Hello everyone,
I'm currently planning a 18kWp 3x MP2 48/5000 100% offgrid system.
For the 15 kVA Multiplus I need a minimum battery size of around 15 to 20 kWh. If I install an AC-coupled inverter (e.g. Fronius Symo), the minimum battery size increases to 32 kWh according to the 1:1 rule.
Does this rule also apply to an 100% off-grid system or only to the EES?
15 or 20 kWh is more then enough for our enegy consumption over night.
Thanks for your support
Timo
Battery capacity is irrelevant.
Can the combined batteries Charge and discharge current limit do the amp rating needed for the system?
Off grid is different to ESS. The 1:1 rule applies to AC PV sizing compared to inverter sizing. In other words the AC PV can only be 15kVa if the inverter is 15kVa.
You can add more to DC mppts.
Alexandra is right, 1:1 rule is for ac pv only not for batterys or dc pv
But if you are planning a 100% off grid system, 15-20kw battery is to small, grid connected it should already be about 24kw
I get the Inverter size in the 1:1 rule.
But in capture 3 of the rule.
https://www.victronenergy.com/live/ac_coupling:start
There is also a Regulation with a min. battery size.
1,5 kWp installed AC PV power requires 4.8 kWh of battery storage:
100 Ah at 48 Vdc
200 Ah at 24 Vdc
400 Ah at 12 Vdc
Each additional 1.5 kWp of AC PV will require an additional proportional 4.8 kWh increase in battery storage.
My planed Battery can do all the max. currents.
Hi @tiku
In your planned "100% offgrid system", why use ac-coupled pv at all? By specifying that, you're adding recommended 'constraints' to your options and the need for frequency control. We don't want you back complaining that your appliances don't keep the right time, and it fights with your genset (if you plan one of those).
Victron DC mppts are very efficient, and you can choose your own preferred battery size. The RS models can handle long pv strings.
Not sure why 3x Multis. If for 3 phase loads I'd consider changing them to single phase. You can build awfully large offgrid single phase systems that are very simple to monitor and operate. The KISS principle..
To add to JohnC answer, I would ask you: what is your overall project? Are you planning to use specific loads at day time? Which loads at night time?
This is cheaper, easier to install , and victron does advertising that they work together with Fronius.
We need 3-phases because of the existing electric installation of the buildung, the existing electric motors and the wallbox.
At night time we have no relevant loads, maybe some lights. And also at daytime we need the power only when the weather is good, never at rain or fog.
My question is, why have the battery size to be bigger when I use an AC-coupled inverter. I guess the frequency shifting needs more time, is this correct?
And is this also with an Fronius inverter, or can the cerbo control the Fronius via the dataconnection.
I assume the minimum battery capacity results out of the max. charging current that can occur when AC coupled PV is attached.
Just count up what max. current you could reach if 15kWp is installed and fully delivering power.
Then you reach currents in the range of the max. the 3x MP2 can load/charge, so 210A. A 15kWh battery (most likely a 16S LiFePO4) with 300Ah should not exceed 0.5C, so 150A continously.
The point is now, if this charge current can be reduced by increasing the frequency just a little bit for the AC coupled PV inverter, or if this is not possible....?
