Adding another solar panel to a motorhome or boat.

Adding another solar panel to a motorhome, boat or caravan.

adding another solar panel

Adding another solar panel can be very beneficial.

Are you thinking about adding another solar panel to your motorhome or boat? We hope the following article and diagrams answer any questions you may have.

Do I need another solar panel?

Perhaps your batteries are not charging up enough during the day. Or perhaps you plan to add more appliances to your motorhome, boat or caravan. If you plan to add another solar panel to beef up your existing system the following checklist should help.

1. Is my charge controller large enough?

The charge controller handles all the electrical current from the solar panel to the battery. So it must have the capacity to comfortably carry the extra current from your additional solar panel.

Add together the wattage of the two solar panels. Your charge controller has to be able to handle at least 10% more than this. If your existing solar panel is 100 watts and you want to add a 50 watt solar panel you will need a charge controller that can handle 150 watts plus 10%. So a charge controller of at least 165 watts capacity, will do the job.

Solar panel charge controller

SunWorks SB2C charge controller. 240 watts.

You controller will usually have the wattage written on the label e.g 100 Watts, 200 Watts etc..

If you are not sure about this please give us a call.

2. Is the existing wiring good enough?

Usually, the additional solar panel is connected to the existing solar panel on the roof or deck. You can often use a simple adaptor to connect the two solar panels together. But first you should check that the wiring is in good condition and is of adequate size (thickness) for your additional solar panel.

Have a quick look at the wiring from your solar panel (see diagram 1 below).  You should find the following:

solar panel cable mc4

2-core cable with pre-assembled MC4 connectors

  1. There will be two wires from the solar panel to the charge controller. This might be two individual wires or it could be a 2-core cable with two wires inside. Note that your charge controller might be incorporated within a central control unit such as a Sargent.
  2. There will also be two wires from the charge controller to the battery. Again, these could be individual wires or a 2-core cable.
  3. If your existing system is a dual battery system (so it also charges the engine battery), you will find another pair of wires running from the charge controller to the second battery.
  4. You might also find a cable going to a remote display unit.

Make sure the wiring is in good condition. If you are thinking about adding to your system now is a good time to overhaul the wiring if necessary.

adding another solar panel

Connect two solar panels together with these adaptors

Check the wire size. It should be written on the wire. For systems up to 200 watts (total solar panel wattage) a wire size of 2.5 mm sq (14 AWG) is adequate as long as the total cable length from the solar panel to the battery is less than 8 metres.

For larger solar panel arrays you will need either 4 mmsq or 6 mm   sq cables. Please call us if you need more information about this.

3. Are my batteries okay?

It’s worth checking that the batteries are working well before adding another solar panel. If you find that they are discharging quickly take the battery to your local garage for testing. They should be able to test your battery quickly and easily.

4. What about the fuses?

Fused battery harness

The easy way to add a fuse to the battery connection

There should be a fuse between the charge controller and the battery. If you have a dual battery system there will also be a fuse between the charge controller and the engine battery.

If the system has been designed correctly the purpose of the fuse will be to protect the wiring. For wire sizes of 2.5 mmsq the fuse should not exceed 20 amps. For other wire sizes please call us.

5. Is there enough room for another solar panel?

Have a quick measure of the roof or deck space and make sure there is room for another solar panel. Remember to include the mounting brackets. These will add another 4 to 12 cm to the length and width of the solar panel.

6. I already have more than one solar panel. Can I add another?

We recommend a maximum of three solar panels connected together in parallel. If you want to use more than three solar panels in parallel you may need to take special precautions.

7. How do I fit another solar panel?

solar panel corner mounts

Solar panel corner mountings

You will probably want to fit either a standard rigid framed solar panel or a semi-flexible solar panel.

A rigid solar panel can be attached to the roof or deck using brackets or PVC mounting pads.

A semi-flexible panel should be glued directly to the surface. Your supplier should provide instructions on how to do this.

NOTE: Before doing any work on your solar panel system, cover the existing solar panels and remove the fuses between the charge controller and the batteries.

adding another solar panel

Diagram 1. General wiring arrangement for a dual battery solar panel system. This diagram shows the wiring for a motorhome but also applies to a yacht or boat.


Adding another solar panel

Diagram 2. How to connect another solar panel if you have a connection or junction box.


Adding another solar panel

Diagram 3. How to connect another solar panel if you have a watertight gland.

In conclusion. Adding another solar panel.

Adding another solar panel is usually an easy matter. You must check that the wiring, charge controller and fuses are adequate and can handle the extra panel.

We hope you have found this article useful. If you have any questions about adding another solar panel of about any other aspect of mobile solar energy, please do not hesitate to contact us:

Tel: 020 8144 2475

Email: [email protected]