bmc123 avatar image
bmc123 asked

Off grid upgrade/extension suggestion


Looking for some ideas on how to achieve an extension/upgrade to an off-grid system.


3 years old.

15kVA quattro

150/100 MPPT

Fronius primo 8.2

13kW PV

DC and AC coupled system.

8x BYD B-Plus 2.5 (20kWh total)

We wish to increase the battery capacity however stock of the same type is hard to get. Don’t wish to replace original batteries at this stage.

Also wish to increase the solar, no issues there.

Open to adding another Quattro and therefore having higher power available in the system, along with a new additional battery bank, additional MPPT and extra solar.

Is this our only option, or there any other methods of adding capacity we should consider?

MultiPlus Quattro Inverter ChargeroffgridBYD
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johanndo avatar image
johanndo answered ·

In general, adding storage capacity is not an issue as long as you use the same chemistry, not necessarily the same cells. The added battery should have the same characteristics (cut off voltages, absorption/stop charge, float voltage, stop discharge voltage) Your new battery should have a own BMS, you must think of how you want to manage disconnects and if you want them reported upstream to the energy management (cerbo).

As long as you connect the battery in parallel, and you charge it to roughly the same level as your old battery before connecting, all will be ok. The current will be shared among the batteries according to their capacity / inner resistance, parallel circuits share the same voltage and are current dividers. After a charge cycle the batteries will be equalized / in sync regarding SOC. Make sure your new pack has a BMS that takes care of cell voltages and balancing and it has means to disconnect the pack in case of errors.

You always can add more inverters and more solar capacity.

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