So how bad are string inverters vs microinverters?

[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.

[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.

[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.

[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.

[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

[J.P.M.]

Optimizers are somewhat simpler, and less likely to fail long term

That seems like damning with faint praise to me.

[bcroe]

That may be but at least as a kid I learned and know the difference between a pronoun and a contraction.

So did I. One more item not discussed much. Using micros will much
increase the length of the AC wiring, raising the line voltage at the
micro inverters. Here long AC lines and a Power Company always
inching up the voltage for their own efficiency, caused me grief from
high line shutdown. The cure was a combination of installing much
larger wire, bugging the PoCo till they brought the voltage down, and
reprogramming the inverter voltage monitors. Bruce Roe

[jflorey2]

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.

That's fair. But if there are customers out there that say "I understand the site's not ideal, but I still want solar" that's also a valid request.

IMO the job of an ethical solar installer is to give the customer good advice on the pros and cons of each system they offer - then let the customer make the final decision. (Subject to what's available and supportable from the installer's perspective of course.)

[SunEagle]

That's fair. But if there are customers out there that say "I understand the site's not ideal, but I still want solar" that's also a valid request.

IMO the job of an ethical solar installer is to give the customer good advice on the pros and cons of each system they offer - then let the customer make the final decision. (Subject to what's available and supportable from the installer's perspective of course.)

In some cases the words "ethical" and "solar installer" should not be used. There are a percentage of all sales people that just want to make a sale and don't care who they hurt.

[J.P.M.]

That's fair. But if there are customers out there that say "I understand the site's not ideal, but I still want solar" that's also a valid request.

IMO the job of an ethical solar installer is to give the customer good advice on the pros and cons of each system they offer - then let the customer make the final decision. (Subject to what's available and supportable from the installer's perspective of course.)

Sales people and the outfits they work for are not the moral and ethical guardians of the universe. If they were, there would be a lot fewer of them and they'd be a lot poorer. That would probably be good for humanity but bad for capitalism.

I appreciate and respect your opinion and in some, perhaps many situations, I agree. But there is more to selling than that. There is a moral and ethical component that comes in at times such as when you look in the mirror and know you just screwed someone for a commission.

Before I changed professions to engineering (and took a pretty healthy income hit BTW) I spent 10+ years of my earlier working life as a commission sales rep. peddling industrial process equipment. I learned a lot about human nature from pros and mentors in the sales game including how hard it can be to keep the moral compass pointed in the right direction in the face of customer ignorance.

Sales people who stick with it and learn the profession probably start out honest and stay that way in most selling situations.

But one thing I know from the experience is that there are a lot of people and companies in the world who are naive, can be easily manipulated and separated from their assets by a lot of peddlers who take advantage of such people and their ignorance. Now, I like a buck as much or more than the next person, but sometimes it was challenging to keep my moral compass pointed in the right direction when dealing with such people and organizations.

I believe my experience was probably typical.

If so, a lot of money is made off people's ignorance.

If that were not true, I'm pretty sure there would be far fewer PV arrays on homes and those that did exist would be a lot smaller and better designed.

[foggysail]

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

ay.

[foggysail]

Here I go again with still limited knowledge..........

I agree that a greater number of widgets will increase the failure probability. And yes, a failed micro is going to be a BPITA to identify and repair. For those reasons I started searching for string inverters that will satisfy a system that I hope to install this summer onto my home. But then I realized a string inverter does not solve all problems such as the current requirement for rapid shutdown.

OK, that can be solved with shutdown devices such as those offered by Tigo. But what if a shutdown device fails? I will have a similar search, find and repair as I would have with micros. Now as to optimizers, I have to ask why? Optimize deliver DC to a string inverter when a micro will do the optimization without the need for a string. And they are buried under panels just as mircos. Think failures/repairs!

I find myself behind on Code since I let my licenses expire so I just ordered a 2020 version. From what I understand, wiring DC voltages inside a building greater than 30V OR 8 A has to be in metal tubing! So what advantages do optimizers offer or for that matter, strings?????

As I type I believe there are microinverters in my future. Just my humble thoughts, at this time anyway

[solar pete]

This whole rapid shut down crap is a scam introduced into your regulations via sponsorship from micro and optimiser manufactures and was designed to benefit 2 equipment retailers, thats the truth of it, they tried to do the same in Australia and we fought them tooth and nail and the regulators came to see the sense in the industry s argument against it, I think its a matter of time before they get rid of these stupid regulations in the States, just my 2 cents, (rant over)

[solarix]

Solar Pete: I totally agree... Rapid shutdown is of virtually no benefit to the fire services and causes a lot of expense and greatly decreases the reliablity of a solar install.

[foggysail]

This whole rapid shut down crap is a scam introduced into your regulations via sponsorship from micro and optimiser manufactures and was designed to benefit 2 equipment retailers, thats the truth of it, they tried to do the same in Australia and we fought them tooth and nail and the regulators came to see the sense in the industry s argument against it, I think its a matter of time before they get rid of these stupid regulations in the States, just my 2 cents, (rant over)

OK, fair enough!!! Now when I get my poop together I should tell the town's electrical inspector, ''HEY BUTCH--- I NEED THAT SOLAR WIRING PERMIT NOW, AND THAT RAPID SHUTDOWN YOU DEMAND IS NOTHING MORE THAN A BUNCH OF CRAP''.............. who will tell me to check 2020 NEC 690.12

Your logic is fine and I would agree IF there was an operating solar system on my roof as I type. Don't get your hopes up, once something gets into code, it only grows, not goes away.