How to Wire a Solar Panel in a Campervan
This guide explains how to wire a campervan solar panel safely and correctly using a charge controller, fuse protection and the right cable size. Learn the correct wiring order, cable routing strategy and how to connect solar panel to charge controller and leisure battery in a reliable 12V system.
How campervan solar wiring works
A campervan solar system charges the leisure battery through a solar charge controller. The controller sits between the solar panel and the battery, regulating charging voltage and current so the battery can be charged safely.
In most campervan installations, the wiring path follows the same basic pattern:
- solar panel mounted on the roof
- solar cable routed through a roof gland
- charge controller mounted inside the van
- fused cable from controller to leisure battery
- battery charging through the controller output
Basic campervan solar wiring layout
Most campervan solar systems use the same core layout, whether the panel is 100W, 200W or part of a larger roof array. Once this layout is understood, the installation becomes much easier to plan.
Step-by-step campervan solar wiring order
1. Mount the solar panel securely
The solar panel is usually mounted to the roof using brackets, rails or bonded mounts depending on the vehicle and panel type. Good mounting matters because the cable route normally starts from the junction box or cable tails on the panel.
- avoid sharp bends near the panel cable exit
- keep the cable protected from movement and rubbing
- plan the cable route before fixing the panel permanently
2. Route the cable through the roof gland
The cable entry gland protects the roof penetration where the solar cable enters the vehicle. This is one of the most important points in the installation because it must stay weatherproof over time.
- use UV-resistant solar cable on the roof
- seal the gland properly using suitable adhesive and sealant
- secure the cable inside the van so it cannot move around
3. Connect the solar cable to the charge controller
The incoming solar cable is connected to the solar input terminals on the controller. At this stage, polarity matters and the positive and negative conductors must be kept consistent throughout the system.
4. Connect the controller to the leisure battery
The controller output is then wired to the battery using a shorter, usually heavier cable run. This side often carries more current than many people expect, especially in 12V MPPT systems.
5. Install the fuse close to the battery
The fuse should normally be installed on the positive cable close to the leisure battery. This helps protect the wiring in case of a fault or short circuit.
Where each cable goes in a campervan solar system
There are usually two main DC cable sections in a campervan solar installation, and they should not be treated as identical.
| Cable Section | Connects | Main Design Concern |
|---|---|---|
| Panel to controller | Solar panel or array to charge controller input | Roof routing, cable length and voltage drop |
| Controller to battery | Charge controller output to leisure battery | Higher charging current, short run and fuse protection |
These two cable sections often need different cable sizes, especially when the controller is MPPT and the system runs at 12V.
Connecting the solar panel to the charge controller
The solar panel connects to the dedicated solar input side of the controller. This connection brings panel power into the system and is often routed from the roof down to a cabinet, seat box or service area where the controller is installed.
- panel positive to controller solar positive
- panel negative to controller solar negative
- keep polarity consistent from roof to controller
- use suitable connectors and strain relief where needed
In many campervans, this run is physically longer than the battery-side cable, so voltage drop becomes an important factor when sizing the solar cable.
Connecting the controller to the leisure battery
The controller output cable connects the charge controller to the leisure battery. This cable run is often short, but current can be significantly higher here than on the panel side. That is one reason why this cable often needs to be thicker.
- controller battery positive to battery positive through a fuse
- controller battery negative to battery negative
- keep this run short and neat
- use cable and fuse sizes matched to controller output current
Where to place the fuse in campervan solar wiring
A fuse is normally installed on the positive cable between the charge controller and the leisure battery, placed as close to the battery as practical. This protects the cable in the event of a short circuit or fault.
- install fuse close to the battery positive terminal
- match fuse size to the circuit and cable used
- do not rely on cable alone for protection
The exact fuse size depends on controller output current, cable size and installation design.
Open Solar Fuse Size GuideChoosing the correct cable size for campervan solar wiring
Correct cable sizing is one of the most important parts of wiring a campervan solar system properly. Using cable that is too small can increase voltage drop, reduce charging efficiency and create unnecessary heating in the system.
The cable size normally depends on:
- solar power and current
- system voltage
- one-way cable length
- acceptable voltage drop
- whether the cable is on the panel side or battery side
Longer runs and higher current generally require thicker cable.
Open Solar Cable Size GuideMPPT vs PWM wiring differences
The basic wiring layout looks similar with both controller types, but the electrical behaviour is not exactly the same. MPPT controllers often allow the panel side to run at a higher voltage and lower current, while the battery side still charges at battery voltage.
| Controller Type | Panel Side Behaviour | Practical Effect |
|---|---|---|
| MPPT | Higher voltage, lower current on panel side | Battery-side cable often becomes the heavier section |
| PWM | Panel voltage closer to battery voltage | Panel-side current may be closer to battery-side current |
This is why a campervan solar installation should not be sized purely from a generic diagram without checking the actual controller type.
Read MPPT vs PWM GuideTypical campervan solar wiring example
Here is a simple example of a common campervan solar setup:
| Component | Typical Example | Comment |
|---|---|---|
| Solar panel | 200W roof-mounted panel | Typical single-panel campervan setup |
| Panel cable | 4mm² or 6mm² solar cable | Depends on roof run length and controller type |
| Charge controller | 20A MPPT controller | Common choice for moderate systems |
| Battery-side cable | 10mm² cable | Often heavier than the panel-side cable |
| Fuse | 30A fuse near battery | Typical practical protection level for this type of setup |
Common campervan solar wiring mistakes
- connecting a solar panel directly to the battery
- installing the fuse too far from the battery
- using the same cable size for both system sections without checking current
- ignoring voltage drop on longer panel runs
- routing cable where it can rub against sharp edges
- not checking the controller manual for connection order
Many campervan solar problems are caused by wiring details rather than the panel itself. A good installation is usually the result of careful routing, correct cable sizing and sensible fuse placement.
Use the Solar Cable Calculator PRO
The easiest way to confirm correct cable size is to calculate the panel-side cable and the controller-to-battery cable separately. That gives a much more realistic result than assuming one cable size fits the whole system.
Open Solar Cable Calculator PRORelated solar wiring guides
Plan your campervan solar wiring correctly
Use the MKGT Solar Cable Calculator PRO to estimate the correct panel-side and battery-side cable sizes before wiring your campervan solar charging system.
Open Solar Cable CalculatorElectrical installation safety notice
This guide is provided as a general reference for wiring solar panels into campervan 12V leisure battery systems.
Correct solar wiring depends on controller type, cable size, fuse protection, connection order, polarity, routing method and manufacturer specifications.
Always confirm the charge controller manual before installation and verify that cable size, fuse protection and connectors are suitable for the real current in the system.