The blades of a WT are the wing-like structures attached to the hub. A blade is very similar in look and function to an aeroplane wing air flow past the blade generates aerodynamic lift which, in the case of a WT, causes the rotor to spin and makes power generation possible. Most modern electricity-generating WTs have three blades (the so-called “Danish concept”). However, many two-bladed examples also exist, and even one-bladed designs have been known. Rotors for water pumping and battery charging may have many more blades to allow them to function in low winds.