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

[markharro]

2 hours ago, Radian said:

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.

Can you remind me is it 5% or 20%?

[markharro]

This is a scarily technical thread for me. I may be in the same boat with 3 phase and wanting to instal around 11kw PV to max out. I def want the option for battery storage now or later. I also want to be able to export without constraint ie without having to get the tiresome DNO permission.

 

If there a single recommended 3phase that will do what I need and allow batteries to be added in due course? I really don't have the time to master this particular brief so its really just knowing what I need to be making clear to my proposed installer that I am interested in. Hopefully I can then trust them to set up what I am aspiring to.

[Radian]

28 minutes ago, markharro said:

Can you remind me is it 5% or 20%?

Solar PV + battery installed together attract no VAT. Otherwise they will be subject to the standard 20% VAT rate

[Susie]

19 minutes ago, Radian said:

Solar PV + battery installed together attract no VAT. Otherwise they will be subject to the standard 20% VAT rate

If the build is still ongoing presumably as long as you add the batteries before completion you can still claim the VAT back. For us it could be long build and we’re hoping prices will lower and we can assess a real production before further investment. 

[Radian]

1 minute ago, Susie said:

If the build is still ongoing presumably as long as you add the batteries before completion you can still claim the VAT back. For us it could be long build and we’re hoping prices will lower and we can assess a real production before further investment. 

 

You've got to be very careful. HMRC are very good at weaselling out of this.

A quote from admin on HMRC Customer forums

Quote

the liability of a battery for a solar panel is only allowed if the batteries are installed with the solar panels

at the same time and is essentially supplied as a single supply of solar panels and battery.
 

 

[joth]

5 minutes ago, Radian said:

 

You've got to be very careful. HMRC are very good at weaselling out of this.

A quote from admin on HMRC Customer forums

 

I think the hope here is installing batteries as part of a new build dwelling, batteries are automatically 0% rated due to no VAT on new houses, regardless of if any PV is ever installed.

Problem is I can't see any way you can claim batteries are "ordinarily incorporated" into a new dwelling. Notice 708 by default excludes most electrical appliances, and a battery while being professionally is straight forward to take with you when you move. (It's about the same effort as a washing machine.)

[Susie]

12 hours ago, Omnibuswoman said:

 

 

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. 

 

Is the  ‘Worksop’ a business you run?  Putting this on its own phase could be good depending on what equipment you have in eg welding equipment, lifting, or compressors, for some items we are suppose to tell western power (new name is National Grid) incase we cause spikes on the network. Another useful possibility is putting a meter on the workshop phase just for your own accounting as a business expense rather than the low working from home of £250 apx we claim for the business.  Working from home can be a tax minefield though shared private and business use of a Worksop can often get round this.  
We have 3 phase, one for our workshop, one phase for night storage heaters, immersion cylinder and kitchen and one phase for everything else it’s fairly well balanced but we moved in as it is so we didn’t design the circuits or phases.

I would expect a lot of electricians down here are use to 3 phase and yours should be able to design it ok as it’s a lot more common than back in Manchester my home town. We had 3 phase in our Trafford Park premises but not in the suburbs so most domestic electricians didn’t touch it enough only the industrial electricians like ourselves.  

[Dan F]

1 hour ago, markharro said:

export without constraint ie without having to get the tiresome DNO permission.

 

You can't avoid this I don't think.  If you only export max 3.68kW per phase though, it is simpler.

 

1 hour ago, markharro said:

If there a single recommended 3phase that will do what I need and allow batteries to be added in due course? I really don't have the time to master this particular brief so its really just knowing what I need to be making clear to my proposed installer that I am interested in. Hopefully I can then trust them to set up what I am aspiring to.

 

Most flexible/extensible system IMO is Victron.  Given its seperate composable compoments (inverter-charger, MPPT, brains) it does cost more than a chinese all-in-one hybrid invert though.

[Dan F]

54 minutes ago, Susie said:

If the build is still ongoing presumably as long as you add the batteries before completion you can still claim the VAT back. For us it could be long build and we’re hoping prices will lower and we can assess a real production before further investment. 

 

Yes, in theory, but to simplify things you ideal want the same company to install your PV and batteries as a single package with a single VAT invoice.  To make thing even simpler, find a supplier who will zero-rate it then you don't need to reclaim anything

[Nickfromwales]

3 hours ago, Dan F said:

I couldn't have put it more eloquently 😀

I can't spell it lol. Fill yer boots  

[Nickfromwales]

42 minutes ago, Dan F said:

You can't avoid this I don't think.  If you only export max 3.68kW per phase though, it is simpler.

Hog wash.

 

Hybrid inverter;

then a field full of panels

+ lorry-load of batteries

enjoy zero DNO nonsense.

[Nickfromwales]

Is everyone here remembering that they DO NOT NEED 3ph to have a wedge of solar and batteries? 

[Dan F]

1 minute ago, Nickfromwales said:

Hog wash.

 

Hybrid inverter;

then a field full of panels

+ lorry-load of batteries

enjoy zero DNO nonsense.

 

You didn't read @markharro requirement which I responded to, he said "export without constraint"!

[Nickfromwales]

1 minute ago, Dan F said:

 

You didn't read @markharro requirement which I responded to, he said "export without constraint"!

OK. I'll retract 'hog', and give serious consideration to 'wash' being downgraded also.

DISCLAIMER:

I automatically assumed that nobody would want to install a domestic microgeneration system, designed to provide the grid with cheap power, at their own significant cost.   

[Dillsue]

7 hours ago, Nickfromwales said:

I automatically assumed that nobody would want to install a domestic microgeneration system, designed to provide the grid with cheap power, at their own significant cost.   

Our system isn't designed to feed the grid but export is a consequence of how weve installed things. I dont have a problem with surplus going to the grid if we're not using it.

[Nickfromwales]

9 minutes ago, Dillsue said:

Our system isn't designed to feed the grid but export is a consequence of how weve installed things. I dont have a problem with surplus going to the grid if we're not using it.

Indeed, as if it’s not “worth” capturing with a costly battery / other diversion then 8 agree it’s just simpler to let some leak away. In the grand scheme it’s an acceptable loss but agreed to be the ‘final destination’ for anything generated. 

[markharro]

10 hours ago, Dan F said:

You can't avoid this I don't think.  If you only export max 3.68kW per phase though, it is simpler.

Thanks yes this is what I think I am looking to do to avoid you paying for permission that might be refused. The intent is that (where it makes sense) I can dump the maximum production from the array through the 3 phases. I just have no idea how the system needs to be set up to do that. Hopefully the installer does/

[Omnibuswoman]

On 26/01/2023 at 09:55, Dan F said:

 

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

 

 

Just watched the video - a perfect idiot's guide to how this works. So in effect, it matters not how we set up the house demand across the three phases as long as we have a vector sum meter totting up total in and total out. 

[Omnibuswoman]

On 26/01/2023 at 22:06, joth said:

I think the hope here is installing batteries as part of a new build dwelling, batteries are automatically 0% rated due to no VAT on new houses, regardless of if any PV is ever installed.

 

The interesting question has to be, if vector sum metering means that any electricity exported is offset against any electricity imported, how is a battery economically viable?    Are we not just as well allowing anything that we don't use ourselves to go to the grid as an offset against what we have used? 

 

Or am I fundamentally misunderstanding how this works, and wronly assuming that any electricity exported in any given 24 hour period is offset against anything imported?? @Dan F @Nickfromwales

[SteamyTea]

11 minutes ago, Omnibuswoman said:

how is a battery economically viable?  

They are not, under any scenario at the moment, unless you get them for free.

[Dan F]

2 hours ago, Omnibuswoman said:

Just watched the video - a perfect idiot's guide to how this works. So in effect, it matters not how we set up the house demand across the three phases as long as we have a vector sum meter totting up total in and total out. 

 

In respect to use of PV across phases yes, with a 3-phase supply and vector-sum meter it doesn't matter which phases are producing and consuming. 

 

If you have constant production of 5kW on phase-1 and constant consumption of 5kW on phase-2 for an hour then the meter will record zero import and zero export.  If the meter wasn't vector sum, then it would record 5kWh import and 5kWh export and (given import tarrif is more export tarrif you'd be paying something instead of nothing)

 

Once you introduce a battery though, there is a bit more thought to it to ensure higher levels of self-consumption, as you really want 5kW load on phase-1 to all come from the battery (even if inverter is limited to 3kW/phase.  The video also explains how this works (with batteries that do this)

 

1 hour ago, Omnibuswoman said:

The interesting question has to be, if vector sum metering means that any electricity exported is offset against any electricity imported, how is a battery economically viable?    Are we not just as well allowing anything that we don't use ourselves to go to the grid as an offset against what we have used? 

 

Or am I fundamentally misunderstanding how this works, and wronly assuming that any electricity exported in any given 24 hour period is offset against anything imported?? @Dan F @Nickfromwales

 

Import is not offset against export over time.  Vector-sum metering is the way the instantaous power usage is recorded only.  If you export when the sun is shining and import in the metering the evening then this counts as seperate import and export with different pricing.   The alternative to this is a specific "net metering tarriff" where import cost and export cost price/kWh is the same.  With this type of tarriff a battery makes no sense, you are right, but the only such tarrif in the U.K is the Octopus Tesla Tarrif which required batteries to join.

 

 

Edited January 28, 2023 by Dan F

[SimC]

Battery storage (or any storage) comes in to play when your solar generation profile does not align with your consumption profile, instant by instant over each day.

 

If at one instant in time the PV is generating 5 kW, and your consumption is 2 kW with no storage available, then the 3 kW excess has nowhere to go other than export to grid (potentially at 15p/kWh from Octopus).  If at a later instance in time the PV is generating 2 kW with a 5 kW load, then you have a 3 kW import from grid (potentially at 33p/kWh on the price cap).

 

The battery storage will save any excess solar generation during the day, for consumption later whilst avoiding the cost of grid import.

 

Whilst waiting for my battery install (on a long lead time), I have a solar diverter (MyEnergi Eddi) connected to the hot water immersion heater and 2 oil filled heaters. As soon as the diverter detects any grid export it diverts just the excess power to the immersion heater. Once the immersion is up to temperature, it automatically switches to the heaters. The diverter is fully automatic, so when the solar gen drops off or a household load is switched on, a grid import is detected so the power diversion drops to 0.

 

Assuming your grid export price is less than grid import (almost always the case), you get the fastest payback on the solar PV when you self consume as much of the generation as possible. Energy storage helps with this, as long as it is suitably sized to your generation and consumption profiles.

[SteamyTea]

2 hours ago, SimC said:

If at one instant in time the PV is generating 5 kW, and your consumption is 2 kW with no storage available, then the 3 kW excess has nowhere to go other than export to grid (potentially at 15p/kWh from Octopus).

I have never researched this in proper detail, but I am under the impression that the inverter/diverter can take a few seconds to realise that it needs to import.  When a relatively high load is only going to be on for a few seconds because of excess (above the recent norm) i.e. water heating, some of that advantage may be lost.

So if if it takes say 5 seconds for the inverter to react to higher input, and another 5 seconds for the diverter to react to that input, but the spite in energy is only 20 seconds (scattered cloud), that is half the energy lost as ambient thermal energy (which may be useful or not).

I think @Radian knows haw fast his home made diverter works.

Would be interesting to know.

Edited January 29, 2023 by SteamyTea

[PhilT]

A solar immersion diverter is hard to justify if you have a heat pump which uses one third of the electricity and you get 15p for export - it could COST you (15-33/3)=4p for every kWh solar you divert to the immersion heater

[Radian]

3 hours ago, SteamyTea said:

I have never researched this in proper detail, but I am under the impression that the inverter/diverter can take a few seconds to realise that it needs to import. 

 

I don't think any commercial offerings are as dumb as that. I'm sure there will be some DIY'ers who use the natural poll time of their clamp-on power meters in order to switch on a load when they see above a certain threshold of power being exported. Then there will be an error of variable degree. Worse case might see them needlessly paying to import the dump load for most of the poll period.

 

Commercial diverters (I hope) do what I do and measure the magnitude of power flow (and direction) for every mains cycle. This is accumulated over time to establish a certain number of Joules that are also be being measured by the utility meter. Knowing that all utility meters only bill when a certain number of Joules have passed through them, we can step-in and switch-on our diverted load before we know an export unit will be counted and effectively drag the Joules we just put in - back out from the grid - without incurring any tariff at all.