Making the most of excess solar with a 3-phase supply

[Tom]

Hi All - I'm going a bit cross-eyed trying to work out how best to do this and would really appreciate some advice. I've tried searching but can't find anything that fits.

So, the situation is this:

 

- we have approx 13kW of solar PV on the roof now and due to be connected up next week

- we are on a good (old) feed in tariff

- we have 3 phase going in to the property, next week Octopus will be coming to fit a new 3 phase smart meter

- the same day another electrician is coming to hook up the PV to the consumer unit

- we have an ASHP with 300L cylinder

- I have already bought an Eddi diverter, hoping to send excess generation to the immersion

 

I asked the ASHP installer the question and was told:

 

"It depends on whether your energy supplier uses Net Metering for your 3-phase supply.

To make use of excess across all 3-phases you need to install an Harvi plus 3x CT clamps, set it to 3-phase mode and then set Net Metering on.
 

Then your Eddi will calculate the total export for all 3-phases and operate even though there may be no excess on the phase to which it is connected, so it will virtually but not actually consume excess on the other phases. Go into advanced setting, supply, then check for net metering"

 

Am I right in thinking the Harvi will monitor all 3 phases, if any one or more of them are exporting it will trigger the Eddi to divert the same amount of power (from whichever phase it is hard-wired to) to the immersion? I guess that only works with net metering though? Does anyone know if Octopus do net metering - and if not is there any way to divert all three phases?

 

Thanks all

 

Edited July 4 by Tom

[joth]

Smart meters all do net metering. It's defined by the SMETS V2 spec. Search this forum for "polyphase" and you'll see the many times I  quote the spec.

I don't know about HARVI specifically but sounds like it's designed to work correctly, i.e. only divert to immersion if the sum of all phases is negative (i.e. exporting)

This is all moot really though. With 13kW array and a "mere" 300L tank you'll divert a wee bit but the bulk of your generation will still go to grid. Especially if you're already doing the base of dhw via the ASHP.

 

 

[Nickfromwales]

Was the 13kw of solar removed and refitted? Eg you’re not adding to or upgrading the solar setup that you have the FiT payments for? 

[Tom]

1 hour ago, Nickfromwales said:

Was the 13kw of solar removed and refitted? Eg you’re not adding to or upgrading the solar setup that you have the FiT payments for? 

correct

[Tom]

1 hour ago, joth said:

Smart meters all do net metering. It's defined by the SMETS V2 spec. Search this forum for "polyphase" and you'll see the many times I  quote the spec.

I don't know about HARVI specifically but sounds like it's designed to work correctly, i.e. only divert to immersion if the sum of all phases is negative (i.e. exporting)

This is all moot really though. With 13kW array and a "mere" 300L tank you'll divert a wee bit but the bulk of your generation will still go to grid. Especially if you're already doing the base of dhw via the ASHP.

 

 

Thanks Joth, I'm just thinking in winter when generation will be minimal I still want to capture as much as I can

[Jinglish]

Shoot me down here but...

 

Don't you get paid more to export the surplus than you would if you used it via an inefficient immersion heater? Why wouldn't you use the excess solar to make the heat pump heat the hot water which is much more efficient?

Edited July 5 by Jinglish
Typo

[joe90]

18 minutes ago, Jinglish said:

Shoot me down here but...

 

Don't you get paid more to export the surplus than you would if you used it via an inefficient immersion heater? Why wouldn't you use the excess solar to make the heat pump heat the hot water which is much more efficient?

However a heat pump has a limited temperature rise and it depends if the DHW tank if full (up to temp) or empty, an immersion will provide additional hot water above the temp  achieved by an ASHP. However I agree that with an empty DHW tank solar powering an ASHP is more efficient.

[Tom]

54 minutes ago, Jinglish said:

Shoot me down here but...

 

Don't you get paid more to export the surplus than you would if you used it via an inefficient immersion heater? Why wouldn't you use the excess solar to make the heat pump heat the hot water which is much more efficient?

 

The PV generation has already gone through the generating meter, so I will be paid for it AND by diverting it I get to use it as well - isn't that how it works?

 

Question though: what are the implications of the new smart meter doing net metering?  Am I right in thinking any export to the grid essentially spins the meter backwards, so why divert any to an immersion, just use imported power to run the ASHP? 

[Jinglish]

@joe90 Good point so ASHP gets tank to say 55C but need immersion to kill the Legionella at 65C+

 

@Tom The CT clamp should be fitted before the export meter so it knows how much to divert and when.

[Tom]

1 hour ago, Jinglish said:

 

@Tom The CT clamp should be fitted before the export meter so it knows how much to divert and when.

 

Really? Presumably it should be upstream of the import meter so it can tell when the power being generated is in surplus and is going back to the grid.

I don't think I have an export meter, I've got a generation meter

Edited July 5 by Tom

[joe90]

1 hour ago, Tom said:

The PV generation has already gone through the generating meter, so I will be paid for it AND by diverting it I get to use it as well - isn't that how it works?

Is that true? That’s having your cake AND eating it 🤷‍♂️

[Jinglish]

@Tom Maybe you got your wires crossed (no pun intended) or we are taking about the same. Your smart meter is your export meter also. So from the grid it should go…

Grid > DNO fuse > Smart Meter > Main Fuse box > generator meter > Inverter > PV Array

 

The CT clamp i’m referring to sits between the smart meter and the main fuse box. The generator meter should measure the output of your inverter before it’s consumed by your dwelling load. The CT clamp will measure surplus feed back to the grid and your export meter will tally up with that so your supplier can pay you accordingly.

 

Your wiring maybe different i.e. your Inverter goes directly to smart meter via Henley block instead of through the main fuse box but this still yields the same result

Edited July 5 by Jinglish
Typos

[Tom]

13 hours ago, Jinglish said:

@Tom Maybe you got your wires crossed (no pun intended) or we are taking about the same. Your smart meter is your export meter also. So from the grid it should go…

Grid > DNO fuse > Smart Meter > Main Fuse box > generator meter > Inverter > PV Array

 

The CT clamp i’m referring to sits between the smart meter and the main fuse box. The generator meter should measure the output of your inverter before it’s consumed by your dwelling load. The CT clamp will measure surplus feed back to the grid and your export meter will tally up with that so your supplier can pay you accordingly.

 

Your wiring maybe different i.e. your Inverter goes directly to smart meter via Henley block instead of through the main fuse box but this still yields the same result

 

Thanks @Jinglish, I don't have a smart meter at the moment, so no export meter, only a generator meter. I think it's assumed I use 50% of my generated power - is that right? It's unclear how that changes when I get my smart meter (and therefore export meter) next week.

[Dillsue]

4 hours ago, Tom said:

 

Thanks @Jinglish, I don't have a smart meter at the moment, so no export meter, only a generator meter. I think it's assumed I use 50% of my generated power - is that right? It's unclear how that changes when I get my smart meter (and therefore export meter) next week.

If you're getting 50% of generation as a export payment then your on the FIT deemed export rate. Once you have a smart meter you can choose to go onto metered export payments or stay on deemed payments, with Octopus seemingly the best payer. Do the sums and see which is the most beneficial. Under the FIT scheme rules you can switch between deemed and metered every 12 months so you're not stuck if you change to metered and it doesn't work out for you.

[Tom]

4 hours ago, Dillsue said:

If you're getting 50% of generation as a export payment then your on the FIT deemed export rate. Once you have a smart meter you can choose to go onto metered export payments or stay on deemed payments, with Octopus seemingly the best payer. Do the sums and see which is the most beneficial. Under the FIT scheme rules you can switch between deemed and metered every 12 months so you're not stuck if you change to metered and it doesn't work out for you.

Aaahh, gotcha @Dillsue. Checked our tarrif and we get about 12p/kWh generated and 5p/kWh for the 50% we are deemed to export. Will do the sums re deemed/metered but with 13kW on the roof I'm thinking metered would be better, and at only 5p/kWh for what we do export any that I can divert would be a bonus

[SteamyTea]

If you get 12p for generation, and half of 5p deemed export on top  that is 17.5p/kWh.

You can buy in lower than that on a ToU tariff.

 

[Mr Blobby]

On 04/07/2024 at 13:12, Tom said:

To make use of excess across all 3-phases you need to install an Harvi plus 3x CT clamps, set it to 3-phase mode and then set Net Metering on.

 

Do you have an electric car? 

My concern with the harvi is that it is wireless only and for our install the signal may not be reach the EV chargers outside.  Or even the Eddi as we have a lot of block walls to go through.

 

It is my understanding that a 3-phase zappi will connect 3 CT clamps easy enough.  Then set the zappi as the master device talking to the Eddi over cat 6, thus removing the risk of wireless signal failure. 

This is the theory.  I would be interested to know if this actually works in practice.

 

[RobLe]

We have PV, heatpump, battery, elec car.  It’s actually cheaper, faster, and simpler to charge the car overnight with 7.5p IOG electricity than use ‘spare’ PV electricity (for which we get 15p) - better for us and the national grid to export it.  Of course we have measured export, not deemed, which seems more ‘honest’ than deemed and a diverter.

[Jinglish]

12 hours ago, RobLe said:

We have PV, heatpump, battery, elec car.  It’s actually cheaper, faster, and simpler to charge the car overnight with 7.5p IOG electricity than use ‘spare’ PV electricity (for which we get 15p) - better for us and the national grid to export it.  Of course we have measured export, not deemed, which seems more ‘honest’ than deemed and a diverter.

Snap, and with IOG you can "charge" your car during peak times at 7p and everything else is at that rate. Strangely my car always needs charging at dinner time, washing time and hot water time

[sharpener]

On 08/07/2024 at 08:14, Jinglish said:

Strangely my car always needs charging at dinner time, washing time and hot water time

Does this work when the car is fully charged? Doesn't Octopus need access to your car setup and so can tell?