Using a few mirrors, solar panels and a microwave transmitter, Fan Guanheng and his team can send power over 100 metres (330 feet) through the air. But they are dreaming much bigger – 36,000km (23,460 miles) bigger.
The team at Xidian University in Xian, capital of northwest China’s Shaanxi province, are testing hardware that could one day be used to generate power in space and send it back to Earth.
On a sweltering June morning, the team were measuring how well light was concentrated by a 4.8-metre, dome-shaped mirror suspended from a 75-metre-tall tower.
The futuristic technology boiled down to three steps, said Fan, an associate professor at the university’s school of mechano-electronic engineering.
First, the mirrors focus sunlight onto solar panels, generating electricity.
Then, the electricity is converted into microwaves and beamed to an rectenna, a kind of antenna.
Finally, the rectenna transforms the waves back into usable electricity.
The best time to gather data was between 10am and 3pm, when sunlight was at its peak, Fan said – even if that meant the team suffered in the heat.
The payoff might eventually be worth the sweat.
While solar energy density on Earth tops out at 200-300 watts per square metre – due to night cycles, weather, and location – in the vacuum of space it can hit six times that. “That is why space-based solar power is a potential way out of the energy crisis on Earth,” he said.
The project, named Zhuri, or “chasing the sun”, is led by Xidian’s Duan Baoyan, a pioneering electromechanical engineer and former president of the university.
Last month, an expert review panel gave the project a major boost by signing off on the results of its experiments. According to Chinese media reports, the campus facility showed it could send kilowatt-level power more than 100 metres, while also proving that a single transmitter could zap power into multiple moving devices at the same time.
Next, Duan hopes to secure enough funding to carry out tests in orbit. “Right now, China is at the top tier of space solar research, neck and neck with countries like the United States and Japan,” he said.
The technical hurdles and financial costs of beaming electricity from some 36,000km away were staggering, Duan said.
For instance, a station capable of generating one gigawatt of power – enough to supply a mid-sized city – would require an array of mirrors spanning several hundred metres.
Deploying an array that massive would require sending folding or self-assembling structures into space, developing a microwave transmitter capable of near-perfect accuracy and strictly controlling microwave strength to ensure the energy beam posed no threat to aircraft or the environment on Earth.
But the underlying technology could also be used in the near future, either in ground-to-ground applications or space-to-space ones, Duan said.
For instance, it could wirelessly charge multiple satellites already in orbit, he said. “It could also be used to beam electricity wirelessly, either from the lunar surface or orbit, to China’s research base on the moon.”
Duan started to work on extraterrestrial power generation in 2012, when he was intrigued by articles on Nasa’s SPS-ALPHA project. That landmark study proposed building a massive solar-harvesting platform out of thousands of small satellites working together like a hive of bees.
The core appeal of space-based solar power was its raw efficiency, Duan said. In orbit, solar concentrators can harvest energy virtually 24 hours a day, avoiding the day-night cycle, cloud cover and atmospheric filtering that plague terrestrial solar arrays.
The Zhuri project’s design has undergone major revisions over the years. Duan and his team pivoted away from a single, massive structure to a modular system of smaller units that fly in formation and coordinate to generate and beam power.
The shift could make the system more resilient – if a single module fails, the rest of the system keeps running. This could drastically reduce the difficulty of deploying and maintaining the system, Duan said.
While waiting for their chance to experiment in space, Fan and the team of about 20 researchers continue to gather data and refine their hardware on the ground. Besides the dome-shaped mirrors, they are also experimenting with lenses based on Fresnel optics.
Fresnel lenses, which have often been used in lighthouses, use a series of concentric sections to concentrate more light using less material.
At the test field, three of these 2.7-metre-wide Fresnel lens arrays focus sunlight onto solar panels beneath them. As this process creates intense heat, the system uses a network of tubes carrying a cooling fluid to prevent the hardware from warping.
“Since there’s no air convection in space, figuring out how to cool the solar panels and use waste heat is a critical challenge,” Fan said. -- SOUTH CHINA MORNING POST
