As anyone following the solar industry understands, the costs of installing solar photovoltaic systems have declined dramatically and consistently over time. Despite massive cost declines over the years, solar PV systems today look a lot like solar PV systems installed a decade ago. This is because iterative improvements to existing technology have historically dictated cost declines in the solar space. Each major component of solar systems becomes cheaper and more efficient, and in turn, modules become cheaper on a dollar-per-watt basis and contain more watts per module.
The increased use of single-axis trackers, which rotate modules to track the sun throughout the day, is one of the most important of recent shifts in solar technology and represent the area where systems do look different than a decade ago. Trackers have helped decrease the levelized cost of energy (LCOE) for ground mount arrays by increasing yield from the same number of modules Another promising technology, bifacial modules, which offer the ability to capture energy from light reflected off the ground through the back side of the module, have struggled to find the same level of adoption. However, a combination with single-axis trackers may signal the most efficient use of the technology in its current form.
The Current State of Bifacial
As we’ve written in the past, bifacial modules can substantially increase a system’s yield, but estimates of the benefit vary widely. One leading manufacturer, LG, claims a 5-30 percent increase in production compared to standard modules. This wide range is due in large part to the widely varying albedos, or reflectivity, of the surfaces above which systems are installed. Highly reflective surfaces such as sand or snow can offer ideal results for bifacial systems, but the system configuration is important as well, as there also needs to be space between array rows for that light to reflect off the ground. The modules also benefit from being higher up from the ground than normal, as more light gets reflected to the back side of the module. While all of these factors impact monofacial system design to some extent, they are much more important to bifacial systems, and may change what would be the optimal system design.
Evaluating Bifacial Trackers
Single-axis tracking systems represent one of the more intriguing opportunities for bifacial modules. The benefits of tracking system design have already been thoroughly proven as the preferred method of providing the lowest LCOE in the utility-scale market for most geographies and site types, as its utility-scale market share now approaches 80 percent. With these strong fundamentals over fixed-tilt systems, it’s only natural to look to improve upon that existing benefit with increased yield from bifacial modules. While tracking systems’ bifacial gains may be slightly reduced compared to fixed-tilt systems due to the fact that they face the sun more directly, they also benefit from a low ground-coverage ratio, typically 30-40 percent (compared to 50 percent for fixed-tilt systems). Simply put, the extra space means more light hits the ground than it does for other system types, and provides more opportunity for light to reflect towards the energy producing back side of bifacial modules.
Leaders in the tracker space that have tested the scenarios have been supportive of the idea. Dan Shugar, CEO of NEXTracker, the largest producer of tracking systems in North America, told PV Magazine “the bifacial tracker is one of most exciting untapped opportunities in the solar industry. There will be a huge drive toward this.” In one test done by NEXTracker using both standard and bifacial modules on trackers reported gains of 14-17 percent for the bifacial units.
Can it Work?
Though trackers have found their market and the price premium for bifacials has dropped to below 5 percent, the lack of data is still hindering bifacial technology. The wide range of new factors affecting energy production and low rate of adoption make it significantly harder to model production for bifacial modules. Without a track record of reliable performance, investors, developers, and customers will naturally show skepticism of the approach. This lack of bankable information makes it difficult to achieve the scale of capacity that could alleviate the concerns. Concerns shared by engineers at Sol Systems include:
- The effects of uneven light on modules are poorly understood. Solar systems with bifacial modules will have partial shading on the backside due to the structure of the system. This uneven shading will reduce production, and the magnitude of the effect is currently poorly understood.
- The structures used to support modules are highly evolved and trusted by the industry and investors, but have also been designed with minimal thought to the back side of the modules. Racking structures that minimize this back side shading are just starting to be released, and need to gain acceptance by the industry.
Bifacial modules will necessarily have slightly different constructions than standard modules, as all bifacial modules will have either a backsheet made of glass or a transparent polymer. Glass-glass modules show promise for reducing degradation, but also pose different and new risks, and transparent polymers are also a new product that does not have as extensive of field testing as traditional backsheet materials.
Given the inherent problems of needing scale to build trust in the technology and the need for trust to build that scale, it will take some calculated risk taking by developers and customers to build more field data for bifacial modules and those on trackers. However, with the large potential for LCOE reductions that a bifacial tracker system could produce, it’s something surely to excite engineering geeks in the coming years.
This is an excerpt from the June 2018 edition of The SOL SOURCE, a monthly electronic newsletter analyzing the latest trends in renewable energy based on our unique position in the solar industry. To receive future editions of the journal, please subscribe.
ABOUT SOL SYSTEMS
Sol Systems, a national solar finance and development firm, delivers sophisticated, customized services for institutional, corporate, and municipal customers. Sol is employee-owned, and has been profitable since its inception in 2008. Sol is backed by Sempra Energy, a $25+ billion energy company.
Over the last eight years, Sol Systems has delivered 700 MW of solar projects for Fortune 100 companies, municipalities, universities, churches, and small businesses. Sol now manages over $650 million in solar energy assets for utilities, banks, and Fortune 500 companies.
Inc. 5000 recognized Sol Systems in its annual list of the nation’s fastest-growing private companies for four consecutive years. For more information, please visit www.solsystems.com.