Solar energy recovery

RV solar panel size and quantity calculator

Estimate the solar-array wattage needed to replace an RV or off-grid system’s average daily electrical use.

Enter the daily energy target

Peak sun hours are not daylight hours; they represent equivalent hours at full rated solar output.

Solar assumptions

Overall efficiency covers panel-to-load losses, including heat, wiring, controller, battery and inverter losses, panel angle, dirt, and ordinary mismatch. Use the original appliance Wh/day here; do not also divide by the battery calculator’s efficiency. Roof obstructions and shading can require a substantially larger array.

Optional battery-deficit recovery

Choose one method; the two deficits are never added together. In missing-energy mode, leave Wh at zero for daily replacement only. In charge-level mode, use the battery voltage above and the whole-bank values below; the Wh entry is ignored.

Use nominal bank Ah, not usable Ah: the charge-level difference already selects the capacity to restore. For series/parallel packs, find whole-bank volts and Ah with the battery configuration calculator. Use chemistry-appropriate charge targets from your manufacturer; the example 50% to 90% range is not a battery operating recommendation. Nominal volts × Ah is an energy approximation, not a voltage-based state-of-charge measurement.

This recovery path includes panel, wiring, controller, and storage losses but excludes later inverter discharge losses. The daily-load efficiency above applies only to the daily appliance budget. Each recovery day assumes the entered peak sun hours. This energy balance excludes charge-current limits and absorption/taper; verify those separately in the charging-time calculator and equipment manuals.

Formula

Solar-panel sizing formula

array watts = daily Wh ÷ peak sun hours ÷ (efficiency % / 100)

Use seasonal peak-sun-hour data for the travel area and month. Flat panels, roof vents, antennas, trees, and nearby vehicles can reduce real output.

Controller check

Match voltage, current, and battery chemistry

Controller amp rating alone is insufficient. Check maximum photovoltaic open-circuit voltage, cold-weather voltage rise, series/parallel layout, battery charge settings, and conductor protection.

Electrical load calculatorFind daily Wh →Battery bank calculatorSize storage →Charging-time calculatorCombine sources →

Return to the solar, battery & RV planning workflow

Size an RV solar array and count panels: worked example

For 1,200 Wh/day, four peak sun hours, and 70% overall efficiency, the minimum array is 428.6 W. With 200 W panels, round up to three panels: 600 W and an estimated 1,680 Wh/day. Check their actual dimensions against usable roof space.

Battery recovery formula and worked example

extra array W = stored deficit Wh ÷ recovery days ÷ peak sun hours ÷ storage efficiency fraction

For charge-level mode, stored deficit Wh = nominal bank V × bank Ah × (target SOC% − starting SOC%) ÷ 100. A 12.8 V, 250 Ah bank going from 40% to 90% needs approximately 1,600 Wh restored. Do not apply depth of discharge or discharge efficiency again. Add this to the daily-load array requirement before rounding up to whole panels. For 1,200 Wh/day, four sun hours, and 70% load efficiency, daily use requires 428.6 W. Restoring 1,600 stored Wh in two productive days at 80% storage efficiency adds 250 W. The 678.6 W total rounds to four 200 W panels. After daily use, their surplus stores about 1,188.6 Wh/day, suggesting 1.35 productive days before charge-rate or taper limits.

Frequently asked questions

Are peak sun hours the same as daylight hours?

No. They express the daily solar resource as equivalent hours at full reference irradiance. Use local, seasonal data for the travel month; four hours is an example, not a US-wide guarantee.

Does this also recharge an empty bank?

Choose missing stored energy or enter whole-bank capacity and starting/target state of charge in the optional recovery section. The tool adds enough generation to restore it over the selected productive days while covering daily appliance use. Recovery has a separate panel-to-storage efficiency, so do not add the same deficit to daily energy.

Is the controller current an installation rating?

No. The displayed 25% current allowance is only a screening assumption, not a code requirement or final controller selection. Check photovoltaic voltage, short-circuit current, cold-weather limits, output limits, and manufacturer sizing instructions.