Adding Battery to a 2012 4kw system...

[Mulberry View]

My Father-in-Law has a 4kw system on the bumper tariff. Lucky him. We both bought in at the same time, but I moved house to enjoy the delights of self-building!

 

Anyway, he's interested in adding some battery storage. Do we have anyone here that can give me some clues as to what might be involved?

 

He still has the original Sunny Boy inverter, running flawlessly and has since connected a Solar iBoost to it for the immersion heater.

 

He's not looking for the pinnacle of technology, more a cost-effective way to utilise the energy he's generating. He has no export meter by the way. 😉 He isn't really in a position to go EV at this stage.

[JohnMo]

Just do AC coupled battery then leave everything else as it is, maybe bin the iBoost and let that power go to the battery instead. Plenty of offering on the market from about 2kWh and upwards

[DamonHD]

If the iBoost is set correctly (I have an Eddi so have more knobs to twist to make it work) then the battery will get in first anyway.

 

Yes, AC-coupled is the way to go.

 

Tell/ask the FiT administrator before doing it.  Exports will go to deemed if not already so.

[Mulberry View]

55 minutes ago, DamonHD said:

If the iBoost is set correctly (I have an Eddi so have more knobs to twist to make it work) then the battery will get in first anyway.

 

Yes, AC-coupled is the way to go.

 

Tell/ask the FiT administrator before doing it.  Exports will go to deemed if not already so.

 

I think they were deemed from the start? No export meter, just a 50% payment for export

Edited Tuesday at 13:22 by Mulberry View

[Mulberry View]

What sort of cost is to be expected for a modest battery installed?

[JohnMo]

https://www.solar-hub.co.uk/products/sunsynk-lifelynk-all-in-one-s-2-5kw-hybrid-inverter-2kwh-battery?srsltid=AU7gw4Wfmv0CQ7E9o5jbAHEG7L0hf7RTpp81SWdFPNikp0QgveW1Guh9

 

Is about £1k, have a shop about

[Mulberry View]

1 hour ago, JohnMo said:

https://www.solar-hub.co.uk/products/sunsynk-lifelynk-all-in-one-s-2-5kw-hybrid-inverter-2kwh-battery?srsltid=AU7gw4Wfmv0CQ7E9o5jbAHEG7L0hf7RTpp81SWdFPNikp0QgveW1Guh9

 

Is about £1k, have a shop about

 

Looks pretty reasonable. The description makes this sound DIY'able. Is it as easy as plugging it in and away we go?

Edited Tuesday at 15:39 by Mulberry View

[JohnMo]

Almost, plenty of videos available on YouTube. Basically 3 wires to the consumer unit and a CT clamp I believe. Add one or add a few they just daisy chain together.

[Dillsue]

Have a read of the FIT guidance for generators so you get your set up correct. Adding an AC coupled battery between the generation meter and your consumer unit/incoming supply is likely acceptable. The guidance will also tell you if the change has to be notified to your FIt payer, which lots of things do have to be notified.

 

If your FIL already has a 4kw system he'll need to get consent from his DNO to add any more potential export such as a battery.

 

Don't be put off by the red tape as its all straight forward once you understand the constraints.......no one want to loose early FIT payments:)

[Andeh]

I'm in exactly the same boat myself, so watching with interest.

 

I figure a battery and AC inverter standalone, doesn't interact with my PV and the FIT meter which monitors them... So I hope not an issue!

[SteamyTea]

On 06/10/2026 at 08:20, Mulberry View said:

has since connected a Solar iBoost to it for the immersion heater

How well is the energy produced currently used?

May be worth having a look at what is happening before spending any cash.

[JohnMo]

22 minutes ago, SteamyTea said:

How well is the energy produced currently used?

May be worth having a look at what is happening before spending any cash.

That I would suspect depends on the cost of charging the cylinder - if you charge the cylinder only during cheap periods, and on a sunny day its charged via excess solar, then solar excess used to add heat to a water cylinder has a value equal to cheap rate electricity - any excess from the PV after charging the cylinder and direct home use is pretty much worthless. 

 

If however you don't charge the cylinder with excess PV, the energy stored in the battery is worth whatever expensive time periods that battery energy displaces.  So a simple E7 tariff, cheap periods cost circa 13p and expensive 33p.  Energy in battery is worth 33p, while energy pushed in to heating hot water is only worth 13p.  So effectively the energy diverted to the battery is worth 20p more than that directed to hot water.