Here Comes the Sun

A little extra free power can provide a redundant system that will keep instruments up and online.

If you're reading this magazine, chances are you're not a tree-hugger: You burn lots of fossil fuel to push your boat at high speed through a relatively unyielding medium. Then when you get where you're going, you burn more to generate enough electricity to power all your appliances. So why am I wasting my time telling you about the advantages of solar panels?

Because someday you might have to abandon ship, and if you do, a solar panel could save your backside.

Most boats carry their batteries in the engine room, the part of the hull that's usually first to flood if a seacock pops or you hit something hard and punch a hole in the bottom. If that happens, what about your batteries and the associated wiring? The system can short out pretty darn quick, leaving you with no radio to call for help and no electronics to pinpoint your location even if you're able to raise someone on the handheld. Megayachts often carry an emergency genset on an upper deck to provide power until the last minute—enough for lights, communications, and to operate the davits if it becomes necessary to take to the boats. You can have the same setup in miniature with a couple of batteries and a solar panel. Even if you don't plan on sinking, it can provide handy back-up juice aboard any boat.

This is an easy system to install, as long as you have an unobstructed area high on the vessel on which to mount the solar panel, someplace that gets lots of sun, naturally. A hardtop or radar arch is a good spot, and it should be easy to run wiring from here to a charge controller (essentially a voltage regulator) and battery under the helm console. Use a couple of batteries and an inverter and you'll be able to run the blender and other small appliances, too, without starting the genset. Add a switch to transfer radio and electronics from standard ship's power to the emergency batteries if needed. This is a simple job for a qualified marine electrician.

The solar panel will keep the batteries charged with no operator intervention; it will produce juice even on cloudy days (whenever you can see shadows), although reaching full rated output requires bright, direct sunlight. Experts figure a daily output of about five times the panel's rating under optimum conditions, for example, a six-amp panel will produce 30 amp/hours on a sunny day. Ask your electrician for advice on choosing a panel. At the time of this writing, West Marine was charging $1,059 for a Sensei six-amp panel, plus $40 for a ten-amp controller. A four-amp panel was $849.

Solar-powered boats have crossed the Atlantic Ocean (www.transat, and diesel hybrid yachts are already being introduced. (See "Silent Revolutionary" and "The Way Forward," this issue). If you're not ready to go quite that far with solar power, why not take the first step? One day it might save your life. If it does, when you get ashore, maybe you'll want to hug a tree.


Electric motors are ok for water taxis and yacht-club launches, but they can only make short trips and must plug in every night. Is there an electric propulsion system for real-world use?

Alex Pesiridis is chief engineer of the Marine Power Division of Solomon Technologies (727-859-4447), a leader in the development of electric and hybrid power-drive systems for the marine, automotive, and aerospace industries. A graduate of the University of Colorado with degrees in electrical engineering and physics, Pesiridis has designed electric propulsion for many cruising yachts, some of which carry no fuel at all, but rely only on solar panels and/or other means of recharging.

The best system for "real-world" boats today is a hybrid, says Pesiridis, combining an electric motor with a large battery bank and a genset for recharging. Compact, quiet, high-torque electric motors need no reduction gears or transmissions, require no maintenance, and operate at about 90-percent efficiency across the rpm range. "A diesel engine is most efficient only at a specific rpm," he explains. Because it develops high torque at minimum rpm, the electric motor can replace a diesel of three, four, or even five times its nominal horsepower. "Our smallest motor [6-hp] can spin up to an 18-inch prop."

The Solomon Technologies system uses a 144-volt battery bank—a dozen 12-volt AGM batteries wired in series—recharged by a common genset. The batteries can also power air conditioning and other ship's systems through an inverter. How long the motor will run solely on battery power depends on the total electrical load. Discharge them faster and you have to recharge sooner. An electronic controller monitors the batteries and starts the genset automatically when they reach a preset level of discharge, usually no more than half. If an owner doesn't want the genset to run as often, the controller can be set to delay recharging until 70-percent discharge. However, the life cycle of the batteries will be much longer if they are recharged often, warned Pesiridis.

Although he designs many of them today, Pesiridis doesn't think hybrids are the system of the future. "Someday there will be no fossil fuel in the boat," he predicted. What will take its place? Solar might be the best way to go for many applications, he said, especially if the panels get more efficient—or maybe hydrogen fuel cells. "Electric motors have been around for years; it will be interesting to see what new technology comes out," Pesiridis concludes.

This article originally appeared in the January 2009 issue of Power & Motoryacht magazine.

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