Tilting At Windmills

[hilldweller]

Another windmill seems to have put in an appearence on the Stannington Ridge. From my viewpoint at Lodge Moor it seems to be somewhere in the Load Brook / Hill Top locality.

There's been a smaller black one similar to the one at Mosboro Health Centre for a while now, located by a farm a bit further west.

I seem to remember that that one generated about 4 kW.

The new one looks much taller and is painted white but the distinguishing feature is the tailplane which rises high above the structure like the tail of a cockerel.

I've been doing a bit of reading up on wind turbines and it seems that it's not all summat for nowt. Apart from the high capital costs it seems that ongoing maintenance issues are going to be a problem.

When the windspeed is too great the blades are braked and it seems that this has been the cause of the many failures around the world. If the blades begin to turn (often at windspeeds below the design maximum) large amounts of heat are generated in the brake mechanism and the things catch fire. You would think they could find a method of "feathering" the blades like an aircraft prop.

Lightning damage to the blades is also a problem apart from mechanical failure of the blades/gearboxes/generator.

It makes me wonder if the ongoing costs of servicing these things is going to be a problem, especially when there are hundreds of the things on towers of a hundred metres or so all over the North Sea.

Our politicians are asking us to " Hug a Wind Turbine " but the advice to industry workers is to avoid the area around the base of the tower because ice or bits of a failed blade have been reportedly thrown 300 metres from the tower.

If you Google "Wind Turbine Failures" the number of incidents is frightening.

I think I'll reserve judgement for the time being.

HD

Edit Just found a official website that says that parts of a failed blade travelled 1300 metres------------ooooer

[Bayleaf]

Given that they only generate power when the wind blows, I don't understand the concentration on wind turbines when we are an island with tides twice a day, every day, which can be harnessed, yet the amount of money going into research is a fraction of what's been spent on wind power.

[hilldweller]

Given that they only generate power when the wind blows, I don't understand the concentration on wind turbines when we are an island with tides twice a day, every day, which can be harnessed, yet the amount of money going into research is a fraction of what's been spent on wind power.

The University Of Sheffield had a scale tidal barrage set up in the old foundry on Mappin Street in the 1960's.

I can't remember where it represented (Firth of Forth perhaps) but it was built to exact profiles and contours and even had scaled water flowing into the estuaries. At the "sea" end of the barrage was a large tank over the water with fans to remove the air and create scale tides.in the estuary. Instrumentation measured water depths and flow rates. It was quite large (20 feet across).

Fourty odd years on and still no progress.

HD

[DaveH]

When the windspeed is too great the blades are braked and it seems that this has been the cause of the many failures around the world. If the blades begin to turn (often at windspeeds below the design maximum) large amounts of heat are generated in the brake mechanism and the things catch fire. You would think they could find a method of "feathering" the blades like an aircraft prop.

"Tilting at windmills" HD?

Sounds like you have been reading that Don Quixote novel again!

I thought it was possible to alter the pitch of the blades, or even reverse it, so that the wind would not turn the propellor at all.

"Feathering" the blades means disconnecting them from the mechanism (engine in an aircraft, generator in a wind turbine) so that there is no load on them. If this was done a strong wind would then cause the blades to rotate even faster which would be more dangerous as the blades would be subject to greater damage. Surely altering the pitch to slow the blades down in strong winds would be preferable.

In Europe they have far more of these wind turbines than we do. We once went past a load in France which were subject to strong winds at the time. Our new ones have the tailplane which rotates the windmill into the direction of the wind automatically so that it gets the full force and generates maximum power at all times (as in a conventional windmill) The French ones can be rotated to face the wind, or not from a control centre. They stop their wind turbines and protect them from damage in strong winds simply by turning them at right angles to the wind direction. I suppose they could also moderate it's speed, to an extent, by altering the angle of the blades to the wind direction.

[DaveH]

Our politicians are asking us to " Hug a Wind Turbine " but the advice to industry workers is to avoid the area around the base of the tower because ice or bits of a failed blade have been reportedly thrown 300 metres from the tower. If you Google "Wind Turbine Failures" the number of incidents is frightening. I think I'll reserve judgement for the time being. HD Edit Just found a official website that says that parts of a failed blade travelled 1300 metres------------ooooer

As Tony Hancock famously said in "The Blood Doner" about the quantity of blood he was expected to donate, -

"A pint! That's almost an arm full"

To throw a heavy metal blade 1300 metres is some feat, so in similar vane to Hancock's exclamation, -

"1300 metres! That's almost a mile"

[DaveH]

The University Of Sheffield had a scale tidal barrage set up in the old foundry on Mappin Street in the 1960's. I can't remember where it represented (Firth of Forth perhaps) but it was built to exact profiles and contours and even had scaled water flowing into the estuaries. At the "sea" end of the barrage was a large tank over the water with fans to remove the air and create scale tides.in the estuary. Instrumentation measured water depths and flow rates. It was quite large (20 feet across). Fourty odd years on and still no progress. HD

Also 40 odd years ago (1966 to be precise) the French built an actual full scale working tidal barrage at Rance in northwest France. It worked well and as far as I know it is still working to this day.

The key to success is to harness a wide tidal river through which a large volume of water ebbs and flows. Britain has many of these, the Severn estuary being the best candidate but there is also the Humber, the Dee, the Mersey, the Ribble and even the Thames. So as Bayleaf suggests we are in an excellent position to generate power by this method.

The problem is, that to harness continuous power from a 2 times a day cycle requires the in tide to be dammed off, trapping water inland and releasing it slowly on the out tide. This is likely to cause inland upstream flooding to generate that large "reservoir" of stored up tidal energy. Where would the flooding be and what environmental damage would it cause?

Using the Thames tidal barrier in reverse (to lock water in rather than out) would flood the whole of London, but would probably provide megawatts of power so it is a none starter, and as the other rivers I mentioned are close to big cities and towns like Bristol, Hull, Chester, Liverpool and Preston perhaps we need to rethink the whole idea.

The use of the Solent either side of the Isle of Wight is an interesting idea as it gets a "double tide" each day and is open to the sea at both ends. This may produce a solution to the problem in part, but would seriously interfere with boats and shipping using the solent approaches to Southampton.

[DaveH]

Also 40 odd years ago (1966 to be precise) the French built an actual full scale working tidal barrage at Rance in northwest France. It worked well and as far as I know it is still working to this day.

Rance tidal power station.

Tidal_Power_Station

[hilldweller]

"Tilting at windmills" HD?

"Feathering" the blades means disconnecting them from the mechanism (engine in an aircraft, generator in a wind turbine) so that there is no load on them. If this was done a strong wind would then cause the blades to rotate even faster which would be more dangerous as the blades would be subject to greater damage. Surely altering the pitch to slow the blades down in strong winds would be preferable.

My understanding of feathering a prop is that of altering the pitch of a variable pitch propellor in order to reduce it's wind resistance and turning moment.

This is born out by the Oxford Dictionary I have, and by Googling "feathering a propellor".

I understand that certain long range multi-engine aircraft used it on long WW2 missions by shutting down some engines to save fuel. It was also used if an engine failed.

I think that the prop boss with it's integral feathering mechanism was bolted straight on to the end of the engine crankshaft.

Variable pitch propellors gave a power boost by matching the engine output to maximum performance I believe.

By reversing the pitch reverse thrust can be obtained.

HD

[Bayleaf]

My understanding of feathering a prop is that of altering the pitch of a variable pitch propellor in order to reduce it's wind resistance and turning moment.

This is born out by the Oxford Dictionary I have, and by Googling "feathering a propellor".

I understand that certain long range multi-engine aircraft used it on long WW2 missions by shutting down some engines to save fuel. It was also used if an engine failed.

I think that the prop boss with it's integral feathering mechanism was bolted straight on to the end of the engine crankshaft.

Variable pitch propellors gave a power boost by matching the engine output to maximum performance I believe.

By reversing the pitch reverse thrust can be obtained.

HD

That's right HD. Once fully feathered the blades on an aircraft engine stop turning. Reverse pitch is used mainly for braking effect after touchdown, though I did once watch a Hercules that landed at a Finningley display using it to reverse park between other aircraft. Now that's showing off!

[DaveH]

My understanding of feathering a prop is that of altering the pitch of a variable pitch propellor in order to reduce it's wind resistance and turning moment.

This is born out by the Oxford Dictionary I have, and by Googling "feathering a propellor".

I understand that certain long range multi-engine aircraft used it on long WW2 missions by shutting down some engines to save fuel. It was also used if an engine failed.

I think that the prop boss with it's integral feathering mechanism was bolted straight on to the end of the engine crankshaft.

Variable pitch propellors gave a power boost by matching the engine output to maximum performance I believe.

By reversing the pitch reverse thrust can be obtained.

HD

OK. I'm with you on this one HD.

The feathering you are describing (which is actually called "feathering"), can only be done with a variable pitch propellor with the ability to swing the blade about 90 degrees of pitch (a large variable pitch angle) so that air will flow over it without trying to cause it to rotate so the propellor will stop. Also in this position the blade would be "narrow edge on" to the moving air and so create least amount of drag on for example an aircraft which has a failed engine. The complexities of the variable pitch mechanism and the unstreamlined shape of many engines means that the propellor on an aircraft may or may not be directly on to the crankshaft.

The "feathering" I was describing (which is actually called "autorotation", my error, sorry) is more commonly used on helicopter rotor blades. It is a safety requirement on helicopters that the main rotor can autorotate (using the principles of an autogyro) so that the craft can be landed safely in the event of an engine failure. Autorotation involves a freewheeling mechanism which effectively disconnects the rotor from the mechanism allowing it to turn freely. As the failed helicopter falls under its own weight the freewheeling / autorotating (feathered!!!) rotor continues to be turned by the upward air flow as the copter falls. This generates a small amount of lift slowing the rate of descent, so that the craft descends slowly enough to effect something of a "safer" landing. (Apparently the wing shaped sycamore seeds are shaped to autorotate as they fall)

The confusion, for me between feathering and autorotation has come about because we have treated windmill blades as a "propellor" which it is not.

A propellor has powered blades designed to make the air move as they are turned, in a windmill the moving air is used to turn the blades, the reverse situation.

Feathering a powered propellor will allow it to stop rotating and cause minimal drag to the airstream.

Autorotating an unpowered "propellor" allows it turn freely without doing an useful work or turning a mechanism (like a childs seaside toy windmill).

So with a wind turbine.

Feathering the blade by altering the blade angles directly into the wind direction will stop it turning

Autorotating the blade by "freewheeling" it will make it go faster as the load of turning the generator and doing useful work has been removed.

Turning the entire widmill head at 90 degrees to the direction of the wind (as in France) would have a similar effect to feathering and cause the blades to stop.