Quote check and advice

[Benjseb]

Hi all

 

We are building a holiday let, 50sqm, which will have an electric feed from our main house. 
 

Pitched roof is perfectly east/west. 
 

planning on filling the roof with solar as our main house has just been converted from Oil to 14kw ASHP. Holiday let will also be AS. 
 

So questions

 

Does the below quote sound good? We’re in North West UK

 

6.1kWp sustem with single phase investor, all black panels. In roof low profile system. £6200 ex vat

 

or

 

9kWp system. As above but 3phase invertor. 
Didn’t get price for extra panels but invertor is +£200. 
 

I’m steered towards the larger system as we already use a lot of electric due to it being a big house and no gas. Decembers will was £400. But that’s our total energy consumption with guests staying. Obvs solar won’t help much in December but I’m thinking the shoulder months will benefit. Especially with a holiday let where the guests will likely try to heat rooms warmer than the Congo. 
 

Does it matter that we currently have a 3 phase supply but all our circuits draw from one phase? I presume when they run the new 64a supply for the holiday let they could pop this onto a different phase.  Will it make a difference to the metering or payback of solar (been told we can ask for net meter so any generation will offset demand regardless of phase?)

 

 

 

Edited January 11, 2020 by Benjseb

[ProDave]

Lots to digest there

 

Self usage is the key to PV being viable now.  If you have all your house on 1 phase, the holiday let on another phase and nothing on phase 3, then you don't want a 3 phase inverter.  I would be tempted by 2 separate 3kWp system each split equally e/w and each feeding one of the used phases. That will of course need 2 inverters.

 

I will sound like a cracked record as I say this to all PV queries now, but with no FIT have you properly run the pay back time calculations?

[Benjseb]

My understanding is that with the right meter it doesn’t matter which phase the generation and consumption are on. It will just meter the net consumption. That’s what the solar guy has said?

 

So then we don’t have to worry about exactly matching Consumption up. Makes it easier to run loads in the house or holiday let and be covered

 

 

It’s  hard for me to work our repayment period atm as we’ve only had our ASHp since October so hard to know our consumption over the sunshine months. 
 

does the price look fair?

 

Ben

Edited January 12, 2020 by Benjseb

[joth]

Just to confirm, you're planning to have a single meter for both properties? If so, AFAIK your only option is a three phase meter unless you want everything on one phase. 

If you're installing >4kW splitting it to multiple phases avoids the bother of G99 application, and one 3phase inverter should cost less than two single phase inverters. 

I'm impressed your solar supplier knows that balance of usage and generation across phases is not an issue if you have the right meter. Absolutely noneone I spoke to give a clear (cited) answer on that but in the end I found for myself it's what is specified in the SMETSv2 specification (polyphase section) so certainly the way they are intending it to work. 

 

A pound per watt installed seems pretty competitive compared to quotes I got (also black in roof, but ours is a full roof which adds some additional cost), but everything costs more in our part of the country anyway.

[Benjseb]

Thanks @joth

 

yes we already have a 3 phase meter, but the other two phases are capped off after the meter so presume we’ll just tap into those. Avoids the risk of trips on Christmas Day when we have too much demand!

 

And yes I had no idea about the net metering so impressed he knew. He’s an “ex” Electrician so comes at this from a different angle to the usual double glazing salesmen turned solar salesmen!

 

Glad to heat that sounds competitive. Just need to crunch some numbers and see if it’s worth the larger 9kw array. 

[ProDave]

I am not entirely convinced the metering is going to work as you expect, but I stand to be corrected.

 

So you are generating 6kW, that's 2kW per phase.

 

Both your house and the rental are using 2kW so those 2 phases are at balance neither importing or exporting.

 

Phase 3 is exporting 2kW

 

Your meter is NOT going to count backwards. That 2KW is gone.  *

 

Now consider you are still generating your 6KW split 2KW per phase.  But now your house and rental are both using 3KW

 

If what you believe is the case is true, then your meter will not count up.

 

I am not convinced it will behave like that.  I suspect is simply sums the metered power on the 3 phases, so would be metering a 2kW import even though phase 3 is exporting 2kW

 

I would like to see some official documentation that explains how a 3 phase meter behaves in that situation. 

 

* but you many get the 5.5p export rate for that power that is exported.

[joth]

12 minutes ago, ProDave said:

 

I would like to see some official documentation that explains how a 3 phase meter behaves in that situation

https://www.gov.uk/government/consultations/smart-metering-equipment-technical-specifications-second-version

Page 87

"Consumption shall be the sum of the cumulative Active Energy Imported on 
the importing measuring element(s) of its Electricity Meter less the sum of the 
cumulative Active Energy Exported on the exporting measuring element(s) of 
its Electricity Meter;"

 

I.e. you just add up all the import ever and subtract all the export ever to calculate total consumption.

 

There's also a YouTube video where someone got hold of a decommissioned non-smart 3ph meter and empirically tested it works the same way. However the meters are highly configurable in this (for residential Vs commercial and for different country needs). Talking to a phone support at my supplier, he couldn't vouch for how it was supposed to work, but knew for a fact they generally get it wrong first time and have to send an engineer out to fix it after the customer complains.

 

[joth]

Full disclosure: after a lot of back and forth we're not getting three phase, keeping with the existing single phase and a G99, so I no longer have any "skin in the game" if I've misinterpreted anything

[ProDave]

6 minutes ago, joth said:

https://www.gov.uk/government/consultations/smart-metering-equipment-technical-specifications-second-version

Page 87

"Consumption shall be the sum of the cumulative Active Energy Imported on 
the importing measuring element(s) of its Electricity Meter less the sum of the 
cumulative Active Energy Exported on the exporting measuring element(s) of 
its Electricity Meter;"

 

I.e. you just add up all the import ever and subtract all the export ever to calculate total consumption.

 

There's also a YouTube video where someone got hold of a decommissioned non-smart 3ph meter and empirically tested it works the same way. However the meters are highly configurable in this (for residential Vs commercial and for different country needs). Talking to a phone support at my supplier, he couldn't vouch for how it was supposed to work, but knew for a fact they generally get it wrong first time and have to send an engineer out to fix it after the customer complains.

 

Thank you for that I am always happy to be proved wrong with facts.  I have to say I am surprised by that,