While windpower is restricted to a minority of the boating fraternity, it does, however, deserve inclusion because no other device has the potential to supply as much power without running the engine as a wind generator.
The popular order of priority for generating electricity on the water is: running the engine, secondly solar power, with wind power, generally regarded as a black art, a distant third.
There is no doubt that the potential of a wind generator is impressive. Due to a law of nature, the energy derived from the wind varies by the cube of the wind velocity, meaning that when the wind speed doubles, the resulting energy increases eightfold.
This means that it is possible to extract up to 400 watts from a small wind generator. Compare this to a solar array which usually cannot exceed two eighty watt panels resulting in a maximum output of 160 watts. So what are the pros and cons?
Windpower is almost exclusively restricted to the cruising yacht and is generally preferred in the Caribbean and Mediterranean due to prevailing wind patterns. Very effective upwind where they can take advantage of accelerated air from the sails but not so good in downwind trade-belt conditions.
At the risk of stating the bleeding obvious, they are useless in sheltered anchorages. The primary motivation to install windpower is to free the yacht from running the engine. Windpower is an inefficient method of recharging on an extended voyage, reducing noise pollution and fuel costs, and as a backup for the solar system.
The solar array lies benignly on the boat, soaking up energy and converting it to electricity with no fuss. The wind generator is a much more feral beast. It is designed to produce most of its power in the wind spectrum between five and 30 knots.
Below five knots, physical inefficiencies result in little meaningful power, from 30 knots the output power stabilises up to 45 knots. Above that things start to get interesting.
At high wind speeds a wind generator has the potential to self destruct. So the speed of the blades must be kept under control. Earlier generators relied on physical means of control such as tethering or feathering the blades or manual braking. Considering that the generator should be mounted as far from human contact as possible, the above methods of control are fraught with peril.
Modern units are provided with microprocessor control and computerdesigned carbon blades designed to be self-feathering. When the wind strength increases to destructive potential, the generator’s electronics are able stall the blades, thus preventing damage. However, it is still necessary to intervene by manually setting a stop switch to stall the wind generator.
The regulators on modern generators are also able to profile the power output to the battery exactly like a smart charger so that in particular, AGM and Gel batteries can be correctly charged. And of course, they can charge in parallel with solar; with appropriate isolation and fusing.
Things to consider with wind generation:
- Installation: Ideally on a stern post, as high as possible to increase efficiency and keep it out of the way of human contact. Under load, a wind generator can create vibration, so bracing on the pushpit and extra staying may be necessary. Shock absorbing mounting blocks are a good idea. Some generators are mounted on the mast forward of the mainsail on fractionally rigged boats. Fine, but cannot take advantage of accelerated air.
- Estimate the lowest expected wind strength that will be experienced and choose a generator that is optimised at five to 15 knots for maximum power output.
- The prospect that the generator can be left unattended in any wind strength without fear of damage. A spin-off (pun intended) is that the noise generated by the revolving blades must not be intrusive to both crew and neighbours. This is particularly important on marinas.
- The most effective method of stalling the blades, either by remote switching or by physically tying the blades.
- Output regulation tailored for symmetry with solar and alternator outputs.
- And obviously, price, warranty and the manufacturer’s reputation are of major importance.
*Gavin Sorrell works in collaboration with Aquavolt Electric Boat Parts. Tel: 02 9417 8455