Energy is a critical resource for military operations, particularly in remote and isolated areas where supply lines are precarious. The need for fuel convoys in such regions not only incurs high costs but also exposes troops to improvised bomb attacks, leading to unnecessary casualties. To address this challenge, the Defense Advanced Research Projects Agency (DARPA) has embarked on a groundbreaking initiative called Persistent Optical Wireless Energy Relay (POWER). By utilizing lasers to transmit electricity, this innovative program aims to reduce the reliance on fuel convoys and enhance the efficiency of energy distribution in military theaters.
The Challenge of Energy Supply in Remote Bases: According to a 2009 report by Wired, the U.S. war in Afghanistan required an average of 22 gallons of diesel fuel per soldier each day. The cost of hauling this fuel to the battlefield added an extra $45 per gallon, as it had to be transported through dangerous convoy routes vulnerable to improvised bomb attacks. This scenario not only poses risks to troops’ lives but also drains resources and limits operational flexibility.
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Advantages of Power Beaming:
Power beaming, the process of wirelessly transmitting electricity using lasers, offers several advantages over conventional methods. By reducing the need for fuel convoys, it eliminates transportation costs, lowers the risk to drivers, and minimizes reliance on generators that consume diesel fuel. It would remove the need for generators to convert diesel fuel into electricity, eliminating the need for generator maintenance and, as a quality of life issue, the constant smell of diesel exhaust.
Additionally, the use of wireless power transfer networks allows smaller platforms to carry significant capabilities, such as unlimited range or endurance, without the burden of storing large quantities of energy.
A straightforward way of sending electrical power to a military outpost would have several advantages. It would reduce the amount of fuel needed to be trucked to remote bases, removing the cost of transport fees and the risk to drivers.
Introducing the Persistent Optical Wireless Energy Relay (POWER) Initiative:
To overcome the challenges associated with traditional energy distribution, DARPA initiated the POWER program in October 2022. The goal is to develop and demonstrate airborne optical energy relays, enabling ground-sourced lasers to transmit energy over long distances with high efficiency. These relays will form the backbone of a dynamic, adaptive, and fast wireless energy web, revolutionizing the way energy is delivered to military bases and platforms.
“POWER is an optical power beaming program,” Calhoun says. “There are other potential power-beaming modalities, such as microwaves, that we intend to explore in future programs. For POWER, the propagating wave is a laser [that] provides long-range high-throughput capability when transmitted at high altitudes. The relays redirect the laser energy without conversion, and then the end-user converts that laser energy back into electricity using narrow-bandgap-tuned monochromatic photovoltaics,” he added.
Challenges and Development:
- High-power lasers: The POWER initiative is using high-power lasers to transmit the electricity. These lasers are capable of generating megawatts of power, which is enough to power a small military base.
- Optical receivers: The POWER initiative is also developing optical receivers that can convert the laser light back into electricity. These receivers are designed to be efficient and reliable, even in harsh environments.
- Beam control systems: The POWER initiative is also developing beam control systems that can steer the laser beam accurately over long distances. These systems are designed to compensate for atmospheric effects, such as turbulence and wind.
Here are some of the challenges that DARPA is facing in the POWER initiative:
- Atmospheric effects: The atmosphere can distort the laser beam, which can make it difficult to aim the beam accurately over long distances. DARPA is developing beam control systems that can compensate for these effects.
- Efficiency: Lasers are not very efficient at converting electricity into light. DARPA is working to improve the efficiency of the lasers so that they can transmit more power over a longer distance.
- Cost: Laser systems are expensive to develop and build. DARPA is working to reduce the cost of the laser systems so that they can be used by the military.
“On the technology side, significant advancements have been made in high-energy lasers, wavefront sensing, adaptive optics, high-altitude electric air platforms, safety interlocks, and narrow-bandgap-tuned high-efficiency photovoltaics,” Col. Calhoun explains.
While power beaming holds promise, there are challenges to address, primarily related to conversion efficiencies. The POWER program aims to develop efficient power beaming relays that optimize beam quality and selectively harvest energy along the transmission path.
Relays in the form of long-endurance drones and satellites will play a crucial role in the future. These drones, hovering at high altitudes, will transmit laser energy to each other over extended distances before delivering it to a U.S. military base. Similarly, satellites will perform the same mission in space.
“POWER is developing stratospheric platforms with small apertures ranging approximately 100 kilometers between nodes. With larger apertures and a more benign environment like space, distances between nodes of up to 1,000 kilometers are reasonable,” Calhoun added. The result would be a “globally scalable energy distribution network.”
Converting power back and forth between electrical and propagating wave forms currently incurs losses, but DARPA’s three-phase development effort is focused on achieving a compelling energy relay flight demonstration.
The POWER program is still in its early stages, but DARPA has already made significant progress. In October 2022, DARPA successfully demonstrated a laser system that could transmit 10 kilowatts of power over a distance of 1.5 kilometers. This is a significant milestone, and it shows that the POWER program is on track to achieve its goals.
DARPA is entering the first phase of the Persistent Optical Wireless Energy Relay (POWER) program, aimed at revolutionizing energy distribution through airborne wireless power transfer. Three teams — led by RTX Corporation, Draper, and BEAM Co. — will design and develop wireless optical power relays. The program goals include demonstrating the key components necessary for a resilient, speed-of-light energy network.
“This project has the potential to advance power beaming by orders of magnitude, which could radically reshape society’s relationship with energy,” said Dr. Paul Jaffe, who leads the POWER program at DARPA. “A wireless energy web could unlock power from new and diverse sources, including from space, and rapidly and reliably connect them to energy-starved consumers.”
To support rapid development, the optical energy relays designed in POWER’s phase one will be demonstrated in pods carried by existing aircraft in the project’s second phase. Additionally, power beaming will enable smaller, less expensive future aircraft since fuel storage and engine volume could be dramatically reduced. This will be explored through conceptual designs in phase one. Eventually these new, small, distributed platforms could provide cost-effective aircraft with unlimited range and endurance to support military missions. Each relay design will be evaluated based on accurate and efficient energy redirection, wavefront correction for high beam quality, and throttleable energy harvesting. In the third and final phase of the program, the relays will be demonstrated through an airborne optical pathway that aims to deliver 10 kilowatts of optical energy to a ground receiver that is 200 kilometers away from the ground source laser.
US research agency DARPA has selected three teams to design wireless optical power relays to deliver energy to aircraft in flight.
The first phase of the Persistent Optical Wireless Energy Relay (POWER) programme at DARPA will see the three teams, led by RTX Corporation, Draper, and BEAM , design and develop the power beaming relays. The programme aims to demonstrate the key components necessary for a resilient airborne energy network. The ultimate aim is to show an airborne optical pathway that delivers 10kW of optical energy to a ground receiver that is 200 kilometers away from the ground source laser.
“This project has the potential to advance power beaming by orders of magnitude, which could radically reshape society’s relationship with energy,” said Dr Paul Jaffe, who leads the POWER program at DARPA. “A wireless energy web could unlock power from new and diverse sources, including from space, and rapidly and reliably connect them to energy-starved consumers.” The airborne power relay technology designed in phase one will be demonstrated in pods carried by existing aircraft in the project’s second phase.
Power beaming will enable smaller, less expensive future aircraft since fuel storage and engine volume could be dramatically reduced. This will be explored through conceptual designs in phase one.
Eventually these new, small, distributed platforms could provide cost-effective aircraft with unlimited range and endurance. Each relay design will be evaluated based on accurate and efficient energy redirection, wavefront correction for high beam quality, and throttleable energy harvesting.
In the third and final phase of the program, the relays will be demonstrated through the 200km airborne optical pathway
These power beaming relays will overcome the unacceptable conversion losses that occur when changing from propagating waves to electricity repeatedly in a multiple-hop network. Relays also enable high-altitude transmission, which is vastly more efficient than beaming power through the thick, turbulent, lower atmosphere. This high-altitude optical layer will provide the long-range, high throughput backbone for the wireless energy web.
“Each of the selected teams proposed unique technical approaches to the power beaming relay problem, ranging from novel combinations of existing technologies to high-risk, high-reward technological innovations,” said Jaffe. “The range of proposed solutions encompasses a balance of assured performance and potential breakthroughs in size, weight, and power to enable small distributed systems for the future wireless energy web.”
The first phase will include benchtop demonstrations of critical technologies and is expected to last 20 months with potential for a three-month option of additional risk reduction efforts. The second phase will involve an open solicitation in early 2025 and will focus on integration of the relay technologies onto an existing platform for a low-power, airborne demonstration.
The Potential Impact:
Historically, breakthroughs in energy transport, such as the Roman roads, railroads, mechanized warfare, and air-refueling tankers, have provided decisive military advantages. DARPA envisions the wireless energy web as the next energy revolution, compressing transport timelines and resiliently delivering distributed energy to consumers across various domains—air, land, sea, undersea, and space.
“Energy underpins every human activity, including defense. We need ways to deliver energy that overcome the vulnerabilities and other shortcomings of our current paradigm,” explains Jaffe. “The next leap forward in optical power beaming could hinge on relay technologies.”
Effective relays are a critical missing component necessary for a practical, flexible, and adaptive wireless energy web. These relays will overcome the unacceptable conversion losses that occur when changing from propagating waves to electricity repeatedly in a multiple-hop network. Relays also enable high-altitude transmission, which is vastly more efficient than beaming power through the thick, turbulent, lower atmosphere. This high-altitude optical layer will provide the long-range, high throughput backbone for the wireless energy web.
If the POWER program is successful, it could have a major impact on the military. It could reduce the need for fuel, which would make military operations more sustainable. It could also reduce the number of convoys that are needed to deliver supplies to remote bases, which would make those bases less vulnerable to attack.
“We believe the next energy revolution will be enabled by the wireless energy web,” said Calhoun. “It will dramatically compress transport timelines and resiliently provide distributed energy to consumers in air, on land, on the sea, undersea, and in space.”
DARPA’s POWER initiative offers a transformative solution to the energy challenges faced by the military. By harnessing the power of lasers and wireless power transfer, the program aims to reduce the reliance on fuel convoys, improve operational flexibility, and enhance safety for troops deployed in remote areas. With ongoing development efforts, the future could witness a revolution in energy distribution that empowers military operations with efficient, resilient, and sustainable power sources across diverse theaters of operation.