Bifi UK: Investigation of bifacial and sun-tracking systems for high latitude, and high diffuse climates

The need for sustainable energy sources to tackle climate change, as well as provide energy independence, has seen photovoltaic (PV) systems grow at pace, reaching terawatt scale in 2022. Likewise, the UK government aims to increase PV installations 5-fold by 2030. To achieve this, the UK industry needs to align with growing trends in the global PV market, which include shifting from monofacial to bifacial modules (which utilise light exposure on both front and rear), and from fixed-tilt to sun tracking systems (which follow the sun-path throughout the day). Currently, both these growing technologies, which have significant potential for additional uplift in energy yield are not well understood in high latitude and overcast climates such as the UK. This gap in research leads to increased risk for investors and can bottleneck the growth of the PV sector. This proposal aims to narrow this gap, by developing a state-of-art outdoor testing lab for PV systems, which can accurately measure bifacial performance under sun-tracking, validate energy yield models through experimental data, and then identify systems which produce the lowest levelized cost of electricity under UK climates. Furthermore, combining the advances of bifacial and sun-tracking will help integrate solar energy for dual-land use. This is critical, as the mounting global population (and therefore land scarcity) needs to sustain not only an increase in clean energy sources, but a growing food-water-energy nexus.

Two key challenges for the PV industry are lack of standards for measuring bifacial technologies, as well as lack of validation for the modelling techniques. In both cases, this is primarily concerning the irradiance on the plane-of-array (POA), i.e., light falling on the module as it is titled at an angle. The complexity of this problem is further heightened when considering tracking technologies that move the tilt angle throughout the day. Therefore, the first aim of this research is to develop instrumentation and procedures for measuring such data accurately including standardisation of rear side irradiance (and therefore albedo which is the ratio of front and back irradiance); monitoring the tracking angle; and finally, the temperature and soiling as well. This lays the foundation for validation of different sun-tracking technologies via field testing, creating UK's one-of-a-kind outdoor experimental facilities for PV systems. This includes standard fixed-tilt systems placed at an optimal angle; Single-Axis-Tracking which follows the sun in one direction (typically east-west), and Dual-axis tracking which can follow in both east-west and north-south directions (more expensive, but highest potential for energy yield uplift). These critical measurements will help identify limitation in the modelling techniques (from simple empirical techniques to more complex computer intensive ray-trace models) used to estimate the POA irradiance and help improve accuracy of energy yield estimation by utilising the real-world data. Finally, the levelized cost of electricity can be mapped for different tracking technologies, and analysed in the context of dual-land use, electricity spot price markets, and environmental costs.

The challenges above will be addressed by a collaborative effort from an international and industrial team, led by the University of Southampton, which includes pioneering researchers on bifacial tracking at NREL and SERIS; world-leading instrumentation expertise at NPL and the Chilbolton Observatory; and Corrie-Energy, a UK SME developing low-cost dual-axis trackers. The research will deliver key impact through improving global standards for bifacial tracking measurements; building open-source datasets for validated systems in the UK; and finally identifying economic and environmental viability. This will benefit industries across the sector, from SMEs manufacturing tracking systems, to asset managers installing utility scale systems.