Which is more reliable, Panel Optimizers versus Microinverters

[peakbagger]

A friend is looking at 6 KW array located way up on top his barn that is built into hillside. Its three stories up metal roof with plenty of pitch. It really doesn't have any significant shading but could get winter snow buildup. No need for RSD so my suggestion is skip anything under the panel and just wire the MPPT circuits so that the lower more snow prone panels are on the same circuit. His installer is recommending the microinverter route (which to me is a cop out to make their job easier). My friend tends to be very much into reading and recording daily production and I have told him that there is probably a good chance that at some point one or more of the electronics under each panel will die prematurely and swapping them out will be a major issue despite assurances to the contrary by the installer. As a fall back my suggestion is go with a string inverter and optimizers as they are simpler and less failure prone. Am i correct on my assumption that optimizers should have a lower fail rate than micros?

[Mike 134]

My own opinion about the failure of electronics on a roof based on what the automotive industry has done is no worries. Here's why,
Take the various IC chips, resistors, PC boards, etc. used in autos and solar and put them in two piles on the table without their enclosures. I'd bet a hardware engineer would have a tough time guessing how each pile is used in an industry.
The electronics in a car have a more hostile environment than those on the roof. Both have temperature extremes, but the cars range happens over minutes of time not days (think of those mounted within the passenger compartment or under the hood) plus constantly subject to vibration and shocks that the rooftop never sees.

Just my 2 cents

[bcroe]

If shade is not a problem, a simple string setup has only a fraction
as many connections, and no electronics on the roof. More
complexity equals more failures. Bruce Roe

[oregon_phil]

+1

Also, Enphase requires an internet connection to fully fulfill warranty requirements. I really dislike the requirement of having an internet connection as a prerequisite for full warranty. Communications modules are usually the weak link in the system (compare comm module warranty with microinverter warranty) and communication standards can change over 25 years.

While I'm at it, this requirement for cloud connection is just another gateway for outsiders to try to gain access to your home network. Nowadays, it's easier to hack a company's cloud system and gain access to your system using legitimate credentials.

Companies can also push firmware updates onto your inverter system without your knowledge making troubleshooting a system a nightmare with many unknowns.

[peakbagger]

Like HP reportedly sending a "routine" software update to brick a printer if it detects a non OEM print cartridge

I have already warned him that there seems to be ongoing numerous issues related to the connection out to the internet and that data logging and fault detection that should reside on his equipment is now at the mercy of a remote server. I can only "push on that rope" so hard before I give up. Ultimately its his money to do what he wants with. He has 20 year old string inverter system that has been faultless except for the utility running out of spec for a couple of years until he complained enough. My guess is he assumes that all PV equipment is that reliable.

[J.P.M.]

If shade is not a problem, a simple string setup has only a fraction
as many connections, and no electronics on the roof. More
complexity equals more failures. Bruce Roe

Amen.

[oregon_phil]

Like HP reportedly sending a "routine" software update to brick a printer if it detects a non OEM print cartridge

I have already warned him that there seems to be ongoing numerous issues related to the connection out to the internet and that data logging and fault detection that should reside on his equipment is now at the mercy of a remote server. I can only "push on that rope" so hard before I give up. Ultimately its his money to do what he wants with. He has 20 year old string inverter system that has been faultless except for the utility running out of spec for a couple of years until he complained enough. My guess is he assumes that all PV equipment is that reliable.

My friend tends to be very much into reading and recording daily production

Even my SMA -40 (and my -41 spare inverter) string inverter has been obsoleted after 5 years. It seems like SMA is moving to the hybrid market and is yielding the string only market to the lower cost suppliers. I would still find a string inverter supplier that can be used without the internet (many out there) and if monitoring was still an issue, I would put a CT (like Shelly EM) on the solar breaker and not worry about individual panel output.

[peakbagger]

I am glad you confirmed my observations that stand alone string inverters by mainstream companies appear to be fading away. Fronius units seem to be unavailable in the US market and I have not seen a lot of activity by SMA. Given the RSD requirements it looks like some companies just do not seem to want to supply the non occupied niche.

[nerdralph]

Up here, BayWa and Guillevin have good inventory of Solis 4G-US plus series inverters. Frankensolar carries the Growatt hybrid inverters for about the same price as the Solis non-hybrid.

[solardreamer]

His installer is recommending the microinverter route (which to me is a cop out to make their job easier).

How is the job easier with microinverters? Seems like it would be harder in terms of more labor required. Perhaps, more money for more labor is the motivation.

Am i correct on my assumption that optimizers should have a lower fail rate than micros?

Doubt it. I would take Enphase micros over SolarEdge optimizers.


Without shading issues, there is not much power conversion advantages for micros or optimizers vs string inverters. Unless per panel monitoring is required, string inverters are likely the better choice.

[peakbagger]

My understanding is that solar firms prefer going with microinverters as there are no string calcs and no shading issues. The crews head out with a pallets of panels, cases of string inverters and trunk cable. The only thing custom is the length of the trunk cable and the length of the racking.

[Mike 134]

My understanding is that solar firms prefer going with microinverters as there are no string calcs and no shading issues. The crews head out with a pallets of panels, cases of string inverters and trunk cable. The only thing custom is the length of the trunk cable and the length of the racking.

That makes 100% sense to me. After doing my own install I realized you could train monkeys to do the solar roof work, 2 hardest things I encountered were 1-do not fall off the roof, and 2 finding the roof trusses/joists.

[solardreamer]

My understanding is that solar firms prefer going with microinverters as there are no string calcs and no shading issues. The crews head out with a pallets of panels, cases of string inverters and trunk cable. The only thing custom is the length of the trunk cable and the length of the racking.

For your friend, there is no shading issue so how would string calcs would be that much harder?

[peakbagger]

I have heard that with some installers, actually finding the roof trusses are optional

[peakbagger]

For your friend, there is no shading issue so how would string calcs would be that much harder?

Someone needs to do a bit of prep work at the office to enter the highest and lowest temp and then match the string sizing to the inverter. No need to do that with Microinverters.

With string inverters, the installer needs to inventory several inverter models to match up with different size strings. With microinverters, they just need to stock one model and size.