Build the skeleton, fill it in later

Most people outgrow their first system. The ones who don't have to rebuild made three decisions correctly at the start.

1. Pick the voltage you'll end at, not the one you're starting at. If there's any chance you'll add air conditioning, induction cooking, or a big inverter, build at 24V or 48V from day one. Going 12V because it's simple, then needing 48V two years later, is the single most expensive mistake in this hobby.

2. Oversize the wiring and the charge controller, not the panels. Panels are the easiest and cheapest thing to add later. Rewiring a finished rig is miserable. Run heavier cable than you need now and buy a controller with headroom — then adding panels later is a five-minute job instead of a teardown.

3. Leave physical space and mounting provisions. Battery bays, controller area, cable runs with slack. A system with no room to grow forces a full relocation for a modest expansion.

On adding batteries later: possible but not free. New batteries added to an aged bank get dragged toward the old ones' behavior. If you know you'll want more capacity, buying it up front is usually better.