Advice on Solar and whether to go 3 phase

[d438a1]

Hi there, 

 

I'm just about to go ahead with a deposit for a solar system but wondering if I should be future proofing more.  Currently on single phase which powers the house and a large separate garage and flat above.  That is fed on a dedicated 24m2 cable.

 

Solar wise, we are going sig energy and looking at 16kw batteries and 14kw PV. As part of this, we are also getting the multiphase zappi charger. All of this will be housed in the garage.

 

Upcoming in next year or so: -

 

1. ⁠⁠16kw ASHP. Power input I think is around 6kw. This is sized large to also provide heat for workshop. 
2. New large workshop building. It will have a lot of equipment, some needing 16amp supply but as it’s just me in theory I’d only use a large dust extractor (2-3kw max) and 1/2 machines at a time with max maybe an additional 2-3kw. 
3. The existing garage will be converted at some point to an air bnb which may put more concurrent demand on. Likely we may but a small gas boiler in to utilise existing LPG tank we have in order to remove existing electric shower and small water heater for tap.

 

I've attached a few photos of current setup. 

 

So i guess my questions are...

 

1. With my future demands (whereby there could be a mix of house, airbnb garage and workshop running at same time), should I be considering 3 phase? 
2. Even if the above demands 3 phase, is it worth getting solar 3 phase equipment? Or would it make more sense to seperate phases to garage, house and workshop?
3. I'll also note that utilising 3 phase for the car charger and workshop for bigger equipment is a real nice to have

 

Thanks

 

 

[JohnMo]

Haven't you answered your question.

 

11 minutes ago, d438a1 said:

multiphase zappi charger

Wouldn't that need 3 phase?

13 minutes ago, d438a1 said:

small gas boiler in

That will exclude you from any grants, for a heat pump.

 

 

[d438a1]

The zappi works on single or multiphase. I always charge overnight anyway, so it's not deal breaker if it stays on 7kw.

 

On the main house I'm replacing an existing LPG boiler with heat pump. I didn't realise it would somehow invalidate that grant if i got a separate gas boiler later for other building?

 

Thanks

[nod]

The energy suppliers are mad keen on selling three phase 

Weather you need it or not 

[Kelvin]

We are also going SigEnergy with 24kWh of battery storage. With your demand wouldn’t you better going slightly larger on battery storage? The Sig battery system is very flexible so easy enough to add more later. Adding the extra 8kWh cost £2300. 

 

I put single phase in because it was a few hundred pounds compared to 3 phase which was several thousand. To some extent going 3 phase might have been better but several thousand buys a lot of electricity and the single phase supply seems adequate for our needs. With your likely future demand going 3 phase will be more flexible but don’t underestimate the cost. Get an estimate from your DNO asap. 

[JohnMo]

2 hours ago, d438a1 said:

⁠⁠16kw ASHP

I would make sure this will do all your needs, as the nameplate rating may not (very unlikely) to be correct at your design outside temperature.

 

16kWh of battery isn't going to last long driving a 16kW heat pump. If your max draw is 6kW, less than 3 hours your battery is flat. Especially so if you're in the workshop at the same time. Heat pump at full load and PV generation good at same time is unlikely. 

 

Have you checked the PV output in the winter, so you get to disappointed mid winter doing 140W instead of 14kW.

 

 

 

 

[d438a1]

Thanks for feedback. The 16kw was advised as part of a recent quote I had. I was already stretching budget to get 16kw battery. But I'll take another look! But as you said it seems easy to add later.

 

I've definitely maxed out what I can with solar at 32 panels for suitable roofs. 

[joth]

4 hours ago, d438a1 said:

• Even if the above demands 3 phase, is it worth getting solar 3 phase equipment? Or would it make more sense to seperate phases to garage, house and workshop?
•  

Haven't seen this answered, but, even if you do have different phases to different areas, so long as the whole lot are being supplied via a DNO cut out and single mater,  you can still put a 3 phase inverter onto the main 3 phase supply and then divide the phases out to sub distro boards as needed. To a degree this is always going to be the case - there's no such thing as a 3 phase domestic "ring main" socket so some areas of the house will be on different phases. And you'll probably want all 3 phases in the garage anyway for the car lift or, whatever.

If you're worried about balancing PV generation to demand across phases, don't. Modern meters to net billing so you're only charged for your net import (or paid for net export) across phases at any given moment in time.

 

Couple more things to note:

- you can't buy a 3 phase inverter now "just in case" and upgrade to 3 phase supply later. A 3 phase inverter needs 3 phases to output onto.

- A single battery often has a power limit lower than it's capacity, e.g. a 16kWh sized battery may only be able to supply 5kW at any given moment. This also limits it's usefulness for high demand users

- do you have DNO approval for 14kW PV ? They may look more kindly to this if on 3 phase.

- have you asked for an indicative price for 3 phase? This maybe prohibitive and will answer your question 

- "The 16kw was advised as part of a recent quote I had." - this is obviously just guess work with so much future expansion of use planned. tldr you can always more than you have, the optimum size depends a lot if you just plan to time shift your PV generation or use it for cheap overnight rate time shifting too. With my tariff (Eon Next) it's actually more financially rewarding to sell all PV generation rather than store it, and then fill the battery from grid each night. But that may change when the tariff is updated next year.....

 

 

 

[Kelvin]

The 16kWh SigEnergy system he’s likely looking at is made up of  2 x 8kWh batteries. A single battery outputs at half its capacity but it doubles up with each battery so in this case it will be 8kW. Their inverter system (which they call the Energy Controller) is very flexible and for 3 phase can go up to 30kW but this is all DNO dependent. In my case I’m going with the single phase 8kW unit. Unlike the Tesla PW3 you have to buy the specific Energy Controller to match the system rather than set it in software. Therefore if the DNO upgraded the infrastructure later you’d need to buy an upgraded EC to take advantage of it. 
 

The SigenEnergy system is very flexible, modular and compact. They also have a 12.5kW and 25kW DC bi-directional charger that supports V2L/H/G. It’s not cheap at around £4000 (for the 25kW unit) and they are waiting on the regulator approving it for home use. The downside is they only formed in 2022 so are a relatively new company so there’s an element of risk there. 

[scottishjohn]

having just been through a solar installation i can answer this fairly well

 

I am too old to be going of roofs now so  nooption but a professional job

I already have 3 phase  cos the difference inprice for my supply was only £1000 to do it 

 as for how professional the salemen are that whole other story 

Iwas very happy with the actual engineers who did the job and they stood up well to mt grilling into all the technicalbits of the system and the dno /export systems

 

as for what you put back to the grid you can send back 3.8kw per phase without any problem --they have to let you do that amount --no argument

above that it needs agreement and adifferent permit from the DNO

 that will take time 

  so you need that all sorted out and warrantied that it will happen  before you push the button on a bigger set-up  and give them  some money -

If they will not do that --change your supplier --they are cowboys

 

the DNO judges what you send back by the size of the invertor as its maximum is the max that can be sent back continuosly

the other thing is if you go for a 13kw=invertor it is classed as commercial -so your installation will have vat added pleas check this before making  decision

I was going for that when the 2nd supplier worked out he could get30 panels  on the roof  as ithought that it would pay back well inthe "shoulder months"

 

 they all seem to use "open solar" software which takes a view of house from goggle earth --but it is not scaled exactly --so thats what happened to me --when they came to do it  they had the rails onbefore they saw that they could not get the 30 panels  on

 

!! an opening for a discount !!

or get all your junk offf my

roof and put everything back as it was to start with 

 

the resulting deal was another battery for free  which took me up to the 17kw

an old saying in scotland --"when you see a stick --cut it"

I

went for 26panels which gave me 11.7kw 

and the invertor is a 3 pahse smart 11kw

 and 17kw of giv batteries

 

panels are the cheap bits

and if doing it yourself you will not be allowed to send back more than 4kw total - unless you get it certified by an approved mcs installer 

you need an mcs cert -which you then take to your supplier to get an export M-Pan number

you need to check carefully that the batteries you are getting will comply  to get a bigger KW export cert .

ocotpus  only like giv batteries --but there are some they willalow onthier tariff --check which if you going octopus

Iwould suggest you talk to ther suppliers before signing up 

I found they ALL lie to certain extent on things  and do not be afraid to tell the others you look at what sig have siad then you will find like me all the holes in the quotes

for example when asked they said bird gaurds are std  fitment --not so they wanted to charge extra -- a dull chance that happening  with me

had to get them to alter the contract to include them 

remeber when you sign you are comitted

 

just make sure your quote has all these things clearly marked 

 

I had one supplier who told me exactly what panels and invertor were going to be  and when the quote came --the make was"to be advised"

and another salesman told m the reason why they always specify a smaller invertor than the ouput of the panels  is that the invertor takes 1.5kw to run it 

 

I rung up GIV  energy and spoke to the tech man who pointed me too the spec sheet-- it takes 15w to run  not 1500w

 

so do not believe half of what they tell you

do your homework 

also warrnaties for panels,invertor and batteries

 check with the maker --

for example --giv invertor has 12 years -but if you do not get and mcs cert and one of thier apporved fitters its 5 years   

 

lots of bobby traps -solar panels sales are like car sales used to be in the sixities .LOL-

 

 some do not include scaffolding in the quote  and add it on  

[scottishjohn]

On 30/05/2025 at 14:31, joth said:

you can't buy a 3 phase inverter now "just in case" and upgrade to 3 phase supply later. A 3 phase inverter needs 3 phases to output onto.

unless i have been lied to --again you always have 2 "strings" of panels 

each string ir wired in series then the 2 strings are in parrallel 

you cannot have more than 2 strings on one invertor  so I am told

 

its when it comes out the other end of the 3phase inverytor it splits up the load -not on the input

[scottishjohn]

On 30/05/2025 at 09:27, d438a1 said:

• With my future demands (whereby there could be a mix of house, airbnb garage and workshop running at same time), should I be considering 3 phase? 
• Even if the above demands 3 phase, is it worth getting solar 3 phase equipment? Or would it make more sense to seperate phases to garage, house and workshop?
• I'll also note that utilising 3 phase for the car charger and workshop for bigger equipment is a real nice to have

its what I have done

1phase for house

2nd phase for garage 

3rd phase for expansion if iever build the holidays lets

[SteamyTea]

TL:DR

 

You ideally needs to split your PV across the phases you use during the daylight hours.

Net Metering may be possible with your energy company, but check first, and check if you can get a Net Meter fitted.

 

And, kW is power, kWh is energy.