Overlanding Solar Power Systems: Sizing Panels, Batteries, and Inverters for Off-Grid Living

Size your solar system wrong and you’ve bolted $2,000 worth of equipment to your roof that still can’t keep a 12V fridge running through a cloudy Wyoming afternoon. Size it right and you never run a generator at 6 a.m. in a quiet canyon, never wake up to a dead fridge, never cut a trip short because your comms gear died.

I’ve been dialing in vehicle-based solar setups since 2014 — first on a beat-up FJ Cruiser, then on a Four Wheel Camper, now on a flatbed Ram 3500 I’ve run from Baja to the Yukon. Here’s how I actually size these systems, the math I use in the field, and the components I’d spend my own money on right now.

Start Here: Build a Real Power Budget

Every system starts with a load calculation. Skip this and you’re guessing. I’ve watched guys drop $800 on panels for a system that needed $1,600 worth — and the reverse. Spend 20 minutes on this math before you buy anything.

List every device you’ll run, its wattage, and how many hours per day you’ll use it. Multiply watts × hours to get watt-hours (Wh) per day. Here’s a realistic overlanding load for a two-person rig:

• 12V compressor fridge (ARB 50-quart): ~45W average draw, runs roughly 8 hours/day = 360 Wh
• LED lighting (interior + camp): ~20W, 4 hours/day = 80 Wh
• Phone/tablet charging (2 devices): ~30W, 2 hours/day = 60 Wh
• Garmin inReach + radio charging: ~15W, 1 hour/day = 15 Wh
• Laptop (occasional work): ~65W, 2 hours/day = 130 Wh
• Water pump (12V): ~8W, 0.5 hours/day = 4 Wh

Total: roughly 650 Wh/day. That’s a typical two-person overlanding load. Add a CPAP machine (~30–60 Wh/night) or a diesel heater’s control unit (~20 Wh/night) and you’re pushing 720–730 Wh. Heavy users running a portable espresso machine, a drone battery charger, and a 12V electric blanket hit 1,000+ Wh/day without breaking a sweat.

Tack on a 20% inefficiency buffer for wiring losses, controller losses, and inverter conversion losses. My 650 Wh budget becomes a real-world target of 780 Wh/day that the system needs to produce and store.

Solar Panels: Wattage, Type, and Mounting

How Much Panel Do You Actually Need?

Divide your daily Wh target by your expected peak sun hours. In the American Southwest in summer, you’ll get 5–6 peak sun hours. The Pacific Northwest in October? More like 2.5–3. I design for 4 peak sun hours as a conservative baseline across most of the continental U.S.

780 Wh ÷ 4 hours = 195W of panel minimum. Round up to 200–250W to account for panel degradation, partial shading, and non-ideal angles. For most two-person rigs, a 200–300W array hits the sweet spot between roof space and production capacity.

Monocrystalline vs. Polycrystalline vs. Flexible

Run monocrystalline. Full stop. Poly panels are cheaper per watt but larger for the same output and they degrade faster. Flexible panels are tempting for low-profile builds — I’ve tried them. After two seasons of thermal cycling on a metal roof, I watched two sets delaminate. They also run hotter because they can’t breathe off the surface, and heat kills efficiency. The gap between a quality mono panel and a flexible panel runs 3–5% under real conditions, and that gap widens as the flexible panel ages.

For a roof-mounted fixed array, I keep coming back to the Renogy 200W Monocrystalline Panel or stacking two 100W units. I’ve used Renogy panels across four builds. Build quality has been consistent and their warranty support is real — I’ve actually used it.

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Tilt vs. Flat Mounting

Flat-mounted panels on a roof rack are convenient but you’ll lose 15–25% production compared to panels tilted toward the sun. If you’re stationary for multiple days — base camping, waiting out weather — a tiltable mount or a portable ground-deploy panel like the BioLite SolarPanel 100 as a supplement makes a measurable difference. I’ve logged a 30-degree tilt adding 40–50 Wh/day in shoulder-season conditions in the Four Corners area.

On expedition builds where roof space is maxed, I run a secondary portable panel on a kickstand that I deploy at camp. Not elegant. Works every time.

Charge Controllers: MPPT Is Not Optional

A PWM (pulse-width modulation) controller is a resistor with a marketing budget. An MPPT (maximum power point tracking) controller actively finds the optimal voltage-current combination from your panels and converts excess voltage into usable current. In real conditions, MPPT outperforms PWM by 15–30%. On a 200W array, that’s 30–60W of production you’re leaving on the table with a PWM unit.

Size your MPPT controller for your panel array’s short-circuit current (Isc) and open-circuit voltage (Voc). A 200W 12V panel array typically has a Voc around 22–24V and an Isc around 11–12A. A 20A MPPT controller handles this comfortably. Running 400W or more, step up to a 40A unit.

The Victron SmartSolar MPPT 100/20 is what I run on my Ram build and what I tell everyone who asks. It handles up to 290W on a 12V system, has Bluetooth monitoring through the VictronConnect app, and it’s German-engineered — which means it’s priced accordingly and built to last. Same unit, three years, two vehicles, zero issues.

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If Victron’s price stings, Renogy’s Rover 40A handles up to 520W on a 12V system at roughly half the cost. I’ve used it on two builds without problems. The Bluetooth monitoring isn’t as clean, but the charging performance is solid.

Batteries: Lithium vs. AGM — This Is Where You Spend Your Money

Get the battery bank wrong and the rest of the system doesn’t matter. This decision shapes everything downstream.

AGM: The Incumbent

Absorbed glass mat batteries are proven, cold-tolerant, and significantly cheaper upfront. A 100Ah AGM from Battle Born or Renogy runs $150–200. But here’s the math that kills AGM for serious overlanding: you can only safely discharge AGM to 50% depth of discharge (DoD) without accelerating degradation. A 100Ah AGM gives you 50Ah of usable capacity. Run it deeper regularly and you’ll kill it in 200–300 cycles.

AGM also charges slower, accepts less current — typically limited to 0.2C, so 20A max on a 100Ah battery — and weighs roughly twice what lithium does. For a weekend warrior who plugs in between trips, AGM works fine. For extended overlanding, you’ll feel the compromise every cloudy day.

Lithium (LiFePO4): The Right Answer for Serious Builds

LiFePO4 batteries did for overlanding power what tubeless tires did for trail riding. The upfront cost is real — expect $800–1,000 for a quality 100Ah LiFePO4 — but run the numbers over three years and lithium wins.

LiFePO4 gives you 80–100% usable DoD. That same 100Ah battery delivers 80–100Ah of real capacity. Cycle life runs 2,000–3,000+ cycles at 80% DoD versus 300–500 for AGM. They charge faster, accepting up to 1C (100A on a 100Ah battery), weigh 60–70% less, and hold voltage more consistently through the discharge curve — which matters for sensitive electronics like a Garmin inReach or a CPAP machine.

The one real weakness: LiFePO4 won’t charge below 32°F (0°C) without a battery management system that includes a low-temperature cutoff. Quality units like Battle Born have this built in. If you’re running in Alaska in January, verify your battery’s cold-weather specs before you buy — don’t assume.

For most builds, I recommend the Battle Born 100Ah LiFePO4 Deep Cycle Battery. Made in the U.S., 10-year warranty, and the BMS is genuinely robust. I’ve had one in my Ram build for two years running temperatures from -10°F to 110°F in the Sonoran Desert. It’s performed exactly as advertised.

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How Much Battery Capacity Do You Need?

Take your daily Wh load (780 Wh in our example) and size for 1.5–2 days of autonomy without solar input. That covers cloudy days, tree cover, and nights when you roll in late and don’t get a full charge cycle.

780 Wh × 2 days = 1,560 Wh. With LiFePO4 at 80% usable DoD: 1,560 ÷ 0.8 = 1,950 Wh of nominal capacity, or roughly two 100Ah 12V batteries (200Ah = 2,400 Wh nominal). With AGM at 50% DoD: 1,560 ÷ 0.5 = 3,120 Wh nominal — three to four 100Ah AGM batteries. That’s 90–120 lbs of battery versus 56 lbs for two Battle Born units. The weight math alone closes the case for lithium on any build where payload matters.

Inverters: Sizing for Real Loads

An inverter converts 12V DC to 120V AC so you can run standard household devices. Most overlanding loads — fridge, lights, charging — run fine on 12V direct. But a laptop charger, a power tool, or a camera battery charger often needs AC. That’s where the inverter earns its place.

Pure Sine vs. Modified Sine

Run pure sine wave. Modified sine inverters produce a choppy waveform that damages sensitive electronics over time — laptops, CPAP machines, camera chargers. The price difference between a 300W modified sine and a 300W pure sine is $30–50. Your laptop costs more than that. Don’t risk it.

Sizing the Inverter

Add up the wattage of everything you’d run simultaneously through AC. A laptop (65W) + a camera charger (30W) + phone charging through a USB adapter (18W) = 113W running load. Size your inverter to 1.5–2× your running load to handle startup surges. A 300W pure sine inverter covers most overlanding AC needs without drama.

Running power tools, an air compressor, or a coffee maker, step up to 1,000–2,000W. But understand that a 1,000W inverter drawing from a 12V system pulls 83+ amps — you’ll drain a 100Ah lithium battery in about an hour at full load. Inverter use is where power budgets go sideways fast.

The BESTEK 300W Pure Sine Wave Inverter handles the typical overlanding AC load without complaint. It’s compact, runs cool, and has USB ports built in. For heavier loads, the Renogy 2000W Pure Sine Wave Inverter is what I’d reach for — it handles a 15A AC circuit and has a remote on/off switch, which matters when it’s mounted under a bench and you don’t want to crawl back there every time you need to flip it.

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Alternator Charging: The Missing Piece

Solar is your primary charging source at camp. Your alternator is your backup and your driving-day charger. Most people wire this wrong or skip it entirely.

A DC-to-DC charger (also called a battery-to-battery or B2B charger) sits between your vehicle’s starting battery and your house bank. It takes the variable voltage from your alternator and delivers a proper multi-stage charge profile to your lithium or AGM bank. Running a direct connection with just an isolator is fine for AGM but it undercharges lithium and confuses the BMS — I’ve seen it trigger low-voltage cutoffs on a battery that was actually at 70% charge.

The Renogy DCC50S 50A DC-DC charger with MPPT handles both alternator input and a solar panel input in one unit — useful if you want to simplify wiring. Victron’s Orion-Tr Smart 30A is the premium option with tighter voltage regulation and better Bluetooth monitoring.

At highway speeds, a 50A DC-DC charger delivers roughly 600W of charging power. A 4-hour drive puts 2,400 Wh back into your bank — more than most rigs burn in a day. When you’re running through overcast country, driving is your best charging strategy.

System Wiring: Don’t Cheap Out Here

Undersized wire is a fire risk and an efficiency killer. Use these as minimums:

• Panel to controller: 10 AWG for runs under 15 feet, 8 AWG for longer runs
• Controller to battery: 8 AWG for 20A controllers, 6 AWG for 40A
• Battery to inverter: 4 AWG for 300W inverters, 2/0 AWG for 2,000W
• All circuits: fused within 18 inches of the positive battery terminal

Use marine-grade tinned copper wire, not automotive wire. The tinning prevents oxidation in humid environments and the insulation handles higher temperatures. Anderson SB50 connectors for panel connections, ring terminals with heat shrink for battery connections. Saving $40 on wire is how you start a fire in your rig at 2 a.m.

Cost Tiers: What You’re Actually Spending

Entry-Level System (~$800–1,200)

200W monocrystalline panel, Renogy Rover 20A MPPT controller, two 100Ah AGM batteries, 300W pure sine inverter, basic wiring kit. This powers a fridge, lights, and phone charging indefinitely in good sun. It struggles on cloudy multi-day stretches and the AGM weight adds up, but it’s a real system that works.

Mid-Range System (~$2,000–3,000)

300W panel array, Victron SmartSolar MPPT 100/30, two 100Ah LiFePO4 batteries, 1,000W pure sine inverter, Renogy DCC50S for alternator charging, proper fusing and distribution block. This is what I’d build for a dedicated overlanding rig. It handles extended off-grid use, charges fast, and the Victron monitoring gives you real data on your system’s health instead of voltage guesses.

Premium Build (~$4,000–6,000+)

400–600W panel array with tilt mounts, Victron SmartSolar MPPT 150/45, 300Ah Battle Born lithium bank, Victron MultiPlus 12/2000 inverter-charger (which also handles shore power when you’re at a campground), Victron BMV-712 battery monitor, full Victron GX system with touchscreen monitoring. This is what serious expedition rigs run. Overkill for weekend trips. Exactly right for month-long remote travel.

Installation Complexity: What You Can DIY

Panel mounting and basic wiring is DIY-friendly if you’re comfortable with 12V systems and can follow a wiring diagram. The Victron SmartSolar and Battle Born both have excellent documentation. Renogy sells complete kits with pre-terminated cables that take most of the guesswork out of the job.

Pay a professional for any work near your starting battery, alternator wiring, and roof penetrations on a vehicle you care about. A bad roof penetration leaks. A bad alternator connection fries your charging system. The labor cost on those two items is worth every dollar.

Budget 6–10 hours for a clean mid-range install if you’re methodical and have done basic automotive electrical work. Double that if it’s your first time learning as you go.

Monitoring: Know Your Numbers

A battery monitor isn’t optional on a system you’re depending on. The Victron BMV-712 Smart Battery Monitor gives you state of charge, voltage, current, and historical data via Bluetooth. It’s the difference between knowing you have 73% charge and guessing based on voltage — and voltage is a terrible proxy for state of charge on lithium batteries. I’ve seen a Battle Born sitting at 13.1V read anywhere from 40% to 85% depending on load and temperature. The BMV-712 tells you exactly where you are.

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Running a full Victron system, the Cerbo GX with a touchscreen display gives you a live dashboard of every component. It’s $300 worth of peace of mind on a $4,000 system. On a long trip, that dashboard becomes part of your morning routine.

The System That Actually Works

Here’s the build I’d put together today for a two-person rig running extended off-grid trips:

• Two Renogy 100W monocrystalline panels in series (200W total) on a roof rack with one tiltable mount
• Victron SmartSolar MPPT 100/20 charge controller
• Two Battle Born 100Ah LiFePO4 batteries wired in parallel (200Ah, 2,400 Wh nominal)
• Renogy DCC50S for alternator charging
• BESTEK 300W pure sine inverter for AC loads
• Victron BMV-712 battery monitor
• Blue Sea Systems fuse block and distribution panel

Total cost: approximately $2,400–2,800 depending on where you source components. It produces 780–900 Wh/day in average sun conditions, stores enough for 1.5 days of autonomy, and charges to full in 4–5 hours of driving. I’ve run this exact configuration on two builds — a week in the Sonoran Desert and 10 days on the coast of British Columbia — without a single day of power anxiety.

Build the power budget first. Size the battery second. Then size the panels to fill it. In that order, every time. Get that sequence right and you’ll never be the guy running a generator at dawn.

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