The Interfaces between Silicon and the Transparent Conducting Oxides (TCOs) In2O3, SnO2, and ZnO are investigated by Density Functional Theory and most modern Quasiparticle methods. Natural electronic band offsets at the interfaces are derived by two mesoscopic methods, in the framework of the Shockley-Anderson model and by a modified Tersoff approach. Structural atomistic model geometries of one Si-In2O3 interface and of two Si-ZnO interfaces are constructed with a lattice-coincidence approach and the electronic structure of the interfaces is investigated in detail. The discrepancies between the different mesoscopic approaches and between the natural and microscopic band discontinuities are found to be considerable and quantitatively explained by the charge transfer at the Si-oxide interface. The investigation of realistic structural interface models is found to be the only reliable method of predicting the electronic properties of Si-TCO interfaces by ab-initio methods.