Bifacial Photovoltaic Performance and Optimization in Mid-to-High Latitudes

Abstract

As early as the 1980s, photovoltaic (PV) modules have been deployed in high latitude regions to power buildings and equipment. However, it is only in recent years that significant PV deployments have begun to occur in these regions thanks to the continued drop in PV module costs. Historically, PV technologies have been deployed in low-to-mid latitude locations where solar resource is high and the economics of PV were more suitable. In these regions snowfall is rare or non-existent. This thesis supports efforts to bridge the knowledge gap between PV systems designed, operated, characterized, and modelled in low-to-mid latitudes and PV systems in high latitude, northern locations. Bifacial PV technologies are, in particular, explored due to their added benefits in regions with regular snowfall and cloud cover. The research presented in this thesis spans from the cell-level to the system-level and includes both experimental and modelling work. One of the main challenges for PV systems in high latitudes is predicting their performance under high latitude operating conditions. This is particularly challenging for bifacial PV technologies where the added complexity of rear-side light is heavily influenced by the surrounding environment and illumination conditions. In this thesis, emerging high efficiency and high bifaciality silicon heterojunction solar cells are simulated and measured under high latitude operating conditions. A methodology for testing bifacial devices indoors that incorporates the effects of additional illumination from rear-side ground cover is developed. Several bifacial PV system-level models are discussed and explored in this thesis for simulating mid-and-high latitude PV systems, including emerging vertical PV designs. Vertical PV systems have been deployed in recent years in smaller-scale sites (<1 MW) due to their suitability in high latitudes and in agri-photovoltaic applications. The effects of varied row spacing and module tilt are explored as a function of latitude, and empirical equations are developed for calculating system row spacing given deployment latitude and configuration (fixed-tilt, tracked, or vertical systems). The sensitivity of bifacial PV energy yield models to input albedo is explored via the calculation of spectral albedo mismatch as a function of latitude for 10 different ground cover scenarios, demonstrating a tendency towards increased modelling uncertainty in high latitudes. This thesis also presents the highest latitude location model validation effort to-date at 65°N and validates five PV models for emerging vertical bifacial PV systems. Vertical PV systems are found to have higher modelling uncertainty than equator-facing fixed-tilt systems, however hourly and seasonal trends are generally well predicted by the models. Finally, the degradation of PV systems in cold, snowy climates is reviewed and new analysis is presented for four PV systems >60°N. PV systems deployed in cold climates tend to degrade slower than warmer climates, which is an indication that PV systems in high latitudes may out-live their lower-latitude counterparts. Overall, the six papers presented in this thesis support continued development of mid-to-high latitude PV and demonstrate that PV technologies can be used to provide reliable, seasonal electricity. PV systems must be designed with high latitude environmental conditions in mind, higher tolerances to uncertainty, and to meet northern energy priorities.