Converting 50kW system from micro inverters to 8x SMA inverters

[solardreamer]

Just curious, why did you go with sunMax microinverters in the first place?

[pclausen]

bcroe Yes, I definitely plan to run DC to the back of the shop building where all the string inverters will be located. Here's an overall view from my house looking down at the shop:



And a closeup of the 400A meter base and solar subpanel as they are currently: (there is another SMA 7.7 inside the shop right behind the solar subpanel)



My plan is to move the 200A solar subpanel all the way over right next to the meter base, and then fill up the wall with SMAs as follows:



I was tinkering with the design this morning and was wondering if there would be an issue with only using 2 of the 3 MPP inputs on some of the inverters and still get full output? If so, I was thinking something like this would make more sense and maximize the voltage on each string for the least amount of loss:



Since the cost difference between the 6.0, 7.0 and 7.7 is minimal, I figured I might as well add more 7.7s since I already have a couple of them. This would also give me vacant MPP inputs for adding more strings later if I wanted to. Looking at the efficiency curve of these inverters, there does not seem to be a loss at all from running at less than 80% capacity.

Here's a closer look at the 400A meter base:



It is actually a sub-panel of sorts and does not belong to the POCO. The main 400A sub-panel is up at the house and this one on the shop runs back up to the house via that 500 MCM Al cable you see. So losses are minimal even when pushing 200A.

Ampster Yes, I plan to sell the inverters. The sell new on Amazon @125 and Streakwave has 30 in stock they are selling for $96 each. I figure I'll offer then for $75/obo to start to see how it goes. About 30 of them will be brand new warranty replacements from Ubiquiti and the rest will be used but functional. I will also have a bunch of Y-cables and such to go with them.

This is all the crap I got initially back in October of 2016:



I'm of course keeping the panels and mounting hardware and the non-solar related stuff, but everything else will be put up for sale, along with 48 more of those 250W inverters and Y cables I got later.

[Ampster]

You should be able to sell the micros to recover some of your costs. I have sold old Enphase M215s on EBay, The SMA inverter are reportedly rock solid and last a long time.

[bcroe]

I am wondering, are you going to run DC over to the building and
put all the string inverters there? That would reduce wire losses a
point or 2, and better protect the inverters.

From my experience, there is an advantage of making all the
inverters the same size. Then a spare kept on hand, could
immediately be used to replace any failed string inverter.

If snow is an issue, there is a lot you could do to reduce the
problem. Mounting panels landscape is one, leaving a half foot
gap between a row and the next higher is another. Landscape
mounting here meant reversing every other panel, half had easy
reach for the string connections, and the other half needed a
short MC4 extension cord. good luck, Bruce Roe

[pclausen]

I have finally reached the breaking point in replacing failed micro inverters and want to convert to all string inverters. I have a couple of SMA 7.7s deployed already, and they are great and rock solid.

Here's a summary of my installation:



And here's how the arrays are currently setup:



So mostly Micro Inverters, but a couple of string based arrays as well.

Here's a visual of the layout:



And here's my proposed solution for going all string based:



And what that would look like visually:



Except for the shop building, I can easily remove all the inverters and rewire for DC strings. The shop roof is going to be a pain, and is of course also the array that is a huge pain to replace dead micro inverters on.

From what I understand, there is no issue with me reusing the THHN 10 gauge wire in the conduits for the DC runs. That sure will save me a lot of time and money. Per the chart above, all strings will be well below the 600V rating of THHN.

I was going to redo that 3x15 array in the foreground with 2x SMA 7.0s, but it will be a lot less work to just leave the 7.7 already there and then add a 3.8 to handle the last 15 panels.

I'm getting the failed micro inverters replaced under warranty. I got about 25 failed ones right now, and just don't want to go through this painful process over and over again. I figured I should be able to cover most of the cost of getting the string inverters from selling the new replacement and good used micro inverters.

Anything you guys would do different?