The array effects created between two sets of matching vertical Savonius wind-turbine blades installed side-by-side were examined using two separation distances of 1.0D and 1.5D, and three combinations of rotational directions, making a total of six test scenarios. The three combinations of rotational directions for the two wind turbines consisted of both turbines rotating clockwise, the first clockwise and the second counter clockwise, and finally, the first counter clockwise and the second clockwise. Using a high-precision three-dimensional printer, scaled-down test models of the turbine blades were fabricated, each with a rotational diameter of 0.226m and an aspect ratio of 1.0. The uncertainty of the test was determined to have a mean value of approximately 2.2%. For each test scenario, the torque and revolutions per minute of the blades were measured using the differential tip speed ratio, and the power coefficient was evaluated based on the oncoming airflow speed. The test results clearly showed that there was a combined effect related to the rotational direction of and the separation distance between the two sets of blades. Better performance could be obtained by considering these parameters for adjacent wind turbines. Copyright (c) 2015 John Wiley & Sons, Ltd.