How to Size a Solar System for Caravan, RV or Tiny Home (Step-by-Step)

Sizing a solar system correctly is one of the most important steps in creating a reliable off-grid setup. Whether you’re planning a caravan, RV, or tiny home system, the right combination of solar panels, batteries, and controllers ensures you have enough power for your appliances without overspending.

This guide will take you step-by-step through calculating your energy needs, choosing the correct panels and batteries, and optimising your system for maximum efficiency.

? Step 1: Calculate Your Daily Energy Usage

To size your system, start by determining how much energy you consume each day.

1. List all appliances you’ll use (fridge, lights, TV, water pump, charging devices, etc.).

2. Record or estimate power consumption in watts (W).

3. Multiply watts by hours used per day to get watt-hours (Wh).

Example:

⚡ Step 2: Decide Your Battery Capacity

Your battery bank stores energy for use when the sun isn’t shining. To calculate capacity:

1. Decide the number of days autonomy (how many days you want to run without sun).

2. Account for battery type:

   • Lead-acid / AGM: Use 50% depth of discharge (DoD).

   • Lithium / LiFePO4: Can use up to 80–90% DoD.

Battery size formula:

Battery Capacity (Ah)=Daily Usage (Wh)×Days AutonomySystem Voltage (V)×DoD\text{Battery Capacity (Ah)} = \frac{\text{Daily Usage (Wh)} \times \text{Days Autonomy}}{\text{System Voltage (V)} \times \text{DoD}}Battery Capacity (Ah)=System Voltage (V)×DoDDaily Usage (Wh)×Days Autonomy

Example (12V Lithium, 1 day autonomy, 1770 Wh):

Battery Ah=1770×112×0.9≈164Ah\text{Battery Ah} = \frac{1770 \times 1}{12 \times 0.9} \approx 164 AhBattery Ah=12×0.91770×1≈164Ah

☀️ Step 3: Calculate Solar Panel Requirements

Now calculate the number of solar panels you need to recharge your battery bank.

1. Consider the average sun hours per day for your location. For Australia, use:

   • Coastal areas: ~4–5 hours/day

   • Inland / sunny regions: ~5–6 hours/day

2. Use this formula:

Required Panel Power (W)=Daily Usage (Wh)Sun Hours per Day\text{Required Panel Power (W)} = \frac{\text{Daily Usage (Wh)}}{\text{Sun Hours per Day}}Required Panel Power (W)=Sun Hours per DayDaily Usage (Wh)

Example (1770 Wh, 5 sun hours/day):

Required Panel Power=17705=354W\text{Required Panel Power} = \frac{1770}{5} = 354 WRequired Panel Power=51770=354W

Round up to nearest standard panel size. For example:

• 1 × 400W panel

• 2 × 200W panels

• 3 × 120W panels

⚙️ Step 4: Choose the Right Solar Charge Controller

The charge controller protects your battery and ensures efficient charging:

• MPPT controllers are more efficient (especially for long wire runs and higher voltages).

• PWM controllers are cheaper and simpler for small 12V systems.

Controller size formula:

Controller Current (A)=Total Panel WattageSystem Voltage\text{Controller Current (A)} = \frac{\text{Total Panel Wattage}}{\text{System Voltage}}Controller Current (A)=System VoltageTotal Panel Wattage

Example:

Controller Current=400W12V≈33A\text{Controller Current} = \frac{400W}{12V} \approx 33 AController Current=12V400W≈33A

Choose the next standard size: 40A MPPT controller.

? Step 5: Consider System Voltage

Most small caravan/RV systems use 12V, but larger setups may benefit from 24V or 48V to reduce current and wiring losses.

• 12V: Simple, cheaper components, ideal for systems <600W.

• 24V/48V: Better efficiency for larger systems (>1 kW), longer wire runs.

? Step 6: Optimise Layout & Placement

• Place panels with maximum sun exposure (north-facing in Australia).

• Avoid shading from vents, air conditioners, trees, or roof accessories.

• For caravans and RVs, tilt adjustable panels for peak sun hours.

✅ Step 7: Double-Check System & Add Safety Margin

• Add 10–20% extra panel wattage to compensate for cloudy days or seasonal variations.

• Include fuses, breakers, and proper wiring sizing.

• Ensure battery and controller ratings match your panel output.

? Example System for Caravan

This system comfortably powers fridge, lights, charging devices, and small appliances while staying efficient and safe.

⚡ Tips for Off-Grid Success

• Use energy-efficient appliances to reduce daily watt-hours.

• Monitor battery and solar output with a smart display or app.

• Consider expandable systems — start smaller and add more panels or batteries as needed.