Solar technology may be constantly evolving and it won’t propel you across the water at highway speeds—yet—but sun power does, in fact, have its place on a modern boat. Many different options are available for providing power to your green marine machine, and after an initial investment in hardware the power costs no more than a natural dose of vitamin D.
The sun gives off the equivalent of 1,000 watts of power per square metre on the Earth’s surface area, and solar panels of photovoltaic cells made with a semiconductor (most commonly silicon) can gather a tiny portion of this energy. When the light strikes the semiconductor it essentially kicks electrons free, creating an electrical current. Many boats have large surface areas which are ideal for mounting solar panels, but boaters face a challenge in stowing this energy for future use. To hold that charge, you’ll need lots of deep-cycle battery capacity - which unfortunately, means lots of weight. A single 12-V deep cycle battery with 100 amp hours (the amount of energy the battery can supply for up to 20 hours at a constant rate; 100 amp hours equals a five amp load for 20 hours, for example), usually weighs in at around 60 pounds. In real-world terms, those 100 amp hours are enough juice to propel a 16-foot fiberglass boat at jogging speed for about three hours (or at walking speed for five to six hours) with a modern 12-volt transom-mount electric motor in the 70 pound thrust range. How many horsepower does this equate to? Thanks to current draw, variable motor RPM, declining amperage, and differences between manufacturers, direct conversion from pounds of thrust to horsepower isn’t possible. But when you compare the speed of identical boats powered by gasoline outboards versus electric outboards, you’ll discover that a 70 pound thrust motor pushes you along about as fast as a two horsepower outboard.
For large boats, obviously, this isn’t enough power to accomplish much. To get more power, you’ll need more voltage. And if you up-size to a 48-V system, you can power motors like Torqueedo’s Cruise 4.0, which the manufacturer says delivers over 280 pounds of thrust and as much oomph as a 9.9 horsepower petrol engine. Put a pair on a runabout (Read the Boats.com blog post, 17 Kona: Torqueedo Powered Runabout), and that’s enough juice to do some real cruising. Earlier this year, an Australian company called Aquawatt announced the development of a 30-hp electric. And there are a few “hybrid” model boats out there, which are decked out in solar panels and can slowly cruise for miles on the sun’s input (Read our features on the Island Pilot Hybrid.) Propulsion is, of course, only one of the uses for sun-provided power. Another important and immediate purpose is fueling your current electrical needs. You can use solar power to keep your house and starting batteries up to snuff and prevent future power failures, for example. (Read Solar Battery Maintenance: An Ounce of Prevention.) And solar power can also be used to operate 120-volt items on your boat when you add an inverter into the mix. In fact, the sun can even replace a generator in many cases. Hot water heaters, refrigerators, ice makers, and entertainment centers are all examples of electrical items that can get all juiced up with stellar rays. But you can’t use all of that energy until after you’ve collected it, and that means choosing a solar panel (or panels) for your boat. A surprising number of marine-rated versions are out there, and a 10 square foot rigid panel can put out a potent 100 or so amp hours per day. The 20-year life expectancy of a high quality fixed panel is also attractive, but these panels can cost several thousand pounds.
A more acceptable option for many boaters is a flexible panel, which can match your boat’s shape and costs hundreds, instead of thousands, of dollars. Unfortunately, these have much shorter life expectancies (five to ten years), and commonly provide a fraction of the power of a large fixed panel. Roll-up panels are also on the market; they cost just a couple hundred bucks, provide even less power, and usually last three to five years. And while these may seem pretty wimpy in comparison, the fact that you can roll them up, stow or transport them easily, and use them on different boats, means they’re one of the most versatile ways to harness the sun’s rays. For handling smaller jobs, portable solar chargers come in handy. One of the most useful units I’ve tested is the Solo Rocsta (http://www.boats.com/blog/2011/06/solar-chargers-for-ipods-and-cell-phones/), which can be used to power all kinds of gadgets. It comes with multiple fittings and adaptors that mate up with i-thingies of all varieties, Android cell phones, cameras, video cameras, and just about anything else that charges with a USB, mini USB, or micro USB port. The pocket-sized solar panel has an internal 3.7-volt Li-ion battery inside, so you can even use it as a portable power pack after the sun goes down. Some other units, like the Surge, are designed to charge specific products—most often, iPhones. You can also find portable solar “generators,” which combine solar panels, batteries, and inverters in a single package. Set ‘em up, plug your 110-V item in, and you’re ready to harness the sun’s rays in seconds. A final way to utilize solar power on your boat is with dedicated solar-powered gadgets. Flashlights, radios, vents (Read Installing a Solar Vent), and fans can all be found with built-in solar panels. Even some marine gauges and monitors are available in all-solar models. While using these won’t cut your fuel expenses, it sure can reduce the bill for batteries. And when you consider their usefulness along with the many varied solar power options available to mariners in this day and age, there’s no doubt about it—solar power most definitely has a place aboard your boat.
Read also our feature on solar craft, Solar power: ingenious solutions for boaters.
Lenny Rudow has been a writer and editor in the marine field for over two decades and has authored five books. He runs his own web site at HookedOnFishingBoats.com and writes weekly for Boats.com reviewing new models and covering marine electronics.