RV / Off-Grid Solar Sizing
Enter what you use per day in watt-hours, your peak sun hours and the days of backup you want, and get the panel watts and the battery bank in amp-hours and kWh.
RV / off-grid solar
D09Scenario A
Look up your location on the NREL solar resource maps (nrel.gov/gis/solar).
Solar panels needed
Battery bank: 417 Ah at 12 V (5.0 kWh).
- Solar panels
- 593 W
- Battery (Ah at bank voltage, 80% DoD)
- 417 Ah @ 12 V
- Battery kWh
- 5.0
Estimate. Formula and sources are under “How it works”. Change any input; the result updates as you type.
2026 note: The federal 25C and 25D tax credits ended for installations after Dec 31, 2025. Our numbers use 2026 rules. State rebates, HEAR/HOMES programs and utility programs may still apply.
Formula
How it works
- Panel watts = daily Wh ÷ peak sun hours ÷ 0.75
- Battery Ah = daily Wh × days ÷ 0.8 ÷ bank voltage
- Battery kWh = daily Wh × days ÷ 0.8 ÷ 1,000
The 0.75 is a 25% derate for the charge controller, wiring, dirt and heat. The 0.8 keeps a LiFePO4 bank at 80% depth of discharge. Doubling the bank voltage halves the amp-hours for the same kWh, which means thinner wires. Results are estimates; sun hours change a lot by season, so size for the month you'll use the system most.
Sources: peak sun hours from the NREL solar resource map; 25% system derate; 80% depth of discharge for LiFePO4.
Worked example
A worked example
Making 6,000 Wh in 5.5 sun hours after a 25% derate takes about 1,455 W of panels. Storing one day at 80% depth of discharge takes 7.5 kWh of battery, which is 156 Ah @ 48 V.
Questions
FAQ
How many watts of solar for an RV?
For 2,000 Wh a day at 4.5 sun hours, about 593 W of panels. With only 3.5 sun hours (winter, or a cloudier area), the same use needs about 762 W.
12V vs 24V vs 48V?
Same energy, fewer amps. Two days of 2,000 Wh is 5.0 kWh of battery: 417 Ah at 12 V, 208 Ah at 24 V or 104 Ah at 48 V. Higher voltage keeps currents and wire sizes down; many RVs stay at 12 V because their appliances run on it.
Can I run an RV AC on solar?
Enter the AC's watts × the hours it runs in the daily use field and see the panel and battery numbers. An AC running several hours a day usually outgrows the roof space of an RV.
How many days of backup do I need?
Use the number of cloudy days in a row you expect. Each extra day adds the same battery kWh again: 1 day of 6,000 Wh needs 7.5 kWh; 2 days need twice that.
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