why do wind turbine blades spin so fast?

Sure, but that would cut down on their effectiveness, because a stronger wind would be required to set them spinning.

they DON'T go at 60Hz. That would be 60 revs per second.

Ideal turbine blade speed is governed by the speed of the blade tip. You always want the best ratio of tip speed to wind speed for optimal energy capture. Until recently, most wind turbines could only go at one speed, so you picked the tip speed that was best for your expected wind speed, and then decided how long the blade was, and that told you how fast it should spin. The longer the blade, the slower the rotation rate. You then need a gearbox to get to mains frequency in the alternator (50Hz or 60Hz, depending on which side of the pond you are)

Nowadays most wind turbines are variable speed so they adjust their rotation speed to the windspeed to increase the energy capture - they go slower at low windspeeds. They are also getting bigger, which means they must naturally reduce the rotation rate in the design.

That comes out at something around 15 revs per minute.

You can also reduce the rotation rate by having more blades - but there are engineering problems with that. Notably, the bit of wind turbines that is most likely to fail is the gearbox. The higher the gearbox ratio, the more times you'll have to nurse it. So ideally you want the fastest rotor speed - and that means the smallest number of blades. A single bladed machine is virtually impossible to balance (though an italian company did manufacture one for a while) and a twin bladed machine is still very tricky to balance (and twin blades spook people for some reason). That's why three blades is now standard - the so-called "Danish model".

And finally: I got a letter from the RSPB some years ago supporting positively a proposed wind turbine. The reason? Global warming will kill one heck of a lot more birds than a few turbines (which the birds can see!).

Wherever you have a gearbox, then you have power losses, up to as much as 5% per reduction.

The blades also feather to get the most efficient power from what wind there is available.

You could say the same for a diesel engine, why not make it go slower to get better efficiency. Well in large marine engines this does happen, but these engines are constantly on load and you would do a lot of damage if there were large fluctuatuions in the speed, which I will chance an arm and say the same for wind turbines.

So my answer is,

You can get better governing at the speed at which they turn

Okay..people saying that birds do not fly into wind turbines obviously don't know what they are talking about!! This is a huge problem..and that is why there is always so much controversy when someone wants to build a wind farm. I personally do bird surveys at wind farms to see what types of birds are in the area..I mostly look for raptors as they are the most likely to be hit by them. During a survey I actually saw a raven almost fly right into a blade..luckily it dodged at the last minute and avoided it. Hawks and eagle can hit them while chasing prey...they are so focused on catching the bird or mouse or rabbit that they don't see the blades until it is too late. Larger birds cannot alway manuveur that quickly. During migration...thousands of birds can fly throug a wind farm, and many of them die as a result.

If you're talking about those large towers with three blades erected for the purpose of wind energy, they don't spin very fast at all. They are able to withstand wind speeds in excess of 100 mph, but if the wind blows too hard (near 60 mph) the blades on the wind turbine stop in order to protect it from damage. Depending on the location (how windy the spot), the wind speed of a turbine is around 14 kph.

The actual generator has to turn as a set speed. I am not technical on this even though we have a 30 generator wind farm withing 2 miles but I imagine that the size of the blades and the gear box is the most economical vis vie the cost of manufacture and construction. The two at Swafham in Norfolk are very big (one you can go up inside to a viewing platform) I have been right up to one of them and it makes very little noise. I have never heard of any birds being hit by one I imagine birds have more sense and better flying ability than to allow that to happen. We do have a Little Tern nesting site on the beach right by the wind-farm which is kept under observation by RSPB during the nesting season and I have not heard any reports from them that the birds are in any way affected by the turbines

It will be the optimal speed for energy production.

The vanes are 'variable pitch' much like a plane propellor. This can be varied to give a steady speed - and not have it zipping round.....

I have two (a few months old) about a mile from here..and they make no noticable noise - even close up. As for the 'bird strikes' - the chances are so remote so as to be negligable...think of it this way...3 fixed location spinning vanes...or tens of thousands or vehicles in random motion. How often do you hit a bird in your car? Not very often (if ever), so I think bird, even with their limited brain power can avoid them quite well.

faster they go the more power they create, and it allows them to work in light winds, if they were tighter and harder to move they wouldn't move half the time. And in the history of windturbines i don't think a bird has ever been killed by one, they are cleverer than that

To create the torque at the centre required to turn the shaft.

remember the old dynamo bike lamps getting brighter or darker as you changed speedand got faster same reason