Surface nanostructuration is an important challenge for the optimization of light trapping design in solar cell. We present simulations of the optical properties and efficiency of nanostructured (micropilars-MPs- or nanocones-NCs-) silicon based solar cells as well as measurements of their optical absorption. We address the simulation using the 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 MPs or NCs on the efficiency of the associated solar cell, assuming that one absorbed photon induces one exciton.. We give general trends taking into account diameter, length, period at the same time. Moreover, nanostructured structures have been processed and allow to compare experimental results with simulations. In every case, a good agreement is found.