ReneSola microinverters putting out DC volts at idle

[mcheck]

I finished installing my solar system, with 20 Yingli YL-240P-29B 240W solar panels arranged in 2 strings of 10. Each solar panel has a Renesola microinverter Model Replus-250B rated at 250w 240VAC. Install went smoothly, and I passed electric inspection, I was all excited to go. However, when PSE went to hook up the production meter, they said that when the AC power was off, it was generating DC voltage, which violates UL1741. I confirmed this myself, it generates about 30v DC between each hot and ground. I tried to see if it was one particular bad microinverter, by selectively disconnecting a few, but it seems like they all have the same behavior. When i power up the system, the DC voltage goes away. When i shut AC power, the DC voltage comes back.

The inverters are listed as rated for ul1741, but the company that makes them doesn't seem to be around anymore, so I'm SOL on tech support. I've been working on this project for so long, i can't return the renesola microinverters either

The meter guy from the power company said this is not normal and violates UL1741. I can't actually see the UL1741 spec, so I don't really have any grounds to stand on to disagree.

At this point I'm out of ideas on how to troubleshoot or move forward. If i have to replace all of these microinverters, that's over $1000 down the drain, which blows the payback period for my solar project, but having a solar system that I can never hook to grid is even worse.

Any ideas before I go purchase some enphase microinverters off ebay?

Thanks!
-Martin

[Paul Land]

Penny-Wise. Eat the loss and go with proven long run winners

[Mike90250]

Why do you need micro inverters ? Do yo need to meet rapid shutdown specs on your install ? Do you have shade issues?
Why not a string inverter, or add optimizers if you need rapid shutdown ?

[mcheck]

Why do you need micro inverters ? Do yo need to meet rapid shutdown specs on your install ? Do you have shade issues?
Why not a string inverter, or add optimizers if you need rapid shutdown ?

I do have partial shade rotating across my panels throughout the day. I figured microinverters would not have a much higher upfront cost, and would pay back faster.

I guess I could install a 5000w string inverter for the system, but that would require restarting the whole install and redoing all of the inspections and permits.

Worst case scenario, assuming the microinverters are a total loss, is there a reason I couldn't swap for a better microinverter?

What's interesting is that the microinverters don't show DC voltage between the L1, L2, or N connection. They only show DC voltage to ground... i want to positively rule out that I've wired these wrong... as far as I can tell the neutral connection on the inverters bond to ground at the main panel, so I don't see any other way to wire it. I'll do some more debugging today.

In terms of better microinverter options, does anyone have recommendations? I suppose I could buy a single unit, test it out, and confirm it doesn't show the DC voltage issue (this could at least rule out an install issue vs an equipment issue).

[sdold]

What's interesting is that the microinverters don't show DC voltage between the L1, L2, or N connection. They only show DC voltage to ground...

If there is no DC voltage between any of those, it implies that there is the same DC voltage from all of them to ground, including the neutral. Is there 30 VDC from the neutral to ground?

Also you mentioned that there is 30 VDC from each hot to ground, but that means there should also be 30 VDC from each hot to the neutral, which I think you say isn't happening. So I'm wondering if there is something "funny" about the neutral connection, which should be bonded to ground at the main service panel.

Also is there an intact EGC (green wire ground) in the conduit all the way from the microinverters to the main service panel?

[mcheck]

There is 30vc from each hot to ground, but not from hot to neutral. The renesola AC cable is a 3 wire setup, with two hots and neutral, and ground is a 6 gauge run externally bonded to the inverters chassis and the solar panel chassis, then terminating in the service panel ground bar. Neutral also terminates in the service panel neutral bar (which is effectively the same as the ground bar).

Page 18 of the manual here describes how i installed this per the north america single phase setup:

http://www.westlandsolar.nl/media/Micro-replus_inverter_manual.pdf

One thing I realized looking at the diagram closer is that I bonded the gateway ground to the microinverter neutral wire, whereas the setup guide has them not bonding until they reach the ground bar of the panel. I'm not sure how much difference that makes, but it's an easy fix to apply. Oddly enough, I've found manuals online that show that the inverter neutral is left unused (i.e. this one): https://www.manualslib.com/manual/81...?page=3#manual

My printed manual matches the first one where neutral runs all the way to the panel, so I'm going with that. Not sure which is more accurate, but i can't imagine a floating neutral is going to pass the meter install procedure.

Today i'll go fix the gateway grounding setup, and report back. I also will try setting up a completely isolated single microinverter and panel disconnected from my AC grid and see if it still generates DC voltage.

[mcheck]

I just wanted to close out this thread, I tried all sorts of debugging, including changing ground configurations, adding / removing different inverters and connecting anywhere from 1 to all of them, and almost every time the DC voltage would come back. Finally I bought a few enphase M215 inverters and after waiting for winter to end so I could get some reliable sun, I disconnected the renesola and installed a few enphase microinverters, and they worked flawlessly. I've now replaced all of the renesola inverters with enphase, PSE came out and did the meter install and the system is energized and producing power! As a bonus, the enphase envoy gateway is still supported (unlike the renesola), so I can actually use the web UI for remote management (which is good, since there doesn't appear to be a way to manage the system local only). There is a longer story about the hours i spent putting dd-wrt and hacking together a wireless bridge so I could connect the envoy to my wifi network, but that's the kind of fun i want to have, not debugging faulty hardware that's unsupported

Thanks for those that offered useful advice (sdold mainly ). Here is a link to my system as a "reward" (You'll notice I have a few DOA enphase units that i'm waiting on replacement units for. I'll add another ~10 or so inverts as part of an upcoming expansion): https://enlighten.enphaseenergy.com/...ms/W4aN1842052

[sdold]

Thanks for the update. Did you end up with some dead units out of the box? Based on my limited experience, M215s seem to be good inverters, out of a total of 46 installed by three of us 6-7 years ago, none have failed. I still would recommend a string inverter if possible, but the M215 seems to be solid. Mine are really hot in the summer too, many days over 100 degrees.

You can log into the Envoy directly, but there is limited info. I haven't been able to access much more than basic working/not working info, which might be all you need.

[bob-n]

mcheck: Congratulations. Good work.

sdold: Please forgive me, but something you wrote caught my eye: "M215s seem to be good inverters, out of a total of 46 installed by three of us 6-7 years ago, none have failed. I still would recommend a string inverter if possible, but the M215 seems to be solid. Mine are really hot in the summer too, many days over 100 degrees."

It sure seems like you're saying that M215 works great and has a long history of reliability, but I don't recommend it.

???

[sdold]

It sure seems like you're saying that M215 works great and has a long history of reliability, but I don't recommend it.

I just meant that I don't recommend microinverters at all, unless necessary to overcome a problem like partial shading. I'd rather have the electronics off of the hot roof and down in the garage for simplicity, longevity and ease of service. But if one must use microinverters, I think the M215 is a safe bet. There is nothing sexy or "cool" about them, however.

[mcheck]

Thanks for the update. Did you end up with some dead units out of the box?
<...>
You can log into the Envoy directly, but there is limited info. I haven't been able to access much more than basic working/not working info, which might be all you need.

I actually acquired a batch of used enphase units (ranging from m190 to m215... interestingly the effective power generation is nearly the same on my 240w panels), so the DOA were expected as some of them had probably already lived out a fair portion of their useful lives.

For local login to envoy, I don't think mine supports that (ENV-120), or I haven't figured out how to do so. It doesn't have wifi (connnects via ethernet), would I just connect directly to it's local IP address from my local network?

Another interesting tidbit, i have one solar panel that is cracked that I left installed just since I don't have a replacement on hand. It still produces power, at a rate about half of what a healthy panel produces.

Thanks!
-Martin

[inetdog]

I actually acquired a batch of used enphase units (ranging from m190 to m215... interestingly the effective power generation is nearly the same on my 240w panels), so the DOA were expected as some of them had probably already lived out a fair portion of their useful lives.

For local login to envoy, I don't think mine supports that (ENV-120), or I haven't figured out how to do so. It doesn't have wifi (connnects via ethernet), would I just connect directly to it's local IP address from my local network?

The Envoy will get a local IP address via DHCP protocol from your network router or gateway. So to connect to it locally you will need to know what IP address it has been assigned. But with most DHCP servers you can optionally "lock" the IP address to the MAC address of the Envoy board so that the local IP will remain invariant through network upsets, reboots, etc.
Once you have a stable local IP address you can, if your wish, enable port forwarding from your broadband connection so that the Envoy can be reached from anywhere on the Internet. If you do not enable port forwarding the Envoy can still initiate a connection to server(s) on the Internet, it just cannot receive an incoming connection request.

[sdold]

My Envoy readout shows its IP address, yours might too.

[inetdog]

My Envoy readout shows its IP address, yours might too.

Very helpful, but if you are going to use automated software for monitoring and data collection or are going to implement port forwarding to allow access from the Internet, you still need to lock in that IP address.