Chip Yates Awarded Louis Bleriot Medal by FAI

Chip Yates, founder and head of the Flight of the Century, has been honored by the Federation Aeronautique International for records set in 2013.  Chip’s web site announced the honor last week.

“Record-setting entrepreneur and pioneer Chip Yates will be honored on October 16 by the World Air Sports Federation (Federation Aeronautique Internationale) for changing the course of aviation history.

“Yates has been selected to receive the FAI’s Louis Bleriot Medal for his record-setting flights in 2013, which established new international landmarks in speed, altitude and distance for electric flight.

Chip Yates Setting records in 2013 in Long-ESA which Wired Magazine said "stomps Cessnas"

Chip Yates Setting records in 2013 in Long-ESA which Wired Magazine said “stomps Cessnas”

“The award will be presented at the Opening Ceremony of the FAI General Conference in Pattaya, Thailand, where Yates will become part of the distinguished list of honorees since 1936 who have made outstanding contributions to aeronautics and astronautics. Prior honorees include the inspirational Dick Rutan and other aviation greats from the US, Switzerland, Austria, Canada, Italy, Finland, Australia, the UK and elsewhere.

“Yates paid tribute to those who have worked with him to push electric aviation to the forefront. ‘This is thanks to your efforts to turn a far-fetched dream into reality,’ he said. ‘And we’ve only just begun!’”

The FAI web site explains the Medal was established in 1936 in memory of Louis Bleriot, first to fly the English Channel and former Vice-President of the FAI.  Although “three Medals may be awarded each year to the respective holders of the highest records for speed, altitude and distance in a straight line established in the previous year by light aircraft of the first three sub-classes, as defined in Section 2 of the Sporting Code,” such records are not easily attained.  Chip is the first winner in four years, for his record in his Long-ESA (Electric Speed and Altitude) in the C-1b Group VI class: Electric Land Airplanes weighing 1,102-2,205 pounds.   His flights last year between September and November included this noteworthy record, ratified earlier this year by the FAI.

Altitude: 4,481meters (14,697 feet) World Record on a C Aeroplane (c-1b Landplanes: take-off weight 500 to 1000 kg) on 10.07.2014: Altitude in (sustained) horizontal flight: 4,439 meters (14,559.9 feet).  Interestingly, the FAI does not mention the fact that his airplane was powered by electricity, noteworthy because the record beat those of previous fossil-fuel powered aircraft.


ORNL Makes It Two for Two

Oak Ridge National Laboratory has announced that their researchers have built and demonstrated a high-voltage (5 V) lithium, solid-state battery with a usable life of more than 10,000 cycles, at the end which test the battery retains more that 90-percent of its original capacity.  That makes two such claims in a week, with ORNL’s battery comparable to that developed by Nanyang Technology University (NTU) and reported on in this blog last week.

ORNL solid state battery shows high Coulombic efficiency, high capacity retention after 10,000 cycles

ORNL solid state battery shows high Coulombic efficiency, high capacity retention after 10,000 cycles

ORNL points out that, “For a given size of battery, the energy stored in a battery is proportional to its voltage. Conventional lithium-ion batteries use organic liquid electrolytes that have a maximum operating voltage of 4.3 V. Operating a battery above this limit causes short cycle life and serious safety concerns.”

“In this latest study, the Oak Ridge team replaced the conventional liquid electrolyte with a ceramic solid electrolyte of lithium phosphorus oxynitride (Lipon), and used a LiNi0.5Mn1.5O4 cathode and Li anode at a charge voltage to 5.1V.”

The abstract for Juchuan Li, Cheng Ma, Miaofang Chi, Chengdu Liang, and Nancy J. Dudney’s paper, “Solid electrolyte: the key for high-voltage lithium batteries,” in Advanced Energy Materials shows that the team used an entirely different chemistry from NTU’s titanium oxide-based design.

Voltage profiles of the (a) LiNi0.5Mn1.5O4 solid-state lithium battery and (b) a LiNi0.5Mn1.5O4 liquid battery discharged at different rates. The battery was charged at C/10 before each discharge measurement. Li et al.Click to enlarge.

Voltage profiles of the (a) LiNi0.5Mn1.5O4 solid-state lithium battery

Voltage profiles of the (a) LiNi0.5Mn1.5O4 solid-state lithium battery and (b) a LiNi0.5Mn1.5O4 liquid battery discharged at different rates. The battery was charged at C/10 before each discharge measurement. Li et al.Click to enlarge.

(b) a LiNi0.5Mn1.5O4 liquid battery discharged at different rates. The battery was charged at C/10 before each discharge measurement

This work demonstrates that replacing the conventional liquid electrolyte with a ceramic solid electrolyte of lithium phosphorus oxynitride (Lipon) eliminates the limit of conventional lithium-ion batteries. A model battery of LiNi0.5Mn1.5O4/Lipon/Li has been operated over 10,000 cycles at a charge voltage to 5.1V.  The solid state battery retains more than 90% of its original capacity after 10,000 cycles. Such a battery has a cycling lifetime of more than 27 years with a daily charge/discharge cycle, exceeding the lifetime of most devices and even vehicles. This work infuses new life into the existing chemistry of high-voltage lithium batteries.  

Here, readers can see the first page of the group’s report (with the following five pages coyly shaded to enforce payment of standard fees journals charge for enhancing your knowledge).  Seeing more costs extra, the scientific equivalent of a peep show.

Along with NTU’s work, Sakti3 and Toyota have recently released information on solid-state batteries that show great promise for higher energy density, greater safety and longer lives for batteries.


Audi Drives Hockenheim with “Bobby”

“Bobby” is Audi’s computerized “driver” for their RS 7, which they demonstrated before thousands of spectators in the grandstands at the 4.574 kilometer (2.842 mile) Hockenheim race track in Baden-Wurttemberg, Germany on October 19.

The video, despite the somewhat sometimes annoying narration, gives a good impression of the run, showing the acceleration, braking and cornering through all 17 turns from both inside and outside the car.  The inside views belie the speed the car attains, looking a bit unearthly by the precise, smooth lines the car takes, the envy of any “real” race car driver.

Green Car Congress reports, “The Audi RS 7 piloted driving concept car drove a clean racing line at the Hockenheimring—full throttle on the straights, full braking before the corners, precise turn-in and perfectly metered acceleration when exiting the corners. Forces of over 1.3 g occur during braking, and lateral acceleration in the corners can reach 1.1 g. Tests on the track in Hockenheim suggested an expected top speed of 240 km/h (149.1 mph) and a lap time of 2 minutes and 10 seconds.”  The track record, by the way, was 1:13.780 set by F1 driver Kimi Räikkönen,in a McLaren in 2004.

Audi, of course, could not but help be proud of their accomplishment.  Professor Doctor Ulrich Hackenberg, a Technical Development Board member at Audi AG, said, “The top performance by the Audi RS 7 today substantiates the skills of our development team with regard to piloted driving at Audi. The derivations from series production, particularly in terms of precision and performance, are of great value for our further development steps.”

Dazzling array of sensors, all hidden in bodywork, enable RS 7 to attain race-car speeds - driverless

Dazzling array of sensors, all hidden in bodywork, enable RS 7 to attain race-car speeds – driverless

Unlike Google’s Priuses and Lexuses plying the roads in the Bay Area and their bubble cars scooting around their Mountain View campus, Audi’s driverless car retains its smooth lines and hides all its sensors within its bodywork.   The number of devices on the RS 7, including a differential GPS and 3D camera system front and rear, front, rear and top view cameras, infrared camera, front and rear radar sensors, front, rear and side crash sensors, and ultrasonic sensors, are a bit overwhelming, but allow the car to sense its position on the track within 1 centimeter.  That’s probably responsible for the crowd-pleasing parking job at the run’s finish.

According to Green Car Congress, “Experts from Volkswagen Group Research, the Electronics Research Laboratory (ERL) and Stanford University (both in California) are supporting Audi as partners in the further development of piloted systems.”  Doubtless, the group will continue to refine the technology and produce more practical applications for non-competition drivers.


We’ve witnessed several attempts to produce an “artificial leaf,” a device emulating the photosynthesis of plants, but providing hydrogen and oxygen that could power fuel cells in electric vehicles instead of plant sugars to make trees and flowers grow.  One of the biggest problems so far has been the rare and costly materials necessary to generate hydrogen.

Ècole Polytechnique Fédéral de Lausanne (EPFL) scientists has come up with a low-cost alternative, using abundant materials called perovskites and budget electrodes to produce hydrogen from water with a 12.3 percent conversion efficiency – a record for fairly common materials.

Perovskites are a calcium titanium oxide mineral that come in a variety of colors and can be bog-common or extremely rare, approaching rare earth mineral status.  The CaTiO3 used by Michael Grätzel is of the common variety, but that doesn’t seem to detract from its performance as a hydrogen-production agent.

That, and the inexpensive materials used in the device’s electrodes cause Jingshan Luo, a post-graduate student on the project, to note,” “Both the perovskite used in the cells and the nickel and iron catalysts making up the electrodes require resources that are abundant on Earth and that are also cheap, However, our electrodes work just as well as the expensive platinum-based models customarily used.”

The work, done at the Laboratory of Photonics and Interfaces at EPFL, is led by Grätzel, who directs the Laboratory of Photonics and Interfaces at the Polytechnique.  According to his university biography, “He pioneered the use of mesoscopic materials in energy conversion systems, in particular photovoltaic cells, lithium ion batteries and photo-electrochemical devices for the splitting of water into hydrogen and oxygen by sunlight. He discovered a new type of solar cell based on dye sensitized nanocrystalline oxide films. Mass production has started in October 2009. Author of over 1,000 publications, two books and inventor of more than 50 patents, his work has been cited over 134,000 times (h-index 167) making him one of the 10 most highly cited chemists in the world.”  He’s also won awards that take up a very long paragraph in his bio.

Pulling on past experience, Grätzel and his team have created a solar converter with “spectacular” performance.  It could generate electricity directly, but that would limit its energy use to simultaneous delivery and keep that energy from being used at night.  Grätzel and his researchers chose to store the hydrogen generated by their device.

Profusion of bubbles show perovskites actively making hydrogen and oxygen in water exposed to sunlight.  Photo: EPFL

Profusion of bubbles show perovskites actively making hydrogen and oxygen in water exposed to sunlight. Photo: EPFL

One indicator of the converter’s performance is the fact that it uses only two cells to generate hydrogen.  Jingshan Luo explains, “A voltage of 1.7 V or more is required for water electrolysis to occur and to obtain exploitable gases.  This is the first time we have been able to get hydrogen through electrolysis with only two cells!”  Usually, three or more 0.7 V silicon cells are needed, whereas just two 1.0 V perovskite cells are enough, showing a big bump in efficiency for the more common material.

Grätzel explains, “Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it,”  burning it in a boiler or engine, or using it in a fuel cell to generate electricity when desired.  Either way, the combustion releases only water vapor.

Michael Grätzel and his research team of Jingshan Luo, Jeong-Hyeok Im, Matthew T. Mayer, Marcel Schreier, Mohammad Khaja Nazeeruddin, Nam-Gyu Park, S. David Tilley, and Hong Jin Fan, published their paper, “Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts,” in the September 26 issue of the journal, Science.

The profusion of tiny bubbles escaping from the electrodes as soon as the solar cells are exposed to light say it better than words ever could: the combination of sun and water paves a promising and effervescent way for developing the energy of the future.  Since most such discoveries have applications for solar cells, hydrogen generation, and possibly batteries, we anxiously await the team’s even more efficient perovskite breakthrough.


Reduced weight and component volumes are important for both cars and aircraft, allowing lighter overall construction and greater flexibility in fitting those components into compact spaces.  The U. S. Department of Energy has set 2020 targets for things like batteries and power inverters – the device that turns direct current from batteries into alternating current to run electric motors. 

Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL)used 3D printing and “novel silicon carbide (SiC) wide band gap (WBG) semiconductors to craft a prototype power inverter for electric vehicles that is lighter and can handle more power than current units.  It nearly meets the DOE’s power density and specific power targets and exceeds the efficiency target handily.


DOE 2020 target

ORNL prototype

Power density

13.4 kW/L

13.33 kW/L

Specific Power

14.1 kW/kg

11.5 kW/kg


>94% Power


 DOE has put 1.45 million into integrating WGB technology, novel circuit architectures and advanced packaging into electric drive systems.  They hope to “reduce cost, improve efficiency, and increase power density.”

50-percent 3D printed now, ORNL's smaller, lighter power inverter will eventually be a product of 100-percent additive manufacturing

50-percent 3D printed now, ORNL’s smaller, lighter power inverter will eventually be a product of 100-percent additive manufacturing

Heading this effort, ORNL’s Madhu Chinthavali led the Power Electronics and Electric Machinery Group on this project.  His ongoing efforts can be reviewed in this PowerPoint presentation.

Besides providing greater efficiency over a wide range of temperatures than conventional circuitry, wide bandgap technology enables devices to perform more efficiently, possess higher inherent reliability, and operate at higher frequencies.

Additive manufacturing helped researchers explore complex geometries, increase power densities, and reduce weight and waste while building ORNL’s 30 kW prototype inverter.

ORNL’s design and its advantages were augmented by the use of additive manufacturing (3D printing) to produce the actual hardware.  According to Chinthavali, “With additive manufacturing, complexity is basically free, so any shape or grouping of shapes can be imagined and modeled for performance. We’re very excited about where we see this research headed.”

The ORNL reports that, “Using additive manufacturing, researchers optimized the inverter’s heat sink, allowing for better heat transfer throughout the unit. This construction technique allowed them to place lower-temperature components close to the high-temperature devices, further reducing the electrical losses and reducing the volume and mass of the package.

“Another key to the success is a design that incorporates several small capacitors connected in parallel to ensure better cooling and lower cost compared to fewer, larger and more expensive ‘brick type’ capacitors.”  3D printing also enables rapid changes within one production run, enabling improvements to be incorporated in the next prototype as quickly as computer drawings can be downloaded to the computer.

The prototype 30-kilowatt inverter is liquid-cooled and features 50 percent printed parts.  Future efforts will have up to 3D printing and strive for even lighter, more compact structures – half the size of currently available commercial vehicle units.  Chinthavali projects an inverter with four times the power density of their prototype.

Others involved in this work include Curt Ayers, Steven Campbell, Randy Wiles and Burak Ozpineci.

Research for this project was conducted at ORNL’s National Transportation Research Center and Manufacturing Demonstration Facility, DOE user facilities, with funding from DOE’s Office of Energy Efficiency and Renewable Energy.


Five Years, 685 Entries, Great Readers

Today marks the completion of your editor’s fifth year collecting and reporting on progress that will make electric aircraft and green flight a reality.  It is only possible with the well informed, highly intelligent and unbelievably kind readers who respond to these efforts.

Thank you for your continued readership and excellent critiques of fact and opinion.  Let’s make the future of our dreams happen.


Singapore is only 276.5 square miles, about 27 miles long, and has five and a half million people, according to Wikipedia.  It’s an enormously productive country with an excellent education program from kindergarten on up to graduate schools.  Recently, one of those graduate programs announced an “ultra-fast charging batter[y] that can be recharged up to 70 per cent in only two minutes.”

NTU-associate professor Chen-Xiaodong with research fellow Tang Yuxin-and-pHd student Deng Jiyang

NTU associate professor Chen-Xiaodong with research fellow Tang Yuxin-and-PhD student Deng Jiyang.  Photo: NTU

This breakthrough from Nanyang Technology University (NTU) is also claimed to have a 20-year lifespan, 10 times that of existing lithium-ion cells.

Part of the new battery’s success comes from replacement of the traditional graphite anode with a new gel materal made from titanium dioxide, “an abundant, cheap and safe material found in soil. It is commonly used as a food additive or in sunscreen lotions to absorb harmful ultraviolet rays.”  Although naturally found in spherical shape, titanium dioxide was rolled into nanotubes thousands of times thinner than the diameter of a human hair by the NTU researchers. The nano sizing enables speeding up the battery’s charging.  The gel, created by Associate Professor Chen Xiaodong from NTU’s School of Materials Science and Engineering, is described in the latest issue of Advanced Materials.

The new cross-linked titanium dioxide nanotube-based electrodes eliminate the need for additives normally used in lithium-ion batteries and can pack more energy into the same amount of space.  It’s also easy to manufacture, with titanium dioxide and sodium hydroxide “mixed together and stirred under a certain temperature so battery manufacturers will find it easy to integrate the new gel into their current production processes.”

Researchers are reticent about giving hard numbers for energy density, but suggest that the batteries will be smaller than current li-ion cells for the same amount of storage.

Prof Chen and his team will apply for a Proof-of-Concept grant to build a large-scale battery prototype. With the help of NTUitive, a wholly-owned subsidiary of NTU set up to support NTU start-ups, the patented technology has already attracted interest from the industry.  This seems to be on a fast track, with marketing expected in the next two years.

The University reports Professor Chen as saying, “Electric cars will be able to increase their range dramatically, with just five minutes of charging, which is on par with the time needed to pump petrol for current cars.”

“Equally important, we can now drastically cut down the toxic waste generated by disposed batteries, since our batteries last ten times longer than the current generation of lithium-ion batteries.”  This would lead to savings of at least one $5,000 or more battery change in the life of an EV.

The University has more than one reason to be proud.  “NTU professor Rachid Yazami, the co-inventor of the lithium-graphite anode 30 years ago that is used in today’s lithium-ion batteries, said Prof Chen’s invention is the next big leap in battery technology.”

“’While the cost of lithium-ion batteries has been significantly reduced and its performance improved since Sony commercialized it in 1991, the market is fast expanding towards new applications in electric mobility and energy storage,’ said Prof Yazami, who is not involved in Prof Chen’s research project.”


Speedy – and No Range Anxiety

Breaking a record that stood for 26 years, a team of University of New South Wales engineering students have gained FIA recognition for their 500 kilometer (310 mile) drive at an average speed of 106.966 kilometers per hour (66.32 mph) in their solar-powered Sunswift automobile.

The Fédération Internationale de l’Automobile (FIA), world motorsport’s governing body, ratified the record for the run set by the team in July.  The old record was 73 km/hr. (45.26 mph), making the new record a decisive advancement in electric vehicle technology.

The new record is particularly impressive because it’s set by students, more than 100 of whom contributed to the project over the last two years.  Students are now working on their fifth car, eVe, to be built and raced since the team was founded in 1996.  The University’s press release noted, “’It’s not often you can confidently say you made history before you even graduated,’ Sunswift’s project director and third-year engineering student Hayden Smith said.”

The Sunswift web site lists the following specifications for the car:

  • Exterior: TeXtreme Carbon fibre constructed by Core Builders.
  • Solar Panels: C60 Sunpower silicon solar cells. High efficiency (22.7%) and lightweight.
  • Encapsulation: Solbian high performance encapsulation (polymer protection for the solar cells).
  • Motor: 2 Maran in-hub motors developed by the CSIRO. Low power high efficiency by electric car standards.
  • Battery: Panasonic NCR 18650 A and B.
  • Suspension: Front Bilstein Ohlins. Rear TTX25 spring damper.
  • Wheels: Front: GH Craft carbon front wheels. Rear: 7075 Aluminum wheels.
  • Tires: Michelin Radial X tires specifically designed for solar cars.

Note that none of this is extreme technology.  University and student budgets probably contributed to the “off-the-shelf” nature of the package, generously supplemented by sponsors.

Capable of 140 km/hr. (86.8 mph) and 800 kilometer (496 miles) range, the Sunswift eVe two-seater is now being tailored for on-road driving, showing that it and a four-seat development can be practical road vehicles.  The team extols the virtues of having solar power and batteries as backup.  eVe can drive at night on battery power, or extend its range beyond anxiety because of its solar cells.  It will be fascinating to see if this practicality can find its way into production someday soon.


100 Percent Efficiency? Great! and So What?

A particularly brilliant and demanding manager for whom your editor used to work had a “SO WHAT?” stamp with which he would critique our technical papers and proposals.  His point in defacing our papers was not to be snide, but to force us to defend why we included certain facts – interesting though they may be in themselves.

Two different and equally brilliant discoveries by University of Cambridge and University of California, Riverside researchers bring the “so what?” stamp to mind.  Even with their breakthroughs, approaching 100-percent efficient solar cells in the first instance, solar cells may not yet be a perfect fit for aircraft propulsion.

Each square foot of the earth’s surface receives about 15 Watts of solar energy during a bright day.  100 square feet of solar cells (about what we could expect for an average-size wing on an average light plane) would see 1.5 kilowatts hitting that surface – not enough to sustain flight on anything but a very light, low-powered machine like a human-powered airplane.

Because most current solar cells, especially organic ones, don’t get much better than 25-percent efficiency, that reduces the actual charge reaching the plane’s batteries to 375 Watts.  That will certainly help recharge the batteries while the airplane is parked, and help extend the range even though only fitfully.

How do people like Eric Raymond and the Solar Impulse engineers make this disparity work?  First, they make airplanes that are very light, have large wing areas, and are thus slow by comparison with most cross-country cruisers.  They also carry batteries to help them generate extra power for takeoff and use only about one-tenth of their takeoff power to cruise.  This allows the sun to help the batteries catch up with the power demand.  Eric has the added advantage of being able to soar his aircraft, using no power while things recharge. On the ground, the solar cells bring the batteries up to full charge for the next takeoff.  Both planes can thus make the truthful statement that they are totally self-sufficient in their solar operations.

Singlets or Triplets?

“[Cambridge] researchers have developed a new method for harvesting the energy carried by particles known as “dark” spin-triplet excitons with close to 100-percent efficiency, clearing the way for hybrid solar cells which could far surpass current efficiency limits,” according to research news from the University.

Photons absorbed by a conventional silicon solar cell cause the formation of one free electron that can be extracted as current.  Researchers explain that this is similar to what happens in photosynthesis.  One photon hits the pigment of a leaf, for instance, and generates an exciton that carries the associated energy through the plant.  Solar cells do a bit of biomimicry to emulate this stimulus-response action in plants. explains an exciton is “a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and in some liquids. The exciton is regarded as an elementary excitation of condensed matter that can transport energy without transporting net electric charge.”  This explanation, without the desire to do further research in subatomic or quantum physics, is probably next to useless.  You may now pull out your own “So What?” stamps.

When light is absorbed in pentacene, the generated singlet excitons rapidly undergo fission into pairs of triplets that can be efficiently transfered onto inorganic nanocrystals. Credit: Maxim Tabachnyk

When light is absorbed in pentacene, the generated singlet excitons rapidly undergo fission into pairs of triplets that can be efficiently transfered onto inorganic nanocrystals.
Credit: Maxim Tabachnyk

To transport more energy, the Cambridge researchers added pentacene, “a type of organic semiconductor,” in which absorption of a photon forms two electrons.  Because the pair is bound in “dark” triplet exciton states, the electrons are not free.  Cambridge reports, “’The key to making a better solar cell is to be able to extract the electrons from these dark triplet excitons,’ said Maxim Tabachnyk of the University’s Cavendish Laboratory, the paper’s lead author. ‘If we can combine materials like pentacene with conventional semiconductors like silicon, it would allow us to break through the fundamental ceiling on the efficiency of solar cells.’”

Researchers further explain, “Excitons come in two ‘flavors’: spin-singlet and spin-triplet. Spin-singlet excitons are ‘bright’ and their energy is relatively straightforward to harvest in solar cells. Triplet-spin excitons, in contrast, are ‘dark’, and the way in which the electrons spin makes it difficult to harvest the energy they carry.”

Combining organic and inorganic semiconductors and spin-singlet and –triplet excitons has made it possible to unleash the energy from both, with heightened efficiency.  The team used state-of-the-art femtosecond laser spectroscopy to see that triplet excitons could be transferred directly into inorganic semiconductors, from which their electrons could be easily extracted.

“’Combining the advantages of organic semiconductors, which are low cost and easily processable, with highly efficient inorganic semiconductors, could enable us to further push the efficiency of inorganic solar cells, like those made of silicon,’ said Dr. Akshay Rao, who lead the team behind the work.”  Their work can be found in Nature Materials in their October 5 online edition.

Further work by the research team will focus on other organic/inorganic systems and creating an inexpensive organic coating that could increase silicon solar cells’ efficiency.  This initiative is backed by the UK Engineering and Physical Sciences Research Council (EPSRC) and the Winton Programme for the Physics of Sustainability.

Double Your Singlets in Riverside

Not to be outdone, U of C chemists published a perspective article in the Journal of Physical Chemistry Letters, and had it selected as an Editors’ Choice, “an honor only a handful of research papers receive,” the school states.  The Perspective reviews the U of C research on making a two-for-one conversion (shown as 1->2 in the paper), that could boost solar cell efficiency by as much as 30 percent.  The research could also lead to “more energy-efficient lighting and photodetectors with 200-percent efficiency that can be used for night vision.” 

Singlet fission is a process in which a single photon generates a pair of excited states. This 1->2 conversion process has the potential to boost solar cell efficiency by as much as 30 percent. Image Credit: Bardeen Lab, UC Riverside

Singlet fission is a process in which a single photon generates a pair of excited states. This 1->2 conversion process has the potential to boost solar cell efficiency by as much as 30 percent.
Image Credit: Bardeen Lab, UC Riverside

Current solar cells are limted by the Shockley-Queisser Limit,” around 32-percent efficiency brought about by the reaction to one photon generating one exciton.  Future cells will need to do better while remaining inexpensive.

Christopher Bardeen, head of the Bardeen Laboratory in the Department of Chemistry at Riverside explains that “excitons come in two ‘flavors,’ defined by the electron spins in them.  One flavor is singlet, where all spins are paired.  The other flavor is triplet, where two electrons are unpaired.  In organic semiconductors, these two types of excitons have different energies.”

“’If a triplet exciton has half the energy of a singlet, then it is possible for one singlet exciton, generated by one photon, to split into two triplet excitons. Thus, you could have a 200 percent yield of excitons — and hopefully, electrons — per absorbed photon.’”  Part of the magic is to extract two excitons from a high energy exciton rather than waste the energy as heat.  This spontaneous splitting of a single exciton into two triplets requires further investigation.

Bardeen notes that MIT has demonstrated an organic photovoltaic cell with more than 100 percent external quantum efficiency based on this effect.  He thinks, “It may be possible to integrate this effect with inorganic semiconductors and use it to raise their efficiencies.”

The research was supported by a grant to Bardeen from the National Science Foundation. He was joined in the research by Geoffrey B. Piland, Jonathan J. Burdett and Robert J. Dillon at UC Riverside.

A Final So What?

With at least three major academic institutions pursuing a similar line of research, these advances could become ever more important as researchers dodge around the limits of the  Shockley-Queisser Limit, and possibly the idea of what 100-percent efficiency means today.  This will lead to smaller, lighter solar cells with higher efficiency.  This will allow designers to make smaller, lighter, solar-powered craft, and we may someday see practical machines we can all fly, kept aloft with the power of the sun alone.


A New British Club for HPAs

For the last six decades, the Royal Aeronautical Society (RAeS) has overseen records keeping for human powered aircraft (HPAs). 

They report, “The Man Powered Aircraft Group of the Royal Aeronautical Society originated in 1959 when the members of the Man Powered Group of the College of Aeronautics at Cranfield were invited to become a group of the Society. Its title was changed from ‘Man’ to ‘Human’ in 1988 in recognition of the many successful flights by woman pilots.”

Bryan Allen perilously close to English Channel waters as he pedals toward France, July 17, 1979

Bryan Allen perilously close to English Channel waters as he pedals toward France, July 17, 1979

Mr. Henry Kremer turned the wistful dreams of many to serious competition by donating over 275,000 pounds sterling ($440,000 at today’s exchange rates) in prize money for achievements such as flying a figure eight around to markers a half-mile apart and starting and finishing 10 feet above the ground – won by Paul MacCready, the airplane’s designer and Brian Allen, the pilot.  The won their 50,000 pound prize on August 23, 1977, and scored a second win on June 12, 1979 by flying the Gossamer Albatross 22 miles across the English Channel.

The RAeS hopes to promote human-powered flight as “a Practical Sport For designers these machines offer a most exciting challenge.”   The group notes that “ultra lightweight materials have revolutionized techniques of construction, producing aircraft with a wingspan of around 25 meters (82 feet), and an all up weight of little over 30 kilograms (66 pounds).”

Earlier machines were built of spruce, balsa, and filmy fabrics, and were able to fly in only utterly still conditions because of their fragility.  But the RAeS believe that we have reached a transitional stage, with the next stage leading to “more practical aircraft, which can be built by a group of enthusiasts and flown as a sport.”  Although the slow flight and long wingspans require a refined and special type of piloting skill, “it has become less necessary for the pilot to be a highly trained athlete. Anyone is a potential HPA pilot. One of the ultimate aims of the Group is to promote human powered flight as an Olympic sport.”

Recently, Fred To, Dr. Bill Brooks, Chris Roper and Malcolm Whapshott formed the British Human Powered Flying Club “to advance the sport of flying HPAs.”  Fred To is Chairman of this group and Dr. Brooks is Chairman of the RAeS HPA group.

Promotional poster for 2015 Lasham Human-Powered Airplane Rally showing participants in 2014 Rally

Promotional poster for 2015 Lasham Human-Powered Airplane Rally showing participants in 2014 Rally

The RAeS sponsored the 2012 and 2013 Icarus Cup Rallies and the BHPFC staged a 2014 Rally at Lasham Airfield in Hampshire and are promoting their 2015 meet to again be held at Lasham from July 25 through August 2.

The rally this year included the following contests:

1) Duration.

2) A 200-meter sprint race.

3) A 1-kilometer race.

4) A 500-meter slalom course.

5) Distance around a triangular course.

6) Unassisted takeoff performance.

7) Landing accuracy task.

Videos and images from the 2014 event suggest more of a cooperative and collegial event than a competitive one, but this is a sport that is just finding its way at this point.   One contestant suffered an embarrassing takeoff accident, but the simplified construction of modern HPAs allows relatively inexpensive and quick repairs to be made.

Paul MacCready's Bionic Bat combined human, electric power.  Bryan Allen achieved 26 mph in machine

Paul MacCready’s Bionic Bat combined human, electric power. Bryan Allen achieved 25 mph in machine, was later outdone by Holger Rochelt, who hit 30 mph in Musculair

One of Kremer’s prizes included the use of auxiliary power, which came out in practice as help from small model airplane electric motors or even caged rubber bands which could be wound up by the pilot before a flight and unleashed for takeoff and initial climb.  With small motors being light and efficient, a combination of pedaling and auxiliary power, much like pedelec bicycles now becoming popular, could lead to an entirely new and exciting form of low-speed flight.   Modern, lightweight electronics could help integrating human and electric power, much like the “all-in-one” power systems for bikes that comprise motor, controller, and battery all in one compact package.  Control is often by Bluetooth-type links.

Copenhagen wheel, with motor, controller (complete with regenerative power), and batteries tucked inside

Copenhagen wheel, with motor, controller (complete with regenerative power), and batteries tucked inside

Because of their simplicity and light weight, construction can be fast and inexpensive.  Modern pultrusions and plastic films allow model-aircraft type structures, but with far greater strength than earlier HPAs.

Both the RAeS and the BHPFC have links to design tools that could help you have an entry ready to ship to England in time for the 2015 rally.  Caution: a friend exhausted himself trying to pedal Bryan Allen’s White Dwarf HPA blimp.  One entrant for the Kremer speed prize, a champion athlete, took three days to rest from a first, unsuccessful attempt.  A really clean, long-wing HPA will require at least 0.3 horsepower to stay aloft, and more than that to stay airborne.   Check your endurance riding a bicycle uphill before even thinking about this challenging realm of flight.