IEA PVPS Task 13 has recently published a new report “Best Practices for the Optimization of Bifacial Photovoltaic Tracking Systems” and a Fact Sheet on bifacial tracking (available in different languages). The report, which involves contributions from international experts, provides an in-depth analysis of bifacial tracking systems and aims to offer best practices to optimize their performance. This extensive work includes reviews of recent literature, industry standards, and insights from interviews with leading tracker companies and owners/operators of PV systems worldwide.
The report explores various technical aspects and innovations in bifacial tracking. It covers different types of single-axis trackers, their components, and design principles tailored to specific site conditions. Innovations in tracking technologies, such as backtracking to avoid row-to-row shading and active protection against extreme weather conditions, are also discussed.
Understanding Bifacial Tracking
Bifacial modules are PV panels that can capture sunlight on both their front and rear sides. New cell designs allow light to reach the cell from the rear side with efficiencies from 60% to over 90% compared to the front side. Unlike traditional monofacial modules that only absorb sunlight on one side, bifacial modules take advantage of reflected light from the ground and other surfaces, thereby increasing their energy output.
Tracking systems, which adjust the orientation of the panels to follow the sun's path, can further enhance the performance of bifacial modules. These systems come in various configurations, such as single-axis (SAT) and dual-axis trackers. Single-axis trackers rotate the panels around one axis, usually horizontal, to follow the sun from east to west, while dual-axis trackers adjust both the horizontal and vertical angles, ensuring optimal orientation throughout the day and year. The integration of these tracking systems with bifacial modules leads to more consistent and higher energy production compared to static, monofacial systems.
Advantages of Bifacial Tracking
The synergy of bifacial modules and tracking systems offers notable advantages. According to the 2020 technoeconomic study cited in the IEA PVPS Task 13 report, bifacial, single-axis tracked systems exhibit a 16% reduction in levelized cost of electricity (LCOE) compared to fixed-tilt monofacial systems, with up to a 35% increase in energy yield. The report confirms that bifacial tracking systems currently dominate the utility-scale PV market, with bifacial cells being used in over 90% of modules sold and more than 60% of the market share for PV systems utilizing single-axis trackers.
The additive nature of tracker and bifacial gains—typically 15-20% from tracking and 2-10% from bifacial technology—results in a compelling cost-performance proposition. This makes bifacial tracking systems the most cost-effective option in approximately 90% of global regions.
Challenges
Despite their benefits, bifacial tracking systems encounter several technical and logistical challenges. The IEA PVPS Task 13 report identifies key areas of concern:
System Design Complexity: The dual-sided nature of bifacial modules complicates system design. Minimizing shading from the tracker itself and optimizing ground reflectivity are crucial for maximizing efficiency.
Extreme Weather Response: Tracker systems must adapt to severe weather conditions, such as high winds, hail, snow, and flooding. Advanced trackers now incorporate sensors and weather forecasts to adjust module positions and mitigate damage. However, the effectiveness of these systems can vary. For example, while automated responses to hail are becoming more common, many systems still lack robust strategies for extreme conditions, which can result in significant damage when failures occur.
Performance Modeling: Accurate performance modeling remains a challenge. The IEA PVPS Task 13 report's blind modeling comparison revealed discrepancies of up to 100% in rear-side irradiance predictions among different models, highlighting the need for improved validation datasets and modeling techniques.
Albedo Enhancement: Enhancing energy yield through albedo optimization with reflective materials shows promise but is limited by the durability of these materials. Current research focuses on strategic placement and longevity to make albedo enhancement a viable practice.
Market Development and Trends
Bifacial PV tracking systems, where bifacial modules are mounted on movable racks that follow the sun, dominate the utility-scale PV market worldwide. Today, over 90% of modules sold use bifacial cells, and over 60% of the market share for PV systems utilize single-axis trackers. The financial benefits of these systems are substantial, with typical tracker gains of 15-20% and bifacial gains of 2-10% being additive.
Market development in bifacial tracking is influenced by several factors, including design considerations, terrain topology, and steel prices. Supply chain issues and the importance of reliable delivery schedules are critical. Using local providers can help offset costs and reduce carbon emissions associated with transportation.
Companies are also focusing on specific market sectors, such as dual uses for AgriPV, deployment on non-agricultural or otherwise unusable land, and highly sloped terrains. These divergent perspectives on land-use and value are shaping the strategies and investments in bifacial tracking systems.
IEA PVPS Task 13 obtained data from interviews with 16 tracker companies, representing over 87% of the global market share from 2012 to 2021, and a review of the 2022 Wood Mackenzie Global Solar PV Tracker report. Key findings include that 70% of these companies have been in business for at least 10 years, around 50% sell trackers in more than 20 countries, and over 80% sell in more than 10 countries.
Performance Modelling and Yield Assessment
IEA PVPS Task 13 conducted a blind PV performance modeling study has been organized to compare different modeling tools and their performance predictions for varying system design parameters. Participants have been asked to simulate a set of six imaginary PV systems for which the system design and weather data have been provided. This study aims to compare predictive models, ensuring accurate assessments of system performance and yield. The results can be found in the recent report.
Future Outlook
The future of bifacial tracking looks promising, with continued advancements expected to drive wider adoption. Improvements in module efficiency, tracker technology, and system integration will enhance the performance and reliability of these systems. As more data becomes available, predictive models will become more accurate, helping to optimize designs and maximize energy yield.
IEA PVPS Task 13 aims at supporting the solar industry in overcoming challenges and leveraging the full potential of bifacial tracking through ongoing research, international collaboration, and dissemination of research findings.
This article is part of a monthly column by the IEA PVPS programme. It was contributed by IEA PVPS Task 13 – Reliability and Performance of PV Systems.
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