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nowty wrote: ↑Thu Nov 24, 2022 8:34 pm By throttling back, think of a dimmer switch on a light bulb.

nowty wrote: ↑Thu Nov 24, 2022 9:14 pm Because the G100 device has a CT clamp sensor at the grid point so it knows whether the house is exporting or importing and by how much.

OK, say you have one G98 3.68kW inverter with no export control and one ESS inverter which is essentially a zero export inverter and the batteries are full.

Yes the whole system will export to a max of 3.68kW (if the G98 inverter at full tilt) but that's within the DNO's default approval.

Now say your house has a 3kW load and the G98 inverter is supplying 1kW of that because the sun is behind a cloud. The ESS is controlled by a CT clamp at the gridpoint and is supplying 2kW so the house load is satisfied and there is no export. Now the sun pops out from a cloud and the G98 inverter bangs up to 2.5kW. The ESS will detect export to the grid and back off its export until its giving 500W to add to the 2.5kW coming out of the G98 inverter. Export is zero.

Now say you house load is 1kW and the G98 inverter is producing 2.5kW and thus will be exporting 1.5kW. If the ESS batteries are not full, then that 1.5kW is taken and put into the batteries, but if they are full, then the ESS simply sits there and does nothing whilst 1.5kW keeps exporting.

Oldgreybeard wrote: ↑Thu Nov 24, 2022 9:19 pm If you have two inverters connected to the grid, say a PV inverter and a battery system inverter, then the export sum of both has to remain within whatever limit the DNO will allow under G99 (which used to be called G59). This also applies if you have two G98 (used to be G58) compliant inverters, say a G98 PV inverter (so no more than 16A per phase) and a G98 battery system inverter - the sum of both cannot exceed the G98 limit of 16A per phase unless you get G99 consent.

There are a few options. You can request that the DNO grant consent under G99 to allow the sum of the potential exports, if either inverter is G98 compliant, then you can use a G100 limiting device (some inverters will do this) so that when one inverter is outputting 16A per phase the other cannot export, or you can sometimes get both inverters to communicate with each other so they act in concert to ensure that the export never exceeds either the DNO set G99 limit or the always permitted G98 limit.

As an example, my system at the moment has a G59 (now G99) PV inverter that can export up to 26A (6kW) on a single phase (DNO approved to this export level). I also have a Sofar battery inverter that can deliver up to 13A on the same single phase. The Sofar battery inverter has a CT on the grid that stops it from ever exporting (effectively a G100 limit of zero), so the export is limited to whatever the PV inverter can deliver under the G59 approval.

I'm shortly going to add another 2kW (~8.7A) PV inverter, and because the DNO will not allow anymore export, I'm fitting a G100 limiting relay, that will disconnect this second inverter from the grid if the total export (from both PV inverters) exceeds the 26A (6kW) G59 approved export level. This will allow both PV inverters to export up to the 6kW G59 limit, and as soon as this is breached the second 2kW inverter will be disconnected from the grid.

The whole thing can get a bit challenging to get your head around, not helped by the fact that most inverters (battery and PV) are designed to work in many different countries, so understanding how they behave with respect to UK restrictions can be a bit of a headache. It's not helped by a general dearth of information from manufacturers and UK suppliers as to how their system behaves in conjunction with the products from other companies.

vantech2022 wrote: ↑Thu Nov 24, 2022 9:35 pm

nowty wrote: ↑Thu Nov 24, 2022 9:14 pm Because the G100 device has a CT clamp sensor at the grid point so it knows whether the house is exporting or importing and by how much.

OK, say you have one G98 3.68kW inverter with no export control and one ESS inverter which is essentially a zero export inverter and the batteries are full.

Yes the whole system will export to a max of 3.68kW (if the G98 inverter at full tilt) but that's within the DNO's default approval.

Now say your house has a 3kW load and the G98 inverter is supplying 1kW of that because the sun is behind a cloud. The ESS is controlled by a CT clamp at the gridpoint and is supplying 2kW so the house load is satisfied and there is no export. Now the sun pops out from a cloud and the G98 inverter bangs up to 2.5kW. The ESS will detect export to the grid and back off its export until its giving 500W to add to the 2.5kW coming out of the G98 inverter. Export is zero.

Now say you house load is 1kW and the G98 inverter is producing 2.5kW and thus will be exporting 1.5kW. If the ESS batteries are not full, then that 1.5kW is taken and put into the batteries, but if they are full, then the ESS simply sits there and does nothing whilst 1.5kW keeps exporting.

Great explanation. Is there any way to prevent the other G98 inverter exporting to the grid when the batteries are full (refer to your last paragraph).

I actually have a G100 ESS and a G100 solar inverter, both have consumption CTs, so I would think I could prevent any export even when the batteries are full and the solar production is higher than the house consumption.

What I am struggling to understand, is how the solar inverter knows to “produce” power. Imagine if during the hours of darkness a 500w load is being powered by the ESS. The sun comes up, and there is 750w of solar available. How does the solar inverter “inject” this when in theory, it won’t see a demand on the system as this is being covered already by the ESS?