Key takeaways:
TÜV Rheinland’s analysis showed that using LCOE rather than upfront price offers a clearer comparison of long-term module performance
Under the study’s assumptions, the BC module delivered higher energy yield and lower LCOE across multiple deployment scenarios
Results highlighted the importance of module-specific testing, as findings cannot be generalized beyond the evaluated products
At the TaiyangNews webinar: Unlocking the Utility Potential of BC Technology, Christos Monokroussos from TÜV Rheinland presented an evaluation framework for comparing PV modules using Levelized Cost of Electricity (LCOE) instead of simple upfront metrics like dollars per watt. He explained that relying only on module price overlooks critical performance characteristics, including degradation, temperature behavior, low-light response, and bifaciality, that influence lifetime energy yield. In contrast, LCOE provides a more complete measure by incorporating CapEx, OpEx, financial parameters, and energy production over the system’s full operating life.
Monokroussos outlined TÜV Rheinland’s methodology, which combines laboratory testing with field testing. Lab testing covered parameters such as power at STC, temperature coefficients, spectral and low-light performance, incidence angle modifier (IAM), and initial degradation behavior. Field testing helped validate these characteristics under real weather, determine early-stage degradation, and estimate operating temperature through NMOT analysis. The evaluation compared 2 modules supplied for the study: a TOPCon module (Module A) and a back-contact (BC) module (Module B) with similar dimensions.
The BC module exhibited significantly higher measured power and efficiency, attributable to the absence of front-side metallization shading. The TOPCon module showed higher bifaciality, but overall power output still favored the BC module. Incident-angle measurements revealed that the BC module performed markedly better at high angles of incidence, a result Monokroussos attributed to glass and anti-reflective schemes rather than cell architecture alone. The annual degradation values for the BC module were not verified but were taken as assumptions referring to the product datasheet.
Field tests examined NMOT and shading behavior. The BC module demonstrated marginally lower NMOT (by 0.5°C) and substantially better shading tolerance, the latter being an inherent advantage of back-contact designs where current can bypass shaded regions more effectively. The study modeled different system-level deployment scenarios in Southampton, UK: equal TOPCon and BC DC power and equal installation area, where equal TOPCon and BC modules were used. Across these scenarios, in the first year, the BC module delivered a higher energy yield, about 1.38% more in equal-power setups and over 4.11% more when the installation area was kept constant, driven mainly by IAM performance, temperature behavior, and shading resilience. When projected over 30 years, as per the guarantees provided by module manufacturers, the difference between BC and TOPCon systems further increased by 1%.
Using the CapEx and OpEx assumptions provided by the manufacturer, the study calculated LCOE for all scenarios. Results indicated a lower LCOE for the BC module, with the largest advantage (around 3.2%) achieved when systems were constrained by installation area. Internal Rate of Return (IRR) comparisons showed 2.5-4.5% higher values for the BC cases, reflecting stronger long-term project economics under the given assumptions. Monokroussos emphasized that these findings are case-specific and should not be generalized across all module types. He concluded that LCOE-based evaluations offer clearer insight into lifetime project performance and encouraged project developers and manufacturers to use rigorous, module-specific assessments when comparing technologies.