By sailing for more than 40 years, I have had the opportunity to appreciate these superb ecological machines that are our sailboats which can sail with the force of the wind using only a few square meters of fabrics.
Why not use sails to recover the force of the wind?
Obviously, this has existed for millennia, the "Cretan mills" of the Aegean are the best examples. Besides their primary functions, to draw water or grind grain, they are beautiful, and have even become an aesthetic symbol of the Greek islands.
The principle of these triangular sails, wound on spars, is brilliant, but it has one disadvantage: it requires constant surveillance. Their millers had to set the right sail area, day and night, under threat of destruction with too strong a wind (the Meltem which blows in this region often reaches the force 8 ...).
Our modern sailboats have taken up, by perfecting it, this means of reducing the sail by winding on the forestay for the jibs or even inside the mat for the mainsails. These processes, now generalized on sailboats, are perfectly reliable and operate in the worst weather conditions.
So why not take up this ancestral principle using our current techniques?
A modern sail wind turbine whose winding of the sails would be ensured by electric motors electronically controlled by the force and direction of the wind Measured by a wind vane-anemometer, is perfectly achievable. The necessary material, of marine quality, therefore resistant to extreme conditions, is easily available in all dimensions, since already broadcast on a large scale in yachting. For the realization of the sails, very important progress has recently been made on the quality of the fabrics making them more resistant and perfectly suitable for continuous operation.
Obviously, for high power, a wind turbine will never compete with large three-bladed wind turbines, technical problems would be insurmountable with sail surfaces too large.
By cons, in realistic dimensions (less than 10m diameter), so for small or medium powers, it would be as effective as a traditional three-bladed wind turbine without being more expensive (its cost would be comparable to that of the rigging of a sailboat medium sized).
Moreover, by turning more slowly, it is More quiet, Which would allow to use it in an urbanized but windy as the coast and not necessarily in open country or offshore as with the current wind turbines. Another advantage of this lower speed: it would spare the birds unlike the large trials that make real carnage ...
It would also be more sure for a sail that is torn in the storm is less dangerous than carbon blades playing "flying sabers".
And above all, it would undeniably More aesthetic; And this last quality is far from negligible with regard to the main argument of the anti-wind lobby ...
Its modest dimensions and its specific qualities would facilitate geographical implantation even in inhabited areas, so close to electrical needs. Why not equip them, for example, with marinas, to ensure electric autonomy or roundabouts for their lighting?
A small self-regulating wind turbine :
For domestic use, therefore with small dimensions (less 2 or 3 m diameter), therefore of low power, the control by electric motors of the sails becomes too expensive, and with an energy efficiency too low if the wind is irregular (Which is always the case with small wind turbines close to the ground). With a regulation too often solicited, the electricity produced would only serve to operate the winding motors ... This small wind turbine with sails would certainly decorative, but unfortunately ineffective!
We must find a way to be self-regulated
To wind the sails on the spars, in addition to the force of the wind, the only usable force requiring no external input is the centrifugal force.
Being able to use the weight of the counterweight deviating from the axis as a function of the speed of rotation and therefore of the wind force would be a good solution because it would make the wind turbine autonomous. Nothing invented: it is James Watt who, in the 18ème, had the brilliant idea of the regulator with balls)
Other interest: the speed control function. The mass of counterweights acting as a flywheel could make the wind turbine less dependent on wind variations, which would be conducive to electricity production; The generators working best at a regulated speed.
The idea is therefore attractive on paper, but its implementation reveals many difficulties, as I was able to discover them by making a model 1m20 of diameter (see photos).
1- How to make a ball regulator that works in the vertical plane? Indeed, in this case, gravity intervenes: the upper ball tends to "fall" towards the axis and the lower ball to deviate from it. Only one solution: to connect them by a deformable double parallelogram centered on the axis, which neutralizes the gravity. Easy to achieve for a couple of counterweights, it is much more complex when there are several.
2- The centrifugal force must be sufficient to allow the winding, so that the weight of the counterweights is adapted to the surface of the sails. This essential data is difficult to calculate, only solutions found: a position adjustable with respect to the axis, and ... the trial and error.
3- It is necessary to transform this axial displacement in winding of the sails. I did it by copying what is done on the sailboats by a rope wound on a drum at the base of the sails It is in closed circuit because it has to operate in both directions: winding - flow. And to avoid friction, all crossings must be done on pulleys, the end being put on by a sandow.
4- Another variable that must obviously be taken into account: the length of the "tapping" used to "border" or "shock" the sails. This time, the ball regulator easily gives the solution: by fixing the tapping on the counterweights, whose centrifugal or centripetal movements according to the speed of rotation allow the sails to be automatically adjusted according to their winding.
5- Once wound when the wind is strong, the sails must be able to unwind when they are weak, so it is necessary to provide return springs or sockets on the regulator for its return to the center. Return to zero).
Practical results: The model works well in moderate winds (forces 3 to 6) but I have not tested it yet with storm winds. It is still perfectible for weak winds because the frictions are still too great especially for the axis of rotation which for the moment is not mounted on ball bearings. Finally, electrical coupling with a small generator remains to be carried out.
NB: For this model, the centrifugal regulator may seem oversized (therefore unsightly, which is particularly harmful for a wind turbine) but I think on a larger scale it could be proportionately less important. In addition, to be less visible, it could be placed behind the sails.
