Analysis of my 4.14kw system

[curryitr]

Hello!

I’m new to the forum but would love some help or advice with my proposed solar setup and if I’m missing something. I live in Africa where we get lots of sunlight but have a very unreliable grid.

I’m looking at using 9 JA solar 460 watt panels. 6 of them will be set up as 2s3p going to a victron 150/100 SCC. The other 3 will be in parallel and go to a Victron 100/50 MPPT SCC. These will charge 2x 24v 2.6kw server rack style Pylontech LFP batteries for a total of 5.6kw/h of battery backup. These will feed a multiplus 3000va inverter charger. A Cerbo GX will manage all the different devices. And all 24v DC connections will be to a Lynx bus bar.

The batteries connect to the Cerbo via a ve.can cable, the multiplus connects via ve.bus, and the two charge controllers will connect to the Cerbo via VE direct cables. According to what I have read, the two charge controllers will be able to communicate to each other and to the battery’s internal bms to manage their charge current.

I will have 15amp fuses on each solar panel, 40amp breaker between the 6 pannels and the 150/100 scc and a 40amp breaker between the 3p panels and the 100/50. This is because 3 panels in parallel creates 33 amps. Then there will be mega fuses between the charge controllers and bus bar, a DC breaker between the batteries and bus bar, and mega fuses between the bus bar and inverter.

I will be using 10awg with MC4 connectors for the panels. The amperage of each panel is 11amps so I’ll be at 33amps on the 30amp rated mc4 connectors… However, the runs to the SCCs are only 10-15 feet so I’m hoping it will be ok. Given my location the panels should produce 16-18kw/h per day and my daily usage is around 13kw/h.

I will still supplement with power from the grid but I’m hoping this will save us on a lot of electricity and offer us a good backup for our many power outages and brown outs. We use around 4-5 kw/h at night so that would use up most of the battery capacity on an average day but during power outages we would reduce our nighttime usage down to around 2-3 kw/h to try and make the batteries last.

Am I missing anything that you all can see?

Thanks!

 

[OzSolar]

I will be using 10awg with MC4 connectors for the panels. The amperage of each panel is 11amps so I’ll be at 33amps on the 30amp rated mc4 connectors… However, the runs to the SCCs are only 10-15 feet so I’m hoping it will be ok.

Welcome to the forum!

I would steer you away from this. It will work for a while but will fail in a not so pleasant way when you're least expecting it.

NEC requires wire to be sized at Isc x 1.56 but there's talk of changing that to Isc x 1.25.

Your Isc is at least 1 or 2 higher amps than Imp so using 13 x 1.56 = 20.3 amps per string.

In practice, your 3P array will be at "NOCT" most of the time. For easy math we can use Imp x .8 = 33 x .8 = 26.4 amps but that still too close to be on 10 AWG wire to be trusted for solar.

 

[curryitr]

Welcome to the forum!

I would steer you away from this. It will work for a while but will fail in a not so pleasant way when you're least expecting it.

NEC requires wire to be sized at Isc x 1.56 but there's talk of changing that to Isc x 1.25.

Your Isc is at least 1 or 2 higher amps than Imp so using 13 x 1.56 = 20.3 amps per string.

In practice, your 3P array will be at "NOCT" most of the time. For easy math we can use Imp x .8 = 33 x .8 = 26.4 amps but that still too close to be on 10 AWG wire to be trusted for solar.

How should I resolve this? If I run 3 into 1 parallel adapters near the panels but then run 8AWG wire from that point to the charge controller will that be suitable?

 

[curryitr]

Options I have thought of are:

1. On my 3 into 1 parallel connector, cut off the single MC4 after they merge and have that go directly into a 40amp DC circuit breaker. On the other side of the circuit breaker I will run 8awg the rest of the way to my SCC.

2. Cut all the MC4 connectors off and merge the panels using crimps to ring terminals on a M8 Bolt and nut. I would encapsulate the connection in clear silicone grease inside of shrink wrap and then tape over that for good measure.