After a recent five day voyage aboard our trawler, during which we frequently had to start the genset to power the 115 volt AC freezer to maintain temperatures, I started thinking about options. We worked more than 90 hours on the ship generator in just five days; Time for another oil change! I installed an inverter soon after, which drastically improved the runtime of the generator, but there was still work to be done. Still, I had to keep the batteries fully charged to run the inverter. Then it occurred to me why we shouldn’t research solar panels for use on board our yacht. Solar panels have been used successfully since the mid-1950s, originally in manned space exploration. They have come down in price since around 2004 when their popularity really took off. And now that the green push continues, solar panels are as accepted as ever. So I started looking into them and figuring out how to buy and mount them; I got a big surprise. You can come across many retailers on the internet that will sell you a solar panel, but nowhere have I been able to find a detailed description of how to determine what you are buying and how to install it. much less on board a yacht. So this piece was written as I was moving through the progression; Therefore, this is a truly learnable article.

What exactly is a solar panel and how do they work?

Solar panels are basically any panel that uses the heat energy of the sun to generate electricity. A solar panel may be referred to as a photovoltaic panel, the industry name for panels designed to generate electrical energy from the emission of the sun. Despite the group of solar panels discussed, almost all solar panels are flat. This is because the surface of the panel needs to be at a 90 degree angle from the sun’s rays in order to have the best angle for absorbing the sun’s rays. panneau solaire Solar panels can absorb energy from the sun through a collection of solar cells on their surface. Much like a plant absorbs energy from the sun for photosynthesis, solar cells work in a similar way. When the sun’s rays hit the solar cells of a photovoltaic module, the energy is transferred to a silicon semiconductor. The power is then converted into direct current (DC) electrical energy and then passed through connecting wires to finally enter a storage battery.

Types of solar panels

The types of panels most commonly used in yachting have either multicrystalline or amorphous thin film cells. Multicrystalline modules are the oldest technology available and also the strongest. With proper sizing and paired with proper batteries, these are the panels that can be used to run large loads such as refrigerators.

Thin film amorphous solar panels are only about 50% as effective as multicrystalline panels, but can be purchased in flexible varieties so they can be rolled or folded or changed into the shape of a boat canopy or bimini. They often don’t yield enough for a significant energy refill, but can be used to easily charge a battery bank.

How much electricity can solar cells generate?

We usually measure solar panels by wattage and buy them that way. You can get boat solar panels from as little as 10 watts up to 200 watts or even bigger. But it’s easier to understand if we convert watts to amperage. We calculate these values by multiplying the number of hours the module is in full sun (usually defined as 5 per day in Florida) by the wattage of the module. For a 195 watt solar panel, the amount generated would be 195 x 5 hours = 975 watts/day. We can then calculate, 975 watts/12 volts = 81.25 amps per day.

Power Consumption

Before considering what size panel to buy for your boat, you need to do an energy balance to determine what energy sources you have onboard while at anchor. I use the anchor scenario because that’s where you use the most energy. under power and your trawler can easily cover its needs.

For example, if you have 3 indoor lights that draw 2 amps each and you leave them on 4 hours per night, your consumption is 3 x 2 x 4 = 24 AH/day. We’re not worried about running lights and electronics as they probably won’t be running while we’re at anchor.

DC Loads – Calculate how many amp-hours are being consumed by each device

  • home lighting
  • anchor lights
  • cooling
  • freezer
  • Electric toilet
  • fresh water pump
  • plumbing system
  • stereo
  • Miscellaneous
  • inverter loads

Inverter loads also use DC power, but power AC devices and equipment. If you want to convert watts to amps, use (12 watts/12 volts = 1 amp).

Calculate the ampere-hours consumed by each device

  • computer
  • microwave
  • cooling
  • freezer
  • heating
  • hair dryer
  • TV
  • Miscellaneous

Add up your total daily energy expenditure AH/per day

Generation of solar energy

Various power sources, similar to solar panels, can replace the amp-hours drawn from the batteries. But much like the power budget that determined your consumption, you also need to calculate your replenishment amount in amp-hours. Follow the formula – (12 watts/12 volts = 1 amp). But remember, the formula is just a guide; Complete accuracy can only be achieved when module production is constant and a solar module is intermittently not working due to cloudy skies. Compare daily electricity consumption in AH/day with solar power generation. Your solar energy production must be greater than usage. If it doesn’t, go for a higher wattage panel and recalculate. Always buy more solar panel power than you think you will need; Some experts recommend at least 30% more.

Example: 100 watt solar panel/ 12 volts = 8.3 amps x 5 hours = 41.66 AH/day production

Installing your solar panel

Now that you have your solar panel, where do you mount it on board your yacht? As we have already mentioned, it is best to install the panel ninety degrees to the sun. This way you get the best power generation. But on yachts, finding a suitable spot is difficult at best. A number of boaters have mounted them on railing brackets, others position them on the bimini and I have seen them positioned on trawlers’ dingy supports. But wherever you decide to mount them, remember that to get the most out of them, they should be outdoors, with no shadows from booms, ships’ radar arches, or cabin structures. Remember that during anchoring, the boat faces the sun twice a day due to the tides. I chose to mount our plate on top of the boat aft deck hardtop in a horizontal position. Here it has the best view of the sun and is clear from the shadow of the radar arch as the boat swings at anchor. The inclination to the sun isn’t exactly ninety degrees, but it has to do. I chose a 195 watt panel so I have almost 50% reserve capability in my panel to compensate for the small sun angle inefficiency. We got the panel from Sun Electronics in Miami,, as they had the best prices I could find anywhere on the web. However, keep in mind that the panels must be sent by freight as they are heavily packed to reduce the chance of damage. Be sure to calculate these costs when making your purchase.

What is the best way to attach the panel to your ship?

There are a variety of manufacturers of mounting rails and brackets for solar panels, but almost all are designed for roof or ground mounting. West Marine has a product for attaching small panels to the rails. Many boaters make their own mounts. I found a mount developed by Sunsei known as the Sunsei Glue Mounting Kit that attaches to the ship and plate with 3M 5200 Marine Adhesive. The bracket allows the panel to be installed with approximately 2 inches of clearance below the panel for ventilation. I didn’t have to drill any holes in the hardtop either. You can find these mounts at

Wiring your panel

Ship electrical wiring is incredibly specialized and dangerous; If you are unable to complete this part of the task, please contact an experienced marine electrician. Your panel will be pre-wired for attachment to your vessel but you will need to provide the connection cables which are also sold by your panel supplier; They are known as MC4 cables. The cables are manufactured in different lengths according to your requirements with a plug and a socket; You cut off a plug.

You also need a controller. The controller regulates the flow of current from the panel to your batteries, keeping your batteries charged and stopping charging. A number of controllers are basic, others have LED indicators showing charge amount etc. The more unusual the functions, the more expensive it becomes. Your panel dealer can suggest a controller that suits your needs. I chose a controller developed by Specialty Concepts. It’s basic but does the job. And the company’s employees will be of great help in choosing the best model for your panel. When you contact them, they want to know what panel size (wattage) you have and what the voltage is. Check them out at I also got my controller from the folks at Sun Electronics in Miami.

Specialty Concepts staff have also calculated how heat affects current flow and suggest not placing their regulators in engine rooms, as the heat generated reduces regulator effectiveness by about 25%. I put mine in the switch panel under the lower helm. And finally, you need the right size cables to go from the controller to your batteries and a fuse to connect the controller to the battery bank. When deciding on the correct fuse, you must locate the short circuit current for your panel and rate the breaker at 125% of that number. This will give you the amperage of the breaker you need. You will also find information on this in your control operating instructions.

Owning a solar panel to save your batteries might seem like a great plan, but you want a way to keep track of your batteries. I chose to also install a Trimetric 2025RV battery monitor; This smart device is wired to your battery bank to provide a true measurement of the voltage going into the bank, the amps being used by your yacht, the percentage of the bank full and the amp-hours used since the last charge.

Panel Functionality

In addition to a 1800 watt inverter and a battery bank with 443 ampere hours, we have now also installed a 195 watt solar panel. We ran our tests on the hook this week under clear skies. I concluded that our energy use is 112.5 amp hours per day. The freezer is the main attraction at 60 amp hours, followed by the refrigerator. Did you know that a standard anchor light draws 18 amp hours each night? I think I’ll look at LED bulbs now.

The battery monitor indicated that our actual draw from the battery bank was only 65 amp hours, indicating that we were getting the rest from sunlight, a full 42% was from the sun. Now we turn on the power pack for about an hour to fully charge the battery bank.

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