Guides

Calculator

Solar Size Calculator

Estimate how much solar panel power you need to replace one day of energy use under the conditions you enter. Add daily Wh for DC devices and AC devices separately. The Daily Power Consumption Calculator shows these two totals once you assign a power source to each device.

Not sure what to enter? Read the step-by-step guide.

Your inputs

What gets replaced?

Compatible fields are replaced with values from your saved setup, including blanks. Capacity values and units are replaced together where supported. Other fields stay unchanged. You can undo the replacement until you manually change one of the replaced fields. Edit My Setup

Your daily energy use
What does DC daily energy mean?
Energy used each day by devices powered directly from the battery's DC system, measured in watt-hours. Use Daily Power Consumption to build this total. Do not include loads powered only by shore power or a generator.

Devices powered directly by the battery's DC system. Leave blank if none.

What does AC daily energy mean?
Energy used each day by AC devices powered from the battery through an inverter, before inverter losses. Use Daily Power Consumption for this total. Do not enter the same overall RV total in both fields.

Devices powered by this battery through an inverter. Leave blank if none.

Your solar conditions
What are peak sun hours?
Peak sun hours express a day's solar energy as the equivalent number of hours at full rated sunlight. They are not the same as daylight hours.

Use an estimate for the location, season, and panel orientation you expect to have. Peak sun hours are not hours from sunrise to sunset.

What does solar system efficiency mean?
This is the percentage of estimated panel energy available to power battery-side loads after solar and storage losses. These can include panel temperature, shading, wiring, controller, and battery cycling losses. Avoid counting the same loss twice.

Enter the percentage of energy available after solar and storage losses. Do not include AC inverter losses here; those are handled separately above.

The same appliance belongs in only one energy group. Results update in this browser; no location or weather data is fetched.

Solar size estimate

How much solar you could need

Rated panel power for your daily energy use and solar conditions.

—

Enter daily energy, peak sun hours, and solar system efficiency to estimate array size.

This is a daily energy estimate, not a guarantee of solar output or battery charging. Actual production changes with weather, season, shade, panel position, and equipment. It does not check roof space, controller limits, battery capacity, charge rate, or several days of poor solar conditions.

Edit your inputs
See calculation details, assumptions and sources

Battery energy to replace per day = DC Wh/day + AC Wh/day ÷ inverter efficiency (as a fraction). Panel W = battery Wh/day ÷ (peak sun hours × solar system efficiency), with efficiency as a fraction. The result is the estimated rated panel wattage needed under the conditions you entered. It is not a prediction of continuous solar output.

For example, 600 Wh/day DC and 400 Wh/day AC at 80% inverter efficiency require 1,100 Wh/day on the battery side. At four peak sun hours and 75% solar system efficiency, the estimate is about 366.67 W of rated panels. These percentages are example inputs, not recommended defaults.

Choose peak sun hours for the intended location, season, and panel orientation. Solar system efficiency is the percentage of rated panel energy available to power battery-side loads after solar and storage losses. Avoid counting the same loss in both inputs. This simple daily-average model does not simulate hourly weather or charge scheduling. To estimate exposure needed to refill a known battery energy deficit with an existing array, use Solar Charging Time.

References: NREL PVWatts manual on solar resource and system losses and US DOE on conditions affecting actual solar performance. This calculator is a simplified RV estimate, not a PVWatts simulation. See the site methodology.