Need Help Deciding If / When / Where To Place Fuses (And What Type) In Solar System

Each pair of panels (2 in series) needs it's own 10A fuse or circuit breaker. You need 6 circuit protection devices.

If one panel develops a fault, all the other panels can backfeed it and and cause a fire

in your case, every time you complete wiring 2 panels in series, you need a fuse or breaker. Since you seem to have used cables that have Y connections and have kept parlleling them, you are likely putting 34A into 12ga PV wires rated for 15A That's not good .

You really should have a 6 channel combiner box, so each series pair of panels feeds all the way to the box, where there is a circuit breaker, Breakers are nice, because you can very quickly diagnose 1 bad string of panels.

You need to not wire the panels together with Y connectors which risks overloading the 15A wires with 34A. But it's your life, just don't invite me in for a cold one on a sunny day.

Thanks for the info! If I may ask, then, what good is the 15 amp fuse built into each panel? Aren't they supposed to blow rather than cause a fire?

I used these Y splitters to parallel each 2 pairs of panels together, thus giving me 3 sets of 4 panels running at 11.44 amps (max) per each set of 4. So, while the panels themselves likely have 12ga coming out of them, they are all feeding into -- at least according to Amazon -- 10ga splitters rated at 20 amps each. (All cables running from my splitters onward are also sized at 10ga, btw.) THEN, to join my 3 final sets (of 4 each) together, I made my own 3 way splitter (x2 -- one for positive, one for negative) by taking 3 ends of this and feeding them into this, then this, and then out to this, which is now 8ga cable rated for 55 amps. Thus, I believe I am within normal operating parameters, no?

The six 10 amp fuses as previously discussed aside, are there any advantages to putting, say, 15 amp fuses before the junction box I just spoke of, on the 3 lines, if I were to keep my 3 way splitter the way it is (and not convert it to the 6 channel combiner box you speak of)? Would three 15 amp fuses not help protect against backfeed throughout those 10ga cable lines, from the 3 way splitter backwards, toward the 2 way splitters?

Thanks again for the help. I have always been careful to not overload my setup via amperage. But it was not until recently that I started appreciating the need to install fuses!

I have never seen panels with internal fuses in their J-Boxes.

When I suggested 10A, its because :
it's more than your max amp Isc 6.24A, less than the 15A & is a standard size.

Good for you to be changing ( increasing ) the wire gauges as you parallel panels.

The fuse rating on PV panels is not for the wire protection, it's to protect your panels from backfeeding a failed panel. You have SIX parallel strings and require SIX protection devices. Less than one OCP (over current protection) per panel string, leaves you vulnerable to a fault .

Not to mention that the NEC states if there are more than 2 parallel strings each string requires an over current protection or fuse.

You mention "36V System", are you going to be charging a 36V battery? The panel specs are what you'd typically use for a 12V system, or 24V when wired in series as you've shown.

Fortunately, I had enough money to invest in an EPEVER 60A MPPT Charge Controller, thus allowing me to stick with my 12V battery setup. =)

You are correct though, these are your typical 12V system solar panels (see here).

If your charge controller is the one with 150V max PV voltage input, you could wire them in 6S2P (six in series, then two of those in parallel) and do away with the panel fuses altogether. 6 x 21.6 is less than 130V.

Edit: I think you may have too many panels for the CC. 12 panels x 100W = 1200W, and an MPPT controller would get you around 90A, It would be less due to the horizontal orientation, but have you taken this into account?

I thought about doing it that way, or possibly 4 in a series, then 3 of those in parallel, but I went with the way I did because of the amount of shade I regularly endure. Basically any number of combinations of sunlight hit the roof of my RV, from some in the front, but not in the back, some on the left, but not on the right, etc. I figured, in the end, that if I stick with two panels per series, I could squeeze the most sunlight out of my system at any given time.

You are correct though, my charge controller does have a max of 150V.

Shade (and fuse) issues aside though, are there any distinct advantages to going 6S2P vs 4S3P, or 2S6P, etc? Do predominantly series-based setups yield more electricity than parallel-based ones?

Yep, definitely already factored in a lot of math as I grew from 2 panels onwards. Basically for awhile I was at 10 panels, which rarely output more than 750 watts total. At an average of 13.5 volts, I basically saw a maximum of 56 amps at the battery. Of course, with the final two panels, I am aware that I will now be maxing out my controller, as I will be pushing an average maximum of 67 amps to it. But that's only during peak, peak, peak times of the day, from maybe 11am-1pm. Because my controller has a built-in safety mechanism that caps output at 60 amps, even though more may be coming in, I should be safe feeding it 67 amps. The more important thing, I figured, was that for the remaining 6-8 hours of the day, during non-peak hours, I would be getting an additional 20% with the 11th and 12th panels, which over the course of a day, could easily be an additional 75 amps for me to utilize.

Basically, inside, I have two fridges, two laptops w/ monitors, lights, and some other electronics, which require about 200 amps per day to run. In the summer time, however, I have a 40 amp a/c unit that I like running as well. This year, however, I wanted to see how much I could get away with running it (the a/c) off my solar system, rather than via my aftermarket generator. So, with that additional 75 amps, that's almost two hours worth of electricity to run my a/c with! (On top of the three hours I already calculated needing to run it for.) All this, while also being able to charge my batteries up to full each day, while also not depleting them more than 66% or so each night. (I have three 200AH deep cycle batteries wired in parallel as my power station).

So, on a super sunny day, I should get as many as 576 amps to work with. (I know this because I currently get upwards of 480 amps with 10 panels). Of that 576, I should see about 550, if I factor in the new 60 amp cap for a couple of hours. Then, with that 550, roughly 300 amps of that will go toward charging my batteries and running my rig. Which then leaves me with roughly 250 amps to go toward the a/c unit, which can now run for roughly 6 hours a day (rather than maybe 4 or so with my current 10 panel setup). Basically, getting those two additional hours of a/c time from the sun, could mean the difference between me needing to bust out my generator, or not!

So! For the most part, now that I have my fuses figured out (thanks guys!) I feel like I am all set! Until I find an excuse to upgrade my rig even more, that is. =)

Gotcha, I can see why a parallel arrangement might be advantageous in that environment.