U.S. Conducts Long-Range Power Beaming Demonstration
The first demonstration of long-range, free-space power beaming - a technology that enables energy to be transmitted using lasers - has been conducted at the U.S. Naval Surface Warfare Center in Maryland.
The system involves two 13-foot-high towers, one a 2-kilowatt laser transmitter, the other a receiver of specially designed photovoltaics. In the demonstration, invisible to the naked eye, a laser beamed 400 watts of power across 325 meters, from the transmitter to the receiver. The receiver converts the laser energy to DC power, which an inverter then turned into AC power to run lights, several laptops, and a coffeemaker that the organizers were using to make coffee for the attendees, or “laser lattes.”
PowerLight Technologies is the hardware provider for the Power Transmitted Over Laser (PTROL) project. The demonstration was two years in the making for PowerLight and Paul Jaffe, an electronics engineer with the U.S. Naval Research Laboratory (NRL).
Early power beaming demonstrations took place in 1975, the first in Waltham, Massachusetts in the laboratories of Raytheon, and the second at the Goldstone Station of the Nasa Deep Space Network in California. Those were the two most important such demonstrations in history, Jaffe said, before the demonstration.
Jaffe has been conducting space-based solar energy research for more than a decade, focusing in part on transmitting solar energy from space to Earth. One of the biggest challenges he and others working on the problem have faced is the enormous sizes required for the transmitter and the receiver.
“Radio waves have a fairly long wavelength and in order to steer them effectively ... you need a really big antenna,” he explained. “But as the wavelength gets shorter, as it does for infrared light, which is what we're using here today, the transmitter and receiver can be much, much smaller.”
The photovoltaics of the receiver are similar to those of a typical solar panel, although they are designed to be sensitive to the single color of light of the laser, rather than the broad spectrum of sunlight. They convert that particular wavelength with much greater efficiency than would a regular solar photovoltaic.
The technology is being developed to send power to remote locations and to beam power to electric unmanned aerial vehicles (UAVs). Flight time is currently severely limited by onboard battery life, and charging could be done ground-to-air or air-to-air.
“If you have an electric drone that can fly more than an hour, you're doing pretty well,” Jaffe said. “If we had a way to keep those drones and UAVs flying indefinitely, that would have really far-reaching implications. With power beaming, we have a path toward being able to do that.”
According to Jaffe, power beaming could also make possible the transmission of power from solar-energy-collecting satellites in space to the ground, wherever it’s needed—whether that’s a forward operating base, a developing country or a refugee camp.
“If we could capture the boundless sunlight in space, where it's brighter than anywhere on Earth, [we could] send it to places that are difficult and expensive to get energy to today,” he said. “If we can do that in an effective way and do for energy what GPS has done for navigation, it would truly be revolutionary.”
The technology also has the potential to power underwater autonomous vehicles for both increased enduranced and increased stealth.
The most notable aspect of the demonstration, says Jaffe, is the technology’s integrated safety systems. No one in the test facility that day was wearing laser safety goggles or any other kind of safety gear, including the personnel operating the system. To put that in perspective, a typical laser of just 1/2 watt requires protective eyewear.
Nearly all power beaming demonstrations in the past have involved at least the risk of exposure to hazardous power densities, whether optical or radio or microwave frequencies. The safety system has been designed detect objects such as humans and animals before they reach the laser beam and turn it off.
PowerLight now intends to increase the wattage the laser beam can transmit, increase the distance the system can send it and improve the system’s overall efficiency.
The system has received support and endorsements from the Navy, Marines, Army and Air Force. It’s expected to be ready to make the transition to Department of Defense and commercial use in the near future.