Following a recent five-day trip aboard our trawler where we had to frequently start up the genset to provide electricity to the 115 volt AC freezer to maintain temperatures, I began to mull over options. We put in an excess of ninety hours on the vessel generator in only five days; time for another oil change! I put in an inverter soon thereafter and that improved the run time for the generator drastically, but there was still work to be completed. I nonetheless needed to keep the batteries fully charged to operate the inverter. Then it occurred to me, why not explore solar panels for use aboard our yacht. Solar panels have been successfully utilized since the mid 1950s, originally utilized in manned space exploration. They have been dropping in cost since roughly 2004 when their popularity really went up. And now with the Green pressure going on, solar panels are as accepted as ever. So I commenced to delve into them and find out how to purchase and mount one; I was in for a big surprise. You can come across many retail vendors over the internet that will sell you a solar panel but nowhere could I locate a detailed description of how to determine what to buy and how to install it; much less on board a yacht. So this piece was written as I made my way through the progression; therefore is a truly a learn-as-you-go article.
What Exactly is a Solar Panel and How Do They Work?
Solar panels are basically any panel that makes use of the sun’s thermal energy to create electricity. A solar panel can be described as a photovoltaic panel, the name used in the business, for panels intended to create electrical energy from the emission of the sun. Despite the group of solar panel being discussed, nearly all solar panels are flat. This is because the surface of the panel needs to be at a 90 degree incline from the sun’s rays for the best angle to soak up the sun’s rays. Solar panels are able to absorb energy from the sun through a collection of solar cells on their surface. Very similar to how a plant is able to take in energy from the sun for photosynthesis, solar cells function in a comparable way. As the sun’s rays hit the solar cells on a photovoltaic panel, the energy is transferred to a silicon semiconductor. The power is then changed into (dc) direct current electrical energy and then passed through connecting wires to ultimately enter a storage battery.
Kinds of Solar Panels
Types of panels most normally used in yachting uses have either multicrystalline or amorphous thin-film cells. Multicrystalline panels are the oldest technology obtainable and in addition the strongest. When sized correctly and paired with suitable batteries, these are the panels to make use of for operating large loads such as refrigeration.
Amorphous thin film solar panels are only about 50% as effective as multicrystalline panels, but can be bought in flexible varieties so they can roll or fold, or change to the shape of a boat cabin top or bimini. They don’t often have adequate yield for considerable energy replenishment, but can be used to lightly charge a battery bank.
How Much Power Can Solar Cells Make?
Normally, we measure solar panels by wattage and that is how we buy them. You can get solar panels for boats as small as 10 watts to as great as 200 watts or even larger. But it is simpler to understand when we change watts to amperage. We calculate these values by multiplying the number of hours the panel is in full sun (usually defined as 5 a day in Florida) by the panel’s wattage. For a 195 watt solar panel the amount produced would be 195 x 5 hrs = 975 watts/day. We can then figure, 975 watts/12 volts = 81.25 amps per day.
Before considering which size panel to purchase for your boat, you will need to complete an energy budget to ascertain what sources of power consumption you have aboard while at anchor. I use the at anchor scenario as this is the place you will use the most energy; under power and your trawler can supply its needs without any issues.
Example, if you have 3 inside lights that pull 2 amps each and you keep them on for 4 hours per night, your consumption 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 running while at anchor.
DC Loads – calculate how many amps hours are used by each appliance
Fresh Water Pump
Inverter loads also make use of DC power but they are powering AC appliances and equipment. If you want to change watts to amps use (12watts/12 volts = 1amp).
Calculate the amp hours used by each appliance
Add up your overall daily energy use AH/per day
Solar Energy Creation
Different sources of power similar to solar panels can replace the amp/hrs pulled from the batteries. But similar to the power budget that determined your usage you will also need to compute your re-supply of amp hours. Keep in mind the formula – (12 watts/12 volts = 1 amp). But be mindful, the formula is only a gauge; complete accuracy can only be where the panel production is constant and a solar panel might at times function ineffectually due to cloudy skies. Compare the day by day power use in AH/Day to the solar power creation. Your solar energy production must be larger than the use. If it is not, pick a bigger wattage panel and recalculate. Always purchase more solar panel output than you think you will need; some professionals recommend at least 30% in excess.
Case in point – 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 got your solar panel, where do you put it on board your yacht? As we mentioned before, installing the panel ninety degrees to the sun is best. You will get the best power production this way. But on yachts, finding a fitting spot is tricky at best. A number of boaters put them on brackets placed on the rails, others position them on top of the bimini, and I have seen them positioned on the trawler dingy stanchions. But wherever you decide to mount them, bear in mind that to get the most out of them they ought to be in the open, away from any shading from booms, vessel radar arches, or cabin structures. Bear in mind that while at anchor, the boat will turn to the sun twice daily because of the tides. I opted to mount our panel on the top of the boat back deck hardtop in a horizontal position. Here it will get the greatest view of the sun and be clear from the radar arch shade as the boat swings at anchor. The slope toward the sun is not precisely at ninety degrees but it will have to do. I selected a 195 watt panel so I get almost a 50% reserve ability in my panel to compensate for the small inefficiency of the sun’s angle. We got the panel from Sun Electronics in Miami, sunelec.com as they had the best prices I could find anywhere on the web. But bear in mind, panels must be shipped using freight as they are heavily packed to reduce the chance of damage so be sure to calculate those expenses in your acquisition.
What is the best way to attach the panel to your vessel?
There are a variety of manufacturers of solar panel mounting rails and supports but almost all of them are made for roof or ground mounting. West Marine does carry a product for mounting small panels to the rails. A good number of boaters make their own mounts. I found a mount developed by Sunsei known as a Sunsei Glue Mounting Kit that is attached to the vessel and panel using 3M 5200 Marine Adhesive. The mount allows the panel to be installed with about 2 inches of space beneath the panel for aeration. I did not need to drill any holes in the hardtop either. You can locate these mounts at amazon.com.
Wiring Your Panel
Marine electrical wiring is incredibly specialized and hazardous; if you are not comfortable in performing this part of the task, please check with an experienced marine electrician. Your panel will be prewired for attaching to your vessel but you will need to provide the connecting 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 affixed; you cut one connector off.
In addition, you will also require a controller. The controller regulates the power stream from the panel to your batteries keeping your batteries charged yet stopping over charging. A number of controllers are easy but others have LED displays indicating the amount of charge etc. The more fancy features the more costly it will be. Your panel dealer will be able to suggest a controller that will satisfy your needs. I chose a controller developed by Specialty Concepts. It is straightforward but does the job. And the people at the company are a big help in aiding you to select the best model for your panel. When you get in touch with them, they will want to understand which size panel (wattage) you own and what the voltage is. Check them out at specialtyconcepts.com. I also got my controller from the individuals at Sun Electronics in Miami.
The individuals at Specialty Concepts have also calculated how heat will have an effect on current flow and suggest that their controllers not be placed in engine rooms as the heat produced will diminish the controller effectiveness by roughly 25%. I put mine in the electrical panel under the lower helm. And finally, you will require the correctly sized cables to go from the controller to your batteries and a fuse to connect the controller to the battery bank. In deciding on the correct fuse, you need to 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 will need. Your controller operating manual will have information on these too.
Owning a solar panel to preserve your batteries would seem like a great plan but you’ll want to have a way to keep an eye on your batteries. I opted to also install a Trimetric 2025RV Battery Monitor; bogartengineering.com. This smart device is wired into your battery bank to provide a genuine measurement of voltage going in to the bank, amps being used by your yacht, the percent full charge on the bank, and the amp hours utilized from the last charge.
So we have now installed a 195 watt solar panel in addition to an 1800 watt inverter and a battery bank with 443 amp hours. We ran our tests this week on the hook with clear skies. I concluded that our energy consumption is 112.5 amp hours per day. The freezer is the major draw using 60 of the amp hours followed by the refrigerator. Did you know that a standard anchor light pulls 18 amp hours each night? I think I’ll check out LED bulbs now.
The battery monitor indicated that our actual draw from the battery bank was merely 65 amp hours which indicates we received the remaining from the sunlight, an entire 42% was from the sun. Now we will turn on the genset for around an hour to bring the battery bank up to complete charge.