Adding an AC coupled battery inverter to existing Grid Tied PV system

[Bob Minchin]

I'm a retired electrical engineer who hopefully has not lost all his marbles!
I have a mature Grid Tied Solar PV system all MCS approved and collecting FIT.
I want to explore the pros and cons of adding AC coupled battery storage.

I don't want to lose my MCS/FIT contract
I don't want battery generated power to be exported to the grid.

I do want the batteries to charge automatically from surplus PV power
I do want the batteries to supply power to the home making the grid "supplier of last resort"

I'd hope that the above would be automatically provided by the AC coupled inverter. Is this correct or will only some inverters do this?

A very useful added feature in the event of a power cut would be if the battery inverter would satisfy the anti islanding system in the grid tie inverter allowings the PV panels to contribute power to the home. Obviously this would need the grid power to be isolated for all the usual safety requirements.

Sorry if these are all obvious questions but It's 10 years plus since I researched PV and I need to play catch up when it comes to battery storage.
If anyone can point me to background reading then I'd be very grateful.

Thank,
Bob

 

[Oldman22]

I like you have an existing FiT PV which I didn't want to give up, I fitted one of these. Solis RAI-3K-48ES-5G AC Coupled Inverter https://www.tradesparky.com/solarsp...ger/solis-rai-3kw-48es-5g-ac-coupled-inverter and some 5kw batteries https://www.fogstar.co.uk/products/server-rack-battery-48v-5-12kwh
You wont loose your FiT with this method, batteries will auto charge and supply the home when there is no PV output.
This inverter is only 3kw so kettle & toaster on together may well spike into grid use but only pennies. My daily average bill for last month was 66p and 46 pence of that was the standing charge. I've given you some basics, no doubt others will be along shortly to offer heaps of advice. Its a win win for me, I get to use all my PV or store it for later and I can export any I cant store (batteries full) to offset the standing charge cost.

 

[Bob Minchin]

Thanks very much Oldman22. your reply is a great help.
Have you tried your system in isolation ie to simulate a power cut. IF so did the Solis inverter keep the basic PV inverter from switching off and thus keep the panels producing power?

 

[johnb2713]

I did exactly what youre wanting to do as a DIY AC coupled battery using a Victron Inverter, look out my threads on here 'DIY Battery' or similar search.

https://electricianforum.co.uk/threads/diy-battery-is-alive.55797/

 

[Bob Minchin]

Thanks john. A lot to take in there. Will be reading later.

 

[Oldman22]

Thanks very much Oldman22. your reply is a great help.
Have you tried your system in isolation ie to simulate a power cut. IF so did the Solis inverter keep the basic PV inverter from switching off and thus keep the panels producing power?

Sorry but as I live 2 doors from a sub station and in the 50yrs I have lived here I think I can count on one hand the amount of cuts we have had that lasted more than 1hr. So I've not bothered with the abilities of the Inverter to island.