1. If there is wind, obviously you need less energy to move the air through the device. 2. Second, your estimate based on gravity is off. Apparently, the fan p

1. If there is wind, obviously you need less energy to move the air through the device. 2. Second, your estimate based on gravity is off. Apparently, the fan power to move air is given by [1] Power = (pressure change of air) x (volume/time of air) Volume/air is 1.25e6/10hours = 1.25e5. Assuming that the pressure change through the device is minimal, we can look at the bottom most line (100 Pa) on the first figure, to estimate ideal power to be ~5KW of power. Even with loses, having 10-20 KW power systems is equivalent to the energy consumption of 2-5 large houses. [1] https://www.engineeringtoolbox.com/fans-efficiency-power-consumption-d_197.html https://www.engineeringtoolbox.com/fans-efficiency-power-con...