One of the strangest things that I have to regularly explain to nonsailing friends is why engines are often run offshore to generate onboard DC electricity. While savvy friends understand that charging needs to happen if one is going to rely on their batteries, those less technologically inclined are sometimes stumped. And rightly so. If sailing is so green, they ask, why do sailors emit CO2 to keep their nav lights on?
Contemporary sailors, though, have their choice of several alternatives to producing electricity without starting up their diesel engine, starting with solar panels and progressing to hydrogenerators and wind generators. While plenty has been written about solar panels, this technology depends on the sun, which is dormant during nighttime hours, and sometimes during the day too, especially on my home Pacific “Northwet” waters, as we like to call them.
By comparison, hydrogenerators and wind generators are also highly effective, sometimes for entire 24-hour cycles, and can often satisfy all of a vessel’s DC-power needs. Alternatively, these generators can serve as part of a multipronged energy-producing system aboard yachts with significant DC-power needs to run heating and air conditioning, powered winches, refrigeration and the like. Here, then, is a look at how wind and water generators work, the benefits they provide, and some practical considerations for owners interested in greening up their onboard-power production.
Working with Water
As their moniker implies, hydrogenerators are electromechanical machines that harness the energy of moving water. Hydrogenerators typically capture this energy as alternating current, convert it to direct current, and then send it to a battery for use later. While hydroelectric dams are an everyday form of hydrogeneration ashore, marine-facing systems typically come in different sizes, and with varying charging capabilities, but most employ an underwater turbine consisting of a propeller or impeller that’s part of an assembly that hangs from a yacht’s transom or is fitted to its undercarriage, directly abaft the keel.
“In essence, a hydrogenerator consists of an impeller designed to extract kinetic energy from the water, and an alternator to convert the rotary motion produced to electricity,” Peter Anderson says. He is Eclectic Energy’s managing director. Eclectic’s line of hydrogenerators employs a dive plane beneath the impeller, which allows the system to “fly” through the water at a controlled depth, similar to how a hydrofoil allows a boat to rise above the water at a desired height. This approach differs from other designs that resemble an outboard motor.
“The amount of kinetic energy available in a fluid stream—air or water—varies as the cube of its velocity,” Anderson says. “For a water generator, this means even a modest increase in boatspeed produces a substantial increase in power output. Equally, at lower speeds, the amount of energy available falls rapidly, as do outputs.”
Because of the direct correlation between a vessel’s speed over water and a hydrogenerator’s ability to produce power, the size of its propeller or impeller matters greatly. Spec the system with too small a prop, and it won’t generate much juice; spec too large a spinner, and it will create excessive drag and could possibly break if a vessel’s speed surpasses certain thresholds. Because of this, most hydrogenerators come—or can be ordered—with different size impellers.
With a properly sized system, hydrogenerator-induced drag is minimal, Anderson says. It could cost a 30-footer that’s making 6 knots roughly a 10th (or 1/5 of a knot) of boatspeed; this likely drops to an invisible metric for a 50-footer in similar airs.
Sabrina Huet, communication and sales manager at Watt&Sea, another hydrogenerator manufacturer, echoes this: “Our cruising hydrogenerators produce energy from boatspeeds of 2 or 3 knots up to 20 to 25 knots,” in the case of racing yachts. “It all depends on the propeller size. We offer four propellers with different diameters to accommodate different sailing speeds. The aim is to minimize the drag effect while optimizing the output. To put it in a nutshell: We suggest a bigger diameter for slower boats, and a smaller diameter for faster boats.”
As mentioned, as a boat moves through the water, hydrogenerators initially capture the energy from the spinning propeller as AC power, which is converted to DC. “Most modern generators use alternators,” Anderson says. “AC power is rectified to DC within the housing.” Watt&Sea’s systems work in a similar manner.
As with other technologies described in this article, batteries are sold separately. A sailor can use any kind of battery, they would just have to check if a particular battery or battery bank requires any specific voltages, Huet says. If a battery or bank has needs that are different from Watt&Sea’s factory settings, those parameters can be changed easily, thanks to the system’s integrated mobile application.
That said, it’s important to confirm that a yacht’s batteries are in good shape before connecting them to a hydrogenerator. “A minimum of 300 amp-hours at 12 volts is recommended,” Anderson advises. Most cruising yachts have at least 400 amp-hours of battery capacity, with 200 amp-hours that are usable. Batteries should not be routinely discharged below 50 percent, he notes, so it’s sensible to increase battery capacity if space and budget allow.
Both Eclectic Energy and Watt&Sea employ smart technology to ensure that their systems don’t create overcharging issues. “A charge regulator normally forms part of the installation,” Anderson says. “This terminates the charge once the batteries are full, which prevents possible damage through overcharging.” Once the battery or bank is topped up, the regulator then connects the generator to a power resistor in order to dump additional electrical energy.
Hydrogenerators can make great use of trade-wind conditions, however too much of anything becomes a negative. “Our hydrogenerators can withstand difficult conditions, but it’s essential to lift up a generator when approaching rough conditions, and to secure it with a rope or even belowdecks,” Huet says. “It’s also important to think about the lifting and lowering system, such as a hoist, to make the handling easier in both rough and calm seas.”
“Prudence would suggest water generators be raised out of the water and possibly stowed,” Anderson says of preparing for heavy weather. “However, many owners report operating their Eclectic generators in storm conditions without problems.”
As with all systems, installation is an important consideration.
Watt&Sea recommends hiring professional installers. Eclectic Energy, however, is more geared toward do-it-yourselfers. “Our generators are supplied with standard mounting hardware and installation instructions,” Anderson says. “Many owners do install these systems themselves.”
One concern for sailors—especially those who voyage in log- and debris-strewn waters such as the Pacific Northwest—is an encounter with an unidentified floating object, which could damage the impeller or propeller, or even the entire assembly. Much like during storm conditions, sailors are advised to retract their hydrogenerators based on localized conditions.
The amount of power that a hydrogenerator can produce is an important and subjective question. Much hinges on how fast a boat is sailing (or motoring), the size of a hydrogenerator system, and the size of its impeller/propeller. Because of this, Anderson and Huet advise customers to check manufacturer websites for more information about specific models and impeller/propeller sizes.
While the drawbacks to using a hydrogenerator—aside from turnkey costs, minimal drag, and attention to debris in the water—are minimal for sailors frequently on the move, the upsides are substantial, especially if you don’t care for the sound of a diesel engine or generator. “Water generation is the only renewable technology capable of matching the power consumption of a typical cruising yacht on passage,” Anderson says. “This removes the need for daily engine or genset runs to charge up the batteries.”
Counting on Breeze
The concept behind wind generators is equally simple, and most manufacturers rely on a turbine with blades that are exposed to airflow, which makes them spin. If this sounds to you a lot like an inverted (or dry) water generator, you’re spot-on—with a few exceptions.
First, hydrogenerators are under the water’s surface, while wind generators are fitted on deck atop poles or on struts mounted on a mast. Second, wind generators are typically larger, employing longer blades, with greater cord widths than would be found on hydrogenerators. Third, since hydrogenerators depend on boatspeed to produce power, their performance is typically more consistent and not affected by small puffs and lulls of the wind. Lastly, the two types of generators typically produce different types of electricity.
“All of our wind turbines produce DC Power,” says Dan Kruger, president of RDK Products. His company manufacturers wind turbines under the brand name Nature Power Products. “It starts out as high voltage, but through our controller, the system will step down the voltage to correctly charge your 12-volt batteries.”
Nature Power Products come with a generator, three carbon-fiber blades, and a charge controller. Customers need to supply their own mounting pole, and Kruger notes that most of his customers purchase theirs from fence stores.
As with hydrogenerators, wind generators are available in different sizes, with different energy-producing capabilities. Nature Power offers 400-, 500- and 2,000-watt systems. Kruger says: “These are designed to run most of your smaller electronics, televisions, GPS, fans and lights. They aren’t designed to power air conditioners unless you build a fairly substantial hybrid system that also includes a battery bank and solar energy.”
As with hydrogenerators, wind generators are compatible with a range of battery technology, including lithium and absorbed glass mat batteries. “A typical marine-grade deep-cycle 12-volt battery is fine for a basic wind-turbine system,” Kruger says. “Many sailors will have a bank of batteries. We also manufacture 24- and 48-volt wind-turbine systems for larger, more complex installations.”
Determining the right-size wind generator for your sailboat starts with calculating your vessel’s power needs. “There’s no minimum-size vessel for a wind turbine to make sense,” Kruger says. “But if you’re getting into larger vessels, such as a Swan 88, you would definitely want to be looking at the Nature Power 2,000-watt system.”
Nature Power Products protect their connected battery or battery banks from overcharging by entering a “float” mode when the system’s controller senses that the storage reservoirs are topped off.
As with windmills, wind generators are most effective in a good, steady breeze. The working range for Nature Power’s 400-watt system is 6 to 24 knots of wind, with 24 knots being the optimal windspeed. Kruger says that the goal is to expose the wind generator to steady, laminar flow, not ricocheting gusts. “The higher you mount the wind turbine, the cleaner the wind will be and the more efficiently your system will operate.”
Too much breeze, he says, can be problematic. “The only time you would want to take down the unit is if you feel the storm might jeopardize the actual physical installation,” Kruger says, explaining that Nature Power Products are designed to withstand serious wind without sustaining damage to the turbine, its circuitry, or the connected battery or battery banks. The systems accomplish this by employing its float mode when windspeeds crest certain thresholds. “The system’s actual ‘survival’ windspeed is 96 knots,” Kruger says.
While installing a wind generator isn’t a plug-and-play operation, the systems are relatively lightweight and generally require somewhat basic wiring schemes, making them DIY-friendly. Maintenance is also a typically easygoing affair. Kruger suggests replacing a system’s turbine blades every few years and installing the system’s controller in a dry place near the battery or bank.
As with all technologies, wind generators have their downsides. Breeze can be an inconsistent actor, and air-density changes depend on atmospheric pressure and temperature, both of which can complicate a system’s daily output. Also, some generators are loud, making the owner unpopular, say, in a crowded anchorage. And while they are capable of impressive power generation while anchored in the trades, downwind runs—typical of trade-wind passages—reduce the apparent wind, rendering generators less productive. Lastly, depending on their installation, a wind generator can possibly interfere with running rigging and sails, or depending on their size, they might cast shadows on a vessel’s solar panels.
Otherwise, wind generators can be a great source of green energy, and are commonly bundled with other green solutions to create ample onboard power.
David Schmidt is CW’s electronics editor and frequently reports on other types of gear.