What this calculator assumes
- Battery: daily use × days of autonomy, divided by the usable depth of discharge and a 90% system efficiency.
- Solar: enough to replace one day's use at your peak sun hours with 75% overall efficiency, rounded up to the next 50 W.
- Controller: array watts ÷ system voltage, plus 25% headroom, rounded to a standard MPPT size.
- Inverter: 25% above your largest simultaneous AC load. Motors and compressors may need extra surge capacity; see the inverter size calculator.
Example: weekend campervan
1,500 Wh a day, 12 V LiFePO4, 1.5 days autonomy, 4 sun hours, 1,000 W inverter: about 230 Ah of lithium, 500 W of solar, a 60 A MPPT and a 1,500 W inverter.
After sizing
- Check panel string voltage with the MPPT string voltage calculator.
- Choose cables with the DC cable size calculator; the inverter cable is usually the biggest.
- Pick fuses with the fuse size calculator.
- If winter sun is weak, add a DC-DC charger or hook-up charger.
Frequently asked questions
What size solar system do I need for an RV?
Most RVs use 1–3 kWh a day. That typically means 300–800 W of solar, 200–400 Ah of 12 V lithium and a 40–60 A MPPT controller, depending on climate.
Is 12V or 24V better for a van?
12 V suits most vans because appliances are 12 V. Move to 24 V if you'll run an inverter above about 2,000 W or have a large battery bank.