Is the wind speed so much higher in a vacuum cleaner?

The pressure gradient is a lot steeper (on the order of a tenth of an atmosphere per meter, while the pressure gradients generating winds are less than a hundredth of an atmosphere per kilometer). How that translates to wind speeds is a bit out of my field, but I guarantee you that you will not get a kW out of a vacuum cleaner fan if you stick it in even a gale-force wind.

What about a gearbox? That would take out as much rotation speed as needed.

Yeah. That's what windmills do. Large blades, big gearboxes. That's what makes them expensive. The generators themselves aren't, AFAIK, the main cost.

- Jake

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