Most optimal solution for AC coupled battery installation

_Sam_

I'm seriously tempted to add a battery to our current set up, but am not very good at math and just not sure which set up would be most beneficial. We are limited to the AC coupled installation due to the solar panels being leased.

The solar array that we have is about 3kw (and no option to upgrade this due to the lease). We also have an EV and a tariff with low cost night time electricity. The plan is to keep the battery topped up whenever possible, from solar generation during the day and from cheap electricity during the night. Then use the stored electricity during the evenings for all house needs.

I did read that due to the current cost of the batteries it is often not economically viable to have the battery installed, however would the fact that we will use the cheap night-time electricity in addition to solar generation balance things out, and make the battery a worthwhile investment? 

If so, which size battery would be most optimal to get given the initial cost outlay? Would it be better to get an all in one system where battery and inverter is one unit, or would it be better to get a separate inverter to connect to the battery.

Thank you

2nd_time_buyer

I presume leasing the current panels would not preclude you from installing a separate solar system on a different section of roof.

This may well be better value than a battery. But if you did go for that battery too, you would get the whole install (including the battery) VAT free.

powerful_Rogue

I had solar installed at the end of October. Was quoted with one 6.5kWh battery, but paid an extra £2200 for an additional 6.5kwh battery. Ours is an AC coupled.

We use roughly 10kWh per day, so having 13kWh batteries (11.70kWh useable) is ideal for us. We charge up overnight to 100% on the Octopus Go tariff. It's then topped up during the day via the Solar PV. Come the spring we will change to the Eco7 tariff.

_Sam_

Thank you, unfortunately no other roof available -  it is a bungalow with only two ridges one strictly south and one strictly north, and the south ridge is taken up by the leased panels.

I assume there is not much value installing on the north facing ridge, as it is north - but I may be wrong?

So if we only go for the battery, we would be able to have installation VAT free (even though we are not installing any new solar panels)?

2nd_time_buyer

So if we only go for the battery, we would be able to have installation VAT free (even though we are not installing any new solar panels)?

Unfortunately not. 

It would be borderline worth-it to get panels installed on the north elevation. Unless you have a shallow pitch roof. It is worth running it through PVGIS though.

... Or shed or outbuilding?

_Sam_

powerful_Rogue said:

I had solar installed at the end of October. Was quoted with one 6.5kWh battery, but paid an extra £2200 for an additional 6.5kwh battery. Ours is an AC coupled.

We use roughly 10kWh per day, so having 13kWh batteries (11.70kWh useable) is ideal for us. We charge up overnight to 100% on the Octopus Go tariff. It's then topped up during the day via the Solar PV. Come the spring we will change to the Eco7 tariff.

Thank you that is a good point - I had a look on the Bright app, and we have been using 5-7 kWh per day lately.

It will be less in summer time due to more solar generation available, and no need for the gas central heater (surprisingly ours is using a good amount of electricity to move the warm air around)

£2200 for a 6.5kwh sounds a good price. I've been looking at solaredge 10kwh battery and some websites cost it at £7000 ouch.

_Sam_

2nd_time_buyer said:

It would be borderline worth-it to get panels installed on the north elevation. Unless you have a shallow pitch roof. It is worth running it through PVGIS though.

... Or shed or outbuilding?

A small rickety shed but no other outbuildings. I had a look at PVGIS just now, but don't seem to find a value for north azimuth, they only provide 0=south, 90=west, -90=east. (I tried entering -0 but it calculated the same as 0)

2nd_time_buyer

_Sam_ said:

2nd_time_buyer said:

It would be borderline worth-it to get panels installed on the north elevation. Unless you have a shallow pitch roof. It is worth running it through PVGIS though.

... Or shed or outbuilding?

A small rickety shed but no other outbuildings. I had a look at PVGIS just now, but don't seem to find a value for north azimuth, they only provide 0=south, 90=west, -90=east. (I tried entering -0 but it calculated the same as 0)

Perhaps 180?

_Sam_

Doh you are right - so it showed 1529 kwh yearly for the north side identical array, compared to 2656 on the south ridge. Surprisingly not nothing!

I've no idea if this is viable though, I would have to look at tariffs that allow me to sell generated electricity from the north ridge, as on those days we are not at home we won't be able to use it otherwise. Then the initial cost of a new solar array much higher than just a battery...

Just not sure if an AC coupled battery for the already existing panels may not be a better solution?

70sbudgie

I think the suggestion was that PV panels attract a VAT rate of 0, which would be extended to your batteries if installed at the same time. 

Probably needs some sums to workout how much VAT you would save on the batteries which would cover additional PV costs.

Exiled_Tyke

70sbudgie said:

I think the suggestion was that PV panels attract a VAT rate of 0, which would be extended to your batteries if installed at the same time. 

Probably needs some sums to workout how much VAT you would save on the batteries which would cover additional PV costs.

I managed to get two panels with one micro inverter for the price of the avoided VAT on my battery. So any return on this makes it viable (if of course the battery in it's own right is viable!)