RV Solar Calculator — Size Your Solar Panels and Battery Bank for Any Camper or Van Build

An RV solar calculator sizes your rooftop solar array and battery bank based on your actual daily power consumption, how many sunless days you want to survive, and your local peak sun hours. Enter your daily watt-hours, autonomy days, sun hours, system voltage, battery chemistry, and panel size — the calculator instantly returns your required battery bank in amp-hours, total solar wattage needed, panel count, battery count, recommended charge controller amperage, and an estimated hardware cost.

How to Use the RV Solar & Battery Calculator

Step 1 — Enter your daily energy consumption.

Type your total daily watt-hours in the Daily Energy Consumption field. This is the single most important input — everything else is sized around it. To find your number, list every appliance you run in your RV and multiply each item’s wattage by the hours you use it per day.

Add all results together. The reference table at the bottom of the results panel gives you a useful starting point: LED lights at 60 Wh/day, a roof vent fan at 240 Wh/day, a 12V compressor fridge at 540 Wh/day, a laptop at 260 Wh/day, and Starlink Mini at 280 Wh/day add up to 1,380 Wh — close to the 1,500 Wh default which covers a typical minimal-comfort off-grid setup. A van with air conditioning or an induction cooktop can easily exceed 3,000–5,000 Wh/day and requires a fundamentally different system.

Step 2 — Set your autonomy days using the slider.

Autonomy is the number of consecutive days you want to run on battery power with zero solar input — no sun, no driving, no shore power. Drag the slider from 1 to 5 days. One day of autonomy means you must recharge every day or run out of power.

Two days is the standard recommendation for most US van lifers and RVers who travel regularly. Three or more days suits boondockers who park for extended periods in shaded or overcast areas like the Pacific Northwest or heavily forested campsites.

Higher autonomy directly multiplies your required battery bank size — 3 days of autonomy requires three times the battery capacity of 1 day at the same daily consumption.

Step 3 — Set your peak sun hours using the slider.

This is the daily average hours of full-strength solar irradiance at your typical travel locations. If you primarily travel the US Southwest — Arizona, New Mexico, Utah, Nevada — use 5.5–6.5 hours. For California and Texas, use 5.0–5.5. For the Mountain West and Midwest, use 4.0–5.0. For the Pacific Northwest or Northeast, use 3.0–4.0.

If you travel across multiple regions, use a conservative middle figure rather than the best-case number from your sunniest destination. Note that RV panels mounted flat on the roof typically produce 10–20% less than the same panels at optimal tilt — this efficiency reduction is already partially absorbed in the calculator’s system loss factor.

Step 4 — Select your system voltage.

Choose 12V for standard RVs, travel trailers, and most van builds — the overwhelming majority of RV appliances, inverters, and accessories are designed for 12V. Choose 24V for larger skoolie (school bus) conversions, large cargo vans, or any build with more than 600–800 watts of solar, where 12V wiring becomes impractically thick.

Choose 48V for heavy-duty off-grid builds with multiple kilowatts of solar and very large battery banks — rare in RV applications but used in some full-time living vehicle builds. Higher voltage systems dramatically reduce required wire thickness and charge controller amperage for the same power level.

Step 5 — Select your battery chemistry.

Choose Lithium (LiFePO4) at 80% depth of discharge for modern builds. Lithium iron phosphate batteries are lighter, smaller, faster to charge, longer-lived (2,000–5,000 cycles versus 300–500 for lead-acid), and can be discharged to 80–100% of their rated capacity without damage.

The calculator uses 80% DoD as a conservative lithium standard. Choose AGM or Lead-Acid at 50% DoD for budget builds or existing systems — these batteries must never be discharged below 50% without accelerating plate sulfation and drastically shortening lifespan.

Selecting lead-acid effectively doubles your required battery bank size compared to lithium for the same usable capacity, making it heavier and more expensive in the long run for high-autonomy builds.

Step 6 — Select your standard panel size.

Choose 100W panels for builds with limited roof space or complex roof layouts where smaller panels fit better around vents, skylights, and AC units. Choose 200W panels — the most common RV solar panel size in the US — for standard van and RV rooftop installations.

Choose 400W panels for larger roofs like Class A motorhomes, skoolies, and cargo van builds where maximizing power per panel reduces wiring complexity. The selection changes the panel count output without affecting the total required solar wattage.

Step 7 — Read the three result cards.

Battery Bank Needed shows your gross amp-hour requirement accounting for depth of discharge, your system voltage, and system losses. Solar Array Needed shows the total wattage required to replenish your daily consumption at your selected sun hours, plus your estimated charge controller size in amps. Hardware Count shows the number of standard panels and 100Ah batteries needed, along with an estimated core hardware cost in dollars.

Step 8 — Study the visual layout.

The visual configuration section renders panel icons and battery icons side by side — one icon per unit up to practical display limits. This immediately shows the physical scale of your system and helps you visualise whether your roof has enough space for the required panel count.

Step 9 — Review the appliance reference table.

The Typical RV Appliance Loads table at the bottom of the results gives real-world wattage and daily usage estimates for the most common RV appliances. Use this to validate or refine your daily watt-hour estimate if you are designing a new build rather than metering an existing system.

Step 10 — Export your system report.

Click Export PDF to save a printable system sizing document — useful when purchasing components, sharing with an installer, or comparing different system configurations.

The RV Solar Sizing Formula Explained

The calculator uses two independent calculations that both feed into the final hardware count:

Battery bank sizing: Daily Ah needed = Daily Wh ÷ System Voltage ÷ 0.85 (system losses) Total usable Ah = Daily Ah × Autonomy Days Gross Ah required = Total usable Ah ÷ Depth of Discharge Number of batteries = ceil(Gross Ah ÷ 100Ah per battery)

Solar array sizing: Required solar yield = Daily Wh ÷ 0.90 (charge controller efficiency) Solar array watts = Required yield ÷ Peak Sun Hours Number of panels = ceil(Solar array watts ÷ Panel wattage)

Example — a 1,500 Wh/day van build at 12V with 2 days autonomy, 4.5 PSH, lithium batteries, 200W panels:

• Daily Ah = 1,500 ÷ 12 ÷ 0.85 = 147 Ah
• Total usable Ah = 147 × 2 = 294 Ah
• Gross Ah = 294 ÷ 0.80 = 368 Ah → 4 × 100Ah lithium batteries
• Required solar yield = 1,500 ÷ 0.90 = 1,667 Wh
• Array watts = 1,667 ÷ 4.5 = 370W → 2 × 200W panels

Frequently Asked Questions

Q: How much solar do I need for my RV?

A: The answer depends entirely on your daily power consumption. A minimalist setup running LED lights, a fan, and phone charging uses roughly 300–500 Wh/day and needs only 100–200W of solar in most US locations.

A comfortable full-time van life setup with a 12V fridge, laptop, and internet device uses 1,200–2,000 Wh/day and typically needs 400–800W. An RV with residential AC or induction cooking can exceed 5,000 Wh/day and needs 1,500W or more — often supplemented by a generator or shore power for peak loads.

Start by listing every appliance and its daily usage in watt-hours, add 20% for unaccounted loads, and use the calculator to size from there.

Q: What size battery bank do I need for boondocking?

A: For typical US boondocking with 1,500 Wh/day consumption and 2 days autonomy on a 12V lithium system, you need approximately 350–400 Ah of gross battery capacity — four 100Ah lithium batteries.

For 3 days autonomy at the same consumption, you need six 100Ah batteries. The key rule is to size your battery bank for your worst-case scenario — not sunny Arizona camping but cloudy Pacific Northwest camping where you might go 2–3 days with minimal solar input. A battery bank that keeps you comfortable in Oregon in October will be more than sufficient in Utah in July.

Q: What is the difference between lithium and AGM batteries for RV solar?

A: Lithium iron phosphate (LiFePO4) batteries can be discharged to 80–100% of rated capacity, weigh roughly half as much as equivalent AGM batteries, charge 3–4 times faster, and last 5–10 times longer (2,000–5,000 cycles versus 300–500 for AGM). A 200Ah lithium battery gives you 160 usable Ah; a 200Ah AGM battery gives you only 100 usable Ah.

For long-term full-time van life or RV use, lithium delivers better economics despite the higher upfront cost. AGM remains a valid choice for occasional weekend RVers who want lower initial investment and already have a 12V lead-acid system infrastructure in place. Lead-acid batteries should never be stored below 50% state of charge — leaving them discharged accelerates sulfation and permanent capacity loss.

Q: How many solar panels can I fit on my RV roof?

A: A standard 200W RV solar panel measures approximately 58×26 inches (147×66 cm). A typical Class B van roof has room for 2–4 panels depending on vent and skylight placement. A Class C motorhome roof accommodates 4–8 panels. A Class A motorhome or school bus conversion can fit 8–20 panels or more.

Measure your usable roof space carefully, subtract clearances around vents and AC units, and compare against your panel count from the calculator. If your required panel count exceeds your roof capacity, the solution is to reduce consumption, increase system voltage to 24V or 48V (which requires less charge controller capacity for the same power), or supplement with foldable ground-deploy panels during extended stops.

Q: What size charge controller do I need for my RV solar system?

A: The calculator estimates your minimum charge controller amperage as total solar array watts divided by system voltage. For a 400W array at 12V, the minimum is 400 ÷ 12 = 33A — so a 40A MPPT controller is the appropriate next standard size.

For a 600W array at 24V, the minimum is 600 ÷ 24 = 25A — a 30A MPPT controller suffices. Always use an MPPT (Maximum Power Point Tracking) controller for RV solar — never PWM — because RV panels with 35–45V open circuit voltage lose 30–40% of their power through voltage clipping when connected to a 12V battery with a PWM controller. Popular MPPT options for US RV builds include Victron SmartSolar, Renogy Rover, and Wanderer series.

Q: What is depth of discharge and why does it matter for RV batteries?

A: Depth of discharge (DoD) is the percentage of a battery’s rated capacity that can be safely used before recharging. Lithium iron phosphate batteries have an 80–100% DoD — you can use 80–100 Ah from a 100Ah lithium battery.

Lead-acid and AGM batteries have a 50% DoD — using more than 50 Ah from a 100Ah AGM battery accelerates plate sulfation and degrades the battery faster with each cycle.

This is why the calculator doubles your required battery capacity when you select AGM — 100 Ah of usable capacity requires a 200Ah AGM bank but only a 125Ah lithium bank. Exceeding the recommended DoD repeatedly is the single most common cause of premature battery death in RV solar systems.

Q: Is 200 watts of solar enough for an RV?

A: A 200W solar array produces approximately 700–1,100 Wh per day depending on your location and season — enough to cover a very minimal setup: LED lights, phone charging, a small fan, and a laptop.

It is not enough for a 12V compressor fridge running full-time, which alone consumes 400–600 Wh/day. For a full-time van life setup with a fridge and internet device, 400–600W is the practical minimum. For comfortable boondocking with multiple devices and a fridge, 600–1,000W is the standard recommendation. The 200W figure that many entry-level RV solar kits advertise is adequate for supplementing shore power connections but undersized for serious off-grid independence.

Q: How do I calculate my RV’s daily power consumption in watt-hours?

A: Make a list of every electrical device in your RV. For each device, find its wattage (on the label, spec sheet, or with a Kill-A-Watt meter for AC devices). Estimate how many hours per day you run each device. Multiply watts × hours for each item to get daily watt-hours. Add all items together. Add 20% as a buffer for startup surges, unaccounted phantom loads, and future additions.

Example for a basic van build: LED lights (15W × 4hrs = 60Wh) + roof fan (30W × 8hrs = 240Wh) + 12V fridge (45W × 12hrs = 540Wh) + laptop (65W × 4hrs = 260Wh) + Starlink (35W × 8hrs = 280Wh) = 1,380 Wh + 20% buffer = 1,656 Wh/day. Round to 1,700 Wh as your calculator input.