20kWh Battery Retrofit Advice

dmigsy · 02-02-2026 02:00PM #1

Hi all,

Looking for some up to date advice on the best way to add ~20kWh batteries to my system before I go and get quotes. Don't fancy DIYing this.

Would like to have an automatic switch to battery in case of power cuts too. Currently setup to manually switch the house over to use a petrol generator in power cuts.

Current Setup:

Panels: 6.4kWp
Inverter: SMA Sunny Boy 6.0 (String inverter)
Diverters: Zappi V2 (1 EV but will add another at some point) and an Eddi
Grant: Already claimed the SEAI grant back in 2021
Location: Wexford
Heating: OFCH but have a few electric rads too.

Current usage & recommended plan from EnergyPal.

Estimated Annual Import

11,318 kWh

Average 30.92 kWh per day

Estimated Annual Export

1,851 kWh

Average 5.06 kWh per day

HDF Data Quality

365 days

Total 365 days in HDF file

Best Plan Annual Cost

€2,085.6-

Flogas - Smart Fixed Day & Night Electricity

Libbi looked like a handy option (from a day to day usage perspective since I use the myenergi app already) but also an expensive option and doesn't seem to power the whole house during a cut? Any thoughts on what the best route would be for my setup that would be significantly cheaper/better eg replace inverter / add storage inverter etc.

Thanks in advance!

Water John · 03-02-2026 08:13PM

Would a used EV battery be an option?

dmigsy · 03-02-2026 11:13PM

https://www.boards.ie/discussion/comment/124203296#Comment_124203296

Doubt that's the best option available. Big batteries have really come down in price. eg https://www.nkon.nl/en/nkon-ess-pro-51-2v-32kwh-thuisbatterij.html?

At these sorts of prices I'd likely just buy new. More looking for a steer on whether replacing inverter or adding a 2nd inverter will make more sense. I'll contact a few installers anyway.

graememk · 04-02-2026 10:42AM

https://www.boards.ie/discussion/comment/124203934#Comment_124203934

Replacing the inverter with a hybrid keeps you in line with the NC6 on the ESBN side.

You don't need to send in anything new if there's no change in the power of the inverter.

Also EV batteries are not worth it. That's well on the enthusiast side, well past DIY.

dmigsy · 13-02-2026 03:46PM

Still waiting on responses from the couple of installers I contacted - doing brand new installs is probably more attractive to them than upgrading/replacing/amending an existing one. After doing bit more research I think I'll probably add more panels too since I have the space on the shed.

Add 5.6kw more panels to bring up to a total of 12kW. My current 6.4 array never hits more than 5kW output even on the sunniest days.

Then for inverter, this DEYE can apparently handle the 12kW of panels. This would replace the SMA 6.0 string inverter I have today. Looks to be compatible with the NKON battery too

DEYE 6KW (SUN-6K-SG05LP1-EU) 6kW Hybrid Low Voltage

NKON Battery32.15kWh 51.2V ESS Pro

SteelyDanJalapeno · 13-02-2026 11:49PM

https://www.boards.ie/discussion/comment/124232998#Comment_124232998

Are you sure that inverter can handle all those panels? I see 7800W on the following on the spec

• Rated output power: 6 000 W (6 kW)

• Max PV input power: 7 800 W

• Two independent MPPT inputs

• Battery voltage range: 40 – 60 V

• Max. charge/discharge

dmigsy · 14-02-2026 09:53AM

Sorry, left out a bit of the product code. It would have to be the SUN-6K-SG05LP1-EU-AM2-P

Max PV Access Power: 12,000W
Max PV Input Power: 9,600W

https://www.deyeinverter.com/product/single-phase-low-voltage-hybrid-inverter/sun3-6-5-6-7-7-6-8-10ksg05lp1euam2p-3-610kw-single-phase-2-mppt-hybrid-inverter-lv-battery-supported.html

Would have be careful of not maxing out the voltage limits per MTTP going that route too.

unkel · 16-02-2026 05:12PM

https://www.boards.ie/discussion/comment/124234540#Comment_124234540

On that deye / sunsynk you can put parallel strings on each MPPT, so the voltage limit is not an issue

20kWh Battery Retrofit Advice

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