Two Inverters

Hello folks.

I've been reading this post with great interest, as I am in a similar situation where I would like to add a second inverter to expand our Solar PV system.

Our existing solar PV system is south facing producing 5.5 kilowatts in good sunshine and is run using a Solax hybrid inverter which is connected to a 6.3 kilowatt hour battery. This PV system feeds into a sub-fuse board located in the utility room. The sub-board is connected to the main fuse board with a 16 square wire. The hob, oven, dish washer, kitchen and living room lights and sockets are wired from the sub-board - just providing this information incase it's relevant to my questions below.

I plan to add a second inverter which will either be a Solax inverter or a basic string inverter with two string inputs, the size of this inverter will be approximately 3.5 to 5 kilowatts and the solar panels supplying the second inverter will be West and East facing. The sum of the two systems working together could produce 9 - 10kw on a good day.

I don't know anything about installing solar systems so I have a number of questions I'd like information on just so I'm aware and have an understanding while speaking with the installer.

Questions:

(1) I've been doing some reading online and any of the things I've seen in relation to the installation of a second inverter they talk about wiring the inverters together in parallel or in series. Is it necessary to install or wire the two inverters together in parallel or series or can they be wired independently to the same fuseboard or as it is in my case the sub-fuseboard?

(2) The existing inverter has a CT clamp on the mains wire coming in so it can determine if we're exporting or importing, is it necessary that the second inverter would also have a CT clamp on the mains for the same reason to see if we're exporting your importing?

(3) Should the inverters be connected together in some way so they can communicate with each other (this may not be possible I imagine if the inverters are different e.g. Solax for the existing system and Hypontech for the second inverter)?

(4) When both inverters are generating power will they both send power to the house to satisfy the load while the excess goes to the battery and rest (if any left over) exported to the ESB network or could they inhibit each other in anyway?

Apologies for the long post and questions but any advice you can offer or answers to my questions would be greatly appreciated.

Thanks in advance and I look forward to your reply.

Kind

regards,

SE Galway

As for DIY, super easy. Panels are daisy chained, with the cable from each end plugged into inputs in the inverter. All connectors are MC4's. They all just click together.

The AC side needs to be connected to it's own breaker on the board (or subboard). No CT's needed

You are limited to 25 amps on the new regs, thread here https://www.boards.ie/discussion/2058288583/esbn-new-regulations-on-nc6-form-on-6kw-25amp-inverters-may-31-2023/p1

Hello folks,

Many thanks for all your input it's much appreciated. I've learned a lot through this and earlier posts on this thread.

Thanks for sending link to regulations.

Kind regards,

SE Galway

I've a non hybrid inverter. Am I correct in my reading that I can only get another non hybrid for more panels in a separate string?

I assume I could then get a storage inverter to connect to either one and batteries to the storage inverter.

What's your MIC? It'll say on your connection documents in kVA. As you say, I'd definitely do the research first before paying anything. You can check if it's possible to upgrade your MIC by getting a quote with this process.

You could put in a separate 'new' hybrid with your exisitng grid-tie and they would work independantly of each other. If you're upgrading a grid-tie system to hybrid, most people in that situation would just replace the grid-tie inverter with a hybrid inverter that can do everything you want in one go.

Just another thing on the 25A limit, it should be possible to program your existing hybrid to only allow a max export of that. So, if you size your new grid-tie inverter at 25A or under, you won't go over 25A total as the hybrid will throttle back if it's done charging the battery and house demand is being met.

So having a hybrid and non hybrid inverter isn't an issue.

You just can't really have two hybrids

You can. But it would help if they were identical and they support connection of one as master and one as slave. And the only reason for that setup is to have more battery charging / discharging power than one inverter can give you. Personally I would just look for a more powerful inverter and buy a single one!

The MIC is for import. The NC6 is what will determine your export limit currently.

You would need a NC7 to have more than 25A of inverters connected to the grid.

Email networkservicesbureau@esb.ie explaining and asking them for a copy of the NC6 that was filed on your behalf, so you can see what inverter size was submitted. The NC6 shows the inverter limit. They are very helpful people here have said.

I didn't know what MEC was, Max Export Capacity (kVA) = Total Installed Inverter Capacity. I checked my NC6.

Hello Buffman,

Thanks for your input.

Yeah, we're in receipt of a deemed payment for our solar export based on our 5kw inverter. We haven't gone the smart meter route yet but will considerate it if we can expand our current system. We'd be looking to expand by an additional 3 to 5kw.

One last question on the NC7 form. Is it the case that the solar array is expanded first followed by sending in the NC7 form to the ESB or is the NC7 application made first to the ESB before the solar array is expanded and an additional inveter added?

Keep in mind that we made a NC6 submission in 2021.

Thanks.

Regards,

SE Galway