Series vs Parallel Wiring for RV/Caravan Solar: Step-by-Step with Diagrams & Amp Math

When setting up a solar system on your caravan, RV, or off-grid setup, one of the first questions you’ll face is whether to wire your panels in series or parallel.
Your wiring choice affects voltage, current, cable size, shade performance, and even which solar charge controller (MPPT or PWM) will work best.

In this guide, we’ll explain the difference, show you step-by-step wiring diagrams, and help you calculate amps, volts, and cable sizing for your setup.

1. Understanding the Basics

Each solar panel has two main electrical specifications:

• Voltage (V) – how much electrical “pressure” the panel produces.

• Current (A) – how much electrical “flow” the panel can supply.

When panels are wired together, voltage and current combine differently depending on how you connect them.

2. What Is Series Wiring?

How It Works

In a series connection, the positive terminal of one panel connects to the negative terminal of the next.
This adds the voltages, while the current stays the same.

Example:
Two 200W panels rated at 18V and 11A each →

• Total voltage = 18V + 18V = 36V

• Current = 11A

Series Wiring Diagram (insert graphic):

• Show two panels side-by-side.

• Positive of Panel 1 connects to Negative of Panel 2.

• Remaining Positive and Negative leads go to the charge controller.

Advantages

✅ Higher voltage means lower current → less voltage drop over long cables.
✅ Ideal for MPPT controllers, which operate efficiently at higher voltages.
✅ Useful when panels are far from the controller (e.g., roof to battery bank).

Disadvantages

❌ Shading on one panel affects the whole string.
❌ Total voltage may exceed controller input limits — always check specs.
❌ Risk of mismatch losses if panels have different ratings or orientations.

3. What Is Parallel Wiring?

How It Works

In a parallel connection, all the positive terminals are joined together, and all the negatives are joined together.
This adds the currents, while voltage stays the same.

Example:
Two 200W panels rated at 18V and 11A each →

• Total voltage = 18V

• Total current = 11A + 11A = 22A

Parallel Wiring Diagram (insert graphic):

• Show two panels with positives connected together via an MC4 branch connector.

• Negatives also joined with another branch.

• Combined leads go to the controller.

Advantages

✅ Works well with PWM controllers and 12V systems.
✅ If one panel is shaded or fails, others continue producing.
✅ Easier to expand by adding extra panels.

Disadvantages

❌ Higher current → thicker cable needed to prevent voltage drop.
❌ More connectors and fusing required for safety.
❌ Not as efficient for long cable runs.

4. Series-Parallel (Mixed) Wiring

You can also mix the two to get a balanced voltage and current — for example, two pairs of panels wired in series, then joined in parallel.

Example:
Four 200W panels (18V, 11A each)

• Wire two in series (36V, 11A)

• Then parallel the pairs → total 36V, 22A

This hybrid layout is common in larger caravan or 24V systems.

Series-Parallel Diagram (insert graphic):

• Show 4 panels: two series strings joined with MC4 Y connectors into one pair of leads.

5. Amp Math & Cable Sizing Example

Let’s compare both methods using 2 × 200W panels and a 3-metre cable run.

? Tip: Higher voltage (series) reduces current and cable losses, but check your controller’s max PV input voltage — often 50V or 100V limit.
? Use a voltage drop calculator to confirm your wire gauge (we’ll soon include one in our Solar Cable Sizing Guide).

6. Shading & Performance

Shading affects the wiring type differently:

• Series: A single shaded panel reduces the current of the whole string.

• Parallel: Only the shaded panel’s output drops; others keep performing.

If your panels might experience partial shading (e.g., from roof vents or antennas), parallel wiring or using bypass diodes / optimisers is often better.

7. Choosing Between Series & Parallel for Your Caravan

8. Installation Tips

• Always check the maximum PV voltage (Voc) of your array versus your controller’s limit.

• Use MC4 connectors and weatherproof junctions for all external joins.

• Include inline fuses or breakers on each positive line when wiring in parallel.

• Use a multimeter to verify polarity before connecting to your controller.

• Mount panels securely with correct tilt and spacing for airflow.

9. Common Mistakes to Avoid

• Mixing panel types or wattages in series (causes mismatch losses).

• Forgetting to fuse each panel string in parallel setups.

• Exceeding voltage ratings on cold mornings (Voc rises in low temperatures).

• Using undersized cable (causes significant power loss).

10. Summary

Choosing the right wiring configuration can improve your system’s efficiency, reduce cable costs, and ensure consistent power for your caravan or RV.

11. FAQs

Q1: Can I mix series and parallel panels together?
Yes, but ensure each series string has panels of the same voltage and wattage before joining in parallel.

Q2: Which wiring is better for cloudy conditions?
Series wiring performs slightly better in low light, but if shading is frequent, go with parallel.

Q3: What fuse size should I use for parallel panels?
Each panel should be fused slightly above its short-circuit current (Isc). For example, 10A panels → use 15A inline MC4 fuses.

Q4: Does wiring affect charging speed?
Yes. Series wiring can improve MPPT controller efficiency, meaning faster charging in most full-sun conditions.

Q5: Can I upgrade from parallel to series later?
Yes, as long as your charge controller supports the higher input voltage. Always recheck specs before changing.

Need More Help?

If you’re unsure about your wiring layout, contact our support team for system sizing or wiring advice:
? support@starpoweradvancesolartechnology.com
? Chat live on our Help Centre