Autonomous systems can aid in reducing greenhouse gas emissions and empowering efficient energy consumption.
This summer’s high temperatures and melting pavements have yet again driven home the reality that human-induced climate change is reshaping the Earth on a decidedly non-geological timescale. According to current trendlines, large swathes of densely inhabited coastlines are likely to be submerged with melted Arctic ice water by 2050, from Manhattan to Mumbai, Jakarta to Shanghai.
Currently, the planet will fail to contain global warming to an aspirational 2030 target of 1.5 degrees centigrade, or even the more feasible-seeming 2 degrees. Climate Action Tracker estimates a realistic outcome at 2.4-2.7 degrees centigrade. While that’s down from the 3.6 degrees projected in 2015, dire global consequences could include hundreds of millions more people being exposed to extreme weather and drought.
Perhaps the human activity most central to the onset of global warming—and most key to containing it to an “acceptable” level—is related to energy: the ways humanity produces it, and how efficiently we consume it. Consequently, we face a precarious balance: maturing technologies such as wind and solar infrastructures are positioning renewable energy sources to scale and displace fossil fuels, while war-driven energy instability, the shutdown of nuclear power plants in Germany and a growing population’s legitimate desire to enjoy the benefits of modern life all increase the impact of climate change.
CAN UNMANNED SYSTEMS HELP MITIGATE GLOBAL WARMING?
Autonomous systems have long been billed as ideal for tasks too “dull, dirty and dangerous”—a fair description of much of the labor involved in maintaining globe-spanning energy infrastructure.
Several factors synergize to contribute to the appeal of unmanned systems:
• An unmanned vehicle can be small and light, and thus consume less energy than a manned vehicle performing the same job
• Smaller weight and size make unmanned systems more likely compatible with non-fossil fuel-based propulsion, lessening climate impact
• In some cases, unmanned systems can perform labor- and energy-intensive tasks such as inspecting energy infrastructure faster and at lower cost.
These characteristics greatly incentivize adoption of unmanned platforms, though enduring limitations can be far from trivial. For example, studies have found that drone delivery consumes less energy and produces fewer emissions than trucks and diesel-powered vans—when distances are shorter and only small packages are delivered. And crewless unmanned surface vessels (USVs) may seem ideal for long-distance cargo delivery—until one considers the lack of onboard crew to repair breakdowns at sea.
Thus, the adoption of unmanned systems will be tempered by commercial operators seeking assurance that the technical risks, and the transition and overhead costs of implementing new unmanned-centric paradigms, are outweighed by the efficiencies and savings achieved.
A major impediment to fully leveraging the efficiencies offered by UAS is a lack of a routine permissive environment for BVLOS and autonomous operations.
In the U.S., BVLOS flights are approved on a case-by-case basis with a waiver, which is unsustainable given the volume of such flights. In Europe, a survey of 23 European transmission system operators found only 48% operated under a legal regime permissive of regular BVLOS operations, though 70% could test the capability on a non-routine basis. Coincidentally, 70% also reported they didn’t use drones routinely.
BVLOS regulations arise from legitimate concerns on the adequacy of drone sensors and avionics to mitigate risks of collision with other aircraft. However, technologies like Echodyne’s miniaturized EchoFlight phased-array radar, when combined with mature AI, give UAVs organic collision-avoidance capability at an acceptable cost, weight and energy footprint.
Fortunately, regulators know the current regulatory scheme needs adjusting. Notably, in March an FAA committee released the BVLOS ARC report detailing operator guidelines for future BVLOS operations. The recommendations suggest new rules for manned aircraft in drone-shielded airspace (they only get right-of-way over UAVs if equipped with a beacon or automatic broadcast system), and suggest creating rules to certify drone operators, drone types and third-party servicers for BVLOS operations.
Hopefully, this program will lead to fuller BVLOS policies in the near future. Meanwhile, in June, the U.K.’s Civil Aviation Authority released its own BVLOS guidelines, spelling out the equipment, testing and data sharing needed to pass regulatory scrutiny there.
RENEWABLE ENERGY PROPULSION
As BVLOS becomes more viable for commercial operators, larger drones with greater range, endurance and speed may occupy a greater share of the commercial market. But that still requires making difficult tradeoffs when it comes to weight, complexity, launch method and propulsion system efficiency.
Solar power is difficult (but not impossible) to integrate on vertical-lift drones, but more feasible on fixed-wing aircraft with abundant surface on their wings for solar panels. French Company XSun has developed a solar-powered drone that weighs a respectable 55 pounds and can carry an 11-pound payload (optical/thermal cameras, LiDAR, communications systems). The solar panels on its two sets of wings yield a range of 373 miles and maximum endurance of 12 hours (even at night if the cells are fully charged during the day). “With a goal of achieving more sustainability in a world of ever-diminishing resources,” according to company literature, “XSun pursues a path of innovation, diverging radically from traditional UAV design and manufacturing.”
Renewable energy propulsion is also possible under water. Vista, California-based startup Seatrec, has developed an SL1 Thermal Energy Heavy System (costing $25,000 each), which uses energy generated by changes in water temperature to charge a battery. It can be integrated onto UUVs or in static underwater stations visited by UUVs for recharging.
Such technology may be especially enticing for UUVs performing very long-endurance search or survey missions, and even enable a “return-to-base” capability for otherwise single-use UUVs. Reportedly, the startup has received $2 million in government contracts and $3.5 million in venture capital funding.
BUILDING A BETTER BATTERY
Despite the promise of renewable energy propulsion sources, most small, modern unmanned systems rely on batteries, which contribute substantial mass to the platform with a consequent impact on performance.
Lithium-ion batteries have risen as the gold standard of high energy density to weight. They are complemented by more expensive lithium-polymer batteries, which have less energy density, but are widely employed on smaller commercial drones thanks to lower weight and far more moldable form factor.
Arguably the most exciting successor on the horizon may be lithium-air batteries, which can theoretically achieve five to 10 times the energy as weight-equivalent LiBs (i.e., a density very close to that of gasoline!), or twice the energy for volume equivalence. However, they remain slow to recharge, can only do so over a limited number of cycles and can be volatile when in contact with water vapor. Furthermore, “overhead” weight from electrolytes and inactive components significantly compromises their energy-density edge when factored in.
This year, Japan’s National Institute for Material Sciences apparently made a breakthrough with a battery featuring a density of 500 watt-hour per kilo (twice that of batteries in a Tesla Model 3), and with a longer lifecycle to boot. New materials allow for a 31% reduction in electrolytes.
Another potential LiB successor with greater energy density, lithium-sulfur batteries, is also bedeviled with recharge cycle issues. However, a team from University of Michigan published in Nature Communications that they had developed an Li-S battery that increases charge cycles from 10 to 1,000.
Neither technology has seen much if any commercialization. But if lithium-air or lithium-sulfur technology can be successfully matured, the double whammy of high energy capacity at low weight could substantially improve endurance, range and speed of UAVs, and could make electric propulsion for larger, traditionally fossil-fuel powered UAVs more viable.
DRONES AS POWER GENERATORS?
UAVs are also being developed to serve as rivals of sorts to wind power. Theoretically, kite-like tethered drones can access more powerful winds at altitudes above 660 feet than even the tallest turbines can, with a two-fold increase in windspeed resulting in an eight-fold multiplier to energy created.
The mechanical energy of these aircraft gliding in circles could, for example, be transmitted back via the tether to turn a winch on the ground to charge up a generator.
Companies developing such autonomous Airborne Wind Energy (AWE) systems claim these might generate the same energy as a wind turbine at a fraction of the material costs, and could even be swapped easily into existing wind-power infrastructure. Another study by Kate Marvel in the journal Nature Climate Change finds conversion from ground to air-based turbines could generate 1,800 terawatts, compared to 400 from ground-level turbines.
Challenges such drones must overcome involve developing a sufficiently reliable organic take-off-and-landing system to allow ground crews to service and inspect, and a supportive regulatory regime.
Despite being in development for at least two decades, autonomous aerial power generation only achieved the milestone of commercial deployment in February, when Germany’s SkySails Power deployed a paraglider-style airborne wind turbine off Mauritius that could generate a scant 100 KW.
Ultimately, AWE farms could become flexible and cost-efficient wind energy generators—if economies of scale through mass production can be achieved. That presents a chicken-and-egg challenge due to pressure to demonstrate immediately viable products.
UNDERSEA SURVEY, REINVENTED
The benefits of reduced costs and size and increased endurance offered by UAVs compared to manned aircraft are even truer for unmanned underwater vehicles (UUVs) gliding through the inhospitable depths of the ocean. UUVs have long been used for scientific research and military purposes, but often only in boutique quantities, and most are constrained by the need to remain tethered to a vessel overhead.
Tim Taylor, CEO of UUV startup Tiburon Subsea, believes the technology is here to cut the leash tying commercial drones to their motherships using autonomous algorithms to comb the ocean floor. That way, a single ship could deploy multiple Autonomous Underwater Vehicles (AUVs) simultaneously, avoiding surface weather constraints or a need to tow UUVs into position. For sustained operations, AUVs could offload data and recharge at a fixed underwater charging station.
Taylor has pioneered commercial AUVs since 2007, mapping more than 24,000 square miles of ocean floor and locating the sunken wrecks of seven U.S. submarines lost in World War II. He’s putting that know-how toward developing his own patented AUV design.
With New York-headquartered Tiburon, Taylor is producing a global AUV fleet with maximum diving depths of 1,500 feet and customizable payloads and power sources that could be rented to clients at competitive rates and operated by “by two guys and a laptop.”
Tiburon has initial funding to build the first three or four prototypes. “There are thousands of customers out there that don’t have access to this technology;” Taylor said. “It’s like having an iPhone that costs $20,000.” Instead, Taylor envisions a Robots as a Service model allowing continuous platform upgrades in pace with rapidly advancing technology and customer benefit.
Besides high-resolution surveys and ocean floor mapping, AUVs could also bring about a far more robust inspection regime for underwater infrastructure, particularly pipelines and abandoned wells prone to leaking hazardous chemicals.
“Every well is supposed to be capped by the oil and gas industry with cement, but most of them leak methane gas,” Taylor said. Per unit, methane traps 25 times more heat in the Earth’s atmosphere than CO2.
“Finding the stuff that’s leaking and zeroing in on that is a tremendous effort,” Taylor continued. “Just in the Gulf of Mexico, all of the shallow coastal areas are seeping in methane.” Infamously, methane from a pipeline leak caused a huge “eye of fire” to blaze on the surface of the Gulf of Mexico in 2021.
Taylor believes quality, accessible and affordable AUVs could perform badly needed inspections routinely and efficiently. Offshore wind farm construction would also benefit, he said, as these require detailed environmental impact assessments and ocean floor surveys charting cable connections to the shore.
OVERCOMING THE DARK SIDE
Of course, just because unmanned systems have the potential to be more energy efficient doesn’t mean they’ll always wind up that way.
A major issue involves the inputs needed for drone production and charging. A study for the journal Advances in Climate Change Research by Jarotwan Koiwanit of Bangkok’s King Mongkut’s Institute of Technology amplified this. Koiwanit calculated that production, and the impact of fossil-fuel based energy production to charge them, were by far primary contributors to environmental impact for his baseline system, while actual drone operations had negligible impacts. His study used a 24-pound Canadian drone with a DJI E2000 electrical propulsion system assumed to operate for 5,000 hours.
“The results showed that emissions were mainly from parts production, which include coal mining, electrical generating station operation and parts production while the drone operation showed the least impact.” The latter particularly included carbon fibers for the cargo box and lithium ion production for the battery.
Thus, companies specifically seeking to use drones to reduce environmental impact should also factor in means of production and the environmental regulatory regime where production took place when calculating life cycle costs. That can mean a substantial part of the environmental impact still comes from how electricity was generated (often by fossil fuels).
Studies also suggest low-flying UAVs can negatively impact wildlife, literally in cases of collisions, and by disrupting their hunting and reproductive behaviors. Perhaps the latest generation of collision avoidance sensors can help minimize the former risk, though even a large bird may have a radar cross-section of a hundredth of a square meter.
Despite these factors, unmanned systems are inextricably intertwined with global energy transformation—both contributing to and being affected by it. Already-existing platforms can substantially shorten laborious inspection and surveying activities that must be undertaken across huge areas by fossil fuel and renewable energy providers alike. By themselves, these capabilities are adequate to result in steep annual growth in the UAV market for years to come.
Maturing autonomous operation capabilities and next-generation propulsion systems, combined with development of a standardized regulatory regime driven by safety-enhancing sensors and AI protocols, are poised to dramatically expand the economical application of unmanned systems, deepening their ubiquity in the market. That may include electricity-generating drones, as well as commercial UUVs used for inspection, survey and search missions.
However, reducing costs and energy consumption for a broad variety of tasks remains a crucial function, making use of renewable energies more efficient and ultimately substituting fossil-fuel-consuming platforms with electrically driven ones. UAS will play a key role in this effort.