NX Profile: A Chat with Dr. Bifacial, Nextracker’s Amir Asgharzadeh Shishavan

bifacial performance modeling

One of the reasons I love working at Nextracker is the incredibly talented people we have here, from former rocket scientists to wind testing experts to sales and logistics gurus and more. I’m amazed and humbled by my coworkers every day, by their intelligence, their passion, their commitment, and their teamwork.

In this edition of our blog, I’d like to profile Dr. Amir Asgharzadeh Shishavan, one of Nextracker’s PV system performance engineers. Amir holds a rather unusual distinction: he is one of a handful of people on the planet who wrote his Ph.D. dissertation on what has become one of the hot technology topics in the industry – bifacial solar, specifically bifacial performance modeling. To wit, one of his former supervisors at SunPower, Matt Campbell, refers to Amir as “Dr. Bifacial.”

Amir has shown a passion for optics, photonics, and renewable energy since he was a boy in Iran. This was manifested through his doctoral work at the University of Iowa and eventually became part of a 2016 study funded by the Department of Energy’s SuNLaMP program, which focused on “performance models and standards for bifacial PV module technologies.” The goal of the research project, conducted by a team from the National Renewable Energy Lab (NREL), Sandia National Labs and the university, was to develop “accurate and validated models (that) will allow developers to fairly evaluate the potential benefits bifacial PV technologies for specific projects” and “increase the knowledge about bifacial performance characteristics and provide unbiased third-party data.”

“There were very few performance models for bifacial at the time, so we developed several simulation models to predict the rear-irradiance on bifacial systems and then compared and successfully validated them with field testing data from Sandia Labs,” Amir explains.

Inverter reading at the bifacial testing facility at Nextracker’s Center for Solar Excellence

Given that Nextracker has a growing global pipeline of close to 9 GW of bifacial projects with many of those sites already under construction, Amir’s expertise in bifacial technology and bifacial performance modeling has proven invaluable. He is part of a team taking a very deep dive into the different aspects of the bifacial module and system behavior and performance in order to optimize the design of single-axis trackers to enhance energy yield.

Bifacial simulation modeling is complex, and the importance of linking simulation models and real-world data is something that cannot be overemphasized, according to Amir. “Sometimes I see scientific papers and presentations with very high bifacial gain values that can’t be achieved in real life. There is too much reliance on modeling and not enough empirical calibration. Studies often only look at a single PV module type and don’t account for some of the ways that different technologies can affect the claimed bifacial gains.”

Amir and his teammates are gathering real-world data on the key factors that influence bifacial performance and its impact on energy production. “We’ve seen a wide range of bifacial gain results under the same irradiance and albedo conditions because of the varying structure and surface bifaciality of different module types,” he explains. “We’ve also seen a number of differences when we account for variations in tracker structural elements and as-built configurations.”

Moving forward, Amir would like to see continued improvement in the bifacial performance modeling accuracy of third-party tools. He also notes that “the speed of modeling needs to be increased for specific approaches such as ray-tracing method because it’s very expensive to run a computational high-resolution simulation.” He’s also a bit frustrated by the lack of open-source software, citing one example where “lack of precise documentation and the fact of being a closed-source software, makes it difficult for the industry experts to contribute and improve the model” as a limiting factor in one of the commonly used models.

Amir feels very excited to be part of Nextracker and looks forward to continuing his research on bifacial PV. “It is quite fascinating to have access to a state-of-the-art bifacial test facility such as the one we have in the Center for Solar Excellence in Fremont. Our testbed is heavily equipped with sensors, and we are able to gather and analyze high-quality empirical data for different module technologies and tracker platforms,” he explains.

As someone who’s been researching and implementing the technology for several years, Amir has an interesting perspective on the bifacial boom. “When I started working with the Department of Energy, the market share of bifacial was quite low. Now, I’m so excited to see the recent growth.  Some analysts are saying that within five years, as much as 50% of the modules manufactured will be bifacial. This is a really exciting time, and I hope to give back and share our findings with the industry.”

Dr. Amir Asgharzadeh Shishavan and Greg Beardsworth are coauthors of Nextracker’s bifacial PV technical white paper, Quantifying Your Bifacial Gains: Using Calibrated PVsyst Model Input Parameters to Accurately Predict In-Field Performance.”