Realistic bifacial gains expected for large scale PV systems are in the range of 5% to 15%. This gain is a big game changer when compared with other improvements in PV in the last few years. However, the performance of a bifacial system will be strongly affected by its design and the resulting impact on the irradiance received on the rear side of the modules. To accurately estimate the extra yield generated, new tools able to assess the irradiance reaching the rear side are needed. Different methods are available to estimate the bifacial yield. A very accurate one is to use 3D modeling of all the system components that can interfere with light combined with ray tracing. EDF R&D and Fraunhofer ISE have both developed their own bifacial yield assessment tool based on ray tracing. To validate this approach, both tools have been used for cross comparison simulations. Several validations have been carried out against real bifacial systems – including large scale fixed tilt and horizontal single axis tracking systems. Results of the validation and the tool comparison are presented here.