Two Inverters

Hello everyone,

I’m reaching out to gain clarity on the recent regulations set by the ESB (Electricity Supply Board) regarding Micro Generation connections. I hope the community can shed some light on my queries.

1. Max Limit of 5KW Inverter: The new rules state that with a connection at a low voltage of 230 volts (single phase), the max permissible limit is 25 amperes (about 6kVA). This translates to a maximum inverter size of 5KW. My primary query is: Is this 5KW solely for export, or does it account for both export and internal consumption?

2. Installation of Two 5KW Inverters: Given that our annual energy requirement is between 10,000-12,000 kW, we are contemplating installing two 5KW inverters. Is this allowed under the new regulations?

3. Functioning of the Two Inverters: If we were to install two inverters, could one be set up primarily for exporting while the other manages the house load? Is it possible for one inverter to exclusively manage the load without exporting any surplus energy?

Just to mention, I’m based in Sligo, though I doubt that has any bearing.

Apologies in advance for my limited understanding. I’m a total novice in this area and any guidance would be highly appreciated.

Thank you for your time and insights!

1. That limit is the total for all grid-tied inverters, ie any inverters which are attached to the mains supply on the property which have the potential to export, even if not configured to do so. It would not count independent inverters such as a fully-isolated grid (such as on a shed) with zero connection to the ESB mains.
2. In theory that is possible but I have yet to see a split configuration which would allow greater than 25A to the letter of the NC6 regulations.
3. Again, in theory yes, but see answer 2.

BTW, you're confusing two terms in question 2 which is important to get right; it may be leading you into thinking that you need two inverters:

"Our annual energy requirement is between 10,000-12,000 kW" - It might seem trivial, but it should be kWh. That's the measure of energy over time (hours). So 1kW consumed over a period of 10 hours would equal 10kWh. With inverters then you measure the max instantaneous generation capacity and that's 5kW, but it doesn't tell you what duration that it can supply that wattage for. If you then put solar and a battery behind the inverter then you have storage potential - and that can be measured in kWh. So you can't divide the yearly consumption of 10,000kWh by the inverter's 5kW and size the system that way, you need to break down your usage per-day so that you can obtain a kWh figure.

An example would be by taking 12,000kWh and dividing that by 365 days to get roughly 33kWh consumed per day. Then you know that you'd ideally like your generation capability to beat that in the Summer months. For Winter you commonly would then take what you get and take the remainder off the grid, but your Summer should be paid-for.

Here's a Gary Does Solar to explain that in a graphical way:

In fairness, that's not in the spirit of the rules, the rules are there to protect the electrical distribution network and the ESB are limiting the export potential so that in the event of a fault on your equipment (especially this limitation mechanisim) that it doesn't have the capability of sending excessive current into local distribution.

Once we all have Smart Meters, that will most likely become the "policing" mechanism. If you export over 5kWh in any hour, you're likely to show up with red flags (if they create such reports to flag these)

Exactly. This is also what my original installer reckons. My system is "grandfathered in" so to speak. I put my NC7 on ice last December due to voltage concerns but things will be changing for my supply locally in the next few months so I'm going to resurrect it.

@...Ghost...

You can set the hybrid Inverter to either recognise the export/production of the dumb inverter and charge the batteries, or to ignore it and let it go to the grid. The dumb inverter will first feed the house load before exporting or charging the batteries.

Microinverters would work very well on your shed. You can get 4 port micro's. A string inverter might work out cheaper though.

My mistake, I assumed they would all have the option.

That's poor enough, I wonder is this just a software limitation.

Hoping I don't need to start new thread, as this one is on topic with 2 inverters. Note that a RECI will be completing all relevant work, but I want to know what I am talking about.

I plan to have 30-45kWh of storage (2 or 3 batteries) with the first 15kWh being built this week hopefully. Currently have a 5kW Solis hybrid inverter with a 5.2kWp system on the house. Smart meter installed.

I plan to add about 5kWp to the shed and ground floor extension (2 strings). I know a dumb inverter can feed into a mini CU in the shed and from there to the main CU, or I could bypass the mini CU, set the dumb inverter up beside the hybrid inverter and then feed into the main CU, but I would like some help please, as I am not sure what direction is best to go. Here is my goal…

I want to be able to charge and discharge up to 10kW from the batteries if possible, which would almost eliminate any day rate grid import for me. Likewise, I would like to be able to charge the batteries up over a 3 hour window. What is the best way to do this assuming I have 2 x 15kWh Seplos batteries? The second (maybe 3rd) battery will be bought and ready by August.

From the thread, I see an upgraded hybrid inverter could be an answer, but I would prefer to add to what I have rather than replace, because I will have a total of 4 strings and I don't want to change out the new inverter so soon. Also I think I would still have a battery discharge limit of 5kW???

I currently avail of a standard night rate which I could use to fully charge a full compliment of 45kWh @ 5kW/h over the night, but then I can't take advantage of much cheaper boost rates, or advantageous peak dump rates. Help me out before I start buying stuff please 😊