Source: Energy & Management Powernews, April 27, 2022
The sun sends energy incessantly, it just does not reach all sides of the earth at all times. A research project aims to change that by transmitting energy from space via microwaves.
Researchers at the U.S. military facility Naval Research Laboratory (NRL) have succeeded in transmitting a power of 1.6 kW of energy via microwaves over one kilometer. The terrestrial beaming is said to be the godfather of uninterrupted harvesting of solar energy from space - regardless of the time of day or night.
In a statement, the NRL not only calls it the most significant power beaming demonstration in nearly half a century. The technology, moreover, "can do something no other form of clean energy can do today," said NRL project manager Christopher Rodenbeck, namely deliver electricity around the clock.
Tens of thousands of antennas and a rectifier diode for direct current
At two sites in Blossom Point, Maryland, and Haystack, Massachusetts, the NRL and partner organizations conducted point-to-point transmission of electrical energy across free space using a direct microwave beam. The project is called "Safe and COntinuous Power bEaming - Microwave" (Scope-M).
Scope-M involves tens of thousands of X-band antennas for the frequency range between 8 and 12 gigahertz (GHz) connected to a small rectifier diode. They convert the incident microwave power into direct current. The demonstration, which was successful over a period of one year, "paves the way for power transmission on Earth, in space and from space to Earth," the NRL said.
The experiments involved a microwave beam at a frequency of 10 GHz. The NRL ruled out a higher frequency, Rodenbeck said, because it would be susceptible to losing power to the atmosphere. The chosen frequency was a "good choice because the component technology is cheap and mature," he said. Even in heavy rains, the power loss is less than five percent."
Originally aimed at powering armed forces
At the two sites, researchers have had varying degrees of success. In Maryland, the 1.6 kW transmission was about 60% above expectation at just over a kilometer. In Massachusetts, the NRL achieved lower peak power, but higher average power with significantly more energy output.
For future solar power harvesting using microwave technology, power densities that are harmless to humans and other living things should be maintained. Although the projects were Earth-based, Scope-M electronics engineer Brian Tierney considers the experimental setup a "good proof of concept for a space-power beaming link."
As is so often the case, military considerations are the starting point for this technological development as well. Tierney sees the main advantage of space-to-earth power transmission with the U.S. Department of Defense, the project's financier. Armed forces of the USA could make themselves thereby more independent of conventional fuel supply, which is to be prevented the preferential goal of hostile attacks.
Author: Volker Stephan