am I gonna fry alligators or shoot potatoes?

[HellOnAStick]

hi,
im trying to figure out what to do with the 8 x 110 watt 18.8vmpp 5.9 Impp solar panels that i've acquired. I have a little background, and a victron 100/50 mppt controller, a 24v 240ah lithium battery i created for the panels, and a victron phoenix 24/500 900watt inverter for charging and other ac loads.


i'm still fighting the idea that a 18.8v panel is 12v. if i run 4x 2s panels and parallel each series at a combiner box, i'm making the assumption that from the combiner to the MPPT controller (panel is 18.8vmpp 5.9 Impp) should have (optimally) 37.6v and 23.6a available. if i series-parallel these same 4 x 2s outputs, i should have 75.2v 45.2a.
one of the gaps in my knowledge base is how to manage loss with series or parallel connections, the other would be, my understanding of efficiency in this regard. i work with 48v 26ma systems, but my understanding of "good balance" between A and V as it pertains to solar is lacking. give me a leg up and I'll ride into the west on a solar powered steed.

[chrisski]

For the panels, 4 in series, 2 of those strings in parallel would be 4S2P. That would be for a Victron MPPT if you looked at the tech data and see how much the voltage output would go up as it gets colder to the record low temps of the area you're in.. Exceeding voltage can be bad for the MPPT.

You talk about 4S2P vs 2S4P. Both of those exceed battery voltage + 5 volts that the Victron MPPT needs to start working. The 2S4P option would be better for shading, but with a higher amperage, perhaps driving thicker cables. 4 in Series and 2 in parallel would produce higher volts and need thinner wires. I found once I got thicker than 10 gauge wire, connectors became an issue.

Perhaps there is a more loss for the 4S2P option. I have 3S2P, and if there is a loss, I don't notice it. My panels produce power only when the battery is charging, and on my RV camping trips, I've never went much past 1 pm to charge my batteries with a max draw of 165 AH at 12 volt. Maybe they would have charged 30 minutes quicker had I went 2S4P.

What really drove my panel placement was shading from things like AC and roof space. Depending on the size and shading of where you're going to place your panels, you can fit a little over 1400 watts of panels configured to charge a 24 volt battery.

Think it was Mike who told me, the magic of the MPPT controller is you get to arrange the panels in any configuration as long as you don't exceed amps or voltage. Not so with a PWM controller.

I like the Victron 100/50. I have one of those. I have two 100/30 SCCs.

[Mike90250]

The simple rule of thumb for MPPT controllers (real ones, not toys) is that the PV array Vmp should be about 2x the battery voltage. This gives the controller headroom to work on hot days when the PV voltage droops, and should be far below the kill voltage of the MPPT max input.
The 2nd rule of thumb is Watts in = Watts out. ( given that the Vmp is well above the battery charging voltage )

And the MPPT magic has only to do with the Voltage input - enough voltage to charge, but not so much as to kill the controller. MPPT controllers internally regulate their output amps to their safe limit. Getting too hot - the amps get cut back till it's safe Some controllers let you program the max amps they could output, so you don't fry a small battery