Bifacial Solar Panels System Design, Modeling, and Performance

Abstract

Bifacial photovoltaic (PV) cell technology is currently poised to change solar modules and systems. They provide higher energy yield from its ability to capture both direct and diffuse illumination on the front- and rear-side of the module. At low-costs for implementation in production lines of traditional monofacial silicon cells, lower maintenance needed in fields compared to a similar power array of conventional modules, improved module characteristics like lower thermal coefficient due to better (in average) processes used in production, the implementation of this technology is projected to have a significant impact in the reduction of the cost of solar power, adoptable in a short period of time. Bifacial technology promises even lower $/W and $/kWh costs, continuing to improve solar photovoltaics’ competitive cost with fossil fuel energy sources and help mitigate climate change. However, bifacial PV performance models are not well established, and field validation data is scarce. Furthermore, existing optical models used to calculate the irradiance input into the modules make certain assumptions that have not been scarcely verified. This dissertation performs a study of these optical models for calculating irradiance available to bifacial panels under different deployment configurations. Sensitivity to mounting parameters and modeling assumptions are explored. The models agree between 2-3% despite differences in assumptions and complexity. The results from a test-bed built to validate the optical models are shown, showing good agreement within 2% error (absolute) in the bifacial gain in irradiance. Furthermore, algorithms for bifacial PV modules with single-axis tracking are implemented and presented. Field-data from two locations with single-axis trackers with monofacial and bifacial PV module technology are used to validate the algorithms. A methodology for calculating bifacial gain due to the fact that they can accept light from both front- and rear-side (a property known as bifaciality), and not due to differences in other cell or module properties, is also presented. This methodology has the possibility of addressing the lack of a framework for reporting bifacial versus monofacial fields gains, which has resulted in a wide range of reported gains. The methodology is used to compare performance data for two 100kW bifacial and monofacial arrays in Klamath Falls, Oregon, finding that 2.4% of the measured performance advantage of the bifacial array is due to improved front-side performance, rather than bifacial response. This dissertation concludes with the design of an optical concentrator to improve the specific uses of bifacial PV modules for vertically-mounted systems. Discussion of areas for improvement and future work are also included.