String inverters or microinverters

1 Posts
Dec 9, 2014 07:30 pm
String inverters or microinverters

I'm planning on setting up a roof-mount system, in the range of 7.5-9 kW.  I am building a new garage that will be structure on which the panels will be mounted.  Rather than go through a solar installer, I'll have the roofers and electrician install the system.  String inverters would cost thousands less for materials, but it's my understanding that a string inverter system will cost more in labor.  Which would be the less expensive system to install, including installation labor?  I also read that a string inverter actually would be easier to repair panels.  Is that true, and what are other advantages/disadvantages to each system?  I will not have any shading issues that would make microinverters preferable.  Thanks
47 Posts
Dec 10, 2014 10:33 am
Re: String inverters or microinverters

Ah, the eternal question, which is better, micro or string. It looks like you did quite a bit of research, so I probably won't be telling you anything new.  Without shading as an issue, and if you are not planning on expanding in the future, the string inverter is the more affordable choice.  You won't get per module monitoring, but that can be way more info than you need anyways.

 I think labor is about the same for both types of inverters, just a little different.  With the micros, you mount each of the inverters on the rail first, then put the modules on top of them, and bring the AC wire back to the house to the Mains breaker box.  With the string, you just wire the modules to a combiner box, and bring the wires back into the house to the inverter, which then goes to the breaker box.  Bringing the DC wires for the string and the AC wires for the micro are the same amount of work.   

If, for some reason, an inverter does fail in the future, it is easier to replace the string inverter, many of them are modular and allow field replacements.  The micros require you get up on the roof and remove the panels to get to the inverter.  However, if something happened to a module years from now, after that module is discontinued, finding a matching panel to replace it is required for a string, but not required for a micro, as they are managed independently of each other. 

As you can see, pros and cons to each option.  Both are a good choice, you can't go wrong with either.

If you have a 200A Mains breaker box, I suggest not going above 7.5kW for your system.  A 7.5kW inverter will require adding a 40A breaker into the box for the inverter (regardless of which kind), and that is the max that NEC code will allow for a 200A bus bar box.  Anything bigger would require you to have to pay to have the electrician upgrade you to a bigger box, or do a line side tap, which can add to the install cost.  Just something to keep in mind.

We'd be happy to put a design together for you, give us a call.
« Last Edit: Dec 10, 2014 10:36 am by Amy Beaudet »

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