Combining 3 phase and 1 phase systems?

[Lemna gibba]

We currently have a 3Kwp system from 2015 on the East and West roofs that we get FITT payments for. As part of our renovation we would like to add a 3KW system to the South roof connected to a battery. 

 

Western Power need to move our supply anyway, and are suggesting upgrading to 3 phase at the same time. I don't think we exactly need 3 phase, but later in our renovation we will install an ASHP and at some stage need car charging. This future proofing would be worth while.  I can get quotes for and spec out the new system as a 3 phase system. What I don't understand is how this will play with our existing system that is on a single phase. 

 

Is it possible to have two systems in the same household with one on 3ph and the other a single phase?

Would it be best (and permissible whilst maintaining FITT) to replace the inverter in the existing system with a 3ph one?

Alternatively, if we asked for 6KW solar on a single phase what would the chances be that WP would allow this?

 

I will discuss with local suppliers, but would rather go into the conversation with a bit of knowledge. If it was permissible then option 2 looks the most sensible to me.

 

I really appreciate comments. I have tried google but mostly seem to get information about Australia!

 

 

  

[SteamyTea]

You would have to check the specifications of the inverts.

There should not be any reason, other than capacity limits, why you cannot have a 3 phase system and then add another 1 phase system. That is how microinverters work together after all.

 

You will need 3 phase net metering or you run the risk of some power going down the line without being paid for. The FiT system allows for upgrades, as it can take additional generation into account, and subtract it.

[Lemna gibba]

That's very interesting. I just had a call with a company who were adamant that if we changed the meter to a three phase then we would lose the FiT payments. I'm wondering if they were thinking along the lines that they don't want to be involved with additional complication and paperwork rather than a set up similar to what you propose.

The three phase net metering is the next challenge. 

[Alan Ambrose]

>>> Is it possible to have two systems in the same household with one on 3ph and the other a single phase?

 

Assuming you don't have any actual 3-phase appliances (it is possible to get 3P heat pumps / inverters / EV chargers for instance) then 3P is usually actually just used as 3 separate phases for 220V circuits around the house.

 

That could be 3P into a consumer unit which uses particular phases on each 220V circuits, usually with them vaguely balanced for current draw. That's what I have in my place, and I don't have any actual 3P devices to supply.

 

In the common parts for this building the 'landlord's supply' has a 3P CU with a mixture of 3P devices (garage door opener, lift etc) and single phase circuits (lights etc).

 

Alternatively, you can probably use your current single phase consumer unit and have say a 3P box for the 3P devices, or several single phase CUs on different phases - I don't have any experience of those last two set=ups though.

 

A lot of domestic electricians don't have any experience of 3P though so expect some teeth sucking.

 

 

Edited August 1, 2023 by Alan Ambrose

[SteamyTea]

1 hour ago, Lemna gibba said:

just had a call with a company who were adamant that if we changed the meter to a three phase then we would lose the FiT payments.

The PV generation meter is separate to the supply meter. But I suspect you are right that the don't want the hassle.

[Dillsue]

On 01/08/2023 at 16:59, Lemna gibba said:

That's very interesting. I just had a call with a company who were adamant that if we changed the meter to a three phase then we would lose the FiT payments. 

As mentioned above, you'll almost certainly have a dedicated generation meter to measure the generation from your FIT system, and nothing else. Your service meter has nothing to do with the FIT generation payments unless you've opted for metered export rather than deemed export payments.

 

If the company saying you couldn't have a 3ph meter didnt explain that then you might want to put them at the bottom of the pile of potential suppliers??

[Nickfromwales]

9 hours ago, Dillsue said:

As mentioned above, you'll almost certainly have a dedicated generation meter to measure the generation from your FIT system, and nothing else. Your service meter has nothing to do with the FIT generation payments unless you've opted for metered export rather than deemed export payments.

 

If the company saying you couldn't have a 3ph meter didnt explain that then you might want to put them at the bottom of the pile of potential suppliers??

+1. They just don't want the hassle.

 

Bin.

[Dillsue]

On 01/08/2023 at 14:45, Lemna gibba said:

We currently have a 3Kwp system from 2015 on the East and West roofs that we get FITT payments for. As part of our renovation we would like to add a 3KW system to the South roof connected to a battery. 

 

Alternatively, if we asked for 6KW solar on a single phase what would the chances be that WP would allow this? 

If your current 3kw system is split equally east and west youll get nothing like 3kw at any one time but you'll get a lower output over a longer period. If you add 3kw to the south, again youll never hit 6kw but will get a much longer spread of generation with a peak around midday. Youll not need to ask for 6kw export as youll never hit that with 6kw of panels spread over 3 compass points.

 

You can get a good idea of the max generation by taking hourly figures from PVGIS for each of your 3 arrays then combine the hourly figures in Excel for the same hour, then see what the highest hourly figure is of all the combined figures. That's your highest DC output for the year. Look at your annual FIT generation figures and run the figures for the 2 best years youve had. Our second system has 8.5kw panels facing SE, SW and NW and max generation is around 5.2kw so way lower than the 8.5kw panel capacity.

 

Since 2021 OFGEM have allowed FIT systems to be altered so you can add capacity to your existing system. You only get paid for the original registered capacity so if you added 3kw to a 3kw system you get paid for 50% of what the new 6kw system generates, but... Your existing east/west split will be underperforming compared to if it was all facing south. If you now add 3kw facing south it will more than double your output so 50% of the new system will be more than 100% of what you get now. It's not going to buy you a luxury yacht but you may be better off adding to your FIT system and upgrading its inverter, if needed, rather than adding a second system??

[Lemna gibba]

Many thanks for all the helpful input.  

 

I think I've found the information that Dillsue said on page 81 of this document. Just bookmarking it in case it's useful for others. As it seems like the most economical option for us. 

https://www.ofgem.gov.uk/sites/default/files/2021-12/Feed-in Tariffs_Guidance for renewable installations_V16.pdf

 

For everyone else. We have been in touch with a super helpful company. They have suggested that in our situation the best thing would be to ask WP for permission for 6 Kw on a single phase. If they agree then that will be our best route forward. I'll update with what WP say

[sharpener]

What deal are WPD offering? IIRC they are now fitting 3ph as standard for new housing, if you are considering more PV or an HP or an EV charger in future it might be better to take their offer now. EV chargers are a max of 7kW on 1ph which is quite slow if you are trying to recharge at night rates but 3ph 22kW will fully charge most cars in 4 hours.

 

You can leave the existing PV on one phase and @Dillsue is right, it should not affect your FITs, and put more on other phases, WP should be very happy with that. 3-phase inverter not worthwhile unless a massive amount more PV. Germans e.g. Sunny Boy very keen on them but domestic 3ph almost universal there.

 

OTOH if you have to change the (moved) single phase supply to 3ph later you can be sure WP will want to charge you £££ at that point.

[Lemna gibba]

@sharpener  We need to move the supply anyway. I don't have a price for changing to single phase. But moving the supply and rewiring to 3 phase would be 2.8k (including VAT).  I think single phase would be significantly cheaper. Our electricity supply is very illogical. It comes into the East side of our house, goes round the outside of our house at mid height tacked onto the wall and then comes in on the West side with a meter, fuse and consumer unit squeezed above tho door. We would put everything on the east side. If it is just 1ph, then I think they simply need to replace the box on the East and put everything there. 3ph requires coming from the road and us digging the trench. 

 

We won't add any more PV (as we don't have space). Heat pump is on the cards in 3-4 years. Our house will hopefully be so efficient by then that a small heat pump would suffice. An EV in the future will be very likely. We have sent the G98 to WP, so we'll see what our options are. I feel that they will insist on 3ph. 

[sharpener]

Ah, didn't realise there was already a 1ph cable passing the new location, which changes the logic somewhat. I have a similar setup in that the supply comes in the drive and goes underground all along the back of the house to a point at the other end which is only a few feet from the road again. Have just had WPD check out their fuse, it is only 80A bc of the 80A meter and 16mm^2 meter tails so with EV charger am a bit restricted in the size of HP, no auxiliary heating allowed. Make sure they give you 100A when they do it!

[Dillsue]

5 hours ago, Lemna gibba said:

We have sent the G98 to WP, so we'll see what our options are. I feel that they will insist on 3ph. 

That would be a G99????

 

We have 7.4kw agreed export on 1Ph so dont bank on having to have 3 ph.

[sharpener]

OTOH I am also with WPD and they required my 5kVA battery inverter to be limited to 3.68kW. Which is why my second lot of PV panels is wired direct into the battery through an MPPT so they don't restrict them as well.

[Lemna gibba]

@Dillsue and @sharpener

 

Thanks for the comments. I'll let you know as soon as we hear about our request. 

[Lemna gibba]

A big thanks to everyone for their input. I just want to update on our final decision.   I came to the conclusion that there was no single right answer. I had several different suggestions that all had benefits. It's impossible to know what the best option was, but I think we have chosen a good one.

 

National Grid got back to us and were happy for us to add the extra solar to single phase as long as we capped export at 4kW. In total we will have 3.2 kW panels on the South roof, 1.5 kW on the East and 1.5 kW on the West. WP also quoted us 1.3k for moving the  single phase supply versus 2.8k for installing 3 phase. We've gone for the single phase option.

 

 

 

 

[joth]

 

In practice I don't think you need to do anything to cap the export but you need to confirm what evidence WP need that exceeding 4kW cannot happen.  If they demand export limitation is put on both the old and new inverters it may cost more than the 3ph upgrade

 

Fwiw is you didn't want the hassle of the 4kW cap then going with 3ph you could put the existing 3kW system on one phase and the new 3kW on a single phase inverter on a different single phase, and it'd all be within G98 and no impact to your existing FIT.