We present simulations on both the optical properties and the efficiency of nanowires (NWs), nanopillars (NPs) and nanocones (NCs) silicon-based solar cells, together with measurements on their associated optical absorption. We address the calculation using Green's function formalism and Finite Difference Time Domain (FDTD) method, well-adapted to deal with a periodic set of nanostructures. We study the effect of the period, the bottom diameter, the top diameter, and the height of the NPs or NCs on the efficiency, assuming that one absorbed photon induces one exciton. We give general trends of the involved geometrical parameters with regard to the efficiency of the nanostructures' solar cell. Moreover, nanostructures have been processed and allow comparing experimental results with simulations. In every case, a good agreement has been found.