Output scales with design, size, location and height. With "beyond some height" I mean really tall buildings would need just a tiny propeller. Micro turbines are nice for a very different reason. -- "Unfortunately, micro wind turbines deliver hardly enough energy to power a light bulb." The benefit from not siting in complete darkness starts at about 1 Watt, the example produces considerably more. -- "Payback time: 50 to 750 years" The interesting bit here is the static world assumption. No one can tell how manufacturing, wages/income, the economy, geopolitics, climate, migration, food, etc will change. There is lots of room for the grid to go down and it kinda already regularly does in the best of locations one time every 10 years. (atm the entire grid in Puerto Rico is down) -- While it would be nice to have a heater or a cooker small devices like led bulbs and radios are valuable when the power is out.