# Why wind turbines don't have their dynamos closer to ground?

1. Nov 6, 2016

### kevin_tee

Why don't the electric generator mount closer to the ground. The advantage I can think is that it is easy to maintain(no need to climb) and reduce weight(reduce tower cost), however the extended shaft will cost more. Does the longer shaft cost out weight the easier maintenance and generator weight? Thanks

2. Nov 6, 2016

### Drakkith

Staff Emeritus
Why would the generator weigh less if you put it on the ground instead of up near the top?

3. Nov 6, 2016

### Randy Beikmann

You make a good point that the tower could weigh less with the generator at the bottom. My guess is that the frictional losses in the 90-degree gear drive must "outweigh" that weight advantage.

If the turbine were on a vertical axis (as some are), that wouldn't be a problem. I don't think that's as efficient though.

4. Nov 6, 2016

### kevin_tee

I am refering to the weight that the tower need to support.

5. Nov 6, 2016

### kevin_tee

I see, so there are quite a lot of friction there.

6. Nov 6, 2016

### Nidum

In most designs the actual generator is only one part of the total equipment needed at the tower head . A lot of the equipment would still have to be up there even if you moved the generator to the tower base .

Illustration

7. Nov 6, 2016

The weight of the generator and what this adds to the tower requirements is minor compared to the wind stresses the tower and turbine have to deal with. The weight of the drive shaft would probably be higher, plus the tower would also have to deal with the reaction torque.

8. Nov 7, 2016

### Baluncore

If a long vertical drive shaft was used with insufficient bearings in the tower, it would twirl.

A right-angle gearbox driving a vertical shaft would apply a torque to the tower head that would make the head harder to point into the wind.

The forces on the blades from the wind will probably be greater than the weight of the generator. Maybe more mass in the tower makes the tower more stable and less resonant at some wind speeds.