☀ SolarCalculatorHQ

RV Solar Calculator

Size an RV solar setup in seconds. Free RV solar calculator returns panel wattage, battery Ah, charge controller and inverter using NEC 690.8.

RV Solar Calculator

Battery capacity
800 Ah
Recommended solar wattage
720 W
MPPT controller size
80 A
Inverter rating
1,000 W

What this calculator does

This RV solar calculator sizes an entire 12 V or 24 V off-grid system for a recreational vehicle — travel trailer, fifth-wheel, Class A/B/C motorhome, or skoolie conversion. It takes your daily energy use in watt-hours, your peak sun hours, your battery chemistry preference, and your peak AC load, and returns the four numbers you need to build a parts list: battery bank capacity in amp-hours, solar panel wattage, MPPT charge controller amp rating, and inverter wattage.

Every result includes the NEC 690.8 125% continuous-load factor on the charge controller, so the sizes the calculator returns match what a licensed RV technician would specify on an installation permit.

The four numbers every RV solar build needs

A complete RV solar system is four components that must be matched: panels, charge controller, battery bank, and inverter. Get any one undersized and the whole system fails — too few panels and you never recharge; too small a battery and you run out overnight; an undersized controller throttles the array; an inverter that can’t handle peak loads trips offline mid-microwave.

1. Battery capacity (Ah)

Battery storage is the foundation. The formula is:

Battery Ah = (Daily Wh × Days of autonomy) ÷ (Battery V × Depth of Discharge)

For a 2,400 Wh daily load on a 12 V lead-acid bank at 50% DoD with 2 days of cloudy reserve: 2400 × 2 ÷ (12 × 0.50) = 800 Ah. That’s four 6 V golf-cart batteries (commonly 220 Ah at 6 V, wired series-parallel to give 12 V × 440 Ah) plus another similar bank.

Lithium iron phosphate (LiFePO4) flips the math. Same 2,400 Wh daily load, same 2 days autonomy, but DoD jumps to 80%: 2400 × 2 ÷ (12 × 0.80) = 500 Ah. A single Battle Born 270 Ah or two 100 Ah LiFePO4 modules (Renogy, AIMS, SOK) cover it. Lithium weighs about 30 lbs per 100 Ah versus 65 lbs for AGM, recharges in a third of the time, and survives 3,000–6,000 cycles versus 400–800 for lead-acid. EnergySage and Battle Born put the levelized cost-per-cycle for LiFePO4 at half that of AGM despite the 2–3× higher purchase price.

2. Solar panel wattage (W)

Panel W = Daily Wh ÷ (Peak Sun Hours × System Efficiency)

The “system efficiency” factor lumps together charge controller losses (3–5%), battery charge/discharge round-trip (5–15%), and wiring/MC4 connector resistance (2–3%). 80% is the conservative default; well-built LiFePO4 systems with short cable runs hit 85%.

For 2,400 Wh per day at 4.5 PSH (the U.S. average for fixed flat-mount panels), the math is 2400 ÷ (4.5 × 0.80) = 667 W. Round up to the next commercial step — 720 W (typically two 360 W panels) or 800 W (two 400 W). The NREL PVWatts data shows U.S. PSH ranging from 3.0 in Seattle to 5.8 in Phoenix; pick the lowest PSH for the months you’ll be camping.

3. Charge controller (A)

Controller A = Panel W ÷ Battery V × 1.25

The 1.25 factor is NEC 690.8(A)(1), which classifies PV output as a continuous source and requires the controller’s continuous current rating to be at least 125% of the array’s maximum power-point current. A 720 W array on a 12 V bank needs 720 ÷ 12 × 1.25 = 75 A — round up to an 80 A MPPT (Victron SmartSolar 150/85, Renogy Rover 60 split with a second controller, or a single Outback FlexMax 80). Going to 24 V cuts the controller current in half: 720 ÷ 24 × 1.25 = 37.5 A → 40 A.

The Victron RV Application Guide and Renogy’s sizing tables confirm this method. Always cross-check the controller’s PV input voltage limit (commonly 100 V or 150 V) against your array’s open-circuit voltage at the coldest temperature you’ll camp in. Cold mornings can push Voc up by 12–18%.

4. Inverter (W)

Inverter W = Peak simultaneous AC load × 1.25

A microwave (1,000 W) running while the coffee maker brews (800 W) and a phone charger pulls 30 W needs at minimum 1,830 × 1.25 = 2,288 W — buy a 3,000 W pure-sine inverter (Victron Phoenix 3000, AIMS PWRI300012S, or Renogy 3000 W). For lighter use — laptop, TV, and a Vitamix blender — 1,500 W is enough.

Always specify pure-sine, never modified-sine. CPAP machines, induction cooktops, sensitive electronics, and many newer compressor fridges fail or shorten lifespan on modified-sine waveforms.

Sample sizing for common RV setups

Weekend travel trailer (2,000 Wh/day, 12 V, AGM) — A retired couple running LED lights, a 12 V compressor fridge, a vent fan, and laptop charging. 2,000 ÷ (4.5 × 0.80) = 556 W → 600 W array (two 300 W panels). Battery: 2,000 × 2 ÷ (12 × 0.50) = 667 Ah → four 6 V golf-cart batteries (about 440 Ah usable per pair, double up for headroom). Controller: 600 ÷ 12 × 1.25 = 62.5 A → 80 A MPPT. Inverter: 1,500 W for occasional microwave. Total parts cost in the U.S. as of 2025–2026 surveys (Camper FAQs, HomeAdvisor): $3,400–4,200 installed DIY, $5,800–7,400 dealer-installed.

Full-time fifth-wheel (5,000 Wh/day, 12 V, LiFePO4) — A family with a residential fridge, satellite TV, kids’ devices, occasional microwave, and an instant pot. 5,000 ÷ (4.5 × 0.80) = 1,389 W → 1,600 W array. Battery: 5,000 × 2 ÷ (12 × 0.80) = 1,042 Ah of LiFePO4 — typically four 270 Ah Battle Born or six 200 Ah lithium modules. Controller: 1,600 ÷ 12 × 1.25 = 167 A — split across two 80 A MPPT controllers in parallel. Inverter: 3,000 W pure-sine. Installed DIY: $8,500–11,000.

Class B van with rooftop A/C (8,000 Wh/day, 24 V, LiFePO4) — A digital nomad running a 14,000 BTU rooftop A/C unit at midday plus all the typical loads. 8,000 ÷ (4.5 × 0.80) = 2,222 W → 2,400 W array (rooftop maximum on most Class B’s). Battery: 8,000 × 2 ÷ (24 × 0.80) = 833 Ah at 24 V (about 600 Ah at 24 V LiFePO4). Controller: 2,400 ÷ 24 × 1.25 = 125 A — split across two 60 A MPPTs. Inverter: 5,000 W or split (3,000 W main + dedicated 1,500 W A/C inverter). $14,000–22,000 installed.

Wiring and code references (United States)

RV solar installs in the U.S. follow NEC Article 690 (Photovoltaic Systems) and the manufacturer instructions. Key points:

  • DC-side conductors sized per NEC 690.8(B) and 310 ampacity tables — use the solar panel wire size calculator to pick AWG.
  • Fuses or breakers on every battery-positive conductor within 7” of the battery (ABYC E-11 marine practice, widely adopted in RV).
  • Grounding per NEC 690.41 — bond the array frame and the negative DC bus to the chassis with #10 AWG minimum (use the solar grounding calculator to size the equipment grounding conductor).
  • Smoke and propane detectors required to remain on the chassis battery, not the solar bank — RVIA standard A119.5.

Common RV solar mistakes

  • Sizing only for summer. A 600 W array hitting 6 PSH in July is fine; the same array in December at 1.8 PSH yields only 30% as much. Size for the worst month you camp.
  • Connecting LiFePO4 to a lead-acid charge profile. AGM and lithium have different bulk/absorb/float voltages. Set the controller and converter to LiFePO4 profile or shorten battery life dramatically.
  • Running panels in parallel only. Two 12 V panels in parallel give 12 V × 16 A, which pushes wire size to #6 AWG over a 15 ft run. The same panels in series at 24 V draw 8 A and run cleanly on #10 AWG.
  • Skipping the 125% NEC factor on the controller. A 60 A controller exactly matched to a 720 W array on 12 V (60 A nominal) will thermally cycle every sunny afternoon and fail within a year.
  • Mixing battery ages. Adding a new lead-acid battery to an existing string pulls the new one down to the old one’s capacity within months. Always replace the whole bank.

Sources

Frequently asked questions

How many watts of solar do I need for my RV?
Total your daily energy use in watt-hours, then divide by peak sun hours and an 80% system efficiency factor. A typical North American travel trailer using a 12 V fridge, LED lights, a vent fan, and laptop charging draws 2,000–2,800 Wh per day. At 4.5 peak sun hours that needs 555–778 W of panels — most owners install a 600–800 W array. Heavy users running a residential fridge, microwave, and air conditioner can push 5,000–8,000 Wh per day and need 1,400–2,200 W of rooftop solar.
What battery bank size do I need for RV solar?
Battery capacity in amp-hours equals daily watt-hours times days of autonomy, divided by battery voltage times depth-of-discharge. For 2,400 Wh per day, 2 days of cloudy reserve, on a 12 V lead-acid bank at 50% DoD: 2400 × 2 ÷ (12 × 0.5) = 800 Ah. Switching to LiFePO4 at 80% DoD cuts that to 500 Ah. LiFePO4 also weighs 60% less and lasts 8–10× more cycles, which is why most new RV solar builds use lithium even though upfront cost is 2–3× higher.
Do I need an MPPT or PWM charge controller for RV solar?
MPPT is the right choice for anything above 200 W. RV solar panels are usually 36-cell 12 V nominal or 60/72-cell 24 V nominal. A PWM controller pulls panel voltage down to battery voltage and wastes the headroom as heat — about 25–30% of array output is lost. An MPPT DC-DC converter recovers that loss at 96–97% efficiency. The price gap has closed: a 30 A MPPT now sells for $80–120 versus $25–40 for PWM, so the payback is usually under one trip.
How big does the inverter need to be?
Size the inverter to the largest simultaneous AC load you actually run, plus the NEC 690.8 125% continuous-load factor. A microwave at 1,000 W running with the coffee maker at 800 W needs at minimum 1,800 × 1.25 = 2,250 W — round up to a 3,000 W pure-sine inverter. For occasional small loads (laptop, TV, charger), a 1,000–1,500 W inverter is plenty. Avoid modified-sine inverters: they damage CPAP machines, induction cooktops, and most newer appliances.
Will RV solar work in the winter or under shade?
Solar production drops 50–75% in winter at high latitudes — December peak sun hours in northern Vermont or Washington fall to 1.5–2.0 hours from a summer peak of 5.5. Snow accumulation on rooftop panels blocks production until tilted off (some owners install tilt-up brackets to clear snow and steepen winter angle). Shade is brutal: a single shaded cell on a panel cuts that panel's output by 30–80% even with bypass diodes. Park in open sky, use a portable suitcase panel for shaded sites, and size the array for the worst month you'll camp in.
What's the difference between rooftop solar and a portable suitcase panel?
Rooftop panels charge whenever the RV is in sun without setup — best for boondocking weeks at a time in open campsites. Portable suitcase panels (100–200 W folding kits with a built-in controller) plug into the battery via Anderson connectors and let you park the RV in shade while putting panels in sun. Most full-time RVers use both: 400–800 W on the roof plus a 200 W suitcase for shaded forest sites. The calculator above sizes the rooftop portion; add 100–200 W of portable capacity for flexibility.

Related calculators

📋 Embed this calculator on your site (free, attribution required)

Free to embed on any non-commercial or commercial site, provided the attribution link remains visible. No tracking, no email capture, just the calculator.