Installing Solar Panels on a Motor Home, Caravan or Boat

  1. How It Works

Installing a solar panel on your motor home or boat will allow the battery that supplies your electrical power to be constantly charged up whenever there is daylight falling on the panel/s. Whist the engine is running the batteries will be charged by the alternator but once the engine is stopped the solar panels will keep the onboard system battery charged even if the engine is not used at all.

The amount of power generated is directly related to the amount of light falling on the panel. The most power will be generated when full sun on a cold day is shining at 90 degrees onto the panel. This is not always possible on most vehicle installations as the panels will be fixed horizontally so the maximum power output will be reduced by approximately 5-10%.

The solar panel will charge the battery via a solar charge controller which prevents the battery being over or under charged so will automatically ensure the correct voltage is applied depending on the battery’s state of charge. If two batteries are connected in parallel then both batteries will be charged and reach the same charge state equally. A 12 volt system will require solar panels rated at at least 17 volts VMP to charge correctly and a 24 volt system will require 30 volts VMP. By wiring two 17 volt panels in series you will have 24 volt charging power if you have a 24 volt system.

Most motor homes have a 12 volt system so single 17 volt panels will be perfect. If you require more power then wiring more panels in parallel will give the same voltage but double the amps which gives more watts of power to charge the batteries.

  1. The Kit

A basic solar kit will include the following:-

  • solar panel
  • mounting brackets
  • solar connectors
  • solar cable
  • roof entry gland
  • controller
  • fused cable to battery
  • terminals / adhesive etc.
  1. The Installation

The solar panel should be installed on as flat a surface as possible and as close to the battery as possible. Long cable lengths will affect the voltage drop so shorter is better. If the voltage drop exceeds 3% it may be necessary to increase the cable rating. We offer 6 metres of cable of 4mm2 which is OK for 12 volt systems. Remember you need two cables from the panel so total distance would be 3 metres from panel to battery.

The panel mountings need to be temporarily fixed to the panel. The panel is then placed in it’s position and the mountings marked on the roof. Consider where the cables need to run to get easy access to the inside and down to the battery. The roof entry gland will ensure the cables are installed in a waterproof enclosure which is also glued to the outside of the vehicle; preferably with cable gland nuts facing rearwards. It will be necessary to drill a small hole for the cable entry and the entry gland glued over this.

The panel mountings can be glued using the adhesive supplied which is designed to remain flexible to allow for any flexing in the bodywork or thermal expansion. The adhesive is designed to be used for fixing fibreglass, metal, plastics and wood etc. The full specifications are available here:

Apply a good level of adhesive to leave about a 2-3mm bed and ensure the air is squeezed out by applying gentle pressure until adhesive is seen around the edge of the mountings.

The adhesive will skin over within a few minutes but needs 24-48 hours to fully cure. It is best to ensure the panel cannot move until the adhesive is fully cured.

NB. You may fix the panel to the mountings using adhesive or by drilling and screwing through the plastic mounts.

Ensure the cable is connected to the MC4 connectors from the panel and is routed through to the battery before fixing panels in place. Also ensure that any cables cannot come in contact with the roof as this will cause noise when underway. Zip tying the cables to the panel frames is advised.

The cable needs to be run down to the controller which can be installed in any convenient position inside the vehicle. It is not necessary to be able to constantly monitor the controller although LED lights will show the state of charging if required.  Ensure the BATTERY IS CONNECTED FIRST and then the solar panel.

From the controller cables can be run to the battery ensuring a fuse is included (supplied) with a fuse rated at lower than the cable being used. This will ensure the battery circuit is protected from any accidental short or overload. Connection to the battery is made with ring terminals (supplied).

If an inverter is being used this needs to be connected directly to the battery NOT the controller.

Any 12 volt loads such as LED lighting can be connected directly to the controller’s DC output.

Remember when parking that any shading of the panels will seriously impact their output. Parking near trees will also attract dirt which will need to be cleaned off to ensure continued maximum efficiency.

If you may consider adding another panel in the future bear this in mind when you install the first panel. Adding another panel is very easy as it can be connected with a simple cable branch connector if the second panel is installed next to the first. The controller may need to be 20 amps to ensure it is not overloaded by two panels output.

Additional information:

Panels specifications:

Solar controller instructions:

Battery information - Deep cycle or Leisure battery?

Deep cycle battery is far superior to a Leisure battery. BEWARE! Leisure batteries sold as Deep Cycle- these are NOT true deep cycle and will not give you the amount of capacity you require. Leisure batteries are for starting engines so if you have no engine attached to this battery why buy a leisure battery?