In its PV Module Index 2022, the Renewable Energy Test Center (RETC) raised the question of the deterioration of trend technology caused by ultraviolet radiation.
Each year, Fremont, California’s Renewable Energy Testing Center (RETC) publishes its PV Module Index, which tracks the latest trends in solar module quality, performance, reliability and emerging technologies.
The latest annual report, The PV Module Index 2022 begins with a note on the rise of TOPCon solar modules, a technology that is increasingly being adopted by major panel suppliers.
TOPCon was first introduced at Germany’s Fraunhofer Institute for Solar Energy Systems in 2013 and is now gaining traction and acceptance.
The technology consists of n-type PV cells with passivating contacts. The modules feature strong surface passivation and efficient carrier transmission, both of which contribute to strong open-circuit voltage and high efficiency. The transition to TOPCon comes as p-type passivated emitter and back contact cell (PERC) modules begin to reach their theoretical efficiency limits.
RETC said this increase in efficiency has made TOPCon “the buzzword in solar energy.”
The report noted that while Longi is “betting” p-type TOPCon, many other leading module companies such as JinkoSolar, Jollywood, JA Solar and Trina Solar are making significant investments in modules with n-type TOPCon cell design.
“With higher open circuit voltage values, you can achieve a higher efficiency and power rating. That in itself is likely to move manufacturers to n-type TOPCon cells as soon as they get there,” said Kenneth Sauer, principal engineer at VDE Americas.
RETC said that due to manufacturing complexity, efficient n-type cells using heterojunction technology (HJT) and interdigitated back contact cells (IBC) are relatively expensive to produce and remain a niche market. In comparison, the production of n-type TOPCon cells is very similar to the PERC manufacturing process, making it easier to transition from existing production lines.
“Although today’s n-type TOPCon modules cost slightly more to produce per watt than p-type mono PERC modules, the efficiency gains result in lower levelized cost of energy (LCOE) for large-scale field deployments. Best of all, leading experts expect n-type TOPCon to benefit from an accelerated learning curve” , the report says.
However, the report notes that, as with any new technology, there may be risks associated with moving to TOPCon. Although n-type TOPCon PV cells have proven to be resistant to photodegradation and degradation caused by light and elevated temperature, there is evidence of susceptibility to ultraviolet-induced degradation (UVID), which can compromise module longevity.
Researchers at the SLAC National Accelerator Laboratory and the National Renewable Energy Laboratory (NREL) have documented the benefits and rear side power loss of these technologies. The data do not point to a single degradation mechanism, but suggest that different cell models degrade by different pathways, according to the report.
“We’re not trying to sound the alarm for no reason,” said Cherif Kedir, CEO of RETC. “We just want to test the possibilities of UV degradation to educate ourselves and the industry. If there is no problem, we can all move forward in our lives.”
Kedir recommends that module manufacturers perform accelerated UVID testing as part of their technical due diligence. If the passivation layers of the cells are mistuned, they can break down under this exposure. He recommends evaluating each new cell model on a case-by-case basis.
“If there are problems, we will publish a report so the industry can get in front of the problem,” he said.