Outdoor Performance Test of Bifacial n-Type Silicon Photovoltaic Modules

The outdoor performance of n-type bifacial Si photovoltaic (PV) modules and string systems was evaluated for two different albedo (ground reflection) conditions, i.e., 21% and 79%. Both monofacial and bifacial silicon PV modules were prepared using n-type bifacial Si passivated emitter rear totally diffused cells with multi-wire busbar incorporated with a white and transparent back-sheet, respectively. In the first set of tests, the power production of the bifacial PV string system was compared with the monofacial PV string system installed on a grey concrete floor with an albedo of 21% for approximately one year (June 2016-May 2017). In the second test, the gain of the bifacial PV string system installed on the white membrane floor with an albedo of 79% was evaluated for approximately ten months (November 2016-August 2017). During the second test, the power production by an equivalent monofacial module installed on a horizontal solar tracker was also monitored. The gain was estimated by comparing the energy yield of the bifacial PV module with that of the monofacial module. For the 1.5 kW PV string systems with a 30 degrees tilt angle to the south and 21% ground albedo, the year-wide average bifacial gain was determined to be 10.5%. An increase of the ground albedo to 79% improved the bifacial gain to 33.3%. During the same period, the horizontal single-axis tracker yielded an energy gain of 15.8%.