OK, not free. But close The Magenn Power Air Rotor System (MARS) is an innovative lighter-than-air tethered device that rotates about a horizontal axis in response to wind, efficiently generating clean renewable electrical energy at low cost.
When you buy it is not so low cost because 4 kW MARS (for Cottage & Home Size use) is $9,999. (see the roadmap in page 3)

Electrical power generated at the floating Air Rotor is transferred down the tether to ground level equipment. Depending on size of the Air Rotor, power is sent to users ranging from campers to large power grids. Helium (an inert non-flammable lighter-than-air gas) sustains the Air Rotor which ascends to an altitude for best winds. No towers or heavy foundations are necessary and sizes range from small “backpack” models to large megawatt generating devices.

All competing wind generators use bladed two-dimensional disk-like structures and rigid towers. The Magenn Power Air Rotor system is a closed three-dimensional structure (cylinder). It offers high torque, low starting speeds, and superior overall efficiency thanks to its ability to deploy higher. The closed structure allows Magenn Power to produce wind rotors from very small to very large sizes at a fraction of the cost of current wind generators.

This electrical energy is transferred down the tether to a transformer at a ground station and then transferred to the electricity power grid. Helium (an inert non-reactive lighter than air gas) sustains the Air Rotor which ascends to an altitude for best winds and its rotation also causes the Magnus effect. This provides additional lift, keeps the device stabilized, keeps it positioned within a very controlled and restricted location, and causes it to pull up overhead rather than drift downwind on its tether.

The Magenn system concept is deployment-flexible. Large MARS units may be deployed to supplement established grid systems supporting the electrical requirements of large urban areas. Small MARS units would be deployed in emergency, as-needed, and/or mobile applications (e.g., pack version deployed by a hiker, motorist, boater, or for military and emergency response applications). Various in-between sizes would be ideal for farms, houses and cottages located where grid power is nonexistent. Small to medium sized systems could also be air-dropped into disaster areas for emergency electrical power for medical and all other uses.