The influence of silicon nanowire (SiNWs) geometry on the efficiency of radial p-i-n junction solar cell is studied using experimental measurements. Solar cells based on vertically aligned structures with the SiNWs less than 10 μm in height are practically on par with the planar element in terms of the open-circuit voltage, exceeding it in terms of short-circuit current density by up to 1.5 times (3.9–4.9 mA/cm2). The increase in the short-circuit current density is associated with the broadening of the quantum efficiency (EQE) spectrum. There is a significant broadening of the EQE boundary to the short-wavelength region with a decrease in the diameter of the SiNWs (from 1.8 to 0.7 μm). A decrease in the open-circuit voltage and a decrease in the absolute value of EQE are observed for structures with SiNWs more than 10 μm in height.