Realistic yield expectations for bifacial PV systems - an assessment of announced, predicted and observed benefits

Bifacial PV modules are able to convert solar irradiation from both surfaces. Therefore, larger amounts of produced energy are expected – compared to standard (monofacial) modules. Today, bifacial modules are offered by an increasing number of manufacturers, and marketing material sometimes promises quite optimistic bifacial gains. Reports on bifacial PV systems are also found in the literature, but mainly for test setups or small PV systems only. For large PV installations (as known with standard PV modules), realistic bifacial gains still need an assessment. Currently, none of the widely utilized PV system simulation tools is able to predict the rear surface contribution of bifacial modules accurately. Therefore, our approach combines simulation tools from different fields of (solar) energy technology, the lighting and daylighting domain and the PV system simulation domain. In this way, we are able to deal with solar geometry, sky radiance distribution, scene geometry, surface properties, PV module properties and wiring scheme without any need for severe approximations in the model definition. Using this tool, we calculated realistic yield values for a number of system configurations. The results are discussed with respect to their bifacial gain in relation to space requirements (expressed by ground cover ratio), mounting options and ground albedo. Reasonable ranges for expectable gains from bifacial modules and PV systems are given in the conclusion of this contribution