Export Limitation for AIO and 6kW Enphase PV

Hi,

If I was to pair a GivEnergy AIO & Gateway (6kW/13.5kWh) with approx 6kW of Solar PV with Enphase Micro Inverters and Metered Envoy (gateway) unit I would have approx 12kW of total registered capacity. I doubt very much that my DNO (National Grid) would let me export this much, so expect that I might be limited to somewhere between 3.68kW (ie G98 level) and say 6kW.

This raises a couple of questions:

How does export limitation work in this scenario? Does the Gateway/AIO only limit grid export from the AIO inverter, or does it also limit Enphase output by performing frequency shifting? Is there a priority order for doing this (ie limit AIO export first then limit Enphase export if necessary until DNO export limit met)

I've had a quick search through this forum but haven't been able to find an answer so far, so maybe I'm using the wrong search terms!

TIA

This is a useful I don’t know answer…

If like the Powerwall and gateway2 it monitors the PV, then it might be able to. The gateway2 can export solar only, battery and solar and can work to a site export limit.

So it’s possible with gateways, but someone who owns or knows the GE system will need to answer.

Not sure on max level but with my AIO I had a G99 carried out even though I don't have solar.

T-M the AIO can only discharge/charge at 6kWh so you’d never be able to export more than 6 surely?

I have a solar array of 5.25 kWh on the roof coupled with a Givenergy AIO.
This is what I received from our local DNO:

"Thank you for your recent notification regarding the installation for 5kw Generation and 6kw Battery Storage limited to 2.26kW. Total export for the site limited to 7.36kW."

I beleive the amount that you are allowed to export depends on local conditions with regard to the substation, number of people already exporting etc.

My recent G99 approval for an AIO added to my 4kW panels stated "The total aggregate Registered Capacities of all the Generating Units (including Electricity Storage devices) is less than 60A per phase" - which equates to around 14kW.

Suggest you apply for G99 approval and see what limitation is set.

deanjesper The 6kW inverter in the AIO connects to both grid and consumer unit via the gateway. So with battery set to discharge and 6kW coming from the PV on a sunny day, there is a total of 12kW available, less what the house is consuming at the time. The DNO will look at the total registered capacity of all the inverters connected to the grid when doing their network calcs, as they have to consider the implications for your neighbours if the limitation devices fail. See ENA EREC G100 Issue 2 Amendment 2, Appendix D, Example 1

DreadorUK G99 because the inverter in the AIO is capable of exporting 6kW to the grid, which is higher than the G98 limit of 3.68kW (ie 16A). You haven't mentioned having a limit imposed by your DNO so I assume they were happy to allow you the full 6kW. If and when you add Solar PV to the mix, you will have to re-submit a G99 application, and that's when I suspect your DNO will impose an export limit.

Tenkaykev Yes, there are some examples of how the DNOs go about calculating your export limit in Appendix D of ENA EREC G100 Issue 2 Amendment 2
https://www.energynetworks.org/assets/images/ENA_EREC_G100_Issue_2_Amendment_2_(2023).pdf

T-M I never even thought about the fact that you can discharge the battery at 6kWh and export from the PV at a few kWh at the same time. I assumed that if I’m generating 4kwh and I’m exporting 3kwh and I want to discharge the battery then only 6kwh will be exported, not 9kwh!

I would have assumed that the AIO would back off it's discharge - assuming it knows what the export limit is (the installer should have set it) and it is monitoring the grid current.

T-M
The All in One has an integral 6kW inverter but it’s AC in so your PV will need a string inverter to provide the conversion.
As an example, if you have an 8kW export limit then you would leave the string inverter unrestricted as you will mostly be exporting in summer and then limit the AIO to the remainder. Eg 6kW unrestricted string inverter and AIO restricted to 2kW

deanjesper That would be true if the AIO/Gateway was a Hybrid inverter, but it's ac coupled, so both the AIO and PV inverter (Enphase in my scenario) are connected in parallel to the grid. Tell the AIO to discharge on a nice sunny day when your PV is generating and all that energy has to go somewhere, or the AIO/Gateway has to back off one or both sources to stay within the DNO export limit

Goshiki2 If I was to end up with say, a 5kW export limit, I would hope that the AIO/Gateway would limit the AIO output first, as leaving the electrons in the battery costs me nothing, whereas throttling back my PV generation while continuing to discharge the battery to the grid will cost me

T-M
I had the option (through my installer talking to DNO) of restricting either AIO or string inverter. I chose to restrict the AIO as I only expect to export in summer

Goshiki2 and during saving sessions I hope

Goshiki2, that would be very restrictive, and not actually required.

Both the AIO and the string inverter normally have a grid meter/CT wired to them, so they can both be set with an export limit of 8 kW for example.

Then if 1 is not performing, the other is able to export up to the full limit. If both are performing, then they will automatically back off/control at the 8 kW limit.

Simon_C
Interesting. That was never put forward as an option. How would priority be set?

Goshiki2 Exactly what I'm trying to get my head around!

With 6kW of PV, a 6kW AIO inverter and a DNO limit of 4kW, if the export limitation devices in the AIO and PV inverter operate totally independently, then I have to set one of them (battery, say) to zero export and the other (Solar PV) to 4kW max export. However, the downside of this is that when it's dark, the battery is full and the house is only using 1kW, it won't be possible to force discharge 4kW to the grid. This would limit or even rule out being able to benefit from Octopus Saver sessions and the Octopus Flux tariff.

Alternatively, if the AIO/Gateway is able to manage export from both inverters, perhaps by first throttling back the AIO inverter to zero and then, if necessary, frequency shifting to throttle back the PV inverter, then both systems can perform to their maximum effectiveness whilst still adhering to the DNO export limit.

T-M I just assumed the Gateway handled the PV and AIO so the limit set on the AIO should be the “master” limit?

deanjesper
No, the gateway simply handles the AC coming in from the string inverter. The restrictions are done within the inverters as far as I’m aware.

deanjesper That's what I hope it does, but I haven't found anything to confirm how the AIO/Gateway export limit actually works. There's a brief description in the ENA EREC G100 Manufacturers CLS Product Info, but again, it's not clear whether that just applies to the AIO Inverter or to the whole AIO/Gateway/PV system

T-M
The export limit of the AIO is set by a register in the integral inverter. It can only be accessed by the installer, not by the end user. It doesn’t consider any external inverters as the AIO is essentially stand alone and doesn’t actually need PV input.

Goshiki2 It's a mandatory requirement of ENA EREC G100 Issue 2 Amendment 2 that the export limit cannot be changed by the customer, so I have no issue with that. I also assume for the same reason that the relevant register cannot override this by being set locally via Home Assistant/GivTCP or similar.
If the AIO is not aware of the PV inverter, and has no control over it, then the implications of 6kW PV with a 4kW DNO export limit would be that the AIO/Gateway would have to be permanently locked to prevent any export from the AIO to grid, and the PV inverter would have to be set to 4kW export limit.
This means you could never discharge the batteries to the grid, and only discharge it to support house loads, which limits the flexibility of the system and what you can earn from Saver Sessions and Octopus Flux tariffs.
Other inverter/chargers such as Victron Multiplus II are able to frequency shift their output to throttle back the PV inverter when necessary, so I would have expected the AIO/Gateway to be capable of the same.
Do you have a link to the source of your information?
Edit: Victron Frequency shifting only applies during grid failure as it's physically not possible for a grid connected inverter to change the grid frequency

T-M
I’m only going off what I’ve been told by my (trusted) installer. After the G99 application I was given an 8kW export limit and the option of either restricting string inverter or AIO so I chose to max out the 6kW string inverter and to restrict the AIO to 2kW which does obviously impact export during savings sessions.
I’m interested to hear if anyone has found an alternative way around it.

Goshiki2, does your string inverter have a grid meter wired to it? If not, then that might explain your limited options.

If both your string inverter and the AIO each have their own grid meter, then they can both operate according to their own control strategy with the same export limit value of 8 kW. Both grid meters will be reading the same 8 kW export value regardless of the make up of that value from string inverter or AIO. Essentially 2 separate control loops operating to the same setpoint value and measurement point.

Just thought I'd pop back to confirm what GivEnergy Tech Support have confirmed to me.
If I have a DNO limit of 4kW, then I should set a 4kW export limit on both my PV inverter and also set a 4kW export limit on the AIO. Then, if the PV is exporting 1kW and the battery is on discharge, the AIO can add a further of 3kW of export to the grid. If the clouds clear and your PV exports 2kW, the AIO will add a futher 2kW. If the PV exports 3kW, the AIO will add 1kW, and finally, if it's a really sunny day and your PV hits its 4kW export limit, the AIO will cease to discharge.
In other words, when set to discharge, the AIO dynamically makes up the difference between PV export and the DNO export limit. This is just what you want during a daytime saver session and the sky clouds over

A bit late to this.
I have an AC coupled with 6.6KWp Enphase system. I did not have to go though export limiting as the DNO has put the limit at 8.8kVA.
For Enphase, to limit export to 4KW, your installer will have to request a new grid profile (if this does not exist). I presume something similar for AIO.
Would be interesting to find out which of these get throttled first. I'd probably want the AIO rather than solar to be throttled