FoxESS Community - Owners & Installers Forum

I'm very new to IOG, and before that was with EON and charged my EV in their off-peak hours.
Now that I have a Solar+Battery installation, I have a question that is confusing me.
If I request my EV to be ready at 05:30, the charger turns on during the off-peak hours, and all is good. I pay 7.5p/kWh for the charging. This is also the time I do a battery charge.
If I request the EV to be ready during peak hours (I haven't done this yet), I assume IOG just charges during peak times (what else can it do?). If I have surplus solar and a charged battery, where does the charge for the EV come from, and how is the cost calculated?
I assume no grid import, IOG will see that my EV is charging, but surely the charge is derived from the solar or battery.

Where the power comes from is determined on how the EV Charger is wired up.

The normal process is that the EV Charger is wired up in your meter box via Henley blocks so that the energy is split from your solar. Then you will have CT Clamps from your solar system that measures the power AFTER the splt so that the power that goes to the EV is not even seen by your solar system, this stops the battery from draining.

Without knowing how your system is wired up, it makes it hard to answer your question fully.

Grumps wrote: ↑Wed Mar 04, 2026 12:32 pm If I have surplus solar and a charged battery, where does the charge for the EV come from, and how is the cost calculated?

I don't think it's wise to drain 1 battery to charge another, they do wear out.

What I've been doing is to force charge, even at just 1W, at the same time the hot water system pulls from the grid, so the battery won't try and supply to it.

Check Will's post here regarding the Henley block and wiring.
viewtopic.php?p=9631#p9631

So if yours is wired this way, it won't be draining you battery, the EV charging power is invisible to your solar system and you don't use PV or battery power to fill your car.

I agree about draining one battery (Fox) to charge another (EV).
My wiring is as follows - only a single CU:
So, as it stands, if the solar is generating 5kW (as it is now) and IF the EV was charging at 3kW (which it isn't), then there would be 2kW flowing through both CTs, the meter, and to the grid. What does Octopus think about this? Is it just a SEG of 2kW, or does it want something for the charging?

And if there were no solar generation and the EV was still taking 3kW, there would be an import of 3kW. Does Octopus charge this at 7.5p/kWh or what?

If I understand correctly, the better wiring would be (with an additional mini CU for the EV):

Hi Grumps,

So with your current setup, you are similar to me (wired different, but outcome the same) where your EV Charger is just seen as a load by your Inverter, so it supplies power to it, thus should drain your battery rapidly.

I have my Inverter wired up to a Home Assistant that makes the Inverter charge the battery when it sees Off-Peak rates being applied, so this tops up your battery if you get any random daytime slot, or charges it during the night.

You have two choices here, setup Home Assistant to automate this, or as you are seeing, option two is to split the power that comes out of the meter via Henley blocks and wire your EVCP off one split, and your house (and Inverter) off the 2nd split. Placement of the CT clamps makes the EVCP use totally invisible to your Inverter, so it does not drain the battery.

Grumps wrote: ↑Wed Mar 04, 2026 2:49 pm So, as it stands, if the solar is generating 5kW (as it is now) and IF the EV was charging at 3kW (which it isn't), then there would be 2kW flowing through both CTs, the meter, and to the grid. What does Octopus think about this? Is it just a SEG of 2kW, or does it want something for the charging?

And if there were no solar generation and the EV was still taking 3kW, there would be an import of 3kW. Does Octopus charge this at 7.5p/kWh or what?

So in your example, if the PV was making 5kW and the EVCP was using 3kW, then 2kW would flow out to the grid. So you would get your SEG payment for 2kWh if used for 1hr of charging. So Octopus wouldn't have a clue and you get paid for this.

If no solar, and the EVCP wanted 3kW then you get charge 7.5p per kWh or most likely 30-32p per kWh as peak pricing. The Intelligent part of IOG means it should charge when they instruct your car/charger (depends on how you paired up) and it will then be on the cheap rate of import.

There is a fair bit more to talk about with IOG, as there are changes coming at some point (they are currently delayed)

So, the way I see it with the wiring that I have, is that in peak hours when Octopus wants to charge my EV, then the charge will be coming from my Fox batteries. That seems a crappy idea!

In the off-peak hours (23:30-05:30), my Fox batteries charge, and this is ideally when the EV should too.

The only way I can stop my Fox batteries charging my EV is to only plug in after 23:30.

And another confusion for me...
If solar is powering my house and exporting, say, 5kW to the grid. Then I'm getting 5*SEG rate for this.
If the EV decides to charge and takes 4kW, surely that means my net export is 1kW.
Even though Octopus should be charging me for this 4kW at the EV rate, it won't be because it'll be paying me for the 1kW SEG rate only.
So the charge to my EV isn't 7.5p/kW (or whatever the rate is now) but 12p/kW (which is my loss of export at SEG)?

Grumps wrote: ↑Fri Mar 06, 2026 2:22 pm So, the way I see it with the wiring that I have, is that in peak hours when Octopus wants to charge my EV, then the charge will be coming from my Fox batteries. That seems a crappy idea!

In the off-peak hours (23:30-05:30), my Fox batteries charge, and this is ideally when the EV should too.

The only way I can stop my Fox batteries charging my EV is to only plug in after 23:30.

Sadly this, like me is down the way things got wired up on our EVCP's. Yours is fed off your CU, so the Inverter will see it just as a 'load' and feed it with power from your battery. Mine is wired in the meter box, but there was not the room for the extra Henley blocks, so again, my Inverter see the EV load and feeds it.

I got passed this by wiring in a Home Assistant device and it sends a command to the Inverter to charge the battery whenever the system detects a cheap energy slot price.

The other temporary way is for you to plug in as late as possible in the evening, or depending on what car you have... you can block the car from taking charge until 23:30.

Grumps wrote: ↑Fri Mar 06, 2026 2:32 pm And another confusion for me...
If solar is powering my house and exporting, say, 5kW to the grid. Then I'm getting 5*SEG rate for this.
If the EV decides to charge and takes 4kW, surely that means my net export is 1kW.
Even though Octopus should be charging me for this 4kW at the EV rate, it won't be because it'll be paying me for the 1kW SEG rate only.
So the charge to my EV isn't 7.5p/kW (or whatever the rate is now) but 12p/kW (which is my loss of export at SEG)?

If your charger is 7kW, then odds are in real-use, you would be importing power and using solar to charge your car.
5kW from PV, and 2kW from the grid, so no export at all, and 2x 7.5p per kWh or such.

The post above could help, as you could block the car potentially from taking any power until 23:30 but this bypasses the IOG normal T&C's so you might be kicked off the tariff if they see this too much.

I'm going to see how easily I can get the wiring changed to something like this:
That should work, shouldn't it?

There might be a cheaper choice that *should* work if wired up correctly, and does depend on your DIY skills.

You have a CT Clamp coming from your Fox Inverter clamped onto a feed wire that heads to your CU.
If you buy an identicle clamp, with same rating etc. and in *theory* wire this to your Inverter CT clamp position, but wired in reverse or the CT Clamp fitted backwards to your CU wire that powers the EVCP, it should deduct the power heading to the EV.

So lets say you are charging the car at 7kW and house load is 2kW, for a total of 9kW being seen by the Inverter CT Clamp. Now if you have a 2nd CT clamp wired in reverse on your Inverter, and the clamp is fitted around the cable going to the EVCP, the idea is by being reversed it see now -7kW. So as far as you Inverter would see things, it would see +9kW and -7kW for a balance of 2kW... which the battery supplies to the house load.


I hope that makes sense?

I borrowed your picture, something like this in theory.

Ooh! That sounds clever.
I gotta ask, has anyone tried that already?

Grumps wrote: ↑Fri Mar 06, 2026 10:50 pm Ooh! That sounds clever.
I gotta ask, has anyone tried that already?

Hopefully you will get some other replies.




I believe Matterbox is a commercial installer, that's where I first heard about this. (Scroll down a bit for his reply)

Whilst it all sounds good in theory, and in practice, so it seems, my biggest fear is my wonderful 10-year Fox warranty when/if something goes wrong.

Grumps wrote: ↑Fri Mar 06, 2026 11:11 pm Whilst it all sounds good in theory, and in practice, so it seems, my biggest fear is my wonderful 10-year Fox warranty when/if something goes wrong.

Realistically it'll either work or it won't. Fox could moan if you wired up a reverse CT Clamp, but that's not likely going to happen.

Anyhow, other choice is to split it out via Henley blocks off to a CU dedicated to the EVCP at a cost of £££.
Food for thought, you have time to think about it, and others to reply if they have done this before.