The Battery Design Smarts Behind Rolls Royce’s Ultrafast Electric Airplane

Emulating racing aircraft yielded the most energy-dense aviation battery pack yet

3 min read
Photo of the Rolls ACCEL electric plane
Photo: Rolls Royce

Dozens 0f electric general aviation projects are underway around the world, not counting the urban air taxis that dominate the electric propulsion R&D scene. The first all-electric commercial aircraft, a seaplane intended for short flights, completed a 15-minute test flight in December.

Shortly after, luxury icon Rolls Royce unveiled what it hopes will be the world’s fastest electric aircraft. The current speed record for that type of plane is 335 kilometers per hour (210 mph). The new one-seater craft, slated to fly this spring, will top out at 480 km/h (300 mph). It should also be able to fly from London to Paris, about 320 km (200 miles), on a single charge.

That’s thanks to “the world’s most energy-dense flying battery pack,” according to Rolls Royce. The aircraft has three batteries powering three motors that will deliver 750kW to spin the propellers. Each 72 kilowatt-hour battery pack weighs 450kg and has 6,000 densely packed lithium-ion cells.

Getting all this power on board wasn’t easy, says Matheu Parr, project manager for the ACCEL project, short for Accelerating the Electrification of Flight. Careful thought and engineering went into each step, right from selecting the type of battery cell. Lithium-ion cells come in many forms, including pouches as well as  prismatic and cylindrical cells. Cylindrical ones turn out to be best for holding a lot of energy and discharging it quickly at high power, he says.

Next came the critical task of assembling the cells into a pack. Rolls Royce’s partner, Electroflight, a startup specializing in aviation batteries, began that effort by analyzing innovations in the relatively new all-electric auto-racing space.

“Really, the challenge for electric aviation is one of packaging,” Parr says. “So we’ve looked at how Formula E [air racing] tackles packaging and then taken it a step further.” By using lightweight materials—and only the bare minimum of those—the Formula E teams manage to cut their planes’ packaging-to –battery cell weight ratio in half compared with the amount of battery packaging an electric car has to carry around for each kilogram of battery cell.

The high-power, closely packed cells get pretty hot. So, designing an advanced active-cooling system was important. Instead of the air-cooling used in car batteries, Rolls Royce engineers chose a liquid-cooling system. All the cells directly contact a cooling plate through which a water-and-glycol mixture is piped.

Finally, the engineers built in safety features such as an ultra-strong outside case and continual monitoring of each battery’s temperature and voltage. Should something go wrong with one of the batteries, it would automatically be shut off. Better still, the airplane can land even if two of its three batteries are turned off.

The ACCEL battery comes out to a specific energy of 165 watt-hours per kilogram, which puts it on par with the  battery pack powering the Tesla Model 3. That’s still a long way from the 500 Wh/kg needed to compete with traditional jet-propulsion aircraft for commercial flights (aviation batteries are not expected to store that much energy per unit mass until 2030). For now, Rolls Royce and others believe all-electric propulsion will power smaller aircraft while larger planes will have hybrid fuel-electric systems. The company has teamed up with Airbus and Siemens to develop a hybrid airplane.

With its high-speed racing aircraft, Rolls Royce wants to pioneer the transition to the “third age of aviation, from propeller aircraft to jet aircraft to electric,” says Parr. The project will also provide know-how that will shape future designs. “We’re learning an awful lot that we want to see packed into a future aircraft. Innovations in the battery and system integration, packaging and management will all help us shape any future electric product, be it all-electric or hybrid.”

The Conversation (1)
Dominic Leung 25 Nov, 2021

Zero research done on this article ...

The airframe this plane uses has a maximum takeoff weight of 1200 kg ... how the author thinks Rolls Royce managed to fit 1450 kg of batteries onto it is beyond me ..

More importantly than the above error is this ... 500kwh/kg is nowhere near enough to "compete with traditional jet-propulsion aircraft for commercial flights".

500kwh/kg energy density is 1.75mj/kg

Kerosene energy density is 43mj/kgEven factoring electric motor efficiency at 90% vs a turbofan @ 60% means batteries would need to be @ 29mj/KG or ~8200wh/kg (43 x 60% / 90%) to be comparable (despite the fact hydrocarbon fueled planes will be more efficient over a distance given it loses mass along the way).

Smokey the AI

Smart image analysis algorithms, fed by cameras carried by drones and ground vehicles, can help power companies prevent forest fires

7 min read
Smokey the AI

The 2021 Dixie Fire in northern California is suspected of being caused by Pacific Gas & Electric's equipment. The fire is the second-largest in California history.

Robyn Beck/AFP/Getty Images

The 2020 fire season in the United States was the worst in at least 70 years, with some 4 million hectares burned on the west coast alone. These West Coast fires killed at least 37 people, destroyed hundreds of structures, caused nearly US $20 billion in damage, and filled the air with smoke that threatened the health of millions of people. And this was on top of a 2018 fire season that burned more than 700,000 hectares of land in California, and a 2019-to-2020 wildfire season in Australia that torched nearly 18 million hectares.

While some of these fires started from human carelessness—or arson—far too many were sparked and spread by the electrical power infrastructure and power lines. The California Department of Forestry and Fire Protection (Cal Fire) calculates that nearly 100,000 burned hectares of those 2018 California fires were the fault of the electric power infrastructure, including the devastating Camp Fire, which wiped out most of the town of Paradise. And in July of this year, Pacific Gas & Electric indicated that blown fuses on one of its utility poles may have sparked the Dixie Fire, which burned nearly 400,000 hectares.

Until these recent disasters, most people, even those living in vulnerable areas, didn't give much thought to the fire risk from the electrical infrastructure. Power companies trim trees and inspect lines on a regular—if not particularly frequent—basis.

However, the frequency of these inspections has changed little over the years, even though climate change is causing drier and hotter weather conditions that lead up to more intense wildfires. In addition, many key electrical components are beyond their shelf lives, including insulators, transformers, arrestors, and splices that are more than 40 years old. Many transmission towers, most built for a 40-year lifespan, are entering their final decade.

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