labor:

8. Limited Warranty Limitations and Exclusions. a. This Limited Warranty does not include any cost of labor related to (1) un-installing Covered Product; (2) re-installing a repaired or replacement product, or (3) the removal, installation or troubleshooting of the Covered Owner's electrical systems.

and must be connected continuously to the cloud

This Limited Warranty does not apply to, and Enphase will not be responsible for, any defect in or damage to any Covered Products: (1) if the Covered Product is not connected to the internet within 45 consecutive days following the Warranty Start Date and © 2021 Enphase Energy, Inc. All rights reserved. Effective January 31, 2021 continuously connected to the internet thereafter, unless such lack of connectivity is due to causes outside of the Covered Owner’s reasonable

[Wavelet8]

Where your points are valid and everyone’s situation is different I will offer a few a couple thought for you to chew over regarding the optimizer and micro inverters.


Does kiss apply? I understand the theory of keeping it simple but micro inverters and optimizers are pretty plug and play. Yes, they can be hard to access in the panel array but sellers offer 25 year warranty including labor. Picking up the phone and calling the installer seems pretty simple and failures not costing you anything seems pretty cheap when it only effects a single solar panel vs the entire array.

[J.P.M.]

To be fair, a large portion of those installers really believe that microinverters give you significantly higher performance in partial-shade situations. They are as vulnerable as anyone else to sales tactics. And recommending a good microinverter system (like. say, Enphase) is not a bad recommendation, even if there's not much performance gain by using them.

Every application is different. But, putting lots of smaller capacity and so redundant (and thus in violation of the KISS principle), sensitive to external environment electronics in what can easily be inaccessible places, and in what may often be termed harsh environments are not the path to good design.

Like many things that make life "better", there's more to solar design than chasing perceived but short term economic benefits, and simple efficiency chasing.

I don't cast aspersions on installers who push micros or optimizers, but many solar installers I know don't take the time or make the effort to think critically about the situation. Their job and more often their front and center their goal, is making money by putting solar equipment on other people's property, not designing and installing the most fit for purpose and most cost effective designs for their customers. That's just reality. Besides, if they did, they wouldn't be in business very long. Low ball and low ethics peddlers would eat their lunch. Nobody's fault. It's just the way it is.

If I had a location that needed micros or optimizers to make it work, I'd seriously question the viability of that location as a candidate for a successful solar installation.

Not every residential site is a good candidate for PV, which, for all practical matters, doesn't work in shade. Nothing in == nothing out regardless of how many micros or optimizers get thrown at it.

[SunEagle]

To be fair, a large portion of those installers really believe that microinverters give you significantly higher performance in partial-shade situations. They are as vulnerable as anyone else to sales tactics. And recommending a good microinverter system (like. say, Enphase) is not a bad recommendation, even if there's not much performance gain by using them.

The problem I have seen is that a system with micro is usually more expensive then a basic string inverter. The sales people are pushing them even if you do not have a shade issue. That to is pushing something that is not needed just to get a price increase.

[oregon_phil]

Gees, my understanding of solar would cause me to question why one would want to use a string inverter other than saving cost maybe. I have a lot of planning yet to do before I can speak with a knowledgeable authority. A string inverter allows a system efficiency loss when a panel fails to operate at MPP due to shading. Properly designed individual inverters always operate at MPP

The OP's video in Post #1 is pretty informative. Also, I can run my SMA string inverter without connecting to the cloud. Some of the postings regarding Enphase say cloud connect is required in the latest firmware change. This would not be acceptable to me.

[jflorey2]

I also think that most of the installers rely on unknowing people to think they need micros or their system won't work as well just to get more money from them. IMO they are just shysters' preying on people.

To be fair, a large portion of those installers really believe that microinverters give you significantly higher performance in partial-shade situations. They are as vulnerable as anyone else to sales tactics. And recommending a good microinverter system (like. say, Enphase) is not a bad recommendation, even if there's not much performance gain by using them.

[SunEagle]

It is going to be much dependent on the application. The ground mount array
here has no need for rapid shutdown circuitry. With the longest string wire
loop approaching 1000 feet, the higher operating voltage gives a huge
improvement in the feed wire cost-system loss tradeoff, besides just being
far simpler.

I read 2% or 3% efficiency increased losses from a shaded string configuration.
BUT that condition lasts such a tiny fraction of the day here (before or after
everything is shut down), that the daily percentage loss is really tiny. It is
far less than the wire loss savings.

Yes strings have no individual panel monitoring. In 9 years that has had no
maintenance impact here. For entertainment, before solar we in the country
just settled for watching the grass grow.

I strongly suspect, the #1 reason for micros is the no brainer design. Bruce Roe

I also think that most of the installers rely on unknowing people to think they need micros or their system won't work as well just to get more money from them. IMO they are just shysters' preying on people.

[bcroe]

Gees, my understanding of solar would cause me to question why one would want to use a string inverter other than saving cost maybe. I have a lot of planning yet to do before I can speak with a knowledgeable authority. A string inverter allows a system efficiency loss when a panel fails to operate at MPP due to shading. Properly designed individual inverters always operate at MPP

It is going to be much dependent on the application. The ground mount array
here has no need for rapid shutdown circuitry. With the longest string wire
loop approaching 1000 feet, the higher operating voltage gives a huge
improvement in the feed wire cost-system loss tradeoff, besides just being
far simpler.

I read 2% or 3% efficiency increased losses from a shaded string configuration.
BUT that condition lasts such a tiny fraction of the day here (before or after
everything is shut down), that the daily percentage loss is really tiny. It is
far less than the wire loss savings.

Yes strings have no individual panel monitoring. In 9 years that has had no
maintenance impact here. For entertainment, before solar we in the country
just settled for watching the grass grow.

I strongly suspect, the #1 reason for micros is the no brainer design. Bruce Roe

[foggysail]

Gees, my understanding of solar would cause me to question why one would want to use a string inverter other than saving cost maybe. I have a lot of planning yet to do before I can speak with a knowledgeable authority. A string inverter allows a system efficiency loss when a panel fails to operate at MPP due to shading. Properly designed individual inverters always operate at MPP

[oregon_phil]

The 120 cells are arranged like two smaller 60 cell panels in parallel that share 3 bypass diodes so there are 6 "zones" per panel instead of 3. I agree the type of shade would determine whether or not any benefit would be realized.