Choosing a solar panel system. A little technical help.

A few notes for those who would like more information about choosing and installing a solar panel system in any 12 volt environment. This includes motorhomes, boats and caravans.

These straightforward notes cover the best types of solar panels to use.  We will also provide information on solar panel charge controllers, and all the other components you will need for your solar panel system.

Which solar panel should I choose?

Solar panel system

Rigid framed, monocrystalline solar panel

Always use monocrystalline solar panels. This is the best technology for 12 volt charging applications. Definitely the most efficient silicon based material in common use.

Other cell technologies include polycrystalline silicon which is not as efficient and is now a little out of date. Also available are “thin-film” amorphous silicon panels. These have a very low efficiency. You will need about twice the area of solar panel to achieve the same power output as a monocrystalline silicon panel.

Rigid aluminium framed solar panels are the most commonly available. Also becoming very popular are semi-flexible panels.

semi flexible solar panel

Semi-flexible monocrystalline solar panel with ‘back-contact” technology

These panels are useful if you want to mount the panel on a curved surface such as a motorhome or caravan roof. If you are looking for a semi-flexible panel make sure it is of the monocrystalline type and uses ‘back-contact’ technology. This combination will give the best possible efficiency.

Semi-flexible panels can be used on yachts and boats. These panels are very thin and have a TPT backing. This is a rugged plastic suitable for intensive outdoor use. The backing helps with the durability and flexibility of the panel.

When using on a boat or yacht install these panels away from areas where the crew are likely to walk. Mount them instead on cabin sides, or Velcro them to a bimini-top, wheel-house roof or spray-hood. In these locations, the panel will give a long, reliable life.

Marine quality solar panels.

solar systems for boats

Solara marine solar panels

For the ultimate in rugged solar panel systems for yachts, take a look at Solara marine solar panels. Solara M-Series are one of most successful solar panels in use for maritime applications. Built to withstand the harshest conditions.

Solara panels have been used during several Vendée Globe races. Many skippers sailing around the world rely on Solara quality. They are suitable for all yacht and boat applications. They are also be used on off-shore platforms, buoys and life-rafts.

The total thickness of these panels is only 3 mm. Embedded in the back is a strong aluminium alloy plate. An extremely resistant protective film on the front and back means they are rugged enough to withstand the harshest off-shore environments.

M-series solar panels can be bent slightly to follow a curved surface. They can be walked on. Screw or glue them to the deck of your yacht.

Solar Charge Controller with LCD

SunWorks SB1C charge controller with LCD display

Solar panel charge controllers.

Your solar panel system must have a charge controller to ensure complete and safe battery charging.

A good quality charge controller will:

  • protect your battery against overcharging
  • maximise the charge into your battery
  • prolong your battery’s life

A poor quality charge controller will steadily damage your batteries, costing you more in the long run.

The heart of the system.

We consider the charge controller to be the most important part of the solar panel system.

SunWorks charge controllers are well known for performance, appearance, and ease of use. We design and build our controllers specifically to meet the needs of 12 volt solar system applications. They are ideally suited to boats, motorhomes and caravans.

Our unique PWM and DuoPWM charging method will keep your batteries in peak condition and extend your battery life.

dual battery solar charge controller

SunWorks dual battery charge controllers

The best selling SunWorks charge controllers have a no-nonsense LCD display to keep you informed about the performance of your solar panel system and the state of your batteries. The display shows you exactly how much current is flowing from your solar panel. You will also see the voltage of your battery increase steadily as it charges up.

With a choice of colours, and using our concealed wiring arrangement, these controllers will enhance the interior of any motorhome, yacht or caravan.

The SunWorks range includes single battery controllers and dual battery controllers. A dual battery charge controller will charge your domestic and engine batteries from the same solar panel. Our dual battery controllers use SunWorks’ unique DuoPWM charge system ensuring that both batteries are optimally charged. A special ‘winter mode’ prevents either battery from falling too low in low-light or out-of-season conditions. Perfect if you have equipment connected to your engine battery such as an alarm system.

solar panel charge controller

SunWorks Z-Series charge controllers

SunWorks Z-series charge controllers.

We also manufacture the SunWorks Z-Series charge controllers. These lower cost controllers do not have a LCD display and are designed to be fitted out of sight, close to the battery. They use the same battery charging technology as all our controllers.

Instead of an LCD display, two flashing LEDs indicate the solar panel current and the battery state-of-charge. As the solar panel produces more current, the yellow LED stays on for longer. The green LED indicates the battery charge level in the same way.

If you need more information from your Z-series controller, we also produce the Z-series LCD Remote Display Unit. The optional remote display unit can be used with all Z-Series charge controllers. Position it anywhere that is convenient, so you can keep an eye on your system’s performance. Add this display to your system at any time. Connection is by a thin cable that can easily be hidden from view behind lockers or trims. The supplied cable is 4 meters long. It can easily be extended to 10 meters as required.

Fixing a solar panel system to your roof or deck.

solar panel mounting pads

Solar panel uPVC mounting pads

With the right accessories attaching your solar panel is straightforward. If you intend fixing the panel onto a flat surface such as a motorhome roof then your task is made easy by using our uPVC corner mounts. Glue these mounts to the roof or deck using Sikaflex adhesive.

For fitting to a boat or yacht, we recommend using Z-brackets. Made from robust aluminium, these brackets are screwed or glued in place.

To mount a rigid solar panel to a boat’s pushpit or any other type of structure, the aluminium frame of the panel can be easily drilled to take screws or bolts.

angled-panel-mount-with-panel_web_2Narrowboat owners may also be interested in our adjustable mounting frames. Using this frame you can tilt the solar panel up to face the Sun directly. This substantially increases the yield of electricity, especially during the winter months when the Sun is low in the sky.

This frame is made from strong aluminium sections.  It can easily be adjusted to any angle. Available in two sizes.

Connecting up. It’s easier than it looks!

The solar panel is connected  to the battery via a charge controller and a fuse. See cables 1 and 2 in the diagram.

solar panel system

The cable from the solar panel has to pass through the roof or deck to the charge controller on the inside. We recommend that you use a watertight connection gland.


Connection gland.

The gland covers the hole you make in your roof or deck and is sealed in place using Sikaflex 252i adhesive. This provides a very reliable and watertight solution.

The solar panel is manufactured with two wires already attached. These wires are fitted with ‘MC4’ connectors. Do not try to pass both of these wires through the roof  gland. Instead, connect the two solar panel wires to a SunWorks solar cable with pre-assembled MC4 connectors. The resulting single cable is much easier to route through the gland and onto the charge controller and battery.

solar panel cable with mc4

Solar cable with MC4 connectors

An alternative way to make the connection through the roof or deck is to use a watertight box. Glue the box to the roof or deck with Sikaflex 252i adhesive. A box provides a less streamlined appearance but may be more flexible if you intend extending your system at a later date. The MC4 connectors can be removed from the solar panel wires and passed into the box. The two wires can be joined, within the box, to a 2-core cable using a terminal block. The 2-core cable is then passed through the hole in the base of the box and so into the interior of the vehicle or boat.

Which cable should I use?


Watertight connection box.

Whether you use a box or a gland, the wiring is made much easier if you use a 2-core cable. Make sure the cable is double insulated and has a pair of red and black wires so that you can easily distinguish the positive and negative connections.

You should always use an automotive grade cable. These are much more flexible and smaller in section than standard cables.

We recommend twin core automotive cable of 2.5 sq mm section. This will handle systems of up to 300 watts without excessive power losses or voltage drops.

If your total solar panel output is more than 300 watts or your total cable length is more than 10 m, you may have to use a larger cable section. Please contact us for more details.

Extending your solar panel system.

Extending your solar panel system is always possible. Adding another solar panel will increase the amount of electricity produced.  Your battery will therefore charge up more quickly.


Y-branch connector. Connects two panels together.

Make sure that your charge controller can handle the extra electrical current. If you are unsure about what size of charge controller you should have, please get in contact with us.

The additional solar panel must be connected in parallel to the existing panel. This means that the positive wire of each solar panel is connected together.  The negative wire of each solar panel must also be connected together.

If you have used a roof connection box, remove the MC4 connectors from the solar panel and pass them through into the box. Make the connection to the existing solar panel, inside the box.

fused battery connection harness

Fused battery harness

If you have used a watertight gland on the roof, additional solar panels can be added by by using a Y-branch connector. The Y-branch connector allows the cables from two solar panels to be easily joined together using the existing MC4 connections.

Fusing the solar system.

There MUST be a fuse between the charge controller and the battery. See the diagram above.

To the fit the fuse and to make the connection to your battery easier, have a look at our fused battery connection harness. This has the battery connections and fuse holder already attached.

The harness is supplied with full instructions and the correct fuses.

There is no need to fit a fuse between the solar panel and the charge controller.

If you would like more technical information regarding the solar panel system for your motorhome or for your boat, please contact us: