A combined computational and experimental study optimizing plasmon-enhanced absorption in Si thin film solar cells presented. A model system consisting of a 2-dimensional periodic /aperiodic arrays of Ag nanostructures on a silica coated Si film supported by a silica substrate is used in the simulations. We develop basic design rules for the realization of broadband absorption enhancements for such structures, by simultaneously taking advantage of 1) the high near-fields surrounding the nanostructures close to their surface plasmon resonance frequency and 2) the effective coupling to waveguide modes supported by the Si film through an optimization of the array properties.