Solar PV plan for 3 phase supplied house - Is there an idiot's guide?

[Omnibuswoman]

I have reached the point of having obtained a quote for our PV system, attached, from a local company via my builder. Happy to hear any feedback on it - I thought it seemed competitive for an 8KW system with REC 365w twinpeak black panels. We won't be going with the batteries at this point for reasons of limited budget, but plan to add those in at a later stage. The total cost without batteries is £10,500.

 

Before I seek further quotes,  I really need to better understand how solar systems work for houses, and in particular with a 3-phase supply. I'm not certain that the quote provided is suitable for a 3-phase supply.

 

My knowledge of electrical and electronics is really poor, and I need to have a look at an idiot's guide. Can anybody point me to the most basic of basic explanations of what each bit does, and where it goes in the system?

 

Thanks!

 

[Dillsue]

Googling your inverter and the spec says it can operate on 3 phase. Your quote only has a single phase generation meter so did you ask for a 3 phase PV system and the supplier has made a mistake?

 

Plenty of info on the web but make sure your looking at UK web sites!!

 

If youre not too confident with electrics, you might be best paying your electrician to come and explain your house wiring before you go looking at PV. PV install and wiring will likley make much more sense if you have a grasp of how your house electrics work.

[SimC]

 

Starting with the solar panels part, REC is the manufacturer with a good reputation for reliable products.

If they are installed by an 'REC Pro Installer' then you get a 25 year warranty on the panels that includes the labour costs to swap out any that fail.

Check this link for your local installers.

https://www.recgroup.com/en/installers/search

 

The GSE integration is a mounting system for the panels that fixes directly to the roof slats, so the panels become part of the weather proof cover for the roof with the edges filled in with normal roof tiles. Presumably this is for a new or replacement roof project.

 

With 22 x 365 Watt panels, the peak output in Summer with all at the optimum slope angle on a South facing roof would be 8030 Watts (8.03 kWpeak).

 

But is your roof area all South facing, and big enough to contain all 22 panels, or do you have East and West roof areas big enough for say 10 and 12 panels?

 

To cater for different alignment of roof areas, the inverter has 2 string inputs that operate independantly to optimise the output of the connected panels. So you could have say string 1 of 10 panels for the East roof, and string 2 of 12 panels for the West roof.

 

You can get a prediction of the panel performance for your location and roof layout by using this calculator:-

 

https://re.jrc.ec.europa.eu/pvg_tools/en/

 

Choose your location, even down to your street level.

Input the PV peak power (all 8.03 if all facing in the same direction).

Slope = angle of roof from horizontal.

Azimuth = angle from due South (East = -90, West = +90)

Click the 'Visualise results' button to see the predicted kWh output per month.

 

Run the report twice with different PV peak power and azimuth if you have 2 roof areas, then add the monthly results together.

 

 

 

 

 

 

 

 

 

 

Edited January 24, 2023 by SimC

[Mr Blobby]

On 22/01/2023 at 10:54, Omnibuswoman said:

 I'm not certain that the quote provided is suitable for a 3-phase supply.

 

I share your uncertainty about the 3-phase credentials for the inverter.  The user manual is not an easy read but I did try. For about 5 pages.

 

From what I can see (I'm no expert) it looks like you have been quoted for a single phase invertor that can be configured with two others for a three phase configuration, with one inverter on each phase.  Perhaps that explains the single phase meter. 

 

If your quote is for a single phase inverter and 8 KW of PV attached to one phase then I think that would exceed the DNO limit of 4KW per phase.

 

I'm sure someone will be along soon who knows what they are talking about and give a better informed answer.  I hope so as our requirements are very similar.

 

 

 

 

Edited January 24, 2023 by Mr Blobby

[Dan F]

On 22/01/2023 at 10:54, Omnibuswoman said:

Before I seek further quotes,  I really need to better understand how solar systems work for houses, and in particular with a 3-phase supply. I'm not certain that the quote provided is suitable for a 3-phase supply.

 

It's not just about your 3-phase supply. It's also important to consider:

- Do you need to be able to export from PV on all three phase in order go beyong 3.68kW/phase limitation or is DNO happy for you to export 8kW on a single phase?

- Will you house loads be all on a single phase, or will they use all three phase?

 

 

[SimC]

As others have said, you really need to understand how your 3 phase supply is going to be utilised and what electrical loads will be presented on each of the 3 phases.

 

It may be a legacy use of the property that powered 3 phase motors/machinery. For example a 3kW 3-phase motor will put an even 1 kW load on each phase, whereas a 2 kW 1-phase washing machine will put the full 2 kW load on 1 specific phase based on which it is wired to.

 

Another brand of 3-phase inverter mentions being able to cope with out of balance loads across the 3-phases, with up to 5 kW output on 1-phase from an 8 kW inverter.

https://midsummerwholesale.co.uk/buy/solax/solax-x3-g4-fit-8-tp30

 

Another consideration is the location of the grid incomer (plus utility meter) in relation to where the inverter will be located. The inverter will require a suitably rated power cable, along with a data cable to it's own 3-phase meter. This is so the inverter knows what loads are present on each phase and also once a battery is added what output it needs to provide in order to target zero grid import which minimises your bills.

 

If you want to be paid for export, the installer will need to be MCS approved and provide a certificate for your installation along with DNO approval for connecting the system to the grid.

 

 

[Dillsue]

Plenty of 8kw 3 phase sunsynk inverters listed on the ENA type test database but the only one listed as a hybrid isnt approved so shouldn't be connected to the grid. Probably want to ask the installer about that!!

 

It's been mentioned on here before but if the OP has a 3 phase smart meter, or can get one fitted, then they could well have net metering so its largely irrelevant how the 3 phases are loaded as import and export are offset against each other. As I understand it PV export on any phase cancels out import on any phase to give a net consumption that you get billed for. No MCS needed to get "paid" for your export at a very lucrative equivalent rate. Hopefully someone who knows about 3 phase net metering will confirm?? Another thing for the OPs spark to look into.

[Dan F]

31 minutes ago, Dillsue said:

have net metering so its largely irrelevant how the 3 phases are loaded as import and export are offset against each other. As I understand it PV export on any phase cancels out import on any phase to give a net consumption that you get billed for. No MCS

 

This is correct.   

 

When you bring battery storage into the mix it gets a bit more interesting though, as ideally, if you are using 8kW on phase 1 but the inverter can only cover 3kW you want to export 5kW on the other phases to compensate for the 5kW import on phase 1.  This is why I asked the OP about how they will load the phases, because if loads are spread across phases and battery storage is planned, then IMO it's important to install a solution that supports this phase compensation. 

 

[Nickfromwales]

7 hours ago, Dillsue said:

then they could well have net metering

So who answers this question definitively? Who do I ask for a smart meter to be fitted that supports net metering, and to then evidence it?

[Dillsue]

30 minutes ago, Nickfromwales said:

So who answers this question definitively?

A manufacturer??

[Dillsue]

7 hours ago, Dan F said:

When you bring battery storage into the mix it gets a bit more interesting though, as ideally, if you are using 8kW on phase 1 but the inverter can only cover 3kW you want to export 5kW on the other phases to compensate for the 5kW import on phase 1.  This is why I asked the OP about how they will load the phases, because if loads are spread across phases and battery storage is planned, then IMO it's important to install a solution that supports this phase compensation. 

 

No experience with 3 phase inverters but assume that a 3 phase hybrid inverter will output battery energy evenly across all 3 phases so net metering will still use the battery output to offset an equivalent import?? I assume if theres 8kw load on L1, inverter will provide 8/3 on each phase to try and meet demand on L1 leaving the shortfall on L1 covered by grid import. That import would be offset by the unused export on L2 and 3??? Is that how it works??

[Dan F]

1 hour ago, Nickfromwales said:

So who answers this question definitively? Who do I ask for a smart meter to be fitted that supports net metering, and to then evidence it?

 

I thought we determined that all UK 3-phase smart meters do (or at least should) use vector-sum metering.  I haven't actually looked at mine and tried to determine if it is using vector-sum metering or not though. I guess you'd ask your electriciy supplier, but beware that you might get some strange looks when you ask about "vector sum" from a lot of people.  I found that varous PV/battery suppliers I talked to didn't understand this either.  Our meter is a Octopus installed "Sprint 211".

 

 

Edited January 25, 2023 by Dan F

[Dan F]

1 minute ago, Dillsue said:

No experience with 3 phase inverters but assume that a 3 phase hybrid inverter will output battery energy evenly across all 3 phases so net metering will still use the battery output to offset an equivalent import?? I assume if theres 8kw load on L1, inverter will provide 8/3 on each phase to try and meet demand on L1 leaving the shortfall on L1 covered by grid import. That import would be offset by the unused export on L2 and 3??? Is that how it works??

It works like this if the inverter supports it, yes.  Not all inverters support this though.  Also the correct term is "vector sum metering" I think.  Net metering typically refers to a tarrif which has the same price for import and export.

 

This approach doesn't need a hybrid inverter specifically, it can also work with AC-coupled batteries and with component-based systems.  I know it works with the following:

- Tesla Powerwall (using Gateway)

- Sonnen

- Victron (with an inverter per phase).

 

I think it might work with Solis hybrid inverter, but couldn't get a clear answer from them.  Also couldn't get a clear answer from LuxPower.

 

Importantly the electiricty meter that use used (connected up to powerall, sonnen or victron) also needs to measure using vector-sun.

 

 

[Nickfromwales]

3 hours ago, Dillsue said:

A manufacturer??

Ok, so you can choose which meter gets installed? 

[Omnibuswoman]

Thanks for your replies all. Bit of context:

 

This is a new build, so the panels are going up (integrated into the roof) fairly soon. The array is 8kw spread across an E/W roof - roughly 1/3 on the E and 2/3 on the W.

@SimC I had a look at PVGIS, but I couldn't figure out how to change the roof direction from South facing to East or West. Is that the figure in the box labelled Azmuth?

I don't know how to express the direction in degrees, so any wisdom you can share on this would be great, thanks!

 

Thanks for the comments about the phases and net metering. The 3 phase supply was installed last year by Western Power - their preferred choice for all new properties apparently. We have a digital meter on the outside of our workshop, adjacent to the house. 

 

I have gone back to the supplier of the quote to ask more questions about the inverter and phases - i.e. what his thinking is around this, and have cast the net to some other local suppliers for quotes to see what they propose. 

 

We don't yet have a smart meter - in order to get the supply connected we just went with the first company that could give us a reasonably short date for this - British Gas - many others were unable at that time to even commit to a date at all in late 2021. We plan to move our supplier to Octopus or Ovo, although we're a bit concerned that it might take quite some time to get a smart meter installed, judging by others' experiences here.

 

For reasons of budget, we are not going to go with the batteries at this point, but will design the system to take batteries so that we can install them further along the line. The electrician we have chosen to do the electrics in the new house has no experience with solar panels, so we think we will have to find someone with this expertise to help to design the system, then to have our electrician fit it. 

 

I'll have a look at the posts that DanF referred to, and will do some more googling. I previously joined a forum for electrical and electronic engineers (in order to be able to negotiate with Western Power over the cost of the connection), so I may pose the question about phases and metering on there to see what pops up. Any knowledge I gain, I will bring back over here.

 

Cheers, Omnibuswoman

 

[Dillsue]

9 hours ago, Nickfromwales said:

Ok, so you can choose which meter gets installed? 

Probably not but speak to youre supplier as they may have a standard fitment.

 

I think its mentioned above that net metering is part of the smart meter spec and that's what a bit of googling suggests too.

 

It seems a great way to avoid MCS cost and get "paid" for all your export at the same rate charged for import. Just the cost of a 3 phase upgrade to fret about but it seems a no brainer for a new build if available

Edited January 26, 2023 by Dillsue

[Dan F]

48 minutes ago, Omnibuswoman said:

Thanks for your replies all. Bit of context:

 

This is a new build, so the panels are going up (integrated into the roof) fairly soon. The array is 8kw spread across an E/W roof - roughly 1/3 on the E and 2/3 on the W.

@SimC I had a look at PVGIS, but I couldn't figure out how to change the roof direction from South facing to East or West. Is that the figure in the box labelled Azmuth?

I don't know how to express the direction in degrees, so any wisdom you can share on this would be great, thanks!

 

Thanks for the comments about the phases and net metering. The 3 phase supply was installed last year by Western Power - their preferred choice for all new properties apparently. We have a digital meter on the outside of our workshop, adjacent to the house. 

 

I have gone back to the supplier of the quote to ask more questions about the inverter and phases - i.e. what his thinking is around this, and have cast the net to some other local suppliers for quotes to see what they propose. 

 

We don't yet have a smart meter - in order to get the supply connected we just went with the first company that could give us a reasonably short date for this - British Gas - many others were unable at that time to even commit to a date at all in late 2021. We plan to move our supplier to Octopus or Ovo, although we're a bit concerned that it might take quite some time to get a smart meter installed, judging by others' experiences here.

 

For reasons of budget, we are not going to go with the batteries at this point, but will design the system to take batteries so that we can install them further along the line. The electrician we have chosen to do the electrics in the new house has no experience with solar panels, so we think we will have to find someone with this expertise to help to design the system, then to have our electrician fit it. 

 

I'll have a look at the posts that DanF referred to, and will do some more googling. I previously joined a forum for electrical and electronic engineers (in order to be able to negotiate with Western Power over the cost of the connection), so I may pose the question about phases and metering on there to see what pops up. Any knowledge I gain, I will bring back over here.

 

Cheers, Omnibuswoman

 

 

 

This video will explain phase compensation and how it works with/without batteries: https://www.youtube.com/watch?v=pTfOYlboarw. 

 

The decision you have to make is:

1) Will loads be connected to one phase only or all phases?

2) Do you want i) single-phase AC-coupled PV inverter ii) i) three-phase AC-coupled PV inverter iii) DC MPPT's.

3) In the future will you use a packaged battery/inverter solution (e.g. powerall) or a hybrid inverter + batteries.

4) Aside from storage size of batteries, you need to think about power in kW that you require from a battery storage system.

 

Which type of PV system you use depends on required power output and what battery you plan to use.  A couple of examples:

 

- If you plan to use Tesla Powerall(s) which provides 13.5kWh and 5kW per battery (and supports phase compensation) then you best option would be AC-coupled PV inverter.

- If you planned a Victron system then both DC MPPTs and AC coupled PV inverter would work, but it's likely cheaper and simpler to use MPPT.  Victron system can be system to any storage size or power output and also support phase compensation.

- If you planned to use a all-on-one hybrid inverter then this would work wthout an AC coupled PV inverter and you could buy this now without batterie and then add batteries later.  If would be important though to ensure it supported i) sufficient kW output ii) phase compensation if you have loads on all phases.

 

The SunSync hybrid inverter you have been quoted for is single-phase.   You could defintly use this if you wanted to, the only issue with this approach is that you're future battery storage would be on a single phase and you house load may (?) be split across three loads. Unless you have very high loads or any three-phase equipment you could keep everything on a single phase which would simplify things. SunSync do do a three phase version too https://www.sunsynk.org/3-phase-hybrid-inverter

 

 

Edited January 26, 2023 by Dan F

[SimC]

5 hours ago, Omnibuswoman said:

This is a new build, so the panels are going up (integrated into the roof) fairly soon. The array is 8kw spread across an E/W roof - roughly 1/3 on the E and 2/3 on the W.

@SimC I had a look at PVGIS, but I couldn't figure out how to change the roof direction from South facing to East or West. Is that the figure in the box labelled Azmuth?

I don't know how to express the direction in degrees, so any wisdom you can share on this would be great, thanks!

 

 

For the PVGIS solar output calculator:-

 

Choose your location, even down to your street level.

 

Input the PV peak power (approx 3.0 East, 5.0 West).

 

Slope = angle of roof from horizontal. Typically 30 to 35 degrees for a UK roof. May be your roof builder can provide this figure, or by measurement and trigonometry where the angle = tan[-1] (vertical distance/horizontal distance) of the right-angle triangle formed by half your roof.

For example, angle = tan[-1] (2.5m/4m) = 32.0 degrees.

 

Azimuth = angle from due South (so due South = 0, East = -90, West = +90 degrees)

Click the 'Visualise results' button to see the predicted kWh output per month.

 

If the azimuth angle is not obvious, you can get a figure to the nearest 10 degrees (possible 5 if between graduations) by using this link, enter your postcode, then move your property under the pointer on the map. Each graduation is 10 degrees, so count from due South.

Repeat for each of your roof slope directions. This example is -30 degrees from due South.

 

 

 

 

 

 

Edited January 26, 2023 by SimC

[Dillsue]

7 hours ago, Dan F said:

The SunSync hybrid inverter you have been quoted for is single-phase.   You could defintly use this if you wanted to, the only issue with this approach is that you're future battery storage would be on a single phase and you house load may (?) be split across three loads. Unless you have very high loads or any three-phase equipment you could keep everything on a single phase which would simplify things. SunSync do do a three phase version too https://www.sunsynk.org/3-phase-hybrid-inverter

 

Another problem with using an 8kw inverter on a single phase is that youll need to get DNO permission to put more than 3.68kw on a single phase. I dont know what criteria a DNO would use to accept that set up, but I would have though they would expect you to balance the 3 phases wherever possible and would likely reject 8kw on one phase and zero on the other 2 when all 3 phases could quite easily be balanced.

 

If I remember correctly on a G99 application one of the conditions you have to confirm is that there wont be more than a 16 amp difference between phases. I guess thats important to the grid??

Edited January 26, 2023 by Dillsue

[Dillsue]

7 hours ago, Dan F said:

This video will explain phase compensation and how it works with/without batteries: https://www.youtube.com/watch?v=pTfOYlboarw. 

Watched the video but without sound so don't know if they covered this, but does the vector summing only happen in real time as in export only negates the same import if the two are happening at the same time? An example would be importing 4kw on L1 and at yhe same time exporting 2 x 2kw on L2+3 so the sum would be zero.

 

If it doesnt have to be balanced in real time, then am I right in thinking you could export 2 x 5kwh on L2+3 through an afternoon and then import 10kwh through the evening giving a sum of zero???

[Dan F]

26 minutes ago, Dillsue said:

Watched the video but without sound so don't know if they covered this, but does the vector summing only happen in real time as in export only negates the same import if the two are happening at the same time? An example would be importing 4kw on L1 and at yhe same time exporting 2 x 2kw on L2+3 so the sum would be zero.

 

If it doesnt have to be balanced in real time, then am I right in thinking you could export 2 x 5kwh on L2+3 through an afternoon and then import 10kwh through the evening giving a sum of zero???

 

It's in real-time.

[Radian]

On 22/01/2023 at 10:54, Omnibuswoman said:

We won't be going with the batteries at this point for reasons of limited budget, but plan to add those in at a later stage.

I hope you realise you will have to pay the full rate of VAT on them if you don't get them installed along with the rest of the system.

[joth]

18 hours ago, Nickfromwales said:

Ok, so you can choose which meter gets installed? 

All SMETSv2 polyphase smart meters should use net metering regardless of manufacturer, as this is mandated in the SMETSv2 specification.

I bet if you search this forum for "polyphase" you'll see citations and a few positive confirmations of this

[Nickfromwales]

4 hours ago, Dillsue said:

I think its mentioned above that net metering is part of the smart meter spec and that's what a bit of googling suggests too.

Indeed.
But surely this is down to the laws of physics; as juice out vs juice in is an electrical ballet between the flow of said juice through the 3 coils that perform the metering registering positively or negatively dependant on the sum of the activity of each coil at any given moment? 
Ergo, net metering is happening regardless of request / intention as it’s a physical occurrence.

It would be down to the hardware, yes, and the software registering flow in both directions ( and reflecting that in the reading of the meter display ). 

[Dan F]

57 minutes ago, Nickfromwales said:

juice out vs juice in is an electrical ballet between the flow of said juice

I couldn't have put it more eloquently 😀