The paper presents the optical power absorption simulation in a silicon solar cell utilizing single and double diffraction gratings at varying locations (depths) within the device. The solar cell under discussion consists of a rectangular top grating, P-type Si, N-type Si, a rectangular bottom grating, and a reflective material on the bottom. We use 3D finite differential time domain (FDTD) simulations to calculate the power at the solar cell PN interface at wavelengths ranging from 300nm to 1100nm. Throughout simulation, the structure of the gratings remains unchanged – only its location within the device varies, which is accomplished by varying the thickness of the P and N regions. The spectrum of incident solar light and the photo-responsivity of silicon are also took into account to obtain a total weighted power factor, allowing comparison between all simulated cases. We find an increase in weighted power absorption (compared to the non-grating case) ranging from 42% to 72% across all simulated grating locations. Overall, our simulations show that varying the location of the grating(s) changes the amount of power absorbed, and that certain device thicknesses correspond to increased power absorption and are preferred in the design.