question

jakudo avatar image
jakudo asked

Victron + Pylontech setting - understanding

Hello,

a company is designed a whole system for me and I would like to check/understand whether it is ok or not.

The setting they are going to install in my house:

  • 3x Multiplus II 48V/3000
  • 1x MPPT 150/100
  • 12x Sunpro 450Wp
  • GX monitoring (I expect Cerbo GX)
  • 3x Pylontech US3000C

I've read many articles on the internet, countless topics in this forum and facebook community and I'm still not sure how to understand some things (I'm not an electrician :) ), so I'd like to ask you for a help/explanation or just confirming that I understand it correctly or not.

From the Victron calculator I know that the MPPT with those panels will provide max 100 A.

1. Baterry + MPPT

Each US3000C can be charged by 37A - 3x US300A in parallel can be charge by 111 A total. 100 A < 110 A - so it is OK. And even if I add another MPPT (when I add another panels in future) and the current will be higher then 111 A, the inside BMS connected to GX will manage the current and it still wont be a problem. Is that correct?

2. Battery + Multiplus

This is where I get a bit confused. I've read (for example) this thread https://community.victronenergy.com/questions/127799/question-about-sizing-battery-and-usage-the-batter.html

and this article

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

and I'm not sure, whether the 3x US300C is enough or not. According to datasheet, the bartery can provide 48V*37A = 1776 W (3 batteries 5328 W). So if I have 3x multiplus, where each has 2400 W, the batteries cannot provide sufficient power if there is a 100% load. So I would need at least 4 (better 5) batteries for 100% power. Is that correct? Or am I missing something?


Thanks a lot for any explanation.

Jakub

MPPT ControllersMultiplus-IIbattery48v battery
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3 Answers
wkirby avatar image
wkirby answered ·

Indeed, by my calculations 9kVA (3x 3kVA) inverters would need 188A @ 48V.
188 / 37 = 5.1 US3000C modules.
So a bare minimum of 5x US3000C modules for this kind of inverter power. Better to have 6x modules to be able to provide surge power.

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jakudo avatar image jakudo commented ·
Thanks, just one question, why did you calculated with the 3 kVA and not the 2,4 kW?
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wkirby avatar image wkirby ♦♦ jakudo commented ·
3kVA is the capacity of these inverters. This is the effective DC power which will be taken from the battery.
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jakudo avatar image jakudo wkirby ♦♦ commented ·
ok, thanks a lot for explanation.
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hominidae avatar image
hominidae answered ·

...IMHO this is only relevant, if there are essential loads on AC-out1 that need that much power in case of a grid faiilure. In a scenario with a grid tied ESS, this decision is purely a coommercial one - how much energy can you shift from grid consumption to battery (provided solar intake is substantial to keep the battery at decent level - which will not happen often during autumn/winter season) for these extra peak loads supplied by extra batteries compared to their price.

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jakudo avatar image jakudo commented ·
Yes, of course. I know that it is not necessary since I'll be connected to the grid, so practically it won't matter that there will be not enough power from the batteries, however, in theory in case when grid shuts down (for whatever reason), the batteries wouldn't be able to provide enough power if I understood correctly.
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hominidae avatar image hominidae jakudo commented ·
Yes, but then your loads need to be connected to AC-Out1, not AC-in....and these need to be smaller than the peak, what the Multis can provide. Do you happen to know the numbers of your peak loads that need to be sustained?

Also, when in backup/offline mode, the Multis can provide some excessive power for a short time...see the data sheet ... this load needs to be catered for by the batteries (and suitables cables) a well.


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jakudo avatar image jakudo hominidae commented ·
Sadly no, I don't know the peak.

Yes, I know that when in backup mode, it can provide more power. So basically with the 3x Pylontech, it cannot meet the maximum power.

I will add another batterie hopefully next year, so I will have 5-6 batteries US3000C. Then it should be ok.

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hominidae avatar image hominidae jakudo commented ·
...you could try an measure that, now that you have the ESS running.

This is what I did, before I decided on the size of my setup. Luckily I had another grid-meter in place beforhand.and data for 2.5 years.

I now have a 3ph system with 5000kVA MP2 and 6x US3000C, which is sufficient for a substantials shift of grid energy...but for sufficient backup I'd need to at least double that and there is no way for this going green commercially in the near future ;-)

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jakudo avatar image jakudo hominidae commented ·

It would be really difficult to measure in my case. I have a heat pump, so the difference between min and max is huge. I have been writing down the total electricity consumption each month since we moved to our house, so I now in summer it is about 6 kWh/day and the max in winter is about 22 kWh/day.

I don't have the system running yet. The company, which is doing the installation has already installed the panels and the Victron is going to be installed on Thursday.

I wanted 3x MP-II 5000, however, due to some stupid Czech regulation it is not possible (or at least not everytime). I believe the 3000 would be enough.

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hominidae avatar image hominidae jakudo commented ·

...this is not about Energy (kWh) but Power (W, min/max(average per interval - suggest at least 10secs).

Once you have the Grid.Meter an the GX in place, it is not a big deal to start collecting measurements and inspecting/visualising the data history..all it takes is a RPi and a decent amount of data space to store the values. I use a set of Dockers (influxDB, telegraf, grafana) on my NAS, that is running 24x7 anyway.

Edit: A heat-pump will create a large power spike, when starting. Your installer should give a some hints on that. I suggest to leave it on AC-IN...for securing hot water supply during a grid failure, deploy an electric heater probe into the boiler (maybe there is already one, if your installer was more of an old fashioned guy).

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jakudo avatar image jakudo hominidae commented ·
No, I don't have an electric probe. The heat pump has oni installed inside itself as backup (both for heating and domestic water), so there was no reason to install another probe. Sure, I will install grafana and other stuff to monitor it :)
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thanar avatar image
thanar answered ·

You've run into a very important misunderstanding regarding how BMSs work in general. A BMS does NOT limit the charging or discharging current. If the current exceeds the set amount, the BMS will completely disconnect the battery. You don't want that. Disconnecting a battery when under load, can lead to various issues. That said, you should adjust the charging parameters accordingly on your system, so as the currents don't overshoot.

* There is a chance that the BMS inside the PylonTechs does communicate to the Victron ESS the real-time current limits, which would result in automatic adjustments, but that's not how BMSs work in general.

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hominidae avatar image hominidae commented ·

Yes, the Pylontech US3000C do actively communicate the allowed charge and discharge current to the GX, dynamically

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jakudo avatar image jakudo commented ·
ok, thanks for explanation
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