Confused about adding solar

[George]

Hello, I've got myself confused and would appreciate a steer before any installers quote.

 

I've got a 5.5kW PV array, which is on the 2014 feed in tariff. It's pretty much due south, with no shading and has performed very well. 

 

Due to the electricity prices rising and now we are a much higher demand household (added ASHP, two young children - laundry!), I would like to add a battery to make the most of the solar array.

 

Discussions with installers said that a data cable needs to go back to the main incoming electricity supply. The supply is single phase and runs underground until it gets to the house. This makes the data connection difficult to do for the 5.5kW array (I mean, anything is possible but it is difficult).

 

So this led me to think about a different barn, which I put a future proofing duct to. This other barn has an East-West roof (East-Southeast and West-Northwest). I have drawn a schematic:

 

 

So.... the plan is to put a new solar array on the east-west barn, with a AC battery inside. An AC battery will allow both arrays to charge it during the day, with the east-west array providing good time of day self consumption and the south array doing the heavy lifting to charge the battery for overnight.

 

My confusion is...

 

As it's single phase, will I be able to export limit? (We currently have no export limitation for the 5.5kW (4kW inverter) array so presumably I can just have something to monitor the main outgoing cable and throttle the east-west array and battery.)

 

I have looked at a Powerwall 2, Powervault and a Givenergy. My preference is currently with the Givenergy for price and control. Does anyone know of unbiased reviews of these batteries?

 

As the roof on the east-west barn needs work, can I buy all the equipment upfront VAT free, but only have the battery installed and install the solar at a later date?

 

As the east-west array will largely be self-consumption, do I max out the array size and to make best use into the future, add additional batteries?

 

 

Any help or correction or other ideas gratefully received. 

 

 

 

 

Edited April 9, 2022 by George

[JohnMo]

Believe you can only the vat off if being installed as a package.

 

You will need G99(?) approved inverter this will self limit export in an approved manner.  I think it is connected to the incomer on the main house meter.  The signal will talk to the inverter to control if export occurs or not based in the setting you select on export limitations.

 

Everything else gets complicated as DNO approval is required and will want to charge to loads to study if they will say yes or no.

[George]

Thanks. OK, so it sounds like my basic understanding was correct. It might be that they accept it if we paid for a study - my connection is only me and my neighbour and our transformer is stepped straight from a HV wooden pole line.

 

It's not something that was looked at before - in 2014 they just gave the nod and when we added the heat pump they initially refused based on the 16kW headline figure, before again agreeing when it was pointed out it was actually a peak 4.3kW draw and was inverter driven.

 

My fallback position is just to install the battery and take the hit on VAT.

 

Because I would essentially be using the solar for self consumption I was hopeful a supplier may bend the rules a tad. It's not like cheating a FIT agreement, just offsetting the install time (in fact, the repairs would only take a few days so may just be able to get it all sorted in one scaffold). 

 

(On a more general point, at some point all these solar panel covered houses will need their roofs replacing. Presumably you can disconnect the panels, remove them and fix things without impacting on the FIT agreement. So surely in principle you don't have to have everything installed in one go. 

 

[joth]

4 hours ago, George said:

Discussions with installers said that a data cable needs to go back to the main incoming electricity supply

This data cable only needs to go from the incoming supply to the battery, and you can put the battery anywhere you want, e.g. in the house next to the incoming supply? I don't understand where the requirement for a whole new solar array is coming from, just to avoid running one data cable. 

 

[George]

24 minutes ago, joth said:

This data cable only needs to go from the incoming supply to the battery, and you can put the battery anywhere you want, e.g. in the house next to the incoming supply? I don't understand where the requirement for a whole new solar array is coming from, just to avoid running one data cable. 

 

No you're quite right, it's not necessary. But the location to be able to access the power cable meant it'd be easiest to have it in the east-west barn. That is what then led to considering adding extra as it saves £1k in VAT and adds in better timed power for self consumption. 

[Dillsue]

10 hours ago, George said:

My confusion is...

 

As it's single phase, will I be able to export limit? (We currently have no export limitation for the 5.5kW (4kW inverter) array so presumably I can just have something to monitor the main outgoing cable and throttle the east-west array and battery.)

If youre getting FITs the original system will have been MCS installed and met with all the regs.  Assuming thats the case youll either have an export limited inverter with a 16 amp export limit, or there would have been a DNO application in 2014 to export more than 16 amp... the predecessor to a G99 application.

 

If youre adding another array and /or AC coupled batteries youll need to put in a G99 application to export(or potentially export) more than the 16 amps?? you already have. If you want to throttle the new array youll need a G100 application aswell to cover the export limitation device/system. All gets complicated above the 3.68kw/16amp limit!!

Edited April 9, 2022 by Dillsue

[George]

9 hours ago, Dillsue said:

If youre getting FITs the original system will have been MCS installed and met with all the regs.  Assuming thats the case youll either have an export limited inverter with a 16 amp export limit, or there would have been a DNO application in 2014 to export more than 16 amp... the predecessor to a G99 application.

 

If youre adding another array and /or AC coupled batteries youll need to put in a G99 application to export(or potentially export) more than the 16 amps?? you already have. If you want to throttle the new array youll need a G100 application aswell to cover the export limitation device/system. All gets complicated above the 3.68kw/16amp limit!!

Yeah, it's a 4kW inverter and MCS. I believe in 2014 it would have been done on the notification route. 

 

OK, so it is equally complicated with a battery or additional solar in terms of having to apply for a G99 or G100. I'm pretty set on a battery if possible because I'm pretty sure I'll get 95% utilisation and it'll pay for itself fairly soon. The panel payback time would be a bit worse but they should last 25 years and payback eventually.

 

Like I say, it might be that they can accept more than 16amps because there's only two houses on this transformer. The slightly ridiculous bit is that I don't actually want to export more than 16amps - I imagine given the FIT there's no way to get SEG only for new solar panels - so it would be imperative to self consume directly or charge the battery.

 

 

Edited April 10, 2022 by George

[Dillsue]

8 hours ago, George said:

Yeah, it's a 4kW inverter and MCS. I believe in 2014 it would have been done on the notification route. 

 

OK, so it is equally complicated with a battery or additional solar in terms of having to apply for a G99 or G100. I'm pretty set on a battery if possible because I'm pretty sure I'll get 95% utilisation and it'll pay for itself fairly soon. The panel payback time would be a bit worse but they should last 25 years and payback eventually.

 

Like I say, it might be that they can accept more than 16amps because there's only two houses on this transformer. The slightly ridiculous bit is that I don't actually want to export more than 16amps - I imagine given the FIT there's no way to get SEG only for new solar panels - so it would be imperative to self consume directly or charge the battery.

 

 

3.68kw/16a or less is still notified rather than applied for.

 

Personally Ive not found the G99 process complicated if youre clear on what you want to do.

 

If youre installing a second system with a battery then I beleive you can get SEG if its an MCS install. I think you also have to give up the deemed element of your FIT payments so that all export is metered and paid for via SEG. Youll need a smart meter to do that. If you hoping not to export much then you probably want to have a good think about giving up the FIT deemed payment

 

It wasnt quite clear to me if you were altering your FIT system but I think youre very restricted in what you can do and risk loosing your payments if you fall foul of the scheme rules!

Edited April 10, 2022 by Dillsue

[George]

I don't intend to touch the FIT installation at all. And I was intending to keep FIT - while SEG is good at the moment I'd rather the long term certainty. 

 

I would want the battery to know when the existing FIT solar panels are exporting and instead charge. But I assume all retrofit batteries have the capacity to do that. 

[Christiano]

We have an 8kWh Powervault in an outbuilding that already had a sub-consumer-unit. I had to put in 3 CAT5E cables, 2 from the consumer unit for Mains & Solar, one for internet. Was easy enough.

 

Powervault is noisy, sounds like there are always some fans running. Glad the install surveyor advised to put it away from the house; I haven’t called their support yet to see if this is normal.

The app is nice and you can just put the battery in normal mode and it will do exactly what you expect.

We have Octopus Go so 4 hours @5p/kWh overnight, in the winter I had set the schedule to charge it up cheap every night but now I only need to charge to about 50%, this is a bit more manual (you can only set times in the schedule, you can’t say “charge to 50%”) and seems like slightly hard work to save 10-20p/day. Realistically I just check the weather forecast before bedtime and set the Powervault and heating to something appropriate.

[joth]

1 hour ago, Christiano said:

We have Octopus Go so 4 hours @5p/kWh overnight

Note it's no 7.5p / kWh

 

1 hour ago, Christiano said:

seems like slightly hard work to save 10-20p/day.

According to https://www.powervault.co.uk/wp-content/uploads/2018/07/Powervault-3-specifications.pdf they have an API and a Smart tariff controller via portal. Any use?

I do dislike this trend for needing a subscription to access non-dumb controls.

 

Interesting about them being noisy.  Presumably puts out heat, and I understand batteries prefer a non-freezing environment, hence my thought putting them in the house makes some sense. (Bit unlike inverts in this way)

 

 

 

[Christiano]

Hi joth, I asked their support desk about APIs when it was installed in September last year, they said there was nothing that I could use. I could try & hack it from the app but it’s not really my skill-set. 

 

They also have something called smartSTOR which will “automatically set the best schedule for your PowerVault based on tariff prices and your household’s energy usage”. We set it to this initially but there was a software fault at at the time so have just done the overnight charge. I doubt it is clever enough to forecast our solar and only charge enough to get us to the right place.

 

I have an emonTx in the outbuilding monitoring charge/discharge and the room temperature, it’s been as low as 3c in Nov/Dec and has been between 6c-13c since Feb. Not sure if the battery affects the temperature much? I expect it will in the summer, I may have to put some ventilation in if it gets hot (or leave the door open!).

[joth]

Of course, Powervault ran an Octopus Agile trial

https://octopus.energy/blog/agile-powervault-trial/

 

Kinda ridiculous that a year (or more?) after that finished you still can't use it reliably with the much simpler Go tariff

[Christiano]

They said the fault was fixed but I couldn’t see the point in leaving it to their software when the 4-hour slot is so simple to do using the basic scheduler.

 

It would be nice now we have a bit more sun to be able to automate something with home assistant.

 

Hey it’s a shame they called the product the same as a popular range of Dell servers ‘cos it makes it much harder to google stuff.