Interesting on the fuse requirement. The original generator setup didn't have a fuse that I'm aware of except between the batteries and inverter. Where should the fuse be located?
Typically on the positive wire of each parallel panel (or each parallel string of several panels in series for higher voltage systems.)
For instance, four fuses at the 4:1 "T" or "Y" connector in your case.
The theory is, PV panel wires and traces can handle a particular current, e.g. 15A for a panel designed to put out about 7A. No problem when it is working properly. If you had four panels wired in parallel and one panel developed a fault (short, such as all the bypass diodes fail shorted), then the other three panels would force 7A x 3 = 21A backwards through the bad panel, causing overheating.
At least in the U.S., our NEC specifies OCP of fuse/breaker if available current exceeds capability of wire. I think that's 1.56x available current - we assume 1.25x for extra illumination reflecting off nearby clouds and 1.25x margin. Two panels in parallel don't need the fuse, but 3 or more do.
A few systems require fuses at both positive and negative end; those are specified in inverter documentation for some grid-tie inverters because AC has a path to reach the panels. But for battery systems, just one end is needed.
In your case if you put some panels on the building and some on the wall, you might want three pairs of 2:1 connectors instead of one pair of 4:1, otherwise each panel would have to wire individually back to where you put the connector.
Is your charge controller separate from inverter? Needs to have fuses that would blow if there is a short in the inverter, in the charge controller, or in the wire leading to either. Both could share one fuse, but typically an inverter is wired for some 50 to 200A, and charge controller has smaller wire for 20 to 60A, so each gets its own fuse.
You have a 30A controller (should use at least 10 awg. Now 10 awg actually has ampacity of 40A but NEC specifies 30A fuse. If we plan to run 30A continuous though a wire, should have 1.25x larger or minimum 38A fuse so ought to have 8 awg wire per code. Charge controller isn't expected to deliver more than 30A.
If PV panels are expected to deliver 30A, we would want to size wire (and fuse if required) after the 4:1 leading to charge controller at 1.56x so 47A. That exceeds 10 awg, requires 8 awg. My idea of multiple orientation for PV panels reduces the current, but may not satisfy code if wire too small. Single fuse sized to wire would work, or wire large enough. But you probably can't find 8 awg 4:1 MC. Instead of MC fuses, I have a combiner box with screw terminal fuse holders, and 8 awg or 6 awg from there to my (grid tie PV) inverters.
I'm giving you a bunch of details we concern ourselves with for permitted, grid-tied, higher voltage systems. Although, 12V systems can still overheat a wire and start a fire. If you make a system with more panels in series and fewer in parallel with MPPT controller, that makes higher voltages and lower currents, eliminating need for fusing individual panels when configured 2s2p
You have a 1500W inverter (we don't worry about 3000W peak for fuse so long as not "fast blow). 12V battery, correct? 125A, so much heavier cable. Fuse 1.25x or about 175A, and cable large enough for that.
