A team of German researchers has developed a miniaturized solar cell experiment for nanosatellites. It was used to test samples of new mutlijunction solar cells developed by Azur Space, including novel triple-junction metal wrap through solar cells.
German researchers from the University of Stuttgartt and Azur Space Solar Power, the cell manufacturing subsidiary of Canada-based high-purity materials provider 5N Plus, conceived a miniaturized solar cell experiment (SCE) for nanosatellites.
The SCE was used in low earth orbit to measure the performance of novel triple-junction metal wrap-through (MWT) solar cells being developed by Azur Space for the new space sector alongside quadruple-junction solar cells.
The team’s novel instrumentation successfully sampled more than 5,000 IV-curves, cell temperatures, sun error angles, and total ionizing dose (TID) measurements, as described in “Design and first results of the solar cell experiment on EIVE,” published in Acta Astronautica.
The data gathered in orbit was in turn used to validate the sophisticated temperature and solar simulator characterization tools in the lab on the ground.
“Within the last decade some organizations and universities have launched solar cell experiments on CubeSats, however, with mixed results due to the very constraining nature of such miniaturized satellite platforms,” Markus T. Koller, the research’s corresponding author told pv magazine. “We have shown that well-designed measurement electronics and a reliable satellite platform will enable proper solar cell characterization in the real space environment.”
The experiment is ongoing, with the number of IV curves measured reaching 6,680 as of early February 2025, according to Koller.
The nanosatellite platform in this case was the exploratory in-orbit verification of an E-band link (EIVE), which was developed by a German consortium comprising several research institutes and industrial partners. It is a low earth orbit (LEO) satellite.
“From the technological viewpoint, the study has shown that the metal-wrap-through technology is valid for use in space and does not pose any drawbacks for the solar power generation in space,” said Koller.
On the experiment side, it has proven that solar cell experimentation on nanosatellite platforms with “high mass, size and power constraints are capable of delivering adequate solar cell characterization results that stand up to the sophisticated and bulky space solar simulators on Earth,” according to Koller.
“If both results match well, it means that both approaches are adequate to test new solar technologies for space applications,” he said.
For the experimental setup, the researchers examined earlier solar cell space experiments, deciding to use of electronic load circuit and radiation-sensitive field-effect transistor (RadFET) due to power, mass, and size constraints, despite challenges that “can introduce artefacts in IV-curves,” if not mitigated.
The load circuit was based on a proportional-integral (PI) controller at the gate of a low-transconductance SI3460BDV n-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and current feedback loop, combined with digital point filtering that enhanced the point distribution on the IV-curves.
The team noted that the 4G32 was a preliminary design of a quadruple-junction solar cell with efficiencies of 32% and open-circuit voltages of 3.45 V while 3G30 has a 30% efficiency.
The standard versions of these multijunction cells have flown on many spacecraft to date, according to Koller. As the measurements were gathered, the SCE data was corrected for solar irradiation fluctuation, sun error angle, and temperature. The orbital results were compared with ground-based results.
The researchers found that the “fully corrected in-orbit results” for open-circuit voltage, short-circuit current density and maximum power point (MPP) “show near-perfect voltage and strong current agreement within 0.5% compared to Azur Space’s ground measurement data.”
Further investigations into potential cell degradation are underway, including plans for a follow-on experiment on another satellite destined for medium earth orbit. The group plans to also test a University of Stuttgart team’s prototype perovskite solar cell technology.
It should be noted that the original plan to gather data from the EIVE satellite for as long as possible will be cut short, according to Koller, as the satellite is due to re-enter the Earth’s atmosphere sometime in late March 2025. High solar activity in 2024, the so-called solar maximum, resulted in more atmospheric drag on all satellites in LEO.
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