See how the wind can fill your batteries as well as your sails
Issue 33 : Nov/Dec 2003
Sailors have depended on the wind for propulsion ever since there have been sails. Now, however, not only can the wind take you from point A to point B, it can also keep your beer cold, run your radar, and light your night. Through the magic of wind generators, in areas with high winds you may be able to provide yourself with enough power to be self-sufficient in energy for days or possibly even indefinitely.
Selection
Careful selection and installation are important to assure a steady supply of juice. You’ll want a generator that is powerful, quiet, and cheap. Pick any two. In general, you have to give up one for the others.
There are two types of wind generators: permanent-magnet generators and alternators. Unlike engine alternators, virtually all wind generators have permanent magnets in their rotors; designs differ according to how the alternating current is rectified. The generators rectify the alternating current produced by running it through a commutator with brushes. (Although changing brushes need not be a difficult task, it is a maintenance item.) The alternators rectify the alternating current using diodes, in the same manner as the engine alternator. The general term wind generator as commonly used includes both the generator and alternator types.
Units with larger-diameter blades (typically 5 feet) tend to be of the generator type, while units with smaller blades (typically 3 to 3 1⁄2 feet) tend to be of the alternator type. This is not a strict division, however. There are some large-diameter-blade alternators. Although the power output of a wind generator is a function of the square of the blade diameter, the smaller models have the advantage of being able to withstand very high winds unattended and with no provision for controlling the rotational speed. The larger units all need to be monitored and have the blades locked in high winds. Or they need some mechanism to control rotational speed in high winds. Because of their smaller size, alternator types can usually be left unattended in any wind, while their larger counterparts need some type of braking or furling system to prevent them from flying apart.
Batteries
You must have the storage capacity for all that free power. Your battery(ies) should be able to hold three to four times your daily use and more in areas with unreliable winds. The more capacity you have, the longer your batteries are likely to last.
Power output
A wind generator is no more than expensive weight aloft without wind, so you must decide if where you are or where you are going will provide enough of it to make this sort of purchase worthwhile. Nothing is better then steady trade winds for wind generator use, and most of the brochures gush toward that end. But, unless you’re anchored somewhere in the trade-wind belt, the wind is more likely to be a mix of fairly reliable diurnal breezes, calms, and gusty winds. If your area does not have regular winds, a wind generator is not for you.
Manufacturers’ wind-generator output figures are not standardized so some reading between the lines is necessary. Since wind generator output is determined mainly by the diameter of the blades, the larger wind generator can be said to provide more power. However when comparing outputs, check how the manufacturers rate their machines: steady wind, weighted average, or laboratory tests? Watch out for blue-sky perfect-world figures. As most sailors can tell you, there ain’t no such thing. It’s rare to find a wind-generator output in the real world that compares to published ad slicks.
Specific applications will vary. How much energy do you use? How much wind is there where you are? You may not be able to supply your entire daily energy requirement with a wind generator even if you choose one with a large-diameter blade. If you have to augment your electrical power generation with solar panels or using your engine alternator occasionally, however, the wind generator could supply a large fraction of your energy requirement.
Models
Beside power output, there are several other considerations to make.
- Quality and reputation. What have you heard or read about individual models?
- Ease of maintenance and parts availability. Is the unit serviceable in the field (at sea)? Are parts available locally or do they come from overseas?
- Regulation. Can the unit be left unattended in any wind, or must it be stopped in strong winds? That’s a challenge at times.
- Aesthetics. Does the style complement your boat (not very likely) or does it look like something cooked up in a garage?
- Noise. Though listed last, this may well become the most important item. If you can’t stand the noise (and they all make noise), power output is irrelevant.
Regulation
Regulation of a wind generator is necessary unless your demands and battery capacity are very high or if you are willing to constantly monitor battery voltage and can disconnect the generator.
All wind generators can produce loads of power in high winds — such as a squall or storm — and therefore should have a regulator capable of coping with as much as 15 to 25 amps. Only one of the well-known brands of wind generators has built-in regulation. The models from AirMarine have a regulator built into their housings, eliminating the need for an external regulator — a savings of $200 or more.
Most manufacturers sell regulators for their wind generators and most are of the shunt variety. This means that any excess power is completely wasted as heat at the regulator. These must be installed in a place with plenty of ventilation as they can get hot. In our boat, when the regulator is shunting power (an LED comes on), we know it’s time to turn on more fans or lights. No sense in just making heat.
An adjustable-output regulator is more useful than one that is not, as it can be used to equalize sulphated batteries. And remember, there must be a fuse between the regulator and the positive side of the battery.
Noise
Regardless of slick brochures, all wind generators make noise. Since sailors generally like peaceful anchorages, this must be kept in mind when selecting a wind generator.
The small ones, such as the Rutland 913 on our boat, make about as much noise as wind in pine trees plus a low moaning sound from the alternator itself, which is noticeable but not objectionable. Some, like the AirMarine 403, are well known for the noise made by their blades. When the AirMarine exceeds the safe limits for wind, it cleverly stalls its blades to slow. But this damping is known to be noisy, too. Other manufacturers of larger models use centrifugal air brakes or tilt-back mechanisms, both of which can be quite noisy. Additionally, most wind generators can be electrically braked or slowed by shorting their leads (after disconnecting from the battery). Then if the noise is too great and the battery full, they can be effectively shut down, though this should not be done in high winds, as it can generate a lot of heat.
Mounting
Wind generators can be pole-mounted, hung in the rigging, or mounted on a mizzenmast. If you want your wind generator mast-mounted or hung in the rigging, you’ll probably want to use the manufacturers’ mounts, though it is possible to fabricate them yourself. Most generators are mounted on the stern of the boat. This method has more options.
The wind generator, being akin to a giant food processor, must be located so its blades are higher than the tallest crewmember can reach. Usually a 9-foot above-deck height is sufficient. The easiest (and most expensive, naturally) method is to buy the pole kit from the manufacturer. These typically run from $325 to $450 including the pole. However, most wind generators are designed to mount on 1.5- or 2-inch Schedule 40 polished aluminum pipe. This can be purchased locally for about $5.20 per foot, or less than $50 for 9 feet . . . about $150 less than the manufacturer’s price for the pole. The supports, support mounts, and deck mounts are the only other items needed. The supports, which are usually 1-inch stainless-steel tubing, can also be found locally for about $3.60 per foot, again at a large savings. Two 6-foot lengths are usually adequate. Look for a metal shop or stainless-steel welding shop in your area.
A fabricator can weld attachment points to the pole for the supports. Bimini or dodger eye ends found at marine stores can be purchased to slip on the ends of the supports. You will need four of these, two each for the pole attachment and two each for the deck attachment, which can be stainless-steel angle pieces. The good eye ends can be rather pricey. Their high cost may justify purchasing an attachment kit, as this will also give you the deck mounts, rubber isolators for the pole and supports, attachment points for the pole, and instructions. This kit also allows the whole wind generator and pole assembly to be pivoted downward for easy servicing. The kits sold by Southwest Windpower are well made and sell for less than $200. All that is needed in addition to the kit is the pole, supports, and screws to attach the deck hardware.
An alternative to solid supports is to use two guy wires and turnbuckles mounted on the deck and a solid support to the backstay. This method allows the wind generator to move about a bit more and is more difficult to isolate but can be cheaper and has less weight and windage.
Whichever method you choose, when bedding the supports to the deck, be sure to overbore, fill with epoxy, and redrill any holes in the deck to prevent water from seeping in to the deck core. (See “Clay Saves the Day,” Good Old Boat, January 2002.)
For solid supports, the angle between the pole and supports should be no less than 30 degrees and no more than 60 degrees. The angle between the supports should be as close to 90 degrees as possible. On smaller boats, like our Mercator 30, these dimensions were not possible, the support-to-pole measurement being about 27 degrees. However, with one of the lighter-weight wind generators, this is acceptable.
Also, the wind-generator blades need to be at right angles to the water in order to receive the wind’s full power.
If you are attaching stainless-steel fittings to an aluminum pole with collars from a kit, it would be wise to insulate the two metals to prevent galvanic corrosion.
Wiring
All that wonderful free power will not make it to your batteries without proper wire size and connections. First, calculate the wire run from the wind generator to the batteries including the run to and from the regulator (if any) and double it to find the round-trip circuit length. Next, determine the highest amperage that your wind generator is likely to produce. Then, find the wire size needed in a conductor size chart (most marine catalogs have one). Runs of about 30 feet with a circuit amperage of 20 can use size 12-gauge wire, but be sure to use quality marine-grade wire and connectors. A hole drilled a few inches above the bottom of the pole can be used to let the wire out, provided a grommet is used to protect the wire. It is desirable to have no splices in the wire from the wind generator to the battery (excepting the regulator). Cable Grips, available at marine stores, allow the wire to pass through the deck using a waterproof entrance.
It is vital to install a properly rated fuse in the positive line between the wind generator and the battery. Also, using an ammeter to measure your wind power is useful; when calibrated, it can be used as a substitute anemometer.
The power
Once your wind generator is properly installed, you can begin to see the power available with the first gust. It is truly gratifying to see that the same free power that moves your boat can supply much of your electrical needs. Instead of dreading that coming squall, you’ll be eagerly anticipating all the amp-hours that it holds. Grab a cold drink and thank the wind!
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
