Bifacial technology is proving to be an effective means of reducing the levelised energy costs of PV systems, offering substantially improved energy yield for only a minor additional cost. Hartmut Nussbaumer, Markus Klenk, Joris Libal and Radovan Kopecek report on the state-of-the-art in bifacial PV systems, giving an overview of components such as modules, sub-constructions, tracking systems and inverters, and presenting comparative simulation and measurement results from bifacial and monofacial systems.