How to Size Your RV Solar System: A Step-by-Step Guide for DIY Installers

Designing your own off-grid RV solar system starts with one essential question: How much power do you actually use?

Getting this step right is critical. Oversize your system and you’ll overspend on components you don’t need. Undersize it, and you’ll end up frustrated — running out of power halfway through a weekend or relying on your generator more than you’d like.

In this guide, we’ll walk you through exactly how to size your RV solar system, including:

• How to calculate daily energy usage

• How to translate that into solar wattage and battery capacity

• Real-world tips from the field

Step 1: Estimate Your Daily Energy Use (Watt-Hours)

Every component in your RV draws power. The goal is to figure out how many watt-hours (Wh) you use in a day.

🔋 Here’s how to calculate it:

Make a list of everything you’ll run — fridge, lights, fan, Starlink, coffee maker, etc.

Then for each one:

• Wattage × Hours used per day = Daily watt-hours

Step 2: Determine Battery Bank Size

Batteries store the energy your solar panels collect. You’ll want a battery bank that can cover at least one full day of use, plus buffer for cloudy days.

🧮 Battery Sizing Formula:

Battery capacity (Wh) = Daily energy use × Number of backup days

Using the table above:

• 2,350 Wh/day × 2 days = 4,700 Wh

Now divide by your battery voltage (typically 12V):

• 4,700 ÷ 12 = 392 amp-hours

If you’re using LiFePO₄, you can safely use nearly 100% of your capacity. For AGM or lead-acid, multiply by 2 (due to 50% usable depth of discharge).

Step 3: Determine Solar Panel Wattage

Your solar array should replenish your battery bank based on daily use, ideally with a margin for inefficiencies and cloudy days.

🔆 General Sizing Rule:

Solar wattage = Daily use ÷ Average sun hours × 1.3 (buffer)

Assume 5 hours of usable sun:

• 2,350 ÷ 5 = 470

• 470 × 1.3 = 610W of solar

So, a 600W–800W array would be ideal for this scenario.

Step 4: Choose the Right Charge Controller

Solar panel voltage needs to be properly regulated before reaching your batteries.

• MPPT controllers are more efficient and allow higher panel voltages.

• PWM controllers are only recommended for smaller, budget systems.

Match the voltage and amperage specs of your array to your controller. We typically use Victron SmartSolar MPPT controllers for their flexibility, performance, and Bluetooth monitoring.

Step 5: Consider Inverter Size (if you run AC appliances)

If you plan to run 120V AC appliances, you’ll need an inverter.

• Add up the peak watts of all AC loads you may run at once.

• Choose an inverter with 20–30% headroom.

Example:

• Coffee maker (1,000W) + laptop (90W) = 1,090W

• Recommended inverter: 1,500W–2,000W pure sine wave

If you’ll ever be plugged into shore power or want to run a charger, we recommend an inverter/charger combo, like the Victron MultiPlus.

Pro Tips from the Field

• Start with a 1-day energy audit. Run your system as normal and measure power draw using a battery monitor or watt meter.

• Oversize your solar slightly. Especially if you plan to camp in the shoulder seasons or shade.

• Plan your wiring early. Use heavy enough gauge to prevent voltage drop.

• Roof real estate matters. Ensure you have space and mounting clearance.

Need Help With the Design?

Sizing a system right is about more than just numbers — it’s about how you use your RV. At Cascade RV Solar Solutions, we design systems to match your rig, your goals, and your lifestyle.

We can even drop-ship a custom solar kit right to your door — with everything you need and nothing you don’t.

👉 Schedule a free solar consult now