We study light scattering and absorption in thin film solar cells, using a model system of a sinusoidally textured silver reflector and dielectric layers of ZnO and amorphous silicon. Experimental results are compared to a theoretical model based on a Rayleigh expansion. Taking into account the explicit interface profile, the expansion converges fast and can be truncated typically after three or four orders. At the same time, the use of realistic permittivity data correctly reproduces the intensity of diffracted orders as well as the coupling to guided modes and surface plasmon polariton resonances at the silver surface. The coupling phenomena behind the light trapping process can therefore be assessed in a simple, yet accurate manner.