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I'm building an energy-efficient, hopefully net-zero house in Southern CT.

I've selected a Solar PV engineer/installer who offers either mini-inverters, on each panel, or two inverters in the house. The price is the same. I'm seeking advice on the pros and cons and which option is best.

David Dickson
dd6270@gmail.com

Asked by david dickson
Posted Mon, 04/28/2014 - 10:10

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3 Answers

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1.
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David,
My personal preference is for a large inverter (or in your case, two inverters) mounted in a location where they are easily accessible for troubleshooting and maintenance.

If one of your mini-inverters ever fails, pinpointing the problem and replacing the defective inverter will be a big headache.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 04/28/2014 - 11:20

2.
Helpful? 0

David, you might consider micro inverters if your site has any shading issues. They deal with partial shade better than most central inverters. Martin's correct in saying that if a unit fails it would be a pain to replace, but at least while it's down the rest of your system would continue to function. According to Enphase, they have a MTBF (mean time between failures) of 331 years. Of course we're only on year 6 right now, so we'll have to be patient to see if their reliability predictions hold up.

Answered by Michael McNulty
Posted Mon, 04/28/2014 - 14:08

3.
Helpful? 0

Even without shading issues the fact that micro-inverters optimize output on a panel by panel basis it delivers a small amount more power for the total array. Bird-crap on a single panel can lower the net output of an entire string using the other approach.

Also, inverters don't operate at the same conversion efficiency over any range of DC input power and the 1-2 inverters per whole system approach is always going to be a compromise working across a significant range of panel output but somewhat sub-optimally. Micro-inverters are tuned to the output of a single panel, and come in a small range models relative to the panel sizes &PV types, which means they are pretty application-tuned from day 1, with fewer ways for the array designer to screw it up by over/undersizing a system inverter.

Any failure of the a panel (or the inverter) takes down just one panel. Contrary to Martin's statement, that makes it somewhat easier pinpoint which panel is having the issue (though repairing/replacing it may be more awkward than replacing a large inverter) but the need to replace it isn't as urgent since it's one panel, not a string.

In general the micro-inverter approach to date has been more expensive to implement than centralized inverter approach, despite savings from the wiring being more simplified, but as volumes continue to rise it should become the cheaper approach, since they are readily mass-produced, and cheap when manufactured in million-quantities. Utility scale arrays have been the largest users of micro-inverters for the enhanced reliability/availability of the power at any failure rate, since an micro-inverter failure is the loss of one panel for a few days (or hours, depending on how they are monitoring them), which has negligible impact on the array output relative to when large inverters fail (and fail they do.)

See also:

http://www.greentechmedia.com/articles/read/Reliability-Testing-Front-an...

Answered by Dana Dorsett
Posted Mon, 04/28/2014 - 15:30

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