I have a 8kw Deye inverter coupled to 12 panels and 4 x 5.1 Deye batterries 20kw

These run down to 40% each night

Is it possible or even wise to add two more 5.1 batteries in parallel making battery power 30kw

Advice needed please

33 minutes ago, Johnno Mac said:

I have a 8kw Deye inverter coupled to 12 panels and 4 x 5.1 Deye batterries 20kw

These run down to 40% each night

Is it possible or even wise to add two more 5.1 batteries in parallel making battery power 30kw

Advice needed please

Not worth it. Just stay with the 4. Just set it to 20% cut off and get the extra 4kWh. You have lithium, not lead acid. And you should be able to add 2 more if you really want to, without issues.

49 minutes ago, Johnno Mac said:

I have a 8kw Deye inverter coupled to 12 panels and 4 x 5.1 Deye batterries 20kw

These run down to 40% each night

Is it possible or even wise to add two more 5.1 batteries in parallel making battery power 30kw

Advice needed please

Yes, it is possible to add more of the same batteries in parallel - Deye inverters typically support up to 8 to 16 batteries in parallel (e.g., 48V models), depending on the specific model, BMS limitations, and firmware.

As @Denns mentioned is it worth it? If the aim is to get rid of Eksdom and you have the money - absolutely do it, and add some solar panels.

1 hour ago, Johnno Mac said:

I have a 8kw Deye inverter coupled to 12 panels and 4 x 5.1 Deye batterries 20kw

These run down to 40% each night

Is it possible or even wise to add two more 5.1 batteries in parallel making battery power 30kw

Advice needed please

You don't seem to need it for now, but I'd run this system through the Winter to see how deep you need to discharge during longer colder nights. If you're planning to add loads like more heaters or aircons, or the tumble drier, or if you need to heat up your geyser from colder overnight temperatures, etc. then the extra batteries could come in handy.

Just set your batteries to 20%, just ensure your PV is enough to fully recharge your batteries the next day. You may need to increase your charging rate to achieve this, risking that you may run out of PV, specially on low sun days. So long before I would add batteries, I would just add more PV to the max.

4 hours ago, Johnno Mac said:

I have a 8kw Deye inverter coupled to 12 panels and 4 x 5.1 Deye batterries 20kw

These run down to 40% each night Is it possiblIs it possible or even wise to add two more 5.1 batteries in parallel making battery power 30kw

Let's just get some clarity on this - are you concerned about the 40% SoC discharge level, or are you concerned that the SoC might drop even lower?

Although I personally would prefer my batteries to not regularly drop below 50% SoC, most Forum members are quite comfortable with discharging the batteries to 40% SoC, or even substantially lower. I think there is general agreement that one can work on an occasional discharge down to 20% SoC without serious damage to the batteries, as long as the temperature during charging or discharging is kept between 15 degrees C and 30 degrees C, AND the rate of charge or discharge remains below 0.5C (this "C" is not temperature, but current, with 0.5C meaning not more than 50% of the nominal (rated) current.

I agree with the advice given by @GreenFields - monitor your system during winter, and buy some additional batteries and a few extra solar panels if the batteries regularly drop below 40% (or 20% if you do not expect maximum "life" out of them...

6 hours ago, Johnno Mac said:

Advice needed please

Show your 24h load profile.

2 hours ago, frivan said:

Show your 24h load profile.

Agreed - and also tell us what power rating your 12 solar panels have, and which way they are facing. Oh, and where do you stay - living in Cape Town would have quite different solar requirements than if you lived in Pofadder (or e.g. Bloemfontein, where I live...)

Thanks for your advice

I live on Underberg KZN and all panels face due north

Charge at 6Kw on a good day but a day like today only 1.5 Kw.

I'm waiting for Deye battery prices to drop (very funny)

What model Deye batteries do you have? I don't see batteries coming down in price for a while, they have reached a nice equilibrium price. If anything potentially a price increase due to increased raw material costs as well as the removal of the 6% vat rebate from Jan 2027 onwards. If you are able to and want to get more batteries i would suggest getting them sooner than later. If you are more budget conscious i would suggest rather getting 4 more panels and have two strings of 8 panels.