The rapid expansion of photovoltaic (PV) systems has revealed the presence of losses due to module coupling, better known as mismatch losses, that deprive producers from additional and available electric energy. This book aims to better understand the causes and mechanisms of mismatch losses in grid-connected installations. Two solutions to reduce these losses are proposed, studied, and compared. Also, the modelling techniques for PV systems submitted to shade, along with experimental results, will be presented. The first solution proposed consists in modifying the connection scheme of the array. The second solution uses power electronic devices within the solar array to reduce mismatch losses. This study will conclude with a global comparison of the proposed solutions in both residential and commercial-sized installations.