Validating irradiance models for high-latitude vertical bifacial photovoltaic systems

Erin M. Tonita1,2, Silvana Ovaitt2, Henry Toal3, Christopher Pike3, Karin Hinzer1, Chris Deline2 1SUNLAB, University of Ottawa, Ottawa, ON, Canada /2National Renewable Energy Laboratory, Golden, CO, United States /3Alaska Center for Energy and Power, University of Alaska Fairbanks, Fairbanks, AK, United States

Bifacial photovoltaic systems oriented vertically facing east-west are an emerging design, targeting production in morning and afternoon hours and providing competitive annual energy yield to traditional south-tilted modules for high latitude locations. The accuracy of existing bifacial PV models when modules are oriented vertically has yet to be examined in detail.  Here, we compare four bifacial PV irradiance models in ~150 locations between 15-80°N on the utility-scale, finding higher inter-model deviations for vertical PV systems compared to south-tilted across all latitudes <75°N.  We validate model-predicted irradiance with test-site data collected in Golden, Colorado and Fairbanks, Alaska for E-W vertical and south-tilted arrays. Modelling error increases for the Alaskan test-site, driven in part by high albedo measurement uncertainty during snowy months.