Modular floating platforms have recently emerged as a promising solution for offshore renewable energy applications. This chapter explores the hydrodynamic behaviour of modular photovoltaic platforms and their arrays under wave action. The three-dimensional wave diffraction and radiation problems involving multiple floating bodies were analysed numerically using the boundary element method in the frequency domain. An in-house, parallelized code was developed to assess the hydrodynamic responses of multi-body systems with complex connections. Parametric studies were conducted to examine the performance of an isolated module, a modular solar platform, and an array of interconnected platforms under wave conditions. The results revealed that the motion response of an isolated module exhibited a single resonance peak. In contrast, modular solar platforms demonstrated multiple peaks due to the hydrodynamic interactions between individual modules. Furthermore, the vertical forces acting on the connectors of the weather-facing modules were significantly higher than those on other modules. For photovoltaic arrays, the trends in heave and pitch motion responses as functions of the wavenumber were consistent with those of a single modular platform. However, the loads on the connectors varied notably with changes in the incident wave angle. These findings provide valuable insights for designing and optimizing floating modular structures for offshore renewable energy applications.