Check out this winner of the 2008 red dot design awards by Nils Uellendahl, it's a concept for a helical turbine that mounts directly onto over-head power lines. It's quite interesting in two ways:
I'm sure there are some large issues with the electrical connection and grid stability (to say the least!), and with the additional loading of the power lines, however it's a great concept.
- it generates electricity directly into the line using induction
- It's actually horizontally mounted, however is actually a traditional vertical-axis turbine