Vertical-axis wind turbines have several interesting physical aspects when placed in pairs or rows, changing flow characteristics and often increasing power output. This presentation first summarises literature explaining the physics behind these aspects, and some illustrations of expected power gain by pairing VAWTs. Then, the Actuator Cylinder method is discussed, an extension of the actuator disk model that is capable of modelling VAWTs with relatively high accuracy for its computational speed. My own preliminary AC code, capable of modelling multiple VAWTs, is discussed and shared.