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The windmill experience

by Jim Heath

Copyright. All rights reserved.
Not to be mirrored on other websites.
First published: Isle of Man Weekly Times.
Published on this website: 2 Jan 2004.


THE WORST HAPPENED last January. In a gale, control of the windmill I have -- a 5000 watt Swiss machine -- depends on one steel cable that runs down the centre of the tower. This cable had broken at the top. The wind was Force 8 and increasing.

What's supposed to happen is this: an electric motor pulls the control cable, which pulls on the tail of the windmill, which turns the windmill out of the wind -- step by step -- as the wind rises. But this elegant system doesn't work if the control cable has collapsed like a decapitated snake.

The might of the storm was heaving against the blades. A wild, destructive gale. Trees all around were bent. Small branches were torn off and were flying everywhere.

I consulted London. London consulted Switzerland. Messages flashed back and forth. The situation, I was told, was unprecedented. All I could do was to ride it out. On no account should I turn off the electric heaters fed by the windmill. (If you make a generator work hard, it slows down.)

One of the optimists proposed that if the wind dropped a bit, the blades could possibly be tied. Silence. No volunteers. The tower is 40 feet high. It was dripping wet, shaking in the howling wind. At the top, blades as long as spears whizzed and hissed and veered in every direction.

The storm went to Force 9. Then Force 10. A classic tempest. The blades were spinning at unbelievable speed. To complete the scene, the postman staggered to the door, handed us some fluttering letters, and made admiring comments about the way we made use of gales.

Built like a Swiss battleship

By the rules, the windmill should have been shut off long before. If the control cable hadn't broken, the automatic control would have turned the windmill off at a wind speed of 43 mph. As it was, the machine was facing gusts of more than 70 mph.

But windmills have layer after layer of protection. All the while, another line of defence was operating: a system of springs and weights that turns each blade about its root when the wind goes above 23 mph. This reduces the wind thrust on the blades. In theory, this protection isn't enough in a gale.

If all else fails, the windmill falls back on raw strength. Each bolt, brace, or blade is many times stronger than it has to be. Everything held, even in the screaming peak of the storm. There was no damage.

In the end, the windmill was shut down by a mountaineer. It was a contest between steel nerves and a steel machine. After the struggle, an old piece of hemp was enough to keep the tail tied in the "off" position. For the windmill, the storm was over.

Who screwed up?

The wide-awake reader will wonder why the control cable broke in the first place. Nothing else had broken, so why the control cable of all things?

The answer turned out to be annoyingly simple: when the machine was installed, no one had checked to see if the control cable was placed over a certain pulley inside the generator. It was not. Each time the cable had tightened and moved in its normal work, it had rubbed on a sharp steel corner. After three months of this, it gave up and broke.

In order to get right to the bottom of this, one thing needs to be said: mine was the first windmill ever put up by an enthusiastic London firm that had just started importing the machines. I knew there was a risk but reasoned the Swiss manufacturers would back up their new agents if anything went wrong.

And so it was. The parts and instructions came from Switzerland, and the visiting engineers, humble and hard-working, came from London. At one stage, the whole generator was changed. Everything was put right, great and small, and at no expense to me. In every case, the problems were traced to inexperience, never faulty equipment.

The path to Utopia

To be sure, all this is really my own concern. It would only have curiosity value if no one else on the Island were seriously interested in commercial windmills.

But I know others are interested. They may take heart, because events have moved a long way in the last year. Now there're a lot of windmills like mine in the British Isles, some of them twice as powerful. The United Kingdom engineers who do the installations have learned those obscure or obvious things that are never mentioned in installation manuals, but force their way to light with experience. To borrow words from the great Goethe: real experience is the sort of experience you don't want to have.

The next Islander with a large Swiss windmill will be spared the dramas about broken control cables. For the future, it's more to the point to concentrate on what these machines will do for you, day after day, decade after decade, usually with only a few squirts of grease from time to time, and a yearly change of oil.

A snapshot of what's happening now, as I write this, may help. Outside, it's chilly, grey and windy. Here, in my study, it's comfortably warm -- thanks to the windmill. Part of the windmill's output is also going into electric heaters in the hall and sitting room. The heat from all of these is enough to keep the whole house cosy. A small immersion heater fed from the windmill helps with water heating.

Before this begins to sound like Utopia, let me add that if the wind dropped, we'd be thrown back on using our conventional central heating system. But that was always the plan. Whatever heat the wind could provide would be subtracted from the central heating bill. The system works well in practice. It's only a little more trouble than running the central heating by itself. And when the oil bills arrive, it's rewarding to have saved the world some of it.

The economic analysis of such an arrangement is wonderfully complicated. The snag is that any realistic calculation has to include the relationship between the average rate of inflation of fuel costs and the average bank interest rate -- over the whole lifetime of the windmill. It would be no world record for a windmill to last 30 years, so the economic analysis comes down to guesswork wrapped in mathematics.

That's probably all I can say about windmill economics, even in a general way, without losing practically everyone's attention. (Precise guesswork isn't inspiring.) Anyway, the conclusions I reached after my own deliberations are obvious.

Nearly all the large windmills recently put up in the British Isles are used only for heating. I know this will surprise some people. All that electricity and it's not even used for lights?

A windmill system can easily be installed that creates "artificial mains" electricity, but to do it you need a network of heavy-duty storage batteries. The extra cost is high. On the other hand, the windmill's rather crude electrical output can be used for heating, just as it is. Except for switches and fuses, the wire can run straight from the windmill into almost any kind of electric heater. Each gust of wind then produces a bit of heat.

Fringe benefits and limited war

Even a heating-type system is some help during a power cut at night. An ordinary lamp plugged into the windmill circuit works all right, except that the smooth, uncertain fluctuations in power create an uncanny atmosphere. It's the same sort of random bright-dim alteration you see outdoors when clouds keep passing in front of the sun.

This odd phenomenon is only a fringe benefit. But it's an example of the connection between nature, machine, and man that's almost unique with a home windmill. It's all between you, the windmill and the wind. Nothing else. Limited war, assassinations, strikes, and even the passing years all count for nothing.

In its own way the wind is unusually dependable. From moment to moment it seems fickle, but from year to year its endowment of energy is almost as predictable as the sun and stars.



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