How Much Solar Is Needed For A Boat?

There is no cut-and-dry answer to this question because so many factors and variables must be considered. Along with a plethora of numbers, letters, and equations

This may make this seem beyond a non-mathematical enthusiast’s grasp. Still, it can be pretty simple to calculate how much (and how much of what) you’ll need. So there is no better time to go green!

I’ll cover the numerous aspects that need to be considered to yield an accurate answer so you can charge your boat batteries with solar.

Systems On A Boat Requiring Power

Your boat will require some power, no matter what shape or size. Larger vessels cannot rely on just the wind for sailing and have engines to aid this. These days many ships (especially the bigger ones) have other appliances on board that require power.

When calculating how much solar power is needed for your boat to function, you should compile a list of all the appliances (and their power usage) you have on your boat. Then, when you have added the totals, you will know precisely how much solar power you require.

Unlike standard engines on most boats, vessels that use an electric outboard motor do not require the input of gasoline and can supplement their power from solar fittings.

The output of a solar-powered engine will be lower than that of a vessel powered by gasoline meaning your boat will be slower.

Specialized electric motors need to be fitted to boats for this purpose.

The battery is what is going to be powering all your electronics as well as your outboard. A dedicated battery will provide the motor with the power, and a house battery will be responsible for all other electronics. The size of your battery will depend on the following:

  • The size of your engine
  • The voltage of your motor
  • Maximum amp draw of your motor
  • The number of electronics on board that require power

The battery already fitted to your boat can be used if it is a marine deep-cycle battery. But a specialty battery is recommended for all your solar fixtures.

Marine lithium batteries are the best options for your solar power for the following reasons:

  • Superior energy storing for solar systems
  • Faster charger
  • Lower Depth of Discharge (DoD)
  • No maintenance is required
  • Longer lifespan

Lithium marine batteries may have a high initial cost, but they will be cost-effective over time. Here are some brand comparisons to consider.

Systems like your GPS are essential when out on the water and must be operational at all times. Your VHF marine radio will also need to be connected to the boat’s battery, many of which have GPS built into them.

  • Microwave
  • Laptop
  • Refrigerator
  • Chargers For Small Devices
  • Lights

Power Needed To Maintain Appliances

Once you have an idea of which appliances need to be supplied with power (and for how long), you can calculate your total power needs per day using the following formula:

AppliancePower (watts)Hours of use per dayPower consumption per day in Watt Hours (Wh)Amperage (A)Amps per day (Ah)
Laptop5010500 Wh4.1641.6
Lights206120 Wh1.69.6
GPS3010300 Wh2.525
Fridge1524360 Wh1.2530
Microwave7001700 Wh58.358.3
Total (Wh)1 980 Wh67.81 A164.5 Ah

Solar Set-Up Scenario

A 25 ft. pontoon will only require power for the motor, GPS, and lights (if that). Surplus appliances, such as fridges, won’t usually be found on these boats. Therefore your solar power will be able to run your vessel for longer.

When looking at the design of a pontoon, the best place for mounting a solar panel system would be at the stern and preferably with an angled mount. It will resemble a spoiler on the back of a sports car.

Specifications Of Our 25 ft Pontoon Boat

Boat TypeLength OverallSystems Requiring Power
Pontoon Cruiser25 feetMotor; Lights; Navigational System

Solar Equipment Required For Solar Power Set-Up:

  • An electric motor – or a trolling motor, runs entirely on solar power, responsible for the propulsion
  • Batteries – accountable for the power output
  • Solar panels – will convert the energy emitted by the sun into usable electricity
  • Solar charge controller – acts as a charger for your battery and a control board for your solar power
  • Mounting hardware – what your panels will be secured to
  • Converter – converts direct current (DC) into alternating current (AC)
  • Solar cabling – special cables with a wider jacketing specifically for marine solar cables

Step By Step Guide: Setting Up Solar Power On A 25 ft. Pontoon

I’ve written a detailed guide to marine solar panel installation which I’d suggest you read. To recap though here are steps and a tutorial video below.

  • Select panel size, mounting bracket, and location of where you want it mounted
  • Install mounting brackets with relevant openings for solar cabling
  • Secure solar panels to mounting brackets
  • Run solar cabling
  • Connect solar cabling to the charge controller
  • Linkup the charge controller to the battery bank
  • Connect the battery bank to the converter
  • Connect the converter to the motor, lights, and GPS system.
  • Charge solar panels in the sun

Since a pontoon boat of this size won’t require additional power for appliances, a portable solar panel could be used. But the panel might only be enough to power the battery.

Estimate for solar power needed on a 25 ft pontoon:

SystemPower (watts)Hours of use per dayPower consumption per day
Engine858680 Wh
Lights206120 Wh
GPS308300 Wh
Total (Wh)1100 Wh

🎖️ Pro Tip: If you opt for flexible panels over rigid panels you can benefit from increased surface areas to produce more power.

Solar Power And Electric Propulsion

Many types of boats can be fitted with an electric motor, such as sailboats, jon boats, center consoles, catamarans, etc.

Kilowatts to horsepower is an important aspect to know when talking about electric propulsion.

And anyone who’s used trolling motors will point out that the conversion between thrust and horsepower is the one they talk about.

The most powerful electric outboard motor is the Evoy Storm 300+ HP, released in 2023. Why not try out the calculator below to find out how many kW equivalent that is?

Mechanical Horsepower to Kilowatt Calculator

Enter a value in kilowatts:


Enter a value in horsepower:



Result:

If your boat’s current engine has a power output of up to 135 horsepower (HP), you could find an electric alternative. So anywhere up to 97 kW engine (Kilowatts).

  • More powerful than outboard engines
  • Up to 330 HP (246 kW)
  • Have to option of having a hybrid motor/engine
  • Can have a hydro regeneration capability (can charge while the vessel is under sail)
  • This would only be useful for non-powerboat vessels
  • The range of an electric motor depends on the boat, total weight, propellor, and battery capacity
  • If you go slowly, you’ll have a greater range

So how many solar panels would you need for your sailboat? First, you must consider how much sunlight you would receive daily in the region you will be sailing in.

If you need to get an idea of the amount of sunlight your area of interest will receive, check out: bigfrogmountain.com

For instance, if the area receives only 8 hours of sunlight per day, your solar panel output would be:

2 500 Wh / 8h = 312.5 W

Therefore, your total solar panel power output needs to be 315 W.

Sailboats vs Electric Propulsion Boats

Electric propulsion boats, like these Silent Yachts, rely almost entirely on solar power. Therefore, in comparison to standard diesel-powered sailboats, electric propulsion vessels are more eco-friendly.

They will be the most cost-effective in the long run. However, the initial expense for a Silent Yacht or equivalent vessel will be high.

Boats whose propulsions are entirely solar-powered will not be known for speed. But advancements are being made every day, and soon we could see an eco-friendly solar-powered vessel with impressive speeds.

SailboatsElectric Propulsion Boats
Require a hands-on approachEasier to operate
More training and practice requiredRequire less experience
Save money on fuel; maintenance more frequent but cheaper overallMore costly to maintain; less maintenance overall
Many moving partsFewer components
More reliant on favorable conditions; at the mercy of the windsMore space on board for other purposes
Tides and sail setup crucial in certain conditionsQuieter, fewer fumes and vibrations

Frequently Asked

The size of the solar panel needed to charge a boat battery is contingent on:

  • How many watt-hours do you need per day (to power your electrical components)
  • How much sunlight do you receive per day
  • How much space on your boat do you have for solar panels
  • How many batteries will need charging

Yes, solar panels will still be able to harvest solar energy on cloudy days, although it will be lower compared to a clear sunny day.

Solar panels can be cut into custom sizes within reason. Still, the custom panels will be more expensive than the standard-sized ones.

Ordinary solar panels, like the ones you would find on land, do not respond well to the seaside conditions. The moisture and salt air cause corrosion, malfunction, and a complete technical breakdown of the panel.

As mentioned, ordinary solar panels are prone to corrosion in a coastal marine environment. Marine solar panels are therefore made from special non-corrosive components. All the components, from nuts and bolts to the panels themselves, need to be non-corrosive.

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.