Silicon solar cells, the workhorse of the terrestrial PV industry, are heading for orbit. Source Energy, a US start-up, and Germany's Fraunhofer Institute for Solar Energy Systems ISE have jointly developed a new line of silicon-based PV modules and wings for satellites, aiming to undercut the III-V semiconductor technology that has dominated space power generation for decades.
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III-V cells are highly efficient and radiation-hardened, which is why they remain the standard in orbit. But they are also expensive and supply-constrained, a combination that increasingly pinches commercial missions, particularly the growing fleets of satellites in low Earth orbit. "Together with Source Energy, we have developed silicon-based solar modules for space applications, similar to those already used successfully and cost-effectively on Earth," says Dr Achim Kraft, who heads PV module technology at Fraunhofer ISE.
The resulting modules are small and light: 64 grams, with an area of 629 square centimetres. Prototypes averaged 15.6 W, with the best-performing units reaching 16.1 W at an average efficiency of 18.8 percent (AM0, 25°C), giving a specific power of 252 W/kg that holds its own against other silicon modules in its class.
Built like brickwork
The key to making silicon work in space lies in how the cells are wired together. Source Energy and Fraunhofer ISE use shingled-matrix interconnection, cutting cells into strips and arranging them in overlapping rows, offset like courses of brick, bonded with an electrically conductive adhesive. An industrial stringer for the process, built by German equipment maker M10 Solar Equipment, moved from prototyping at Fraunhofer ISE's Module-TEC facility in Freiburg into Source Energy's own production line in Colorado in June.
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"As the heart of production, it lets us manufacture PV modules for under five dollars per watt," says Bryan Mazor, Source Energy's CTO. "The automated process doesn't just make us cheaper. It makes us significantly faster than current III-V space PV products." The company says it can now deliver modules within six months of order, a notable claim in an industry where III-V lead times routinely stretch far longer.
Why shingled-matrix suits space
Three properties make the shingled-matrix approach particularly suited to orbit, according to Fraunhofer project lead Najwa Abdel Latif: resilience to localised damage from micrometeorite or debris impacts, since current simply routes around a damaged cell rather than losing the whole string; flexible layouts that can be tuned to a satellite's voltage and current needs; and tolerance of the extreme temperature swings spacecraft endure. The interconnection method is also compatible with front- and back-contact wafer cells such as PERC or silicon heterojunction without retooling the line, and its low-temperature bonding process leaves the door open to silicon-perovskite tandem cells as that technology matures.
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The design is holding up under qualification testing. After seven years in orbit, the modules are expected to retain 76 percent of their original power output, clearing the industry's 25 percent degradation threshold with room to spare. The result suggests the cost curves reshaping terrestrial solar, cheap silicon, automated stringing, established supply chains, can work in space too. It remains to be seen how fast the rest of the industry catches up on price. (TF)
