Planning the system

Start with life, not products

List each load, its voltage, rated watts or amps, hours/day, duty cycle, start surge and whether it can run with other loads. Separate daily energy from peak power: battery size follows energy; inverter, busbars and cables follow peak current.

Daily energy

For each load use watts x hours x duty cycle. Add DC loads directly. For AC loads divide by inverter efficiency and include inverter idle draw. Add 10-20% for wiring/conversion loss, then a practical reserve. Measure appliances when possible; labels often show maximum, not real average.

Autonomy and charging

Days of autonomy means how long you can live with poor sun and little driving. Full-timers commonly plan for 1-3 days, then verify that solar, alternator and shore can refill the used energy. A large bank without enough charging only delays the empty-battery problem.

Constraints

Climate controls the answer. Heat adds A/C; cold reduces battery charging ability and winter solar; shade makes roof solar weaker. Roof vents, racks and shading can matter more than nominal panel watts. Leave physical space, busbar capacity, controller headroom and spare fuse positions for expansion.

12 V or 24 V?

12 V is simple and widely supported for systems with modest AC power. Consider 24 V when inverter demand is routinely above about 2-3 kW, cable runs are long, or charge power is high. Choose by a current-and-equipment study, not by fashion.

Load

Power

Use/day

Energy/day

Fridge

60 W

8 h duty

480 Wh

Starlink

45 W

8 h

360 Wh

Lights/fans

55 W

5 h

275 Wh

Cooking

1,500 W

0.4 h

600 Wh

Loss + reserve

-

-

~300 Wh

Total

-

-

~2.0 kWh

CHAPTER CHECK

• I can explain the purpose of every component covered here. • I can identify the exact manufacturer limit that controls my design. • I have added the decision, rating or measurement to my schematic/worksheet.