Autonomous vehicles have been highly anticipated because of the possibility that they will greatly reduce or perhaps eliminate the collisions that cause more than a million deaths each year. But safety isn’t the only potential benefit self-driving cars can offer: Teams of researchers around the world are showing that autonomous vehicles can also drive more efficiently than humans can. A U.S. Department of Energy program called NEXTCAR (Next-Generation Energy Technologies for Connected and Automated On-Road Vehicles), for example, is betting that a mix of new smart-vehicle technologies can boost fuel efficiency by as much as 30 percent.

As part of the NEXTCAR program, San Antonio, Texas–based Southwest Research Institute (SwRI) showcased advances in autonomous vehicle technology that will improve vehicles’ fuel economy—including the fuel efficiency of nonautonomous automobiles that just so happen to be in traffic with autonomous ones. The demonstration was held at the ARPA-E Energy Inovation Summit in Dallas in late May.

Making an Efficient Autonomous Vehicle

The SwRI team retrofitted a 2021 Honda Clarity hybrid with basic autonomous features such as perception and localization. On the day of the summit, they drove the vehicle along a route encircling the parking lot of the convention center where the summit was held. SWRI’s Ranger localization system, which the researchers installed on the Honda, has a downward-facing camera that captures images of the ground. By initially mapping the driving surface, Ranger can later localize the vehicle with centimeter-level accuracy, using the ground’s unique “fingerprint” combined with GPS data. This precision ensures the vehicle drives with exceptional control.

“It’s almost like riding on rails,” says Stas Gankov, a researcher in SwRI’s power-train engineering group. For this project, his group collaborated with other divisions at the institute, such as the intelligence-systems division, which developed the autonomy software stack added to the Honda Clarity.

Just as important, however, was the addition of an ecodriving module, a key innovation by SwRI. The ecomode determines the most economical driving speed by considering various factors such as traffic lights and surrounding vehicles. This system employs predictive control algorithms to help solve a tricky optimization problem: How can cars minimize energy consumption while maintaining efficient traffic flow? SwRI’s ecomode aims to reduce unnecessary acceleration and deceleration in order to optimize energy usage without impeding other vehicles.

“Autonomous vehicles operating in ecomode influence the driving behavior of all the cars behind them.” —Stas Gankov, Southwest Research Institute

To illustrate how the technology works, the team installed a traffic signal along the demonstration pathway. Gankov says an actual traffic-light timer from a traffic-signal cabinet was connected to a TV screen, providing a visual for attendees. A dedicated short range communications (DRSC) radio was also attached, broadcasting the signal’s phase and timing information to the vehicle. This setup enabled the vehicle to anticipate the traffic light’s actions far more accurately than a human driver could.

For instance, Gankov says, if the Honda Clarity was approaching a red light that was about to turn green, it would know the light was due to change and so avoid wasting energy by braking and then accelerating again. Conversely, if the car was approaching the signal as it was about to turn from green to yellow to red, the vehicle would release the accelerator and let friction slow it to a crawl, avoiding unnecessary acceleration in an attempt to beat the light.

These autonomous driving strategies can lead to significant energy savings, benefiting not just the autonomous vehicles themselves, but also the entire traffic ecosystem.

“In a regular traffic situation, autonomous vehicles operating in ecomode influence the driving behavior of all the cars behind them,” says Gankov. “The result is that even vehicles with Level 0 autonomy use fuel more sparingly.”

The Grand Vehicle Energy Plan

SwRI has been a participant in the NEXTCAR initiative since 2017. The program’s initial phase involved 11 teams, including SwRI, Michigan Technological University, Ohio State University, and the University of California, Berkeley. SwRI, in collaboration with the University of Michigan, focused on optimizing a Toyota Prius Prime, already known for its fuel efficiency, to achieve a 20 percent improvement in energy usage through optimization algorithms and wireless communicating with its surroundings. This was accomplished without modifying the Toyota’s power train or compromising its emissions. The team utilized power split optimization, balancing the use of the gas engine and battery-propulsion system for maximum efficiency.

Building on the success of NEXTCAR’s first phase, the program entered its second phase in 2021, with just SwRI, Michigan Tech, Ohio State, and UC Berkeley remaining. The focus of NEXTCAR 2 has been determining how much automation could further enhance energy efficiency. Gankov explains that while the first phase demonstrated a 20 percent energy-efficiency improvement over a baseline 2016 or 2017 model-year vehicle with no autonomous driving capabilities, through the addition of vehicle-to-everything connectivity alone, the second phase is exploring the potential for an additional 10 percent improvement by incorporating autonomous features.

Gankov says SwRI initially intended to partner with Honda for NEXTCAR’s second phase, but when contracting issues arose, the nonprofit proceeded independently. Utilizing an autonomy platform developed by SwRI’s intelligence-systems division, the NEXTCAR team equipped the Honda Clarity with what amounted to Level 4 autonomy in a box. This autonomy system features a drive-by-wire system, allowing the vehicle to automatically adjust its speed and steering based on inputs from the autonomy software stack and the ecodriving module. This ensures the vehicle prioritizes safety while optimizing for energy efficiency.

Employing techniques like efficient highway merging were key strategies in their approach to making the most of each tank of fuel or battery charge. “For example, in heavy traffic on the highway, calculating the most optimal way to merge onto the highway without negatively affecting the energy efficiency of the vehicles already on the highway is crucial,” Gankov noted.

As NEXTCAR 2 enters its final year, the demonstration at the ARPA-E Summit served as a testament to the progress made in autonomous-vehicle technology and its potential to dramatically improve energy efficiency in transportation.

Nearly 400 exhibitors representing the boldest energy innovations in the United States came together last week at the annual ARPA-E Energy Innovation Summit. The conference, hosted in Dallas by the U.S. Advanced Research Projects Agency–Energy (ARPA-E), showcased the agency’s bets on early-stage energy technologies that can disrupt the status quo. U.S. Secretary of Energy Jennifer Granholm spoke at the summit. “The people in this room are America’s best hope” in the race to unleash the power of clean energy, she said. “The technologies you create will decide whether we win that race. But no pressure,” she quipped. IEEE Spectrum spent three days meandering the aisles of the showcase. Here are five of our favorite demonstrations.

Gas Li-ion batteries thwart extreme cold

South 8 Technologies demonstrates the cold tolerance of its Li-ion battery by burying it in ice at the 2024 ARPA-E Energy Innovation Summit. Emily Waltz

Made with a liquified gas electrolyte instead of the standard liquid solvent, a new kind of lithium-ion battery that stands up to extreme cold, made by South 8 Technologies in San Diego, won’t freeze until temps drop below –80 °C. That’s a big improvement on conventional Li-ion batteries, which start to degrade when temps reach 0 °C and shut down at about –20 °C. “You lose about half of your range in an electric vehicle if you drive it in the middle of winter in Michigan,” says Cyrus Rustomji, cofounder of South 8. To prove the company’s point, Rustomji and his team set out a bucket of dry ice at nearly –80 °C at their booth at the ARPA-E summit and put flashlights in it—one powered by a South 8 battery and one powered by a conventional Li-ion cell. The latter flashlight went out after about 10 minutes, and South 8’s kept going for the next 15 hours. Rustomji says he expects EV batteries made with South 8’s technology to maintain nearly full range at –40 °C, and gradually degrade in temperatures lower than that.

South 8 Technologies

Conventional Li-ion batteries use liquid solvents, such as ethylene and dimethyl carbonate, as the electrolyte. The electrolyte serves as a medium through which lithium salt moves from one electrode to the other in the battery, shuttling electricity. When it’s cold, the carbonates thicken, which lowers the power of the battery. They can also freeze, which shuts down all conductivity. South 8 swapped out the carbonate for some industrial liquified gases with low freezing points (a recipe the company won’t disclose).

Using liquified gases also reduces fire risk because the gas very quickly evaporates from a damaged battery cell, removing fuel that could burn and cause the battery to catch fire. If a conventional Li-ion battery gets damaged, it can short-circuit and quickly become hot—like over 800 °C hot. This causes the liquid electrolyte to heat adjacent cells and potentially start a fire.

There’s another benefit to this battery, and this one will make EV drivers very happy: It will take only 10 minutes to reach an 80 percent charge in EVs powered by these batteries, Rustomji estimates. That’s because liquified gas has a lower viscosity than carbonate-based electrolytes, which allows the lithium salt to move from one electrode to the other at a faster rate, shortening the time it takes to recharge the battery.

South 8’s latest improvement is a high-voltage cathode that reduces material costs and could enable fast charging down to 5 minutes for a full charge. “We have the world record for a high-voltage, low-temperature cathode,” says Rustomji.

Liquid cooling won’t leak on servers

Chilldyne guarantees that its liquid-cooling system won’t leak even if tubes get hacked in half, as IEEE Spectrum editor Emily Waltz demonstrates at the 2024 ARPA-E Energy Innovation Summit. Emily Waltz

Data centers need serious cooling technologies to keep servers from overheating, and sometimes air-conditioning just isn’t enough. In fact, the latest Blackwell chips from Nvidia require liquid cooling, which is more energy efficient than air. But liquid cooling tends to make data-center operators nervous. “A bomb won’t do as much damage as a leaky liquid-cooling system,” says Steve Harrington, CEO of Chilldyne. His company, based in Carlsbad, Calif., offers liquid cooling that’s guaranteed not to leak, even if the coolant lines get chopped in half. (They aren’t kidding: Chilldyne brought an axe to its demonstration at ARPA-E and let Spectrum try it out. Watch the blue cooling liquid immediately disappear from the tube after it’s chopped.)

Chilldyne

The system is leakproof because Chilldyne’s negative-pressure system pulls rather than pushes liquid coolant through tubes, like a vacuum. The tubes wind through servers, absorbing heat through cold plates, and return the warmed liquid to tanks in a cooling distribution unit. This unit transfers the heat outside and supplies cooled liquid back to the servers. If a component anywhere in the cooling loop breaks, the liquid is immediately sucked back into the tanks before it can leak. Key to the technology: low-thermal-resistance cold plates attached to each server’s processors, such as the CPUs or GPUs. The cold plates absorb heat by convection, transferring the heat to the coolant tube that runs through it. Chilldyne optimized the cold plate using corkscrew-shaped metal channels, called turbulators, that force water around them “like little tornadoes,” maximizing the heat absorbed, says Harrington. The company developed the cold plate under an ARPA-E grant and is now measuring the energy savings of liquid cooling through an ARPA-E program.

Salvaged mining waste also sequesters CO₂

Phoenix Tailings’ senior research scientist Rita Silbernagel explains how mining waste contains useful metals and rare earth elements and can also be used as a place to store carbon dioxide.Emily Waltz

Mining leaves behind piles of waste after the commercially viable material is extracted. This waste, known as tailings, can contain rare earth elements and valuable metals that are too difficult to extract with conventional mining techniques. Phoenix Tailings—a startup based in Woburn, Mass.—extracts metals and rare earth elements from tailings in a process that leaves behind no waste and creates no direct carbon dioxide emissions. The company’s process starts with a hydrometallurgical treatment that separates rare earth elements from the tailings, which contain iron, aluminum, and other common elements. Next the company uses a novel solvent extraction method to separate the rare earth elements from one another and purify the desired element in the form of an oxide. The rare earth oxide then undergoes a molten-salt electrolysis process that converts it into a solid metal form. Phoenix Tailings focuses on extracting neodymium, neodymium-praseodymium alloy, dysprosium, and ferro dysprosium alloy, which are rare earth metals used in permanent magnets for EVs, wind turbines, jet engines, and other applications. The company is evaluating several tailings sites in the United States, including in upstate New York.

The company has also developed a process to extract metals such as nickel, copper, and cobalt from mining tailings while simultaneously sequestering carbon dioxide. The approach involves injecting CO₂ into the tailings, where it reacts with minerals, transforming them into carbonates—compounds that contain the carbonate ion, which contains three oxygen atoms and one carbon atom. After the mineral carbonation process, the nickel or other metals are selectively leached from the mixture, yielding high-quality nickel that can be used by EV-battery and stainless-steel industries.

Better still, this whole process, says Rita Silbernagel, senior research scientist at Phoenix Tailings, absorbs more CO₂ than it emits.

Hydrokinetic turbines: a new business model

Emrgy adjusts the height of its hydrokinetic turbines at the 2024 ARPA-E Energy Innovation Summit. The company plans to install them in old irrigation channels to generate renewable energy and new revenue streams for rural communities. Emily Waltz

These hydrokinetic turbines run in irrigation channels, generating electricity and revenue for rural communities. Developed by Emrgy in Atlanta, the turbines can change in height and blade pitch based on the flow of the water. The company plans to put them in irrigation channels that were built to bring water from snowmelt in the Rocky Mountains to agricultural areas in the western United States. Emrgy estimates that there are more than 160,000 kilometers of these waterways in the country. The system is aging and losing water, but it’s hard for water districts to justify the cost of repairing them, says Tom Cuthbert, chief technology officer at Emrgy. The company’s solution is to place its hydrokinetic turbines throughout these waterways as a way to generate renewable electricity and pay for upgrades to the irrigation channels.

The concept of placing hydrokinetic turbines in waterways isn’t new, but until recent years, connecting them to the grid wasn’t practical. Emrgy’s timing takes advantage of the groundwork laid by the solar power industry. The company has five pilot projects in the works in the United States and New Zealand. “We found that existing water infrastructure is a massive overlooked real estate segment that is ripe for renewable energy development,” says Emily Morris, CEO and founder of Emrgy.

Pressurized water stores energy deep underground

Quidnet Energy brought a wellhead to the 2024 ARPA-E Energy Innovation Summit to demonstrate its geoengineered energy-storage system.Emily Waltz

Quidnet Energy brought a whole wellhead to the ARPA-E summit to demonstrate its underground pumped hydro storage technique. The Houston-based company’s geoengineered system stores energy as pressurized water deep underground. It consists of a surface-level pond, a deep well, an underground reservoir at the end of the well, and a pump system that moves pressurized water from the pond to the underground reservoir and back. The design doesn’t require an elevation change like traditional pumped storage hydropower.

Quidnet’s system consists of a surface-level pond, a deep well, an underground reservoir at the end of the well, and a pump system that moves pressurized water from the pond to the underground reservoir and back.Quidnet Energy

It works like this: Electricity from renewable sources powers a pump that sends water from the surface pond into a wellhead and down a well that’s about 300 meters deep. At the end of the well, the pressure from the pumped water flows into a previously engineered fracture in the rock, creating a reservoir that’s hundreds of meters wide and sits beneath the weight of the whole column of rock above it, says Bunker Hill, vice president of engineering at Quidnet. The wellhead then closes and the water remains under high pressure, keeping energy stored in the reservoir for days if necessary. When electricity is needed, the well is opened, letting the pressurized water run up the same well. Above ground, the water passes through a hydroelectric turbine, generating 2 to 8 megawatts of electricity. The spent water then returns to the surface pond, ready for the next cycle. “The hard part is making sure the underground reservoir doesn’t lose water,” says Hill. To that end, the company developed customized sealing solutions that get injected into the fracture, sealing in the water.