Does this 3000w 12v configuration work; and how should this kind of system be grounded?

[eriemountain]

I'm cobbling together an off grid system with some renogy batteries I bought on sale, which cannot be wired in series (something I did not understand the implications of at the outset). I intend to eventually build a more sensible 48v system, but I'm the meantime I'm going to get started with what I have.

This is what I have so far. I'm struggling to understand grounding and how to do it properly. I would also appreciate knowing any red flags this setup raises:

8 panels @ 200w (12v x 15a)
2 paralleled series of 4 = 48v @ 30a
15a mc4 in-line fuses on each series positive
10 gauge wire to charge controller w/
In-line On/off switch on positive
100a mppt charge controller
4 gauge wire from controller to 600a pos & neg busbars w/ 100a in-line breaker on pos
4 @ 0 guage wires from busbar to 4 li ion 12v 100ah batteries (pos and neg)
125a terminal mounted fuse on each batt positive
0/4 cables from busbars to 3000w 12v inverter w/ 300a terminal mounted fuse at inverter pos

To ground the batteries do I just bury a copper bar into the ground nearby and run a wire from the neg busbar? If so, what size, and how deep? Etc.
Do the panels need grounding?

Thanks in advance!

 

[rmaddy]

All of your fuses are too small. They are the same as the corresponding max amperage you will see on the wire which means your fuses will pop during regular usage.

For your 100A SCC you want a 125A fuse. 4AWG wire is OK as long as you keep the wires from the SCC to the bus bars short (under a few feet).

Your 3000W 12V inverter can pull up to 300A from your batteries. So you want a fuse that is about 375A which means a 400A fuse.

You have 1600W of solar. On a 12V system that means about 114A of charge current. Your SCC supports 100A. Your 100A controller can make use of about 1400W of solar input. So that's actually a good amount of over paneling since you rarely get a full 100% out of your panels.

What is the max PV input voltage of your SCC and what is the Voc of your panels? What is the coldest temperatures you will ever see? You need to be sure your SCC can handle your panels in 4S2P.

Not sure about the best way to ground. But you may find the following helpful:

Grounding Made simpler - Part 2: Stationary Systems

To get the paper, click on the orange button at the top of the screen. The subject of grounding is a complex, multifaceted subject, that is often treated as an after-thought but needs to be considered from the beginning of the design and build...

diysolarforum.com

 

[eriemountain]

Very helpful reply, thanks!

The scc is this one: https://ca.renogy.com/rover-100-amp-mppt-solar-charge-controller
which has a max pv input rating of 5200W/48v.

The panel (https://ca.renogy.com/200-watt-12-volt-monocrystalline-solar-panel/) specs say
Open-Circuit Voltage (Voc): 27V
But they are sold as 12v panels? How does that work?

We're in the Kootenays, so it rarely goes below -15c in the winter, it might snap down to -20c once or twice a season. The batteries have a self heating function to protect against cold charging.

I'll order some larger fuses. In the meantime, I assume the ones I have will suffice if we keep the load under 2000w?

Thanks again.

 

[Rednecktek]

The panel (https://ca.renogy.com/200-watt-12-volt-monocrystalline-solar-panel/) specs say
Open-Circuit Voltage (Voc): 27V
But they are sold as 12v panels? How does that work?

Yeah, it's marketing speak. There's no such thing as a "12v" panel, there's a panel that will produce enough voltage to charge a 12v system. Likewise there's no "24v" panel, just panels that create enough to charge a 24v system. That panel will produce enough for a 36v system, but isn't high enough for a 48v, so you can use it for anything 36v and down. Your controller will do the voltage modification bit out the other end.

In your case the VmP on the panel isn't always going to be enough to charge a 24v battery if it's trying to do it's boost or equalization charge which is done at a higher voltage. Remember, it needs to produce battery voltage + a few volts to work.

We're in the Kootenays, so it rarely goes below -15c in the winter, it might snap down to -20c once or twice a season. The batteries have a self heating function to protect against cold charging.

The panels are going to make higher voltages as they get colder, so the concern is not only the batteries but if your panels get cold enough will they produce a higher voltage than you SCC can take. There should be a temperature coefficient listed for the panels that you can math out how high the voltage could be.

I'll order some larger fuses. In the meantime, I assume the ones I have will suffice if we keep the load under 2000w?

If your panels hit full clean sun it's quite possible to pop the fuses. Having the load down will help though.

Thanks again.

 

[rmaddy]

The scc is this one: https://ca.renogy.com/rover-100-amp-mppt-solar-charge-controller
which has a max pv input rating of 5200W/48v.

The max PV input voltage is 150V. Your panels have a Voc of 27.0V. In 4S they will be 108V. At -20ºC the Voc would be about 123V. Since that is obviously still below 150V then you will be fine with a 4S2P array of those panels.

I'll order some larger fuses. In the meantime, I assume the ones I have will suffice if we keep the load under 2000w?

That's fine for the inverter but if you get sufficient solar from your panels you might get close to the 100A charge current which might blow your 100A SCC fuse.