ETERNAL ENERGY

Space solar power refers to the concept of collecting solar power in outer space and transferring it to Earth. Ge Changchun, an academician of the Chinese Academy of Sciences, published an article in China Science Daily in May 2021, saying that space solar power stations and controlled nuclear fusion power stations are considered the two most likely energy solutions for sustainable power. “However, controllable nuclear fusion is still in the preliminary research stages, while there are no basic scientific problems for space solar power stations. Although the project is huge, relevant technologies can make important breakthroughs in a certain time through continued research and development,” Ge wrote. He estimated that by the second half of this century, China will create a space solar power generation industry, which will be an important component of China’s energy infrastructure. 　

Weather and geographic conditions restrict solar energy collection on Earth, causing a high rate of energy loss. Collecting solar energy in space has a higher collection rate and a longer collection period because of the attenuation effect of the atmosphere. Attenuation means that incoming solar radiation is weakened, scattered and absorbed by other solid and liquid particles as it passes through the Earth’s atmosphere. 　

Yang Shizhong, an academician of the Chinese Academy of Engineering and director of the Institute of Communication and Measurement and Control of Chongqing University, told NewsChina that because of atmospheric attenuation, power generated by ground solar power stations is limited and varies significantly based on location. For example, in northwest China, which has sufficient sunshine, a square meter of photovoltaic cells can generate 0.4 kilowatts (kW) per hour of electricity, but only 0.1 kilowatt per hour in the foggy city of Chongqing. In a geosynchronous orbit of 36,000 kilometers, power generation would be up to 10 kW to 14kW per hour. In space, diffusion of the atmosphere, seasonal changes or daily light changes do not affect solar panels. There is steady and sustained solar radiation up to 99 percent of the time, which can generate uninterrupted power with an energy efficiency dozens of times that of solar energy generated on the ground. 　

Microwaves and lasers are the two long-distance wireless energy transmission carriers for space solar power stations. Microwaves are more efficient, have lower cloud penetration loss, and are the safer, more mature technology. 　

The concept of space solar power satellites, originally known as satellite solar-power systems, was first described in 1968 by CzechUS engineer Peter Glaser as a method to transmit power over long distances (from an orbiting station to the Earth’s surface) using microwaves from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna, on the ground. In the 1970s, the US government invested about US$50 million in this research and by 1979, the world’s first concept project, “1979 Reference Solar Power Satellite (SPS) System,” was designed. 　

Amid the global oil crisis, NASA and the US Department of Energy designed a system to supply half of the nation’s electricity needs in the 21st century. The 1979 Reference SPS system planned to deploy up to 60 solar power satellites into geostationary Earth orbit, with each system generating power ranging from 5 to 10 GW of continuous energy. The estimated cost was US$250 billion. 　

The 1979 Reference SPS architecture aroused debates. Reviews of the National Research Commission and the Congressional Review Committee deemed it technically workable but programmatically and economically unachievable. Research in the US has since stagnated because of the difficulty, low efficiency and high cost of the plan. Since 2007, the US Department of Defense National Security Space Office conducted a 2007 study titled Space-based Solar Power as an Opportunity for Strategic Security, which concluded that the US should begin a coordinated national space solar program, pointing out that space power satellites can supply power for remote locations such as military bases. 　

The International Academy of Aeronautics published its report the “First International Assessment of Space Solar Power: Opportunities, Issues And Potential Pathways Forward” in 2011. John C. Mankins, former Commission Chair of the International Academy of Astronautics, said at the press conference for the assessment report that SPS appeared to be achievable during the next one to three decades, but “more information is needed concerning both the details of potential system costs and the details of markets to be served.” 　

Japan has been the world leader in the research of microwave wireless energy transmission technology, thus it boasts advantages in developing space solar. It is the first country to formally include the development of commercial space solar power in its national space program. In 2017, Japan announced a development road map, claiming it would build a commercial space power station by 2050. 　

In reality, apart from a demonstration test on long range wireless power transmission by the Japan Aerospace Exploration Agency and Mitsubishi, only China has entered the ground verification stage for space solar power, while it is purely conceptual in other countries. 　

Yang Shizhong, technical head of the Bishan space solar project, told NewsChina that the key to space solar power is steady wireless transmission of power from space to the ground power grid. As a result, the major obstacle is high-power and long-distance wireless energy transmission technology. 　

Major issues include whether the transmission efficiency is large enough and whether the beam points to the prescribed reception caliber to reduce error as much as possible. These technologies should be tested on floating platforms to lay the foundation for a real space solar power system plan. 　

The Bishan project covers an area of about 200 mu (133,333 square meters), costing about 2.6 billion yuan (US$0.4b), although only 100 million yuan (US$15.43m) in funding is in place. 　

“It’s like launching a new satellite. People have to test it on a balloon or plane at high altitude to solve technical problems before sending the satellite up by rocket. The role of the Bishan experiment is similar,” Yang said. 　

Duan, an expert in antennas, handled the overall design of the Fivehundred-meter Aperture Spherical Radio Telescope (FAST) in Southwest China’s Guizhou Province. On the campus of Xidian University, the team has set up a 75-meter test tower which will function similar to the Bishan floating platform. 　

According to Duan, the spotlight mirror, photoelectric conversion system and transmission antenna have been installed on the tower, and it can transmit power to the ground from a height of 50 to 60 meters. Construction started in 2018.　

Formal discussions on space solar power began in China in 2006. In July of that year, China Aerospace Science and Technology Corporation organized a seminar on the concept of space solar power. An expert in the field from the China Institute of Space Technology, who attended the seminar told NewsChina that a private enterprise, Pulande Electric Power Technology from Shanxi Province raised the issue and submitted a proposal to the Bureau of Science, Technology and Industry for National Defense. The bureau leader realized its importance and assigned the China Aerospace Science and Technology Group to conduct preliminary research and evaluation. 

In 2014, China released its development plan and road map for space solar power. By 2030, it indicated there would be a small 1 megawatt (MW) station, and the second stage is by 2050, to scale up and upgrade the existing station to the gigawatt level or 1 million kW, 1,000 times that of the MW level. 　

The planned solar power station would be in geosynchronous orbit about 36,000 kilometers above the equator, or high orbit. Most satellites orbit the Earth at around 160-2,000 kilometers in near-Earth orbit. The International Space Station (ISS), orbits around 400 kilometers up. Space starts around 100 kilometers up. 　

The expert from the China Institute of Space Technology said that SPS is very large system engineering that far exceeds existing space facilities in both scale and weight. It is considered the “Manhattan project” of the space and energy field. 　

The weight of a small MW space solar station is already larger than most of the ISS today, and the in-orbit assembly of a station is far more challenging than the construction of a space solar array the size of the ISS. 　

Space stations have several compartments which space robotic arms can assemble. However, a solar station requires assembling many modules, which cannot be done with current space technology. It requires the creation of a space assembly system to simplify the interface as much as possible which will involve complex space robotics. 　

“Just imagine thousands of modules being launched into the sky, first into the near-Earth tracks, then advancing to the high orbit before being released and assembled. The process is certainly far more complex than we can think about now,” the expert said. 　

According to the road map, the first stage of the MW level solar space station construction is divided into three steps: first, to conduct the ground and floating test to verify the key technologies, which is conducted by the Bishan project and the trial of the Xidian University team, respectively; second, to conduct high-altitude ultra-high voltage power transmission verification, and finally, to test space wireless energy transmission. 　

Experts interviewed by NewsChina said that Japan, the US and China are planning to test an space solar system by 2050, but because of the high cost, whether any country will achieve the second stage by that time is uncertain. 　

“Technically, it’s viable, but the key is sufficient confidence, which will decide our willingness for future investment. If investment can be enhanced, there is a chance we’ll achieve the goal earlier than planned,” the expert said. 　

The space expert said that because of the scale and complex structure of a space-based solar power station, achieving the required orientation while transmitting power at the same time is highly complex. 　

A new space solar satellite concept, a focusing one, has been proposed. John C. Mankins termed it “SPS-ALPHA” (Solar Power Satellite by means of Arbitrarily Large Phased Array) in 2012. According to Mankins in a project report, SPS-ALPHA would be in geostationary Earth orbit, where it would intercept sunlight using a collection of individually pointed thin-film mirrors, convert that sunlight across a large radio frequency aperture into a coherent microwave beam and transmit the power to markets on Earth or in space. Thus, it does not require the reorientation of the antenna fixed toward Earth. 　

In Duan’s opinion, the biggest problem with non-focusing space solar satellites is low efficiency. Therefore, the focusing scheme will remain the current target of research. 　

A tall triangular tower stands on the campus of Xidian University On the tower, at 55 meters above the ground, there are four hemispherical focusing devices, each about 6.7 meters in diameter. When sunlight shoots into the spherical reflector, it gathers into a fixed concentrating area, enters the photovoltaic cell and generates DC electricity before turning into a microwave and transmitting to the ground through the transmitting antenna. This is a new scheme named SSPSOMEGA by Duan’s team under the premise of the same power hypothesis as the ALPHA scheme. According to Duan, with the same power collection of the ALPHA scheme, the proposed scheme has a higher and more stable solar concentration efficiency. 　

By the end of the year, Duan told the reporter that his team expects to complete OMEGA’s ground verification test, and if successful, the next step would be to attempt to raise it up.