The efficiency of bifacial photovoltaic modules, which can capture light from both sides, is significantly influenced by the reflectivity of the surrounding environment, for example in agrivoltaic settings. We investigate the retroreflective properties of grass and their impact on the energy yield of bifacial solar panels. By combining spectro-angular reflection measurements with computational modeling, we quantify the contribution of grass reflection to overall solar electricity production and evaluate the inaccuracies associated with the assumption that grass behaves as a diffuse reflector. Our results show that this assumption can lead to an overestimation of energy yield by up to 10%, due to the actual retroreflective behavior of grass. This effect is particularly pronounced for long grass configurations. The research underscores the importance of considering the detailed reflectance properties of vegetation in optimizing the placement and performance of bifacial photovoltaics in agricultural environments, with implications for improving the efficiency and sustainability of solar energy generation.