With firsthand experience of the complexity of testing indoor PV devices, researchers at Simon Fraser University in Canada identified how certain testing setups and protocols can skew results, then proposed protocols for standardized testing.
Backed up by experimentation and validation, the recommendations cover key procedures, such as where and how to focus the light source on samples and the use of the IPV reference cell method.
Indoor photovoltaic (IPV) devices harvest energy from various artificial light sources: incandescent light bulbs, fluorescent lights, and light-emitting diodes (LEDs). It is not the only way they differ from conventional solar PV technology. “Unlike solar photovoltaics, IPV involves a wide diversity of illumination conditions, instrumentation, and testing procedures, making accurate characterization particularly challenging,” corresponding author Vincenzo Pecunia told pv magazine.
The sheer variety of lamps and unique spectra used to assess IPV performance makes it almost impossible to benchmark results across the literature. “This motivated us to explore better ways to standardize IPV characterization and benchmarking, not just for our own research, but to benefit the broader research community and advance genuine progress in the field,” said Pecunia.
Details of the work appear in “Accurate performance characterization, reporting, and benchmarking for indoor photovoltaics,” published by Joule.
Accurate characterization is essential to determine whether or not reported results reflect “true advances or merely differences in testing conditions or inconsistent characterization practices.”
“Getting the numbers right is critical to advancing the technology and realizing the many potential applications that could benefit from IPV,” Pecunia explained.
The team sought expertise from Behrang Hamadani at the National Institute of Standards and Technology (NIST) early on to explore the versatility of the IPV reference cell method. This effort eventually enabled them to experimentally establish the primacy of the IPV reference cell for characterization across different spectra, angles of incidence, and device types, according to Pecunia.
He described the function of the IPV reference cell as a calibrated PV device that translates measurements taken under any indoor light into the corresponding results under standard reference conditions, which enable direct IPV benchmarking across labs.
Later, the team collaborated with Germany-based organic photovoltaic manufacturer ASCA and Canada-based Rayleigh Solar Tech, a developer of perovskite solar cell technology, to test devices at “real-world scales” while gaining insights into industry requirements and practical considerations.
The work has reinforced the researchers’ view of IPV as a “highly promising opportunity” for emerging photovoltaic technologies. “Unlike large-scale solar, indoor PV is more approachable in terms of performance. In fact, perovskite and organic materials offer a notable efficiency advantage under typical indoor conditions, which is almost the reverse of what we see in conventional solar photovoltaics,” said Pecunia.
The study addressed key characterization challenges, “issues that were previously unresolved in the literature and in the recently issued IEC standard on IPV characterization,” such as angular effects, device-dependent inaccuracies due to light source features and the limitations of benchmarking based on colour-temperature and spectral-coincidence, according to Pecunia, who added that the group can now focus on “advancing IPV technology itself, based on measurements it can trust” and a solid characterization platform.
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