question

Hello @S_Forsberg,

I don't understand what you mean by "... The Victron guide on Pylontech only covers off grid use which is more demanding compared to ESS. ..." - because as far as I understand and know ESS is not designed for Off-Grid usage. And I am wondering a little bit about your PV system with 13 kWp modules and an inverter for 8 kW.

There are two basics for minimum battery capacity:

1. Victrons document about Pylontech
2. Victrons document AC-coupling and the Factor 1.0 rule

With basic 1 you get a minimum number of four pieces US2000B per Multiplus-II 5000 with gives for a 3-phase system 12 pieces.

With basic 2 you get based on the rule from Victron: per 1,5 kWp PV there should be Liion batteries with 100 Ah

PV with 13 kWp / 1,5 kWp = 8,6 | 8,6 * 100 Ah = 860 Ah | 860Ah x 50 V = 43 kW battery capacity

Which gives you in thinking of US2000B units with 2.200 W usable capacity 20 units US2000B or when using US3000B with 3.200 W usable capacity 14 units US3000B

In case you calculate with your PV inverter of 8 kW you need 12 units US2000B or 8 units US3000B.

Keep in mind this are all recommendations from Victron. But there are many additional factors which have to be respected. I found out, that the surrounding temperature of the place where the Pylons are will have an influence to the BMS which limits at higher temperature the charging current. Which will directly influence the possibility of the ESS system to store energy in batteries or have to feed it back to the grid or have to downforce the power of the PV system. So the answer couldn't be just a simple figure in number of Pylontech batteries. It is a complex system.

Concerning to your question: "... Can I add more US2000 Plus modules several years later even if they have different state of health? ..." I think only Pylontech can give an answer because they know in detail about the bulitin BMS and if and how the BMS can handle this.

And about: "... Can I add other battery types in the same installation? ..." - I think in case to mix different brands, different BMS etc. the answer will be: No

In case to mix different capacities but same brand there was a discussion here about, but I don't find it just now to link you to it and I can't remember the end of it. In my understanding keep a system as simple as possible I wouldn't mix different battery types.

DayAndNight

Looking forward to a comment on this from @Guy Stewart (Victron Community Manager) :)

@Ned Yu (Pylontech) is more qualified than I am to comment :)

4 x US2000B's seems a bit low to me on a system of that size. I would expect things would work fine as long as the grid is connected, but you could have issues in a grid blackout (AC PV leading to battery overvoltage/overcurrent near 100% with loads turning on and off, when there is no grid to help stabilise voltage).

Adding new batteries to old is always a risk. Might be fine, but definitely always better to have them as close to each other as possible.

I will have a few Pylontech's arriving shortly for a new Victron Professional Online Training Course, so will have the chance to do some more edge case testing then.

@Guy Stewart (Victron Community Manager) Thanks for your invitation.

Hello @S_Forsberg, to answer your questions:

1. For 4*US2000 battery system. The maximum discharge power is 9.6KW from the battery for 54 minutes. And in the case of communication with the inverter, it can only be realized in the off-grid mode, grid blackout and no PV power available (BMS considers it as an emergency situation)

In your system, most of the time, the inverter will listen to the recommended charging and discharging value of the battery BMS, which is a 0.5C charge and discharging rate. 1.2KW for each US2000. Four batteries is only 4.8kW. Other power will withdraw from the grid, or PV. If this can meet your requirements, you can start with four US2000 batteries.

BTW, If Our batteries work at below 15 °C or above 45 °C, BMS will limit the charge and discharge rate to 0.2C. A good installation location is crucial to the operation of lithium batteries.

2. Can I add more US2000 Plus modules several years later even if they have different state of health?

Yes. For our 48-V system, you can add new batteries to the old system at any time. New batteries with better SOH performance will share a bigger charging-discharge rate than old batteries.

3. Can I add other battery types in the same installation?

Our Phantoms, US2000 and US3000 are compatible. You can mix use these batteries in one system.

However, our system can not add other brands or types of batteries.

Hope this information will help

Regards

Ned

ive a similar Project with 5x uc2000c.

In the room with the components is a constant temperatur of 31°C, will that be a Problem or shuld i place these somewhere else wich results in longer Cables from the MPII to the Grid and Loads.

thank you

the next question is for the Battery cable.

victron writes 70mm2 but pylontech uses 25mm2 between the units and for the connection kit.

do i have to build new ones in 70mm2 by my self?