Microinverter Installation Question

[manny1856]

Hello,
New to the group. Just starting to design my system and am going back and forth on the string vs. micro-inverter configuration. I am leaning towards the micro-inverter and have looked into the APS YC500A inverter. One of the biggest complaints that I can find is the unreliable nature of the microinverter, they all have fairly strong warranties but replacing them is a chore. My solution to this is to install all of the micro-inverters under first panel in the row and using MC4 extension cables to connect the remaining panels. I figure this way if I have to ever replace an inverter, I only have to remove that one panel. Has anyone seen this done this way? I am currently planning to have 3-4 inverters under the first panel of each row.

Thanks

[solarix]

That would be an interesting approach I've never seen done. Kind of a band-aid on a bad idea.
I'd be interested to know what your reasons are in choosing microinverters?

[SunEagle]

Hello,
New to the group. Just starting to design my system and am going back and forth on the string vs. micro-inverter configuration. I am leaning towards the micro-inverter and have looked into the APS YC500A inverter. One of the biggest complaints that I can find is the unreliable nature of the microinverter, they all have fairly strong warranties but replacing them is a chore. My solution to this is to install all of the micro-inverters under first panel in the row and using MC4 extension cables to connect the remaining panels. I figure this way if I have to ever replace an inverter, I only have to remove that one panel. Has anyone seen this done this way? I am currently planning to have 3-4 inverters under the first panel of each row.

Thanks

I am not familiar with the APS hardware. If that type of installation is allowed then I see two potential issues.

The first is depending on the length and size of the wire of those MC4 extension cables from the last pair of panels to their micro-inverter you may experience an undesirable voltage drop.

The second issue I see is that the APS design is a "daisy chain" which mean if one inverter should fail then worst case they all fail or at least all of the ones up stream of the failed unit stop working. That is why most other micro inverters use a Trunk line to pass the AC power.

Have you contacted the manufacturer yet concerning your installation design of grouping all the micros for a row of panels in one location?

[manny1856]

That would be an interesting approach I've never seen done. Kind of a band-aid on a bad idea.
I'd be interested to know what your reasons are in choosing microinverters?

I have a bit of shading on my roof in one area and feel like I would get better efficiency with micro-inverters. I also like the individual monitoring and ease of installation.

[manny1856]

I am not familiar with the APS hardware. If that type of installation is allowed then I see two potential issues.

The first is depending on the length and size of the wire of those MC4 extension cables from the last pair of panels to their micro-inverter you may experience an undesirable voltage drop.

The second issue I see is that the APS design is a "daisy chain" which mean if one inverter should fail then worst case they all fail or at least all of the ones up stream of the failed unit stop working. That is why most other micro inverters use a Trunk line to pass the AC power.

Have you contacted the manufacturer yet concerning your installation design of grouping all the micros for a row of panels in one location?

Thanks for the reply.
The way I have designed it, the longest extension would be 20', 10AWG. I figured the voltage drop would be fairly small over that length, the resistance is about .009 Ohms/ft (.018 total). I am looking at using Suntech STP255-20/Wd panels that run at 30V. As far as teh APS design, I am going to follow up with them about your concern of whether I will lose other units if one goes out. I will update with their response. Thanks

[SunEagle]

Thanks for the reply.
The way I have designed it, the longest extension would be 20', 10AWG. I figured the voltage drop would be fairly small over that length, the resistance is about .009 Ohms/ft (.018 total). I am looking at using Suntech STP255-20/Wd panels that run at 30V. As far as teh APS design, I am going to follow up with them about your concern of whether I will lose other units if one goes out. I will update with their response. Thanks

Well 20 feet one way is really 40 feet round trip which should be used for your DC Voltage drop calculation. Based on the specs the minimum voltage input to that micro is 22vdc. So depending on what those Suntech panels put out and how much of a volt drop the micro may not "wake up" and work.

As for "if one goes the others go too". That is more than likely using a "Daisy chain" configuration. It is like the old Christmas lights when one goes out they all do because the circuit is "open".

Let us know what APS tells you. It is an interesting idea to group the micros. I hope it works for you.

[emartin00]

The second issue I see is that the APS design is a "daisy chain" which mean if one inverter should fail then worst case they all fail or at least all of the ones up stream of the failed unit stop working. That is why most other micro inverters use a Trunk line to pass the AC power.

I believe you are incorrect in your assumption. Just because they daisy chain together, does not mean they are dependent on each other. The wiring still passes through the inverter, it just does not require a separate wire, which saves cost and installation time.

[Naptown]

The op is correct
Instead of a separate trunk cable the AC connects through in parallel like the old M190's
However if a connector fails everything will go down from the bad connection to the dead end of the string( furthest away from poco power connection )

[SunEagle]

I believe you are incorrect in your assumption. Just because they daisy chain together, does not mean they are dependent on each other. The wiring still passes through the inverter, it just does not require a separate wire, which saves cost and installation time.

You may be correct. It all comes down to how the circuit is wired inside the micro. There may be a "trunk" connection that passes through each micro with a connection or "drop" between the MPPT CC in the micro and the "trunk".

The question is that if the micro or even one of the MPPT CC inside stops working, what does that do to the power going down the "trunk"? Hopefully a single MPPT can stop working without affecting the rest.

My concern would be what type of over-current protection is designed for each MPPT circuit and the Micro should a "fault" occur somewhere inside the micro or DC leads from the solar panel.

Again based on the design there could be nothing to worry about but it APS cut corners then who know what might happen.

[SunEagle]

The op is correct
Instead of a separate trunk cable the AC connects through in parallel like the old M190's
However if a connector fails everything will go down from the bad connection to the dead end of the string( furthest away from poco power connection )

Good to hear they at least designed it with "single point" failures (unless a trunk line opened) not messing with the rest of the micros.

[manny1856]

Good to hear they at least designed it with "single point" failures (unless a trunk line opened) not messing with the rest of the micros.

I just talked to APS. The tech support rep told me that if one inverter goes down or even "half" down, it will not affect the others. Although, I do assume that if a connector fails that is a different story. I asked out my bunch configuration and he thought it would work fine just to make sure each inverter has some room dissipate heat(although he was not very concerned), he wanted me to check the NEC code for my state due to the length of the extension cables to the panels. He wasn't sure if there were any disconnect requirements due to the length. Anyone have any thoughts on that?