ESS Design/build - See my diagram of components and configuration if best method?

DIY
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ESS Electrical Layout Neil.pdf (792.5 KB)

Hi All,

Seeking advice/confirmation of an ESS I’m building to install at my home using some Victron parts I already have surplus from jobs at my company. So, where possible, the system is being designed around what I’ve already got to make use of these parts (as listed below).

I’ve attached a drawing to detail the components layout and basic connections of my proposed system and would like to know if all think this could be a suitable option or what/how it could be ‘better’ from different products to use or configurations? I can then buy the remaining parts or reconfigure system based on the advise. Further details listed here below;

Infrastructure existing/installed; 7x 250W solar panels supplying PV inverter coupled to AC grid with feed-in metering. 6x 250W solar panels (from a redundant system) to supply SmartSolar MPPT 150/85

Parts I already have for ESS; 4x LiFePO4 Battery 12.8V/100Ah, 2x BMS Lynx Smart 500, SmartSolar MPPT 150/85 VE.Can, 6x Solar panels 250W, Generator 8KVA, Auto Transfer Switch, Android tablet.

Remaining parts in question: Multiplus 24V/5000/120, Cerbo GX

Typical maximum demand from AC loads: 5KVA

ESS functionality priority: Power backup when loss of mains/grid input. (All AC loads switched to inverter from batteries, generator enabled when batteries minimum Soc reached to supplement AC load and charge batteries with excess VA from generator.)

Secondary priority: Low level of self-consumption from 24VDC batteries and MPPT solar. (Batteries not to be cycled below approx. 80% Soc and always need to remain near to fully charged ready for use when grid fails, AC-coupled PV inverter is already connected as self-consumption and excess feed-in back to grid.)

Question 1: Is the MultiPlus 24/5000/120 the correct product? Is there benefit of configuring batteries to 48VDC to allow for a better suited product as the inverter/charger. Note that I require relay switching option for generator control from whichever product may otherwise be suggested I could use.

Question 2: Can/should the solar array as pictured supplying the MPPT (150/85) be instead configured as 3x 2-string series parallel therefore inputting the controller at 225Voc, 53.16Isc? Will the controller safely limit the input voltage to 150V when exceeded?

Question 3: Should I upgrade the existing solar PV inverter coupled to AC for a more user-controllable inverter and one which will connect to Victron MultiPlus for synchronizing? I don’t believe the existing inverter can be connected elsewhere in any AC circuit input/output without it detecting a grid failure and shutting off via anti-islanding function. The main objective of a new inverter being installed on this solar array coupled to AC would be to continue inputting it’s yield when there is a grid outage. Either way, I can do this upgrade at a later date if deemed worth while however I just wanted to mention this incase perhaps this may have come into account in considering the suitable and future proofed option of what main charger/inverter the ess should utilise (like the MultiPlus.)

Thank you in advance of any response to my post here. I will try to return and respond daily to any info provided here with queries.

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Hi answers to your questions

1: the higher the voltage the lower the current, so thinner cables and you need one less lynx bms

2: the mppt voltage is a hard limit stay well below that with VOC! 250v will blow it up, keep it 3s

3: you can use a ac pv inverter on ac out side of the multi, but it has to support frequency shift and it needs to be smaller than the multi (stay below 4000w/5000va)

If you want Pv on ac in, use an energy meter on it if its not a fronius or other supported brands

also a grid meter is adviced for ess

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Consider a Quattro rather than a MultiPlus, it has two ACin so you can save the AC transfer switch.

You could consider 48V, would let you use smaller fuses and cables, but then has other implications like the PVs 3s Voc not being much higher than the typical 54-56V in a 48V system

The 50A PV MCB will never trip, your Isc is only 17.7A. Personally id not fuse it at all, theres no point in single or two parallel strings, the fuse rating would have to fall inbetween Impp and Isc and thats a very narrow window.

If you wire it up as drawn, the bottom battery will receive a higher voltage from the MPPT, since its directly connected to it. The top battery, due to the added cabling up to the inverter and back to its own BMS will receive less charge voltage. The top battery will lag behind with SOC. Personally i would not botherr with a redundant battery setup in this case, since you also got mains and genset as alternative power sources should the DC side fail. But rather think about using a bypass switch on the AC side