Wind Energy for Boats

Summary

Because they have a smaller footprint, vertical-axis wind turbines (VAWTVertical-axis wind turbine) are better suited to boats than horizontal-axis wind turbines (HAWTHorizontal-axis wind turbine). They are somewhat less efficient but can take advantage of turbulent and gusty winds. Cost performance and size remain barriers. Small turbines around 600 Watts (WWatt) capacity cost USD $5,000 or more and have a spinning diameter around 2 metres (mMetre, SI unit of length).

Vertical Axis Wind Turbines

There isn't the space on a boat necessary for a horizontal-axis wind turbine for supplementary power. Even a small vertical-axis wind turbine is problematical. Think an egg beater, with the gearbox and generator located at the bottom of the mast. VAWTs are omnidirectional and can take advantage of turbulent and gusty winds because they require a lower wind speed to self-start. They rotate at 1/3 to 1/4 the speed of HAWTs, which reduces their noise and vibration levels.

Early designs (Savonius, Darrieus and giromill) had significant torque variation on the blades during each revolution, which tended to break the blades. Later designs based on the Darrieus model solved these issues with a helical twist of 60 or 120 degrees in the blades; and by using composite materials for the blades.

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Efficiency

Wind turbines are not very efficient. That'sSecond why you always see such large horizontal machines in the countryside (plus of course their utility scale). The best ones have an efficiency of around 35-47%percent in an ideal wind. According to Betz's law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind. Practical utility-scale wind turbines achieve at peak 75% to 80% of the Betz limit. ^[4]

Vertical turbines are less efficient than horizontal ones, around 30%. In a design with a diameter of 2-3 m (6-9 ftFoot) you can expect a maximum output of around 2.5 kiloWatts (kWKiloWatt, 1000 watts) (3.35 hphorsepower). Small (or “residential”) vertical systems may be suitable for boats. They range from 400 W to 500 kW.

Cost

Small vertical turbines cost in the range of USD $5,000 to 10,000.

Size

The problem of size remains. For example, the Windspire is a small 1.2-kW vertical-axis wind turbine. The turbine tower is 9.1 meters tall, and its rotor area is 1.2 by 6.1 meters. ^[5]

The WePower Falcon is sized as small as 600 W with a 1.6-m diameter and a rotor height of 1 m. ^[6]