After a recent 5-day cruise aboard our trawler where we had to constantly start up the genset to provide electrical power to the 115 volt ac freezer to sustain temperatures, I started to think about alternate options. We put more than ninety hours on the vessel generator in just five days; time for another oil change! I put in an inverter shortly afterwards and that enhanced the run time for the generator significantly, but there was still work to be done. I still needed to keep the batteries fully charged to operate the inverter. Then it occurred to me, why not explore solar panels for use on our trawler. Solar panels have been effectively used since the mid 1950s, originally utilized in manned space exploration. They have been falling in price since roughly 2004 when their popularity increased significantly. And now with the Ecological movement afoot, solar panels are as accepted as always. So I set out to delve into them and ascertain how to purchase and install one; I was in for a surprise. You can locate many retail suppliers online that will sell you a solar panel but nowhere could I find a comprehensive explanation of how to determine what to purchase and how to mount it; much less on board a vessel. So this commentary was written as I made my way through the process; therefore is a truly a learn-as-you-go article.

What Exactly is a Solar Panel and How Does It Work?

Solar panels are basically any panel that makes use of the sun's thermal power to create electricity. A solar panel can be described as a photovoltaic panel, the name used in the industry, for panels designed to create electrical energy from the rays of the sun. Despite the category of solar panel being mentioned, almost all solar panels are flat. This is because the face of the panel needs to be at a 90 degree tilt from the sun's rays for the most favorable angle to soak up the sun's rays. Solar panels are able to soak up energy from the sun through a group of solar cells on their face. Very similar to how a plant is able to absorb energy from the sun for photosynthesis, solar cells perform in a comparable way. As the sun's energy hits the solar cells on a photovoltaic panel, the energy is transferred to a silicon semiconductor. The power is then turned into (dc) direct current electricity and then passed through connecting wires to finally enter a storage battery.

Types of Solar Panels

Types of panels most often used in boating applications have either multicrystalline or amorphous thin-film cells. Multicrystalline panels are the oldest technology available and also the strongest. When sized appropriately and paired with proper batteries, these are the panels to make use of for operating great loads such as refrigeration. Amorphous thin film solar panels are only about fifty percent as effectual as multicrystalline panels, but can be bought in bendable varieties so they can roll or fold, or correspond to the shape of a vessel cabin top or bimini. They don't often have enough production for significant energy replacement, but can be used to lightly power a battery bank.

Just How Much Energy Can Solar Cells Create?

Usually, we measure solar panels by wattage and that is how we buy them. You can purchase solar panels for yachts as little as ten watts to as great as 200 watts or even larger. But it is easier to comprehend when we change watts to amperage. We calculate these numbers by multiplying the number of hours the panel is in complete sun (typically defined as five a day in Florida) by the panel's wattage. For a 195 watt solar panel the output would be 195 x 5 hrs = 975 watts/day. Taking it step further, 975 watts/12 volts = 81.25 amps per day.

Power Consumption

Before considering which size panel to buy for your boat, you will want to compute an energy budget to determine what sources of energy utilization you have aboard while anchored up. I make use of the at anchor scenario because this is the place you will utilize the most energy; under power and your yacht will be able to provide its requirements exclusive of any problems.
Case in point, if you have 3 interior lights that draw 2 amps each and you turn them on for four hours per night, your use would be 3 x 2 x 4 = 24 AH/Day. We are not concerned by running lights and electronics as they will not likely be working while at anchor.

DC Loads - calculate the amp hours each appliance uses.

House Lighting
Anchor lights
Refrigeration
Freezer
Electric Head
Fresh Water Pump
Sanitation System
Stereo
Other

Inverter Loads - calculate the amp hours each appliance uses. Inverter loads also make use of DC energy but they are powering AC equipment and appliances. If you need to change watts to amps use (12watts/12 volts = 1amp).

Computer
Microwave
Refrigeration
Freezer
Heater
Hair Dryer
Television
Other

Calculate your overall daily energy use AH/per day

Solar Energy Production

Alternative sources of energy similar to solar panels can replenish the amp/hrs drawn from the batteries. But similar to the energy budget that calculated your usage you will also need to compute your re-supply of amp hours. Bear in mind the formulation - (12 watts/12 volts = 1 amp). But remember, the formula is only an estimate; total precision can only be where the panel output is consistent and a solar panel might at times function ineffectually because of shading by clouds. Compare the day by day energy expenditure in AH/Day to the solar power creation. Your solar energy production must be larger than the utilization. If not, go for a larger wattage panel and recalculate. Always purchase more solar panel output than you imagine you will require; some professionals urge at the least 30% in excess.

Example - 100 watt solar panel/ 12 volts = 8.3 amp x 5 hours = 41.66 AH/Day production

Installing Your Solar Panel

Now that you have your solar panel, where do you install it aboard your vessel? As I said already, installing the panel ninety degrees to the sun is optimum. You will get the best energy creation this way. But on boats, finding a suitable location is difficult at best. Some boaters place them on brackets located on the rails, others position them on top of the bimini, and I have seen them located on the vessel dinghy stanchions. But wherever you decide to install them, keep in mind that to get the best output they must be in the open, free from any shade from booms, yacht radar arches, or cabin structures. Bear in mind that while at anchor, the vessel will veer in the direction of the sun twice every day as a result of the tides. I opted to install our panel on the top of the trawler back deck hardtop in a horizontal manner. At this point it will have the best view of the sun and be away from the radar arch shade as the trawler turns while at anchor. The angle in the direction of the sun is not exactly at ninety degrees but it will have to suffice. I selected a 195 watt panel so I have more or less a 50% reserve capability in my panel to compensate for the minor inefficiency of the sun's angle. I purchased the panel from Sun Electronics in Miami, sunelec.com because they had the best prices I could find anywhere on the web. But bear in mind, panels have to be shipped via freight as they are heavily packed to lessen the chance of damage so be certain to calculate those costs in your acquisition.

What is the Right Way to Attach the Panel to your Yacht?

There are many suppliers of solar panel mounting rails and supports but almost all of them are designed for roof or ground mounting. West Marine does carry a product for mounting small panels to the rails. A lot of boaters make their own mounts. I located a mount made by Sunsei referred to as a Sunsei Glue Mounting Kit that is affixed to the boat and panel using 3M 5200 Marine Adhesive. The mount enables the panel to be installed with about 2 inches of clearance under the panel for ventilation. I did not need to drill any holes in the hardtop either. You can find these mounts at amazon.com.

Wiring Your Panel

Marine electrical wiring is extremely technical and hazardous; if you are not comfortable in performing this task, please seek advice from a skilled marine electrician. Your panel will be prewired for affixing to your trawler but you will want to provide the linking cables that will also be sold by your panel provider; they are known as MC4 cables. The cables will be made in different lengths appropriate for your needs with a male and female connector attached; you cut one connector off. Additionally, you will also need a controller. The controller regulates the power flow from the panel to your batteries keeping your batteries charged yet preventing over charging. Some controllers are simple but others have LED displays indicating the amount of charge etc. The more whistles and bells the more costly it will be. Your panel dealer can recommend a controller that will meet your requirements. I picked a controller made by Specialty Concepts. It is simple but does the job. And the people at the company are a huge help in assisting you to select the right model for your panel. When you get in touch with them, they will need to be familiar with what size panel (wattage) you have and what the voltage is. Check them out at specialtyconcepts.com. I also bought my controller from the individuals at Sun Electronics in Miami.

The associates at Specialty Concepts have also computed how temperature will have an effect on current flow and suggest that their controllers not be located in engine rooms because the heat created will decrease the controller effectiveness by about 25%. I put mine in the electrical panel beneath the lower helm. And finally, you will require the appropriately sized cables to go from the controller to your batteries and a fuse to connect the controller to the battery bank. In choosing the right fuse, you need to locate the short circuit current for your panel and pick the breaker at 125% of that figure. This will provide you the amperage of the breaker you will require. Your controller operating handbook will have information on these also.

Buying a solar panel to uphold your batteries seems like a great thought but you'll want to have a method to keep an eye on your batteries. I opted to also put in a Trimetric 2025RV Battery Monitor; bogartengineering.com. This intelligent contraption is wired into your battery bank to give a genuine measurement of voltage going in to the bank, amps being utilized by your vessel, the percent complete charge on the bank, and the amp hours utilized since the most recent charge.

Panel Operation

So we have now installed a 195 watt solar panel along with an 1800 watt inverter and a battery bank with 443 amp hours. We tested our system this week on the hook with clear skies. I concluded that our power consumption is 112.5 amp hours each day. The freezer is the major pull utilizing 60 of the amp hours followed by the refrigerator. Did you know that a standard anchor light uses 18 amp hours per night? I think I'll look into LED bulbs now. The battery monitor told me that our actual draw from the battery bank was only 65 amp hours which means we received the remainder from the sunlight, a full 42% was from the sun. Now we can turn on the generator for about an hour to bring the battery bank up to complete charge.