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44 Focus | Solar cells As mentioned, bypass diodes are one way to get around these problems, and some panels will incorporate a bypass diode for every six-to-10 cells, although increasing the count will increase the design and manufacturing costs. Alternatively, ‘multi-busbar’ architectures are increasingly being applied to solar modules. The result might be modules with eight to 12 busbars spread across the PV cells (rather than being limited to two) for greater redundancy and potentially lower resistivity losses depending on the cell structure. Long-term survivability of modules against micro-cracks is also enhanced, because fewer hotspots will result from any cracks and the busbars act to strengthen the comparatively fragile cell material. That reduces the chances of micro-cracks occurring in the first place, and also decelerates the rate at which they grow, which tends to occur owing to repeated thermal expansion and contraction. Also, the interconnection wirings – typically soldered ribbons of copper or silver – between cells and strings typically cause ohmic and optical losses as well as increasing the manufacturing costs. By replacing a lot of the wiring with busbars though, these associated issues can be substantially reduced. There are many other interconnection solutions to improve the efficiencies of solar modules. For example, tiling ribbons – which have a circular cross-section rather than the more conventional rectangular interconnect cross-sections – cover up less solar cell area than standard ribbons and reflect some angular sunlight into the cells, contributing to higher energy capture. Some companies also provide specialised coatings for PV interconnects to enhance internal reflections and hence achieve similar results to the tiling ribbons. Other solutions propose entirely new approaches to cell interconnection: for example, ‘shingle’ interconnections increase the packing densities and active areas of solar cells by eliminating busbars in the illuminated zones, and practically eliminate the ohmic losses associated with conventional wiring. Conclusion The expansion of solar’s production and demand, as well as its consolidation around silicon and multi-junction cells, has spawned many valuable architectural advances. That said, solar technologies are far from mature, and regular increases in conversion efficiency and specific power are still expected. If architectural trends continue, however, solar will become a game-changer for unmanned vehicles. Acknowledgements The author would like to thank Ray Chan at MicroLink Devices, Luca Bonci at Solbian Energie Alternative, Brad Clevenger at SolAero Technologies, Desmond Wheatley at Envision Solar, Neil Spann at Power Roll and Oliver Gochermann at Gochermann Solar Technology for their help with researching this article. October/November 2020 | Unmanned Systems Technology FRANCE Armor SAS +33 285 529 383 www.asca.com GERMANY Gochermann Solar Technology +49 410 390 4488 www.gochermann.com ITALY Solbian +39 011 966 3512 www.solbian.eu LITHUANIA Metsolar +370 650 69905 www.metsolar.eu UK Power Roll +44 191 543 9254 www.powerroll.solar Oxford PV +44 1865 951500 www.oxfordpv.com USA Ascent Solar Technologies +1 720 872 5000 www.ascentsolar.com Envision Solar +1 858 799 4583 www.envisionsolar.com MiaSole +1 408 940 9658 www.miasole.com MicroLink Devices +1 847 588 3001 www.mldevices.com Osazda Energy +1 505 218 7228 www.osazda.com SolAero Technologies +1 505 332 5000 www.solaerotech.com SunPower +1 800 786 7693 www.sunpower.com Examples of solar power-related suppliers