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

This article discusses the basic steps for connecting solar panels to the batteries on a boat and the wiring of the system is also outlined.

For a thorough step-by-step guide on the actual mounting, refer to my marine solar panel installation article which walks you through everything from tools to hardware.

Step By Step Guide To Hooking Up The Solar Panels

I’ll illustrate using a complex multi-panel solar system suitable for a live-aboard cruiser as an example. Smaller systems will still use the same principles.

    I’m not going to spend a ton of time here because I’ve written far more in-depth in this solar requirements for a boat article.

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

    • Whether output power can be AC and DC or DC alone.
    • The maximum voltage required for specific appliances (AC 120V, DC 12, 24 Volt, etc.)
    • The amperage of the system.
    • The watts needed to be produced by the solar panels.

    This evaluation spreadsheet will help you do just that.

    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.

    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.

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

    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.

    I’d suggest doing your research on electric boat batteries before finding 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.

    • It should be as close to the breaker box as possible.
    • It should be as close to the batteries as possible.
    • It must be easily accessible to the boat occupants.

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

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

    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.

    Frequently Asked

    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.

    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.

    I’m the founder and chief editor here at Kite Ship. The electrification of boating is the most exciting thing to happen to the marine industry in a generation! Welcome, and I hope that we can provide the portal you need to dive into the world of electric propulsion and power.