wongfeihong187
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Microinvertors vs. Single invertors, what's the difference?

Tue Oct 07, 2014 5:12 pm

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.

Bob
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 5:21 pm

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

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Randy
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 5:27 pm

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....

KillaWhat
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 5:47 pm

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.

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Nekota
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 6:02 pm

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.
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WisJim
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 6:12 pm

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.

camasleaf
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 6:57 pm

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)
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JeremyW
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 7:10 pm

camasleaf wrote: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.
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camasleaf
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Re: Microinvertors vs. Single invertors, what's the differen

Tue Oct 07, 2014 8:58 pm

JeremyW wrote:
camasleaf wrote: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.
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Re: Microinvertors vs. Single invertors, what's the differen

Wed Oct 08, 2014 12:17 am

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.

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