Solar Panel Installation & MPPT Charge Controller Setup
How to install a roof-mounted solar panel on your motorhome or caravan, wire an MPPT charge controller, and maximise charging efficiency.
What This Is
A 100W solar panel can provide 30–50Ah per day in a UK summer — enough to maintain a 100Ah leisure battery through normal use. This guide covers the complete installation process.
Tools & Parts Required
- Solar panel (100W–200W)
- MPPT charge controller
- MC4 connectors and crimping tool
- 6mm² twin-core cable
- Cable gland (roof entry)
- Drill and step bit
- Multimeter
- Sikaflex 512 sealant
- Lap sealant
Step-by-Step Instructions
- 1
Select a roof location that avoids shading from roof vents, satellite dishes, and roof bars. South-facing is optimal in the UK. Locate roof battens with a stud finder before drilling.
- 2
Mark bracket positions ensuring they align with roof battens. Apply a generous bead of Sikaflex 512 under each bracket foot before bolting down. Torque bolts to 8–10Nm. Apply lap sealant over the bolt heads and bracket edges.
- 3
Drill a 20mm hole for the cable entry gland, positioned close to the panel and away from roof vents. Apply Sikaflex around the gland flange before screwing down. Feed the MC4 extension cables through the gland into the vehicle interior.
- 4
Run 6mm² twin-core cable from the roof entry gland to the charge controller location. Connect the positive and negative panel cables to the PV input terminals on the MPPT controller. Do not yet connect the battery.
- 5
Connect the battery terminals to the controller BATTERY terminals — positive first, then negative. Configure the battery type (AGM, gel, lithium) on the controller display. Set absorption voltage (14.4V for AGM, 14.6V for lithium) and float voltage (13.6V for AGM).
- 6
Connect 12V loads to the LOAD terminals if required. Fit an appropriately rated fuse within 300mm of the battery on the positive cable.
- 7
Cover the panel and check all connections. Uncover the panel — the controller should show PV voltage within seconds. A 100W panel in full UK summer sun will deliver approximately 5–6 amps.
Common Mistakes to Avoid
- Insufficient sealant around roof penetrations — the leading cause of damp ingress
- Using undersized cable — 6mm² minimum for runs over 3 metres
- Connecting the panel before the battery — always connect battery first
- Not accounting for shading — even partial shading of one cell can reduce output by 50%
Safety Warnings
- Working on the roof carries a fall risk — use appropriate access equipment and never work alone.
- Solar panels generate voltage as soon as exposed to light; cover with a blanket during installation.
- All electrical work must comply with BS 7671 wiring regulations.
When to Call a Professional
If you are not confident working at height, or if the electrical installation requires integration with a complex existing system.
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