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The key to efficient and powerful modules is to preserve the cell efficiency during encapsulation.Therefore it is essential to first understand all factors which influence the module efficiency and second to derive methods to decrease the losses or increase the gains.We classify the losses and gains into optical,electrical and design factors.They are arising from the interconnection and encapsulation.We describe the mechanisms behind these factors and illustrate methods to increase the module efficiency.Especially the interactions of several optical effects are evaluated in detail.The main result is that the optical coupling gain,which is generated by the higher refractive index of the cell surrounding materials,strongly depends on the type of cell which is encapsulated.To illustrate the divergence of the cell to module ratio a case study is performed showing that multi-crystalline,mono-crystalline and IBC solar cell require different strategies to increase the module efficiency.The second goal of this work is to suggest a method to measure and illustrate the cell to module ratio in a scientific way to avoid misunderstandings by comparing different CTM publications.The work discusses how to define the initial cell parameters (mean value,minima/ maxima or sum) and how to deal with measurement uncertainties,which mostly overlay the measured encapsulation effects.It reviews the definition of the aperture area of a module and discusses the impact of pseudo square edges on the module efficiency.Finally,we present a cell to module ratio of 0 % in maximum power for a 16 cell polycrystalline MWT-solar module which is produced at the Fraunhofer ISE and measured at ISE CalLab PV modules.