How to Size a Lithium Solar System for Your Van or RV (2025 Guide)

One of the most common questions we get at Lightharvest Solar is: "How much solar do I actually need?" Whether you're building out a Sprinter van, a school bus conversion, or a camper, sizing your lithium solar system correctly from the start will save you money, headaches, and dark nights in the middle of nowhere.

This guide walks you through the exact process we use when designing custom systems for our customers — no guesswork, no oversimplified rules of thumb.

Step 1: Calculate Your Daily Power Consumption

Before you buy a single panel or battery, you need to know how much energy you actually use each day. This is measured in watt-hours (Wh) or kilowatt-hours (kWh).

Go through every device you plan to run and estimate its daily use. Here's a realistic example for a full-time van dweller:

• 12V compressor fridge (60W × 8 hrs average run time) = 480 Wh

• Laptop + phone charging (60W × 4 hrs) = 240 Wh

• LED lighting (20W × 4 hrs) = 80 Wh

• Fan (30W × 6 hrs) = 180 Wh

• Misc (water pump, Starlink, etc.) = ~150 Wh

Total: ~1,130 Wh per day. That's a solid baseline for a two-person van setup. Digital nomads running Starlink and an induction cooktop regularly hit 1,500–2,000 Wh/day.

Step 2: Size Your Lithium Battery Bank

Here's where lithium (LiFePO4) makes a huge difference over AGM lead-acid. Lithium batteries can safely use 80–100% of their rated capacity. AGM batteries should only be discharged to 50% to avoid shortening their lifespan. That means a 100Ah lithium battery gives you roughly double the usable power of a 100Ah AGM.

We always recommend sizing for at least 2 days of autonomy — meaning your battery bank should hold enough power to run your setup for two full days without any solar input. This is critical for cloudy stretches in the Pacific Northwest (we know those all too well in Oregon).

Formula: Battery Bank Size (Wh) = Daily Consumption × Days of Autonomy

Using our example: 1,130 Wh × 2 days = 2,260 Wh. At 12V, that's roughly 188Ah of lithium. In practice, most van builds land in the 200–300Ah range for comfortable daily use.

Step 3: Size Your Solar Array

The goal of your solar panels is to replenish your battery bank on a typical day. But here's the catch: solar output varies dramatically depending on your location, season, and how much shade you're parked under.

A practical starting point: plan for 200 watts of solar per 100Ah of lithium battery capacity. So a 200Ah battery bank pairs well with 400W of solar panels. This ratio holds up well for most 3-season van living in the continental US.

If you spend winters in the Pacific Northwest, the Rockies, or anywhere with long cloudy stretches, size up. We regularly build systems with 600W+ of roof panels for full-time dwellers who need reliable power year-round.

Step 4: Choose the Right Charge Controller

Always use an MPPT (Maximum Power Point Tracking) charge controller for lithium systems — not the cheaper PWM type. MPPT controllers are 15–30% more efficient and properly manage the charging profile that LiFePO4 batteries require.

Size your MPPT controller to handle your full solar array with some room to grow. Victron SmartSolar controllers are our top recommendation — they're built to last, pair seamlessly with Victron's monitoring ecosystem, and handle the demands of full-time van life.

Step 5: Pick the Right Inverter

If you plan to run any AC devices — a laptop charger, blender, or induction cooktop — you'll need an inverter. Always use a pure sine wave inverter, not a modified sine wave. Modified sine wave inverters can damage sensitive electronics and don't play nicely with lithium battery systems.

To size your inverter, add up the wattage of every AC device you might run at the same time. That's your minimum inverter size. A 2,000W pure sine wave inverter covers most van builds comfortably.

Quick Reference: Common Van Solar System Sizes

• Weekend Warrior: 200W solar + 100Ah lithium — powers lights, phone charging, and a small fridge on short trips.

• Part-Time Nomad: 400W solar + 200Ah lithium — handles a fridge, fans, devices, and occasional laptop use.

• Full-Time Van Dweller: 600W solar + 300Ah lithium — reliable power for fridge, Starlink, lighting, devices, and a mini-split.

• Power-Hungry Builds (induction cooking, AC): 800W+ solar + 400Ah+ lithium — for serious off-grid living with no compromises.

Don't Guess — Get a Custom System Design

The rules of thumb above are a great starting point, but every build is different. Roof space, budget, how and where you travel, and what appliances you use all affect the ideal system for your specific situation.

At Lightharvest Solar, we specialize in designing custom lithium-based off-grid solar systems for vans, buses, RVs, campers, tiny homes, and cabins. Our team provides free tech support Monday through Friday, 10am–5pm, and we're happy to walk through your specific build with you.

Visit our Vehicle Solar Estimate page to get started, or call us at 971-712-6468. We're based in Coburg, Oregon and ship no-sales-tax to all 50 states.