🌞 Solar Panels Explained (Campervan Guide)

Everything a van builder needs to know before choosing and installing solar panels.

Solar panels are one of the most important upgrades in a campervan electrical system. They keep your leisure batteries topped up, reduce dependency on hook-up or driving, and give you genuine off-grid freedom.

This guide explains the types of solar panels, how they work, how much power you can realistically expect in the UK, and how to size your system properly.

1. How Solar Panels Work

A solar panel converts sunlight into DC electricity (typically 18–22V open circuit).
This power is fed into a solar charge controller, which safely regulates the voltage down to charge your 12V or 24V battery bank.

Basic flow:

Solar panel → Charge controller → Leisure batteries → 12V system

Your fridge, lights, fans, pumps, etc. all run from the batteries — not from the panel directly.

2. Types of Solar Panels for Campervans

🔹 Monocrystalline (Recommended)

• Highest efficiency

• Best in low-light (UK cloudy weather)

• Longest lifespan

• Typically black-coloured
  Best all-round choice for most vans.

🔹 Polycrystalline

• Cheaper

• Lower efficiency

• Perform worse in shade

• Blue speckled appearance
  Good budget option but less ideal for UK conditions.

🔹 Flexible Panels

• Lightweight

• Can bond directly to the roof

• Follow curved roof shapes
  BUT:

• Lower efficiency

• Overheat more easily

• Shorter lifespan

• Often fail after 2–4 years
  Use only if weight or stealth is the priority.

🔹 Rigid Glass-Framed Panels (Recommended)

• Best performance & durability

• Ventilated air gap prevents overheating

• Can last 25+ years

• Reliable output
  Ideal for campervans—especially for fridges.

3. Series vs Parallel Wiring

How you wire your panels into your charge controller affects performance.

Series Wiring

Voltage adds, current stays the same.

Pros:
✓ Best efficiency in good sunlight
✓ Lower current = thinner cable
✓ Works perfectly with MPPT controllers

Cons:
✗ Shade on one panel reduces output from the whole array

Parallel Wiring

Voltage stays the same, current adds.

Pros:
✓ Shading affects only one panel
✓ Better in woodland / UK winter / cloudy conditions

Cons:
✗ Requires thicker cable
✗ Higher current = more voltage drop
✗ Slightly less efficient overall with MPPT

Best setup for most vans

Series for open-roof vans with minimal shade
Parallel for roof bars, roofboxes, vents causing shadows

4. How Much Solar Do You Actually Need?

Here’s realistic UK output (not brochure numbers):

UK winter solar is extremely poor. Never rely on solar alone for heating or fridges in winter.

5. Choosing the Right Charge Controller

PWM Controllers

• Cheap

• Basic

• Good only with small panels
  Not recommended for modern campervan systems.

MPPT Controllers (Recommended)

• 30–40% more efficient in cloudy weather

• Handle high-voltage panels in series

• Maximise every watt of energy
  Mandatory for fridges, lithium banks, and year-round use.

6. What Size Solar System Should I Install?

For Weekenders

• 100–150W

• Keeps lights, USB, fan topped up

For Full-Time Vanlifers

• 200–350W

• Essential for running a 12V fridge reliably

For Off-Grid Lithium Systems

• 400W+ recommended

• Ideal for heavy loads like laptops, routers, fans

7. Solar Panel Cable Sizes

Solar runs are normally long, so use thicker cable to reduce voltage drop.

Never use cheap speaker cable — use proper automotive thin-wall or solar PV cable.

8. Fusing & Safety

Every positive cable must have a fuse near the power source.

Solar system fuses:

• Between panel & controller (if parallel)

• Between controller & battery

• Between battery & distribution panel

Common sizes: 10A, 15A, 20A, or 30A depending on cable and controller.

9. Roof Mounting Options

Rigid Panel Brackets

NB – We DO NOT recommend bonding only on rigid panels. You must use nuts/bolts or tech screws as well as adhesive when bonding brackets to your van, Whilst the adhesive itself is extremely strong, it is only as good as the paint on your van which,  on many vans, can be pretty poor, and simply flake off of its own accord given time.

• Corner mounts

• Side mounts

• Roof-rail clamps

• Adjustable tilt brackets

Flexible Panel Bonding

• Sikaflex / Dekasyl MS-2 or MS-5, etc

• 3M VHB tape
  Ensure the roof is absolutely clean before bonding.

10. Common Mistakes Van Builders Make

❌ Using 1.5–2.5mm² cable
❌ No fuse on the battery side
❌ Flexible panels glued flat (overheats and fails)
❌ MPPT placed too far from the battery
❌ Putting panels in shade behind roof vents or fans
❌ Expecting solar to run heaters