How Do You Hook Up Solar Panels To A Boat Battery?

This article discusses the basic steps needed to be followed for solar installation, including panels, on a boat. The wiring of the system is also outlined.

Keep reading as we install a complex solar system of more than one Thin-Film Copper Indium Gallium Selenide (CIGS) panel on a horizontal, fixed-mount. To be used on our hypothetical live-aboard cruiser as a practical example.

A reliable solar system installed securely and wired correctly on a long cruise makes all the difference. Solar is available each sunny day and is free for everyone. Let’s face it, in the middle of the ocean, solar may be the difference between a successful sail and a disaster.

🔢 A Step By Step Guide To Hooking Up The Solar Panels

In this article, I use a more complex solar system of more than one panel that may be used in a live-aboard cruiser as the example being used to set the system up.

A much smaller and basic system used to power low-voltage accessories on a leisure or fishing boat will still require the same principles, however, on a much smaller scale.

Size the system and gather the components.
Find a suitable space for the solar panels to be installed.
Install the battery bank.
Install the inverter (or solar charge controller in a smaller system).
Run the wiring.

Size The System And Gather It Together

I’m not going to concentrate on this step because other articles on the site address this in more detail. I suggest reading our guide to charging boat batteries with solar panels in conjunction to grasp the topic.

When you have completed the sizing task, you will know the following system requirements.

1️⃣ Whether output power can be AC and DC or DC alone.

2️⃣ The maximum voltage required for specific appliances (AC 120V, DC 12, 24 Volt, etc.)

3️⃣ The amperage of the system.

4️⃣ The watts needed to be produced by the solar panels.

This information will inform your choice of equipment to be purchased.

Find A Suitable Space For The Solar Panels To Be Installed

Depending on the wattage of the panels, they will range in size from

48.5 inches × 25.6 inches (100-watt panel)
74.8 inches × 48.6 inches (350-watt panel)

Assuming you will be installing 6 X 350-watt panels, you will need an area of at least 144 square feet to install them.

The installation site should receive constant sunlight (roof) and be out of the way of daily vessel operations. Regularly used mounting spots for fixed panels include

Cabin tops.
Stern rails.
On top of the dinghy davits.
On radar arches
On bimini tops where flexible panels are often sewn into the bimini cover.

In this example, I will assume they will be Thin-Film Copper Indium Gallium Selenide (CIGS) panels on a horizontal, fixed-mount installation.

Install The Solar Panels

Each solar panel manufacturer uses its own fixation systems; however, as a general principle, the surface must be solid, and screws must be able to establish a secure hold on the mounting surface.

If you can install an adjustment mechanism that enables the panels to be re-orientated to the sun, it will help your overall yield of solar power.

Hook Up The Solar Panels

Once the solar panels have been installed, it is time to wire them up. To hook the panels up, you will need the following.

Standard 4 Solar Cable and male/female connectors – Amazon link (the cable must be sufficiently long to reach the inverter and battery.)
Spare male/female connectors – Amazon link.
Bypass diodes – Amazo link (check first because these are installed in some connectors.)

I recommend wiring them in two banks connected via parallel connections if you have four or more panels.

This will ensure that if one panel fails, only the panels on that bank will be affected, and the system will still produce 50% power.

With the panels being split into two wiring banks, wire each, so the panels are wired together in series. This means the positive connector on one panel will connect to the negative connector on the next-door panel.

Once the bank is connected, there will be a single negative and a single positive connector left disconnected.

Connect the unattached red (+) positive terminals on one bank to the unattached red (+) positive terminals on the other bank.

Connect the unattached black (-) negative terminals on one bank to the unattached black (-) negative terminals on the other bank.

The last connection in this step is to connect a positive and negative wire to the solar panels and run it to the charge controller (or inverter).

To do this, connect the longer wires to the finally connected red (+) positive and black (-) negative connectors.

Route this from the panels to the charge controller/inverter.

Install The Batteries And Inverter

Find a secure and out-of-the-way place to mount the batteries and inverter.

If Lithium-ion batteries are used (recommended), they must be securely fastened to the surface to prevent them from moving around as the boat weathers rough seas.

The charge controller and inverter should be similarly mounted.

The location of the inverter/charge controller should ideally be in a position with the following characteristics.

1️⃣ It should be as close to the breaker box as possible.

2️⃣ It should be as close to the batteries as possible.

3️⃣ It must be easily accessible to the boat occupants.

Hook The System Up

The makeup of the wiring circuit will be different for a charge controller and an inverter.

Wiring A Charge Controller

If the system is connected to a charge controller, it still requires a separate fuse/breaker box for each bank of panels.

Connect the two cables from the solar panels to the input positive and negative plugs.

Connect the cable from the outlet plug on the charge connector to the batteries. They will be connected in parallel if there is more than one battery.

Connect the correctly marked outlet plug from the charge controller to the appliance (or through a separate breaker box.

Wiring An Inverter

If an inverter is installed, fuses are critical.

The positive and negative wires from the solar panels are connected to a fuse/breaker box.
The cables run from the fuse/breaker box to the (+) and (-) terminals on the inverter.
Connect the cables from the indicated outlet cables to the batteries (which should be linked in parallel).
Connect the AC out terminals to the breaker box.
Connect the DC outlet terminals to a breaker box that connects all of the DC appliances.

The system is wired and should be tested very carefully.

❓ FAQs

Can I Just Connect A Solar Panel Directly To Battery?

If the solar panels produce under 1.5% of the battery capacity (amps), you can run a cable directly from the panels to the battery.

The sun’s position and intensity determine the power produced by a solar panel, so in high sun areas, the current produced by the panels may be higher than you estimated.

I recommend installing a small MPPT solar charge controller between the panels to protect the batteries, which will accurately regulate the power being sent to the batteries.

Do I Need A Fuse Between Solar Panel And Battery?

While it is not always considered necessary on a small system, I recommend that a fuse is always installed between the panels and the battery.

On larger systems that include an inverter, it is a requirement that a fuse is installed on each side (input and output) of the inverter.

While there is a minimal chance (not impossible) of a power surge from the panels, they can be struck by lightning. A fuse will hopefully prevent damage to the batteries, inverter, or charge controller.

🔑 Key Takeaways

It is not difficult to hook up solar charging and panels to the vessel’s batteries (possibly via a charge controller or inverter). As long as the connections are done correctly, the system will produce current and charge the batteries.

The key steps that were covered are below:

1️⃣ Size the system and gather it together

2️⃣ Find a suitable space for the installation

3️⃣ Install the solar panels

4️⃣ Hook up the panels

5️⃣ Install the batteries and inverter

6️⃣ Connect the system together

For the wiring job, this resource should tell you everything you need to know about getting the connections right – Solar wiring diagram