How to Size Solar Panels for a Cruising Boat

Many people live the dream of cruising a boat to distant exotic locations. Some of them fill their power requirements by running an engine-driven alternator that charges batteries. Many others, however, charge their batteries with solar panels. One issue sailors have with solar panels is determining how many panels are needed and the size of each panel. By using some simple calculations, almost any cruising sailor can determine the size of the solar panel system that is needed.

Things You'll Need

  • Pencil and paper
  • Hourly power requirements for appliances and electric accessories
  • Average peak sun hours in the anticipated cruising area
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Instructions

    • 1

      Write down the hourly power requirement for each electrical appliance and accessory. The hourly requirement is normally located on the back of the appliance or in the user manual.

    • 2
      Power from solar panels.

      Add the anticipated number of hours of use for each electrical appliance or accessory during a week. For instance, a laptop computer uses approximately 40 watts of power per hour. If the laptop were used one hour a day for seven days during the week, then there would be a total of 280 watts of power used per week for the laptop. Add the amount of electricity used by each electrical appliance and accessory together to form the weekly power requirement.

    • 3

      Use an average sun chart to determine the average number of hours of sun that is available in the cruising area. The total number of hours of sun that is available is usually much less than often believed by sailors. The total number of hours of sun that are available on an average day in a tropical setting is normally between four and six hours. This average is lower in northern climates, and is also lower during the winter.

    • 4

      Determine the size of the solar panel needed. Divide the total weekly watt requirement by seven to determine the average daily requirement. Divide that by the average hourly amount of sun available per day. The result is the size of the solar panel required. For instance, if the total weekly load is 3500 watts, you would take 3500 divided by seven, and divide that total by five (for an average amount of sun available on an average day in a tropical setting) for a figure of 100.

    • 5

      Purchase a 100-watt solar panel system to charge batteries and supply power to cruise the boat in the selected cruising area.