How to Size a Solar Panel and Battery System for Your Van Build

How to Size a Solar Panel and Battery System for Your Van Build

One of the biggest mistakes new van builders make is guessing at their solar and battery setup. They either underbuild and run out of power on the second day — or overbuild, spend twice what they needed, and give up roof space and payload capacity they can't afford to lose.

The fix is simple: do the math before you buy. This guide walks through how to size a solar panel and battery system for a camper van or RV, step by step, using real numbers. By the end, you'll know exactly how much panel wattage, battery capacity, and what charge controller you need.

Step 1: Figure Out Your Daily Power Consumption

Everything starts here. You need to know how many watt-hours (Wh) you'll use in a typical day on the road.

Make a list of every device you plan to run, estimate its wattage and how many hours per day you'll use it, then multiply:

Wh per day = Watts × Hours

Here's a realistic example for a typical van build:

Device Watts Hours/Day Wh/Day
12V compressor fridge 50W avg 24 1,200
LED lights (4 puck lights) 20W 5 100
Laptop charging 65W 3 195
Phone charging (x2) 15W 3 45
Roof vent fan 15W 8 120
Wi-Fi hotspot 10W 12 120
Total 1,780 Wh

Your number will be different. If you're running a diesel heater controller, a CPAP machine, or a microwave, add those in. The key is to be honest about what you'll actually use — not what you hope you'll use.

Not sure about your numbers? Use our free Power Station Size Calculator to estimate your daily load in under 2 minutes.

Step 2: Size Your Battery Bank

Your battery bank needs to store enough energy to get you through a full day — plus a safety margin for cloudy days, inefficiency losses, and battery health.

The formula:

Battery capacity (Wh) = Daily consumption × 1.5

That 1.5× multiplier accounts for two things: inverter efficiency losses (typically 10–15%) and the fact that you should never discharge a lithium battery below 10–20% regularly if you want maximum lifespan.

Using our example: 1,780 Wh × 1.5 = 2,670 Wh

To convert to amp-hours (Ah) at 12V:

Ah = Wh ÷ 12

2,670 ÷ 12 = 222 Ah

So you'd want at least 200Ah of lithium battery capacity — ideally 300Ah if you want comfortable headroom for cloudy stretches or heavier usage days.

What we recommend

For most van builds, a single Renogy 12V 200Ah Lithium Battery PRO with Bluetooth hits the sweet spot — 2,560Wh of capacity with built-in Bluetooth monitoring so you can check your state of charge from your phone. At $899.99, it's one of the best value-per-Wh options in the LiFePO4 market.

If you're running a heavier load or want multi-day autonomy without solar, step up to the Renogy 12V 300Ah Mini Lithium Battery — 3,840Wh of capacity in a surprisingly compact form factor. This is the highest Wh-per-dollar option in the Renogy lineup.

For lighter builds — weekend trips, minimal electronics — the Renogy 12V 100Ah Lithium Battery PRO with Bluetooth at $599.99 is a clean entry point with room to add a second unit later.

Step 3: Size Your Solar Panels

Solar panels recharge your batteries during the day. The goal is to put back at least as much energy as you use — ideally more, so you have a buffer.

The formula:

Panel wattage needed = Daily consumption ÷ Peak sun hours

"Peak sun hours" is the average number of hours per day where your panels produce near-rated output. In the US, this ranges from about 4 hours (Pacific Northwest, winter) to 6+ hours (Southwest, summer). A conservative planning number for full-time van life is 4–5 peak sun hours.

Using our example: 1,780 Wh ÷ 4 hours = 445W of solar panel capacity

But panels don't operate at 100% efficiency in real-world conditions. Heat, angle, partial shading, and wiring losses eat into output. A realistic efficiency factor is about 75–80%.

Adjusted panel wattage = 445W ÷ 0.75 = ~593W

Rounding to available panel sizes, you'd want 400–600W of panels for a build with this consumption profile.

What we recommend

For permanent roof-mounted setups, the Renogy 200W 12V Solar Premium Kit with Rover 20A MPPT Charge Controller is a great starting point at $529.99 — it includes two 100W rigid panels and an MPPT charge controller in one box. Add a second kit or pair it with additional panels to reach your target wattage.

For portable and ground-deployable setups, the suitcase-style panels are ideal for van builders who don't want to permanently mount anything on the roof:

The advantage of suitcase panels: you park in shade for comfort and deploy the panels in the sun. Best of both worlds.

Step 4: Choose the Right Charge Controller

The charge controller sits between your solar panels and your battery. It regulates the voltage and current to safely charge your battery bank. For LiFePO4 batteries, you need an MPPT charge controller — not PWM. MPPT controllers are 20–30% more efficient and extract significantly more usable energy from your panels.

How to size your charge controller:

Minimum controller amps = Panel wattage ÷ Battery voltage

For a 400W panel array on a 12V system: 400 ÷ 12 = 33A minimum

Always round up to the next available controller size to give yourself headroom and room to add panels later.

What we recommend

  • Renogy Rover Li 40A MPPT with Bluetooth — $209.99 — Handles up to ~520W of panels at 12V. This is the sweet spot for most van builds. Bluetooth monitoring pairs with the Renogy app and with the Bluetooth batteries for a fully connected system.

  • Renogy Rover Li 60A MPPT — $429.99 — Handles up to ~800W at 12V. The right pick if you're running 400W+ of panels and want room to expand.

  • Renogy Rover Li 100A MPPT — $749.99 — Handles up to ~1,300W at 12V. For serious builds with large panel arrays and 300Ah+ battery banks.

Putting It All Together: Example Builds

The Weekender (light use, under $1,000)

  • 100Ah LiFePO4 battery
  • 200W portable suitcase panel kit
  • 20A MPPT charge controller (included in kit)
  • Good for: weekend trips, minimal electronics, phone and laptop charging

The Full-Timer (moderate use, $1,500–$2,000)

  • 200Ah LiFePO4 battery with Bluetooth
  • 400W of solar (roof-mounted or portable)
  • 40A MPPT charge controller with Bluetooth
  • Good for: full-time van life, compressor fridge, laptop, lights, vent fan

The Power User (heavy use, $2,000+)

  • 300Ah LiFePO4 battery
  • 600W+ of solar
  • 60A MPPT charge controller
  • Good for: full-time living with heavy electronics, multiple devices, extended cloudy stretches

The Bottom Line

Sizing a van solar system isn't complicated once you break it into four steps: calculate your daily usage, size the battery to cover it with margin, size the panels to replenish it daily, and pick a charge controller that can handle the array.

The most common mistake is undersizing — either the battery bank or the solar. Building a little bigger than you think you need today saves you the hassle and cost of upgrading later.

Browse TrailVault's full lineup of solar panels, LiFePO4 batteries, and charge controllers — all shipped free with full manufacturer warranty.

Need help figuring out the right combination for your build? Use our Power Station Size Calculator or reply to any of our emails — we're happy to help.

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