ENERGY FROM THE WIND

I got interested in wind energy in the mid-1970s. I had already been working with aerodynamics for several years, and so had a reasonable idea of what might be involved in harnessing the wind. In addition, I had been introduced to the findings of some extensive research into the economics of alternative energy, by a client (Natural Energy of Jersey) for whom I had just finished designing a solar powered water-heater.

I started by researching what had already been done in the field, and examining all of the known practical wind harnessing devices. I then set about discovering where the greatest potential might lie. I wasn't exactly surprised to arrive at the same conclusion as my client - that is, the heating of water.

Having thus arrived at the need to focus on 'wind to heat', I then set about discovering the possible options with respect to 'best conversion' technique. The result of this clearly placed mechanical conversion way ahead of any other, with options, one for supplying hot water, the other for steam.

The most efficient way to harness the wind on a continuous process basis, is to convert it to rotary motion. This would not surprise anyone. But, the most efficient non-enclosed device for collecting wind energy is not the propeller. Now, this does surprise most people. (See Note.1)

Some years back, there was an attempt made to propel ships by harnessing the wind, not with sails, but with tall rotating cylindrical 'fans' which drove conventional water screws. It didn't catch on exactly, but the work did provide some valuable information regarding conversion efficiency. I recall mentioning this to a friend who has a great interest in marine history, and telling him that I was going to resuscitate the technology. "But it didn't work!" was his concerned reaction, a response which I have encountered far more times than I could possibly recall. But it did work! In fact it worked exceptionally well, it just wasn't quite suitable for ships.

By this time, the design was entirely clear in my head. I would capture the wind using such a rotating column, and I would solve the problem of potentially destructive wind speeds rendering extraction from lesser winds non-viable, by making the system self-reefing. I would directly connect the rotational motion to that of a paddle submersed in a fluid (water where appropriate – high temperature fluids for steam production) and thus achieve the lowest possible transmission losses. By making the effective areas of the wind collector and the paddles proportional to the densities of the air and the fluid, I would get a 'perfect' match.

With the above conditions in mind, I set about the design of the 'wind column'. This ended up as a stack of units (rather like empty cable drums) each of which was fitted with two or three flexible 'sails'. These stretch from the outer edges where they are supported by a steel rod, in towards the centre where they are 'anchored' by springs. Wind arriving at the device is steered into the exposed sail, the other being shielded. Rotation is induced, even in low speed winds, and the springs 'give' and so spill a proportion of the wind if the sail speed cannot match the wind-speed. In addition to the springs effecting reefing, as the sail moves behind the structure, some of the energy stored in the springs is returned to the motion of the sail.

The primary reason for the array being split into sections, was to make the sails stable without calling for undue weight. A secondary benefit, though, is that the assembly can be as long as suits its application - a factor, the importance of which will be revealed in due course.

The most efficient way to convert mechanical energy into heat is to use it to 'stir' a liquid. (Every first year science pupil should know this). Obviously, the liquid needs to be protected from radiation losses (lagged) and the stirring device should impart maximum disruption of the fluid within its practical speed range. (See sketch H1.1) Another 'practical' consideration of our particular application, is that the fluid should be pumped, either to a place where it is required per se, or to where it is required to drive another process. This pumping action can also be incorporated into the stirring device, rendering the system independent of external energy requirements and additional engineering. At low wind velocities, the above description covers all of the essential engineering detail.

However, with higher energy inputs, another useful mechanism may be harnessed, with clear benefits to certain applications – cavitation. Cavitation may be induced into a fluid by several different methods. We, however, only have physical disruption at our disposal and so I shall ignore all other techniques. Cavitation is most widely known as the effect suffered by the propellers of boats, particularly boats with small, high rotational speed, propellers - Its effect is to erode the propeller. The known forces of friction, etc., cannot be used to explain this effect. Furthermore, it is a very simple matter to show, by practical experiment, that this is the case. Cavitation causes gas bubbles to form, which ultimately collapse, releasing extraordinarily high energy forces, mostly as heat. These forces can give rise to the conditions required for spontaneous chemical reactions to occur. Resonance is the key factor in inducing cavitation, and the tendency to resonance can be deliberately designed into a paddle system.

Inducing cavitation does not significantly raise the amount of energy which can be extracted, but what it can allow the designer to achieve, is significantly higher 'practical' temperatures, over a reasonable range of input energy levels. Ergo, it is better employed for the production of steam, and requires a different heater configuration and a high temperature working fluid.

To return to the less esoteric:

Clearly, the transportation of energy, even supposedly "low loss" energy, such as electricity and domestic gas, is where most energy projects fall short in terms of overall efficiency. We lose, for example, at the very least, 50% of the energy which goes into our electricity supplies, and the real losses incurred in our exploitation of the North Sea gas, are even worse. The only substantial supplies of 'free' energy available to us come from the Sun and the Moon, in the form of solar radiation, the wind, and the tides. My RLA study clearly pointed to the fact that my wind converter would give (by far) the highest returns, if it was located close to the point of consumption. Don't laugh – on the roof of the building.

On tall buildings, say four or more stories, a phenomenon, often referred to as "adiabatic wind", occurs. This results in the amplification of speed, and increase in density of the wind, which rises up the face of the building. This flow emerges at the top with sufficient energy, even on relatively calm days, to usefully drive a cylindrical style wind converter (of the type described above) but laid horizontally, and leaning out over the edge. This is the particular application for which most of our development work was carried out.

Two working models were produced: One roof-top as described, and one free-standing vertical device. The vertical device was constructed from a disused lamp-post. It had a self-aligning wind director and was able to withstand gale-force winds, whilst performing useful work in relatively light airs. This particular design was inspired by a separate study which revealed a substantial use for such power on farms. It was also thought to be of considerable value to the third world, particularly as a cheap 'low-tech' means of pumping water. Compared with the established classical 'fan' type water pump, it was shown to cost less than half, and return more than four times the work.

NOTE.1 Not only is the cylinder style windmill more efficient in both cost and 'work for space' terms than is a conventional propeller design, for 'wind farms' it also offers a significantly higher density. That is to say, that the units may be placed much closer to each other, without the risk of potentially damaging harmonic interaction, or reduction of unit performance. This 'close packing' is of particular interest when it comes to off-shore sites, where the mills could present an 'angled wall' to the prevaling wind, substantially reducing the cluster's profile with respect to the shore.

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• A 1970s survey revealed there were more than sufficient, suitable, buildings in the UK, for the mill to effect a major contribution to our national energy supply.
• At entirely practical energy levels, the system was shown to be inconspicuous enough not to invoke aesthetic objections, and operationally quiet enough not to qualify as a source of noise pollution.
• The cost / yield benefit was shown to be greater than for any other wind system - existing or proposed.
• Service and maintenance costs were shown to be lower than those for any other wind-harnessing project.
• The ecological / economic benefit was shown to be better than 200% greater than for any other wind-harnessing project.
• Application for its inclusion in the national wind-energy evaluation project was refused on the grounds that the system was not suitable for the production of electricity!!
• In the absence of the opportunity of such ratification, it was (reluctantly) deemed that the project would have be abandoned.

John Allen

NOTE. This is the windmill which John proposed for use on alcohol producing farms, both to drive the distillation, and to enhance the fermentation process. See ALCOHOL