  Bifacial photovoltaic technologies are estimated to supply >16% of global
energy demand by 2050 to achieve net-zero greenhouse gas emissions. However,
the current IEC bifacial measurement standard (IEC 60904-1-2) does not provide
a pathway to account for the critical effects of spectral or broadband albedo
on the rear-side irradiance, with in-lab characterization of bifacial devices
limited by overestimation of rear incident irradiance, neglecting spectral
albedo effects on the rear, or both. As a result, prior reports have limited
applicability to the diverse landscapes of bifacial photovoltaic deployments.
In this paper, we identify a general bifacial illumination method which
accounts for spectral albedo while representing realistic system operating
conditions, referred to as the scaled rear irradiance (SRI) method. We describe
how the SRI method extends the IEC standard, facilitating indoor testing of
cell or module performance under varied albedo with standard solar simulator
set-ups. This enables improved comparisons of bifacial technologies,
application-specific optimization, and the standardization of bifacial module
power ratings.
