Renewable energy systems have at least two power sources: the renewable energy source itself (solar panels, wind or hydro generator, or a combination), and the batteries. Any time we have a power source and wiring, we need to ensure that the number of amps (current flow) is kept within the capacity of the wire. Too much current through too small a wire leads to melted insulation or even fires.
Fuses and circuit breakers are an essential part of code compliance, not to mention common sense. The National Electrical Code requires “overcurrent protection and a disconnect means” between any power source and any appliance. DC-rated fuses and circuit breakers cover both these requirements.