A cabin has no bill to read, so you size it from its loads. Add up what each appliance uses in a day, then work out the array, the battery and the inverter. The numbers below use 4.5 sun hours and 20 percent losses.
| Load | Use per day (kWh) |
|---|---|
| LED lights, 100 W for 5 hours | 0.50 |
| Refrigerator, about 8 hours of running | 1.20 |
| TV, 120 W for 4 hours | 0.48 |
| Laptop and router, 80 W for 6 hours | 0.48 |
| Water pump, ½ hp, 1 hour | 0.37 |
| Total | 3.03 |
3.03 ÷ (4.5 × 0.8) = 0.84 kW, then add about 15 percent for battery losses: 0.97 kW, so about 1 kW. That is three 400 W panels (1.2 kW) or two 550 W panels (1.1 kW).
For two days of autonomy: 3.03 × 2 ÷ 0.9 = 6.7 kWh of useful energy. The nominal size is that divided by usable depth of discharge: about 7.5 kWh of LiFePO4 at 90 percent, or 13.5 kWh of lead-acid at 50 percent.
If the refrigerator, lights, TV, laptop and pump can run together, the total is 823 W, with a start-up surge from the pump. A 1.5 kW pure sine inverter with a 3 kW surge rating on a 24 V bank is a sound choice. See how to size a solar inverter.
Add a small controller sized by the MPPT guide. Next step: see matching kits and parts.
