A Vertical axis windmill with wind guiding device for diverting wind, the windmill comprising - a base structure having a polygonal shape; - inclined plates inclined from a bottom of the base structure to said top portion thereof and being tapered-shaped in an inwardly radial direction, - vertical plates, said base structure having a periphery which is entirely surrounded by said inclined and vertical plates (5, 6); - radial tie beams located on a top portion of said base structure; - peripheral tie beams extend horizontally and transversally to said radial tie beams; - a rotor assembly, said radial tie beams extending in a radial direction from an axis of rotation of said rotor assembly, the rotor assembly comprising: - a central shaft; - a vertical rotating pipe; - top and bottom bearings; and - a plurality of rotor blades being mounted on said central shaft and on said vertical pipe with said top and bottom bearings, wherein each of said rotor blades is fixed to said vertical pipe and is shaped as a portion of a hollow cylinder to form a wind receiving concave surface and a convex surface opposite to the concave surface, and wherein each of said rotor blades has caps located at top and bottom edges of the concave surface of each rotor blade, said caps being formed as portions of lids of such hollow cylinder in order to restrict the upward and downward movement of wind after striking the rotor blades; and - a gearbox, coupling systems and a generator installed inside the base structure to convert mechanical energy from the rotor assembly into electrical energy, characterized in that each of said inclined and vertical plates (5, 6) has an inbuilt window having a spring tension shutter to allow excess wind to by-pass. - a base structure having a polygonal shape; - inclined plates inclined from a bottom of the base structure to said top portion thereof and being tapered-shaped in an inwardly radial direction, - vertical plates, said base structure having a periphery which is entirely surrounded by said inclined and vertical plates (5, 6); - radial tie beams located on a top portion of said base structure; - peripheral tie beams extend horizontally and transversally to said radial tie beams; - a rotor assembly, said radial tie beams extending in a radial direction from an axis of rotation of said rotor assembly, the rotor assembly comprising: - a central shaft; - a vertical rotating pipe; - top and bottom bearings; and - a plurality of rotor blades being mounted on said central shaft and on said vertical pipe with said top and bottom bearings, wherein each of said rotor blades is fixed to said vertical pipe and is shaped as a portion of a hollow cylinder to form a wind receiving concave surface and a convex surface opposite to the concave surface, and wherein each of said rotor blades has caps located at top and bottom edges of the concave surface of each rotor blade, said caps being formed as portions of lids of such hollow cylinder in order to restrict the upward and downward movement of wind after striking the rotor blades; and - a gearbox, coupling systems and a generator installed inside the base structure to convert mechanical energy from the rotor assembly into electrical energy, characterized in that each of said inclined and vertical plates (5, 6) has an inbuilt window having a spring tension shutter to allow excess wind to by-pass.