Vertical axis wind turbine, or VAWT, is any turbine with vertical axis of rotation. There are many sub-types of these turbines, but the technology itself has some general advantages and disadvantages when compared with horizontal axis wind turbines.
One advantage is that VAWTs are omni-directional and can utilize all ranges of wind directions and utilize gusts of wind. On the other hand, since wind is still blowing only from one direction, this creates uneven dynamic loads on different blades and other components, which makes it less reliable. Also, it leads to a certain amount of self-braking, as the same blade passes the wind flow at different angles.
Another advantage is that it is easier to produce due to lack of hub yaw and blade pitch mechanisms; and maintenance is also easier, because most components are placed near the ground level. Unfortunately, they also produce less, because of smaller working area of the blades, so despite the lower cost they may still may not be a good investment.
One clear benefit is that they are more suitable for the urban area, both aesthetically and from the safety point of view.
VAWTs and HAWTs can be considered as separate classes of products much in the same way as wind and solar generators, and should be used to achieve different goals.