Way-Distributed Wind Generation

By Paul Miller

Technology Trends

While I no longer own a cruising sailboat, I remain a sailor at heart and try to keep up to date on what’s happening in the boating world from a technology perspective.  On occasion, this sometimes intersects with my work here at ARC.

I recently came across some current information on wind generators for sailboats provided by PRACTICAL SAILOR magazine, one of the best (and certainly the most objective) sources of information for sailboat owners.  (Like CONSUMER REPORTS, PRACTICAL SAILOR does not accept any advertising…). This reminded me that, while wind generation on a large scale is really just starting to come into its own as a renewable source of electric generation (in North America at least), sailors have been using small-scale wind generators for decades now to recharge the batteries on their boats.  These are referred to as “micro turbines” in the industry and it appears that micro turbines for sailboats have much in common with other small-scale distributed wind generation applications.   

PRACTICAL SAILOR’s “Wind Generators 101” summary provides a good basic explanation of the respective pros and cons of AC vs. DC wind generators for this type of “way-distributed” wind generation:

Wind turbines convert the kinetic energy of the wind into mechanical power, and ultimately electricity. This electricity can be used immediately to power equipment, but is typically stored in batteries for future use. Larger turbines may generate enough power to carry or "float" larger loads (such as a small fridge during an overnight stay aboard), while smaller units produce enough electricity to power smaller loads for a few minutes (bilge pumps, etc.) or perhaps top off your battery banks after a weekend outing.

All generators share a few basic components: a rotor - they don't propel, so they're not propellers - with aerodynamic blades, an electrical generator, some form of rotor over-speed control, and a mounting system (pole, arch, etc.). Most also will have rotating electrical contacts, which enable the unit to operate in a continuous 360 degrees of rotation.

Wind turbines either produce direct current (DC) or alternating current (AC) power, which is then converted to DC via a rectifier… Each approach has its pros and cons: AC can be transmitted over longer wire runs with less power loss (due to overall resistance of system wiring), even when smaller gauge wire is utilized. DC systems, on the other hand, don't require the use of a rectifier, which reduces expense, cuts down on the number of parts that might fail, and eliminates a few installation steps. As for cons, DC motors have brushes and commutators, both of which require periodic maintenance to prevent generation of electromagnetic interference (EMI), which can disrupt onboard electronics. The rectifying diodes in AC-producing units can also be damaged if exposed to reverse-polarity voltages during installation or maintenance.

I learned that the small-scale wind generators designed for sailboats also share many of the same constraints that apply for larger, commercial-scale installations.  These include siting issues, safety, blade noise, reliability, and the inherent variability of wind itself (which makes most wind generation inappropriate for baseload generation).  We’ll touch on siting here.

While siting commercial scale wind generators (not to mention entire wind farms!) involves rigorous, time-consuming, and expensive site assessment plans, engineering studies, environmental permitting, and community approval; siting wind generators on sailboats is largely a matter of the sailboat owner finding someplace on a small vessel that is accessible to the prevailing winds, but also where the rapidly spinning blades do not pose an undue hazard to humans, pets, or other vessels that might be anchored, moored, or docked nearby.  This is not as simple as it may sound.

The best spots are those that offer an unobstructed flow of wind, while keeping whirling blades well clear of rigging, self-steering vanes, davits or – most importantly – the outstretched arms of the tallest crew member. As on land and/or for near-shore wind farms, aesthetics often enter into the picture.  Just as no one wants a wind turbine to encroach on their scenic views, sailboat owners are generally loath to have a wind generator spoil the beautiful lines of their sloop, ketch, yawl, or schooner.

In a future OTV post, I’ll explore another example from my own personal experience of what I call “way-distributed” wind generation.  These are the small wind generators mounted to the roofs of many of the relatively remote Appalachian Mountain Club huts in the White Mountains of New Hampshire.  These are intended to make the huts both self-sufficient and reduce their respective environmental footprints on the pristine mountain environment.  

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