How to size an RV solar system in 4 steps
- Daily energy use: add watts × hours for each device. 120 V devices running through an inverter use ~10% extra.
- Battery bank: daily use × days of autonomy ÷ usable depth of discharge (90% for LiFePO4, 50% for AGM).
- Solar array: daily use ÷ (peak sun hours × 0.75) so you can refill the battery in one day.
- Charge controller and inverter: controller amps = panel watts ÷ battery voltage × 1.25. Inverter = biggest simultaneous AC load (incl. start-up) × 1.25.
Example systems
| Setup | Daily use | LiFePO4 battery (12 V) | Solar | Inverter |
|---|---|---|---|---|
| Weekend camper: lights, fan, phones, 12 V fridge (1 day reserve) | 742 Wh | 100 Ah | 200 W | none |
| Van life + remote work: Starlink Mini, laptop, 12 V fridge (2 day reserve) | 1,675 Wh | 350 Ah | 450 W | 300 W |
| Full-time RV: fridge, TV, coffee, microwave (2 day reserve) | 3,138 Wh | 600 Ah | 850 W | 5,000 W |
Calculated with 5 peak sun hours and a 12 V LiFePO4 bank.
12 V, 24 V or 48 V?
12 V is simplest for vans and small RVs with mostly 12 V appliances. Go 24 V or 48 V for systems above ~3,000 W of inverter power: lower current means thinner, cheaper cables and less heat.
LiFePO4 vs. AGM
| LiFePO4 (lithium) | AGM (lead-acid) | |
|---|---|---|
| Usable capacity | ≈ 90% | ≈ 50% |
| Cycle life | 3,000–6,000 | 300–700 |
| Weight (100 Ah) | ≈ 25 lb | ≈ 65 lb |
| Cold charging | Needs heating below 32 °F | OK |
| Cost per usable kWh over lifetime | Lower | Higher |
Don't forget
- Fuses or breakers on every positive cable, sized for the wire gauge.
- A battery monitor (shunt) to see the real state of charge.
- DC-DC charger to charge from the alternator while driving.
- When in doubt, have a qualified RV electrician check your design.
Frequently asked questions
How much solar do I need for my RV?
Weekend campers typically need 200–400 W; full-timers with a residential fridge and TV usually need 600–1,200 W plus 300–600 Ah of lithium battery at 12 V.
How many batteries do I need for RV solar?
Divide your daily watt-hours by 12.8 V and 90% usable capacity. Example: 1,500 Wh/day needs about 130 Ah, i.e. two 100 Ah LiFePO4 batteries for some reserve.
What size inverter do I need for my RV?
Add the watts of all 120 V appliances you run at the same time, plus start-up surge, and add 25%. A coffee maker or microwave alone requires a 1,500–2,000 W inverter.
Can I run RV air conditioning on solar?
Yes, but it needs a big system: about 600–800 Ah of 12 V lithium, a 3,000 W inverter, a soft-start kit and 1,000 W+ of solar for a few hours of AC per day.