The most dramatic new advances and visions have no name initially. So it is with electric vehicles that need no external charging or refuelling - no, not even wireless charging. "Energy autonomous vehicles" or "energy independent vehicles"? The acronym EIV has been coined and although that may seem to embrace everything from rowing boats to sailing boats, gliders and bicycles it is intended to mean just the electric-powered electricity-independent ones.
EIVs make their own electricity as needed, using rapidly renewable clean, free-of-charge sources. No diesel gensets or even fuel cells burning biofuels: this is primarily about on-board equipment converting wind, waves, tide and sun into motive electricity as needed.
On the one hand, it about making the vehicle much more efficient by lightweighting and streamlining, including use of structural electronics such as bodywork doubling as a supercapacitor. Add energy harvesting such as regenerative braking, 3D movement capture and other electricity generation internally. On the other hand, it calls for better creation of electricity from ambient energy outside by increasing conversion efficiency and number of types of ambient energy captured. All that needs to be affordable of course.
Although Google destinations with the EAV or EIV terminology are, as yet, pitiful in number, attention is building rapidly. There is an on-line debate about creating standards, not least to define what qualifies. For example, the solar racers crossing Australia on sunshine alone do start with a full battery charge under the rules.
Other debates concern how best to make such vehicles using the latest inventions. For example, researchers from Case Western Reserve University wired four perovskite solar cells in series to directly photo-charge lithium batteries with 7.8% efficiency, which they believe to be the most-efficient potentially-flexible technology reported to date. Flexible can mean conformal to give larger area over a vehicle and therefore more power.
"We found the right match between the solar cell and battery... Others have used polymer solar cells to charge lithium batteries, but not with this efficiency," said Liming Dai, the leader of the research team, adding that the coupling appears to have outperformed all other reported pairings of photo-charging components and compatible batteries or supercapacitors.
Perovskite has been one of the most promising solar cell technologies to emerge recently. It converts a broader spectrum of sunlight to electricity when compared to silicon-based cells and rapid advances have pushed efficiency up to 20% in certain forms. The crystalline material has a structure identical to the mineral of the same name. Its potential for quick payback in terms of energy savings over traditional power sources have made it one of the fastest growing research sectors in the solar power field, some research groups having abandoned organics to concentrate on perovskites alone. Some versions emit light at night, functioning like a flexible OLED light. The new IDTechEx report, The Rise of Perovskite Solar Cells 2015-2025 gives a full analysis and forecasts. It concludes that there is work to be done before they hit the big time. There are issues of toxic lead and lifetime for instance.
Dai's laboratory created cells with three layers converted into a single perovskite film and then wired four of the one millimeter square cells in series, achieving a solar-to-electric power conversion efficiency of 12.65%. When charging small coin-sized lithium-ion batteries, the team achieved a conversion and storage efficiency of 7.8% and maintained it over a number of cycles. The research was published in the most recent issue of Nature Communications.
"We envision, in the not too distant future, this is a system that you could have at home to refuel your car and, eventually, because perovskite solar cells can be made as a flexible film, they would be on the car itself," said contributing author Jiantie Xu.
This would seem to make the technology a perfect fit for cars with a more traditional look than the Immortus solar sports car concept, with every available sky-facing surface covered totalling seven square meters (75 sq ft). In single crystal silicon that might donate up to one kilowatt to an EIV on a good day. See the new IDTechEx report, Energy Independent Electric Vehicles 2016-2026 for more.
