List what you run off-grid. You get the lithium battery, solar panels, inverter, cable and fuse sizes for a 12 V or 24 V setup in your caravan, camper or 4WD.
Daily amp-hours are watt-hours divided by battery voltage. That's multiplied by your days without charging, then divided by usable capacity: 90% for lithium, 50% for AGM so it lasts.
Panel watts are daily watt-hours divided by peak sun hours, with 25% added for heat, dust, angle and wiring losses. The solar regulator (MPPT) is sized at 125% of panel current.
The inverter covers your largest mains appliance plus 20%. Battery current is inverter watts ÷ volts ÷ 0.9. The fuse is 125% of that, and the cable is sized for both current and under 3% voltage drop.
Add up the watt-hours you use each day, divide by 12 to get amp-hours, multiply by the number of days you want to go without charging, then divide by 0.9 for lithium. A typical setup with a compressor fridge, lights, water pump, phone charging and a TV uses around 60 to 80 Ah a day, so a 200 Ah lithium battery covers about two days without sun.
Divide your daily watt-hours by the peak sun hours where you camp, then allow about 25% for losses. Using 900 Wh a day with 5 sun hours needs roughly 240 W of panels. Plan for winter sun hours if you travel then, which can be half the summer figure.
Choose a pure sine wave inverter rated above the largest mains appliance you will run, plus about 20% headroom. A 1000 W microwave draws around 1500 W from the inverter, so it needs a 2000 W inverter. Add up anything you plan to run at the same time.
Work out the battery current: inverter watts divided by battery volts, divided by 0.9 for inverter losses. A 2000 W inverter on 12 V draws about 185 A, which needs a 250 A fuse close to the battery and around 67 mm² (2/0 AWG) cable so the cable is rated above the fuse. Keep the cable as short as possible.