Single Phase Inv/Battery on House with 3-phase supply

Take a house with 3-phase supply, Phase 1 has single phase Heat Pump, Phase 2 has single phase Car Charger and Phase 3 has remaining house load. Can someone please confirm that if a GE 5kw GEN2 Hybrid Inverter and 9.5kwh battery were installed on phase 3 to support the house load, then the battery cannot also net out the loads on the other two phases? The grid supply meter will net out the loads across the 3 phases, i.e. if importing 1kw on each of phases 1 & 2 and exporting 2kw on phase 3 then net grid charge is zero. I assume since the 5kw inverter can only monitor the single phase with its one CT clamp then it will not see any load on phases 1 & 2 and therefore not be able to respond to these loads. I know for example that the Single phase Myenergy Zappi car charger can monitor all three phases and only divert the net surplus power to the car in eco+ mode.

Your assumptions are correct. The Giv system will only see phase L3, and the CT clamp should be fitted to L3.

Thanks for confirming.

Brookydave Is it a given that a grid supply meter – a Smets 2 in my case - will alway net out loads across phases? I too have a single phase heat pump in a three-phase domestic system with PV panels and an AC3/9.5kw battery on each phase. The ASHP is hungry in winter and will account for up to 60% of domestic energy requirement, should be less so in summer. This makes it impossible to balance properly the load across all phases in all seasons. It does mean that all too often we have recently been importing on L1 – the phase with the ASHP attached – while exporting on one or other of L2 and L3. Our installer told us how important it is to balance the load, but we have limits. Does balancing matter if the grid supply meter always cancels out import on one phase against export on one or other phases? Any ideas? I have asked Octopus but there has been a deafening silence for some time.

Dougal Is it a given that a grid supply meter – a Smets 2 in my case - will alway net out loads across phases?

No, it depends on the meter.

Dougal Does balancing matter if the grid supply meter always cancels out import on one phase against export on one or other phases?

Balancing load only matters to the DNO. They prefer their distribution transformers to have similar loads on each phase and usually supply every third property from the same phase. Hence if your (single phase) power is off, your neighbours could still be on if the cause of the failure was a fuse on one phase.

While your smart meter might nett off across phases, it won't nett off import/export; they are separate registers because you can have separate tariffs from different suppliers. It would be handy to have an old-style rotating disk meter where your 40p/kWh peak import is negated by (what might otherwise be) 4.1p/kWh export.

Tim Octopus have finally got back to me and answered some of my queries I had asked of the Octo R&D team - the main ones being about load balancing and whether export and import cancel one another out. The man from Octopus seems quite clear on this: "the meter will simply measure the 3 flows of energy and apply the vector sum metering." He added that: "The meter, and our billing, has no knowledge of any settings in either GivEnergy or R&D - it'll simply take the vector-sum result per half hour and bill/credit you." He suggested that "It sounds like it makes sense to set a schedule to export from one whilst the phase with the ASHP is importing as the export would effectively 'cancel' the import charge - but you're on Agile so that only makes sense when the import rate is higher than the export rate." He was referring to the Agile fixed export rate of 15p per kWh. Anyway, I am confused with so many views on how three phase billing works. I have to assume my vector sum meter does cancel out import versus export if that is what Octopus are telling me. Single phase would probably be a lot simpler, I am discovering if not so versatile or powerful.

Dougal I understand what Mr Octopus is saying about the vector sum but I am sure he doesn't understand about import/export registers. I accept that if you are generating on a phase, it will reduce your grid import on that phase but if you generate more than you are consuming, it sounds like Mr Octopus thinks that the meter would decrement the import register rather than incrementing the export register.

That said, if there was perfect alignment between your import and export tariffs (ie they were the same rate at the same time and with the same supplier), then what he is saying would make sense. If you have separate tariffs and/or suppliers it would make sense to have separate registers for import and export which only ever increase.

Can anyone else shed any light of metering with Octopus? @hoggy?

Tim Thanks, Tim. I remain in a state of confusion over this. If Vector Sum doesn't mean what the man from Octopus is suggesting it means – export and import are netted off for billing purposes – then what is the point of a Vector Sum meter? It is clear that there is a general uncertainty about this whole issue. This may explain why it has taken so long to get any response from Octopus on this? Can you suggest how I might get a credible answer to this, please?

Dougal what you're talking about there is net metering, if the register records both import and export the net result is billed. We don't usually do that in the UK, so have import and export register on our meters.

Vector summing means that the meter can record import and export simultaneously across all 3 phases and record the total import or export on the relevant register, so instead of needing 3 import and export registers (1 for each phase), you only need 1.

Cdent @Dougal As @Cdent says, vector summing is the sum of energy import across the three phases to increment the import register and the sum of export across three phases to increment the export register. He also points out that netting off the import and export registers (whether single phase or vector summed three phase) isn't usually done in the UK.

At the end of the day, since your import and export tariffs are with Octopus, if they do as your man said, you will be getting paid for export at your import tariff rate and you will be quids in. Don't tell anybody, keep your head down and good luck. On the other hand, if they bill for import and and credit for export separately, you'll be paying for what you are actually consuming and getting paid for what you are actually exporting. Doesn't help with balancing the cost of your ASHP.

See what your bill says after the first months operation.

Sorry missed this one:

3 Phase SMETS2 Smart Meters are relatively new (in Smart Meter terms) so they may not all work exactly the same as each other however from others with them on Octopus they use: - EDMI ES-30B which is net summing compliant & people are being billed as such.
Anecdotal evidence suggests that this is the only version Octopus fit.

Net Summing: if you export at 1kW on L1 and import at 1kW on L2 and L3 your export is 0kW and import is 1kW.

This is not net billing, so if you export 1kWh during the day and import 2kWh in the night on the same phase then you get paid (if eligible) for 1kWh and pay for 2kWh import.

hoggy Net Summing: if you export at 1kW on L1 and import at 1kW on L2 and L3 your export is 0kW and import is 1kW

You mean ... "and import 1kW on L2 and 1kW on L3 your export is 0kW and import is 1kW"? If so that's what I think Mr Octopus is saying to @Dougal but your second bit about net billing is the fact of separate import and export registers, each settled financially at the contracted tariff rate. With your example of net summing, the finances would be for 1kW(h) export at pittance p/kWh and 2kW(h) import at idon'tbelieveit p/kWh (if these values were maintained for the whole hour)?

Tim I'm sure that there's a video somewhere that can explain it far better than my ramblings but it's about timing of your imports & exports so what I'm aiming for is:

Simultaneous import & export at same time across different phases = summing of all 3 phases so you basically pay for the difference of whatever the sum of that is (be that import or export).

Non simultaneous (Delayed) import & export would work essentially the same as having 3 single phase meters so your get paid say 5p export and buy it back at 40p or (I don't believe it! rate as you say!)

GE are rumoured to have a 3phase inverter up their sleeve (for real this time - the first ones didn't seem to make it out the brochure pages) which should in theory be able to take advantage of this quite lucrative feature of polyphase meters.

hoggy Simultaneous import & export at same time across different phases = summing of all 3 phases so you basically pay for the difference of whatever the sum of that is (be that import or export).

Interesting! If you ignore the fact of there being three phases into the house and picture "the supply" as a single entity, then this is the way an ordinary single phase meter works; you are billed/paid for the difference between demand and microgeneration output for the 30 minute period. The meter increments only the import or export register depending on what the difference is.

@Dougal, from what Mr Octopus and @hoggy says, it looks like you can have load and generation on any phase and you'll be charged only for the net difference for that meter period (30 minutes?). So it looks like your export on the other two phases will balance your ASHP consumption on one phase. I never knew that. Of course, if you have energy stored in batteries on the other two phases, they won't see the ASHP load and so won't export to reduce your net import. Not a problem during bright sunny days in winter but when it's dark outside, you could really do with a changeover switch to move your AC3s from the (PV and grid) "charging phase" to the (ASHP) "discharge phase".

Yes it takes quite a bit to get your head around it. I am however only on a single phase so I’d be very keen on hearing from people that have this setup as to how they get on with it!

Thank you @hoggy and @Tim and @Cdent. I feel that I am truly at the 'B-leading Edge'. I have had a separate conversation with 'Phil' at Octo R&D. Your collective final reasoned conclusion bears out what I thought I have. That is, net summing and net billing results in net metering. The very helpful Octopus installer who put in my EDMI meter last October told me as much. The trouble is I have heard so many opinions since then and three-phase domestic supply is fairly uncommon as yet, so I had started to doubt whether it was net billing. Our panels and batteries have been working properly only for six weeks so we have yet to be able to assess fully the billing from Octopus. A wet dreary March short of sunny days has also constrained the ability to check export as a standalone. As you will know one has to set up a separate export account (Octopus Export Fixed in our case paying 15p per kWh for a year.) Given that on Octopus Agile in the last couple of weeks we have had days when we have managed, using GE's functionality, to get our import down to <20p per kWh then we should be able to do well through the summer. The downside is that I am having constantly to manage 3 cloud portal websites to do this. If I can get OctoR&D scheduling going satisfactorily this may simplify matters.

I have one final question of you guys. If net metering is what I have got and I am sure it is, then load balancing across the phases shouldn't matter as it will all be balanced out at the Smart meter. So if my hungry ASHP is drawing lots at any time, more than any solar generation or overnight import on its L1 phase, then if I am able to export on L2 and L3 it should net against L1. The nub of the question is: Does Vector Sum Net Metering reduce the need for load balancing?

Thank you for your thoughts and considerable experience on this matter.

Dougal Does Vector Sum Net Metering reduce the need for load balancing?

Yes.

Dougal So if my hungry ASHP is drawing lots at any time, more than any solar generation or overnight import on its L1 phase, then if I am able to export on L2 and L3 it should net against L1.

Yes.

But, have a word with your installer as I believe that if you had changeover switches on the L2 and L3 AC3s, you could have them connected to L2 and L3 during solar generation but switch them over to L1 at other times. Doing this would enable them to divert export to charge during solar generation but discharge to L1 to feed the ASHP. I'm not suggesting that the switching is done dynamically (ie in response to grid import/export), but maybe once or twice a day.

If the Solar PV and Battery is single phase then the inverter will only be monitoring that phase and will only respond to loads on that phase, so if the ASHP is on a separate phase it wont see that load and be able to export to cancel out the load on the other phases. If GE had a "net-sum" CT monitoring solution then this would be possible but I am not aware they do. I have a single phase MyEnergi Zappi EV charger and it is able to monitor the "net-sum" of all three phases (using the Harvi device) so this is one advantage of Myenergi over GivEnergy.

Jon-boy I have yet to get the connection of three-phase 22kw Zappi2 charger to enable Eco and/or Eco++. At present I can only use it on Fast charge importing from the grid. I already have a Harvi monitoring the phases at the supply unit and Smart meter. Will I need another Harvi to move to Eco charging? I thought the magic number of Harvis was 1?

Dougal if you have the Zappi installed ie you can use it on Fast mode, and you have the Harvi installed which monitors grid import/export then as far as I am aware there is nothing else needed. Why can’t you use it on Eco/Eco+ ?

Jon-boy I have been offline for a few days. I don't know the answer to your question. We have a Harvi at the supply meter with its three CT clamps, This has a LORA connection to the Zappi2. I have been led to believe that we also need a cable run fo Cat5 cabling to link a set of CT clamps monitoringg the each of the three AC3.0 inverter directly to the Zappi2. Because we have effectively three PV systems each of 4.15kw nominal, i understood we needed another three CT clamps to measure the solar generation for ECO++. Given we have generated over 70kw today with wall to wall sunshine I really need to bottom this one out. Maybe you are right and we already have what we need? We have only tried charging in Fast mode. The schematic will give you an insight into our set up.

Have you tried it on Eco/Eco+ modes to see what happens? I think the extra CT clamps are used to visualise the generation/battery on the App, but I thought charging was controlled by grid surplus.

Jon-boy @Dougal With AC-connected, the additional CTs do enable visualisation of those devices on the myEnergi app but they are also needed to "prevent drain". However, I do think it worth testing the Zappi in ECO+ (not sure what the difference is with ECO++) mode with 100% MGL to see if the Zappi will charge the car from diverted export alone.