No breaker is required on the panel side. A switch on the input to the MPPT
controller is a good idea. The concern about DC breakers/switches is not relevant to solar panels
because the current
can never exceed the panel's short circuit current. Thus a high current arc
can never happen which is what drives the DC rating of a breaker or switch.
A fuse or breaker is definitely required where the MPPT
controller feeds the battery
. Ideally this fuse is very close to the battery
. In this application the breaker or fuse must be rated for the voltage and very high short circuit current. Very few breakers are rated for this application due to the high DC current interrupting rating. Best to only use a fuse of the proper interrupting rating based on the battery bank size.
Circuit interrupting devices have 3 main ratings:
Opening current (I.e. Trip current)
Operating voltage both DC and AC
Maximum interrupting current (usually thousands to tens of thousands of amperes)
The maximum interrupting current is often ignored by DIY boaters because they don't understand the importance of this specification. A battery bank can deliver thousands of amps to a short circuit. The DC voltage rating is next most ignored specification but is also critically important. Ignoring these two ratings means that the device may not interrupt a fault thus causing a fire. There is more to it than just the number stamped on the handle.