Innovation has driven the growth and development of the PV industry. With that innovation has come increased reliability, bankability, optimized energy yields, and higher efficiencies – making solar more and more appealing to stakeholders.
One of the most promising innovations is the emergence of bifacial PV cell and module technology. By producing electricity from both the front and backside of a solar module, PV project owners and developers can profit from increased energy yields from the diffused light hitting the backside of the module.
Optimizing the financial return for bifacial
When coupled with an optimized and reliable PV tracking system, bifacial modules could represent a particularly powerful solution, however, the application of bifacial with tracking is only at its early stages, and a number of challenges remain for large-scale adoption to occur.
With the backside yield only a second-order effect, the frontside production remains the dominant factor determining total yield. Avoiding the pitfalls that disproportionately drive up cost in order to optimize backside performance is paramount: ‘Cutting off your nose to spite your face,’ so to speak. Optimizing the financial return for bifacial is key.
The nature of bifacial solar modules means that the output of the backside is highly dependent on a number of natural as well as mechanical factors. Specifically, the amount of light that reaches the backside of the module depends greatly on the albedo, or reflectivity of the ground substrate on which the cell is installed. The power gain percentage versus albedo of common installation substrates can range from 5.67% for grass, up to 24.60% for white painted surfaces. (Trina Solar) This large disparity in albedo means that it is impossible to generalize the potential gains from a PV system deploying bifacial technology – making the bankability site specific.
Taking a proactive approach to bifacial with tracking PV applications, Array Technologies has been gathering data from a test array at a Nevada test site for over 12 months. Bifacial modules from a leading producer have been paired with the DuraTrack V3 tracker architecture at the site.
Preliminary findings from a yearlong study revealed that a 9.15% power output gain can be achieved in a bifacial with tracker array when compared to monofacial modules in the same configuration. Although the field data to date shows that two-module-in-portrait (2MIP) orientation delivers the best total power output, the added cost of taller foundations and installation of 2MIP suggest that this maximum power output configuration may not provide the maximum financial return in the aggregate.
At a time when the PV industry is under enormous cost pressure, the opportunity to improve LCOE and boost production for only a slight increase in project cost is promising. While preliminary numbers are impressive, results will vary greatly based on site substrate conditions, geolocation, and a variety of other variables. In the end, the cost of bifacial is the most easily analysed, whereas the benefit is much more difficult to define.
Through its test site and other efforts, Array has also made good progress in growing the industry’s understanding of modelling bifacial with tracking power output – which is carried out when a PV system is still in the design stage. Models currently deployed as industry standards, such as PVsyst, are still in development and currently appear to have shortcomings when it comes to accurately forecasting bifacial with tracking system output.
Modeling and comparison needed
It is crucial for the industry to evaluate the actual production gains and the NPV of a bifacial tracking PV asset, and to determine whether costs incurred in an attempt to optimize for the bifacial boost have a beneficial impact on LCOE. Does the additional backside energy harvest justify the increased total project CAPEX costs?
While good progress has been made with standard forecasting and evaluation models, they are dependent on accurate annual albedo data and tracker impact models. Potential bifacial gains have little value without bankable models, and as of now, the industry needs a standardized module-on-tracker test for modelling and comparison.
In continuing expansion of its R&D efforts, Array Technologies has partnered with a national laboratory in New Mexico with state-of-the-art solar technology research facilities. Extensive field tests are underway on bifacial modules and will provide the industry with a better understanding of benefits when coupled with solar tracker technology.
The laboratories’ extensive experience and attention to detail are fundamental to the success of their joint efforts with Array. Impartial, systematic investigation of factors impacting production will support energy modelling methodology and validation. In addition, advanced instrumentation is being deployed to carefully study the effects of independent variables on the power output of bifacial with tracking systems.
The nature of this testing being undertaken by Array points toward a push in the solar industry to ensure the bankability of new developments. The results of these studies aim to provide the data necessary to provide responsible cost vs. benefit modelling that will relieve any uncertainties, and aid in the early adoption of innovative technologies in solar energy production. Not only will studies such as these benefit the companies involved, but the light shed by them should be invaluable in encouraging the widespread adoption of solar as a whole.
Written by Ron Corio, founder of Array Technologies