Recent studies have revealed that the interactions between clustered vertical-axis wind turbines (VAWTs) can help improve the total power production. Thus this study compares four typical arrangements (I, II, III, IV) of multi-turbines placed in close proximity to investigate their efficiencies of power generation. A series of computational fluid dynamic (CFD) simulations, based on two-dimensional (2D) unsteady Reynolds-averaged Navier-Stokes (URANS) theory, are performed for all four arrangements to achieve the maximum average power coefficient. First, the accuracy of the CFD model is validated against the field test results of 1.2 kW Windspire VAWT in reference. Then the performance of each arrangement at different proximities is investigated. It is found that the constraint effect in the lateral direction and the upstream turbines’ blockage effect can be triggered at a certain separation distance, which greatly affects the average power generation. In most cases, the 3-VAWT cluster is of higher efficiency than the 2-VAWT cluster in terms of the average power coefficient. The developed 3-VAWT cluster (Arrangement IV) has an average power coefficient up to 11.1% higher than that of an isolated turbine. In order to demonstrate the useful guidance of this study in practical applications, the performance of a newly developed wind-solar-aquaculture (WSA) system with multi-VAWTs is appraised. For the foundation of this system with restricted space, employment of the 3-VAWT cluster (Arrangement III) will yield yearly energy generation greater than that by three isolated turbines. •Separation distances of clustered vertical-axis wind turbines (VAWTs) are optimized.•Constraint effect and blockage effect affect the efficiency of clustered VAWTs.•In most cases, the 3-VAWT cluster is of higher efficiency than the 2-VAWT cluster.•3-VAWT cluster yields yearly energy generation higher than that by 3 isolated VAWTs.