"Ballooning" Spiders Use Electrostatic Forces to Generate Lift

The negative charge on spider silk has also recently been discovered to enhance the ability of webs to capture insects:

http://newscenter.berkeley.edu/2013/07/04/spider-webs-more-e...

I saw this in the story:

“This field exists globally in the atmosphere with an average surface magnitude of 120 Volts per metre pointing downward,” says Gorham.

I never knew this. Where does it come from? Why can't it be used to generate power?

Wow, I wonder if this effect could be scaled up? I'd love to try to build a small prototype.