Microinvertors vs. Single invertors, what's the difference?

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wongfeihong187

Well-known member
Joined
May 14, 2014
Messages
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Hi I'm trying to get myself edumacated on solar before purchasing for my house. Can anyone tell me the difference between micro and single invertors, and which one is better? Thank you in advance for reading my questions.
 
For any situation with less than optimal sun, microinverters are better. For example, if you have solar panels on your roof and a cloud shadows part of the array, it will cause part of the array to put out very little. With a single inverter, that means that the whole panel will see very little output. With microinverters, the array is divided into individual pieces, and each piece supplies energy separately. So in the single inverter case, with 50% shade, you might get 10% energy out. In the microinverter case, you will get 50% energy out.

Microinverters are more expensive for the same total kilowatts.

It isn't clear if microinverters are more reliable because one can fail without the whole array failing, or if they are less reliable because there are so many of them.

Bob
 
There are pros and cons...

String inverters are affected by shading on any panel on that string. The output for the whole string will be reduced if/when shading occurs.

Microinverters are usually installed so there is one for each panel, so shading only influences that shaded panel.

For a microinverter system, 240 volts AC comes out of the panels and goes down to your main or sub panel. On a string inverter system, DC power comes down from the roof or where your panels are located and is converted to AC power at the string inverter location. So if it makes a difference, the wire is usually smaller on a microinverter system of a decent size down from the roof.

There are online debates about reliability, both ways. But if your string inverter goes out, your system won't produce any output until it is replaced. A microinverter failure only affects the output of that panel.

So no one system is always the best, it depends on your house, your system, and what you're trying to accomplish. Microinverter systems generally cost a bit more...

I have a chimney that does have some shading on my south-facing panels, and I didn't have room in my garage on the wall for a string inverter (and I didn't want it outside), so I choise to go with a microinverter system....
 
I just went through this whole debate.

What it came down to for me was:

Microinverters are like lots of little systems added together. If 1 goes down it doesn’t take the whole system down.
Also, if you have shading issues, then you want microinverters. The new ones are very sophisticated and dead on with voltage and frequency. But as the system gets bigger, the cost exceeds a single inverter system.

“Single” inverter. HIGH DC Voltages are generated, and then transmitted to the Inverter.
High DC voltages kinda spook our code people here.
A decision sticking point was that SMA makes a new inverter that provides a dedicated outlet that will produce AC even when the grid goes down.

If you are going off grid, single inverter.

I went with Enphase M250 microinverters and ET Black on Black Mono 255 Panels for my Solar Leaf Charger.

Good Luck
 
Most of the points about multiple microinverters and single string inverter have been covered but I will add two additional considerations. One drawback to a high voltage string inverter is a power loss that comes from potential induced degradation or PID. So if you go with a single inverter you should ask about how much PID loss is expected. The second factor is if you want to go off the AC grid and use DC battery power the single inverter will enable that DC interface and provide AC power from the DC batteries as well as the DC from the PV panels.
 
I went with Enphase microinverters a couple of years ago for the latest addition to my PV system. One reason was outside temperature. I didn't have a good place to install a single string inverter inside and didn't find any readily available units that were listed to operate at 40 below zero. The microinverters do operate at those lower temperatures. Also, the Enphase units are warrantied for 25 years, versus 5 or 10 for most string inverters. Also, the DC switching and fusing required for the string inverters can be more expensive than regular AC equivalents used with the microinverters. And the microinverters have MPPT which ends up giving more wattage output from the panels.
 
I went with single inverter (does have MPPT). Next time I want to go on the roof is too put new panels on. Potential induced degradation might not be such a big issue for 1000V rated string panels were the panel on the ungrounded end reaches 340V.

But for me the main driving factor going the DC route was the possibility of dumping the PV power directly in the Leaf battery without any charger. Unfortunately the fire marshal wanted a path to the roof so my string voltage (under full load) is around 340V instead of 373V, and I have two panels siting in the garage. I am still thinking of installing the extra panels on different mounting system or hinge them so the firefighter can lift the two panels and walk to the top of the roof. After that I can play with the PV to Leaf directly (well, I plan to use one diode and fuses)
 
camasleaf said:
After that I can play with the PV to Leaf directly (well, I plan to use one diode and fuses)
You'll loose MPPT going that route. Ideally you'd have a DC/DC converter and something doing CHAdeMO on the leaf interface end. A subject for another thread, though.
 
JeremyW said:
camasleaf said:
After that I can play with the PV to Leaf directly (well, I plan to use one diode and fuses)
You'll loose MPPT going that route. Ideally you'd have a DC/DC converter and something doing CHAdeMO on the leaf interface end. A subject for another thread, though.

That is a setup to use just for emergency only, MPPT efficiency is not really a concern in that situation. I lost power for longer than a few minutes just 3-4 times in 15 years.

Going back to Micro vs. Single the cost was also a big factor for me. The DC disconnect that was mention as extra cost for the single version came with the inverter, the combiner box I built from individual bought components for about $40.
 
Lots of pros for microinverters already listed. I'll leave Andy to posting about all the negatives.

I originally went with Enphase microinvereters because I was DIY and figuring out string sizes, code requirements for DC wiring, designing the system, picking an inverter, etc. was making my head hurt. I also had some significant southeast shading that I figured they would help with.

This turns out to have been a great idea because my first phase of 21 then turned into a second phase of 35 more which included adding one one more on the south roof, 4 more on the west roof and the rest on the east roof. Then that turned into 15 more. The simplicity of adding more with a microinverter is a pretty nice benefit if one is leaving roof space. I also appreciated that all the wiring was just standard 240 volt stuff (except for the special grounding requirements) so it make it simple using my existing skills.

Now I'm producing more than 100% of my usage for an EV, and heat pump space and water heating.

http://kemp.solar" onclick="window.open(this.href);return false;
 
Warranty on string inverter is typically 10 years, and I was told I might have to replace it in 12-15 years @~$4000.

Warranty on micros is 25 years and Enphase monitors them, if one goes down they contact you and your install company to fix it, and pay you for lost production.
 
DNAinaGoodWay said:
Warranty on micros is 25 years and Enphase monitors them, if one goes down they contact you and your install company to fix it, and pay you for lost production.

Sure... good luck there.

I've had eight out of my thirty micros fail in the past year and Enphase hasn't once contacted me or my installer. I always have to open a case with them, and, even then, they are slow to offer replacements. In addition to the eight, complete failures, there are six others which are defective (producing low power output during the day). Enphase refuses to replace those, because they aren't completely dead.

They, definitely, have never offered to compensate me for lost production.
 
As Nekota noted another advantage or disadvantage of a single inverter system is the ability to supply power even if the grid goes down. It requires a battery setup and that is added cost, so if you main goal is just to recover the cost of installation then go with battery less single inverter since it will be the least expensive and fastest payback. If you want battery backup, think HUGE UPS powered by solar, then go with a battery setup, be aware that a battery system may never break even because of battery replacement, but it may pay for itself over time, and a genset will never do that :)
 
Re: battery backup;

AC coupling can be used to keep grid-tie inverters operating when the grid goes out, by using a battery-based inverter to provide the "clean" AC source that a grid-tie inverter is looking for in order to activate. You need a few extra gubbins to make sure the whole thing is properly isolated from the grid (e.g. blackout relay) and a way to control the PV system and/or a dump load in case you're producing more energy than you can use with the batteries fully charged.

This scheme should work regardless if you use traditional or microinverters.
=Smidge=
 
Weatherman said:
DNAinaGoodWay said:
Warranty on micros is 25 years and Enphase monitors them, if one goes down they contact you and your install company to fix it, and pay you for lost production.

Sure... good luck there.

I've had eight out of my thirty micros fail in the past year and Enphase hasn't once contacted me or my installer. I always have to open a case with them, and, even then, they are slow to offer replacements. In addition to the eight, complete failures, there are six others which are defective (producing low power output during the day). Enphase refuses to replace those, because they aren't completely dead.

They, definitely, have never offered to compensate me for lost production.

Sorry to hear that. I don't know the details, but if I had that experience, I could bring it to the attorney general's office and get some resolution. Are you saying they have breeched your warranty? Or, do you have older micros, from when the warranty was less than today's? First negative I've heard of Enphase.

My two year old system has never lost a micro. I've had to shut off off some notification settings as it would notify me for trivial stuff like low voltage at sunset. My biggest problem is when Enlighten can't report because my cable is down (Charter Sucks!) but that doesn't affect production. I've gotton calls from my installer to check, when that happens, so I know the communication lines are working.

I hope you can get it resolved.
 
They have never failed to replace a completely dead micro. The fuzzy part of the warranty language is what they consider to be "defective". Here's the wording from the warranty:

"During the Warranty Period, Enphase will, at its option, repair or replace the Defective Product free of charge, provided that Enphase through inspection establishes the existence of a defect that is covered by the Limited Warranty. Enphase will, at its option, use new and/or reconditioned parts in repairing or replacing the Defective Product. Enphase reserves the right to use parts or products of original or improved design in the repair or replacement of Defective Product."

http://enphase.com/warranty/15-year-warranty/" onclick="window.open(this.href);return false;

There's nothing in the warranty, which defines what "defective" means. Obviously a micro which produces no power is defective, but one which cuts power back and runs about 8% less than its neighbors? Apparently Enphase doesn't consider that "defective".

There's nothing in the language of the warranty which says Enphase is obligated to compensate customers for lost production and nothing says they are obligated to monitor customer systems and take action on their own to correct "defects".


The m190 and d380 models have been shown to be very unreliable. I'm not the only one having problems with m190s. I fully expect a majority of my m190s will be replaced in the next five years and none will survive the entire 15-year warranty period.

I've read that the m215 and later models are more robust, so I wouldn't write off Enphase completely. It's just that a lot of us m190 owners got bad batches.
 
Just to add to the confusion there are also power optimizer systems like Solaredge provides. Basically a power optimizer is installed on each panel like with a micro inverter but you also have a main inverter like with string system. You get the benefit of being able to monitor each panel and it also deals with shading issues better then a single inverter system.
 
kaikara said:
Just to add to the confusion there are also power optimizer systems like Solaredge provides. Basically a power optimizer is installed on each panel like with a micro inverter but you also have a main inverter like with string system. You get the benefit of being able to monitor each panel and it also deals with shading issues better then a single inverter system.

The SolarEdge system is basically a DC to DC converter attached to each panel. If a panel is shaded the DC to DC converter raises the panel's output voltage to match the rest of the string. By keeping the voltages consistent the shaded panel does not drag down the output of the rest of the array. The other advantage is the DC to DC converters allow the panels to kick-off earlier and stay on a bit longer. This is possible because the DC to DC converters are able to raise the output voltage so the string inverter can operate longer.
 
The Enphase M190s were unreliable, but they did pay the bill for my friend's installer to replace the failed inverters, they upgraded them to the better M215s, replaced ALL of them (not just the failed ones), paid for the lost power AND extended the warranty from the day of the new install.

I really want solar, but I generally use less than 500kW per month, which barely keeps me in Tier 1 at 11.8 cents per kW. Hard to justify the cost of solar with those numbers, but I hope for a solar breakthrough that increases efficiency and lowers cost to make it easier to justify.
 
kaikara said:
Just to add to the confusion there are also power optimizer systems like Solaredge provides. Basically a power optimizer is installed on each panel like with a micro inverter but you also have a main inverter like with string system. You get the benefit of being able to monitor each panel and it also deals with shading issues better then a single inverter system.
You also seem to get the worst of both worlds, IMHO.

Outside of service and initial cost, I don't see any advantage to having a single inverter. Having remote optimizers means you still have to pay for the single inverter but also each optimizer on top of that. You still have all the HVDC wiring so installation isn't simplified at all. You can't even retrofit the optimizers to an existing system as it needs the inverter with the "smarts" in it to work properly.
=Smidge=
 
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