"Infinite with Just the Sun"… Space Solar Power is Rising [Reading Science]

Major Space Powers Developing Space Solar Power Technology
Emerging as Key Energy Source in Carbon Neutral Era,
Lower Launch Costs and Higher Solar Power Efficiency Enable 'Practical Use'
Much More Efficient and Eco-Friendly Than Ground-Based Systems, Commercialization Expected in 2030s
Korea Lags by Decades... Must Secure Core Technologies and Launch Vehicles for International Cooperation

[Asia Economy Reporter Kim Bong-su] Isaac Asimov, a master of science fiction (SF) novels, presented a surprising idea in his 1941 short story "Reason." The concept was to generate electricity using solar power on a space station and transmit it to Earth, Mars, or other planets. Although it seemed like "science fiction," it has recently emerged as an alternative power source amid the urgent carbon neutrality (Net Zero) challenge and the dawn of the New Space era. As related technologies such as space launch vehicles and solar power generation advance, major countries worldwide are accelerating efforts to realize this vision. As early as the 2030s, megawatt-class space solar power plants are expected to be constructed, ushering in an era where electricity is sent to Earth, satellites, spacecraft, and lunar bases. South Korea is a latecomer, lagging at least ten years behind other countries. Voices are rising that Korea must secure core technologies through convergent research and participate in the construction of space solar power plants, which will be achieved through international cooperation, to claim its share.

◇ Why Space Solar Power?

Humanity, which must prevent global warming, is desperately pursuing the development of non-fossil fuels that do not emit carbon, i.e., renewable energy. Solar power is a representative example because it causes little environmental pollution and can produce infinite electricity. However, solar power generation on the Earth's surface has many limitations. Solar rays entering the atmosphere are absorbed and reflected by clouds and dust, and scattered by the atmosphere. In particular, solar power generation has a fatal weakness in that its efficiency drastically decreases on cloudy or rainy days and is impossible at night. There are also large variations depending on season and latitude. Large-scale solar power facilities cause many side effects such as aesthetic damage, forest destruction, and reduced agricultural productivity.

However, it is different in space. The intensity of solar power is much stronger. It can operate 24 hours regardless of weather or day and night. Accordingly, major countries worldwide are researching space solar power plants to produce clean electricity. The concept is to place a giant solar power device, 3 to 6 km wide, on a satellite in geostationary orbit at about 36,000 km altitude, generate electricity, and then transmit it via microwave or laser beams to be converted back into electricity for use. According to the Korea Aerospace Research Institute (KARI), if a 1㎡ solar cell generates 0.4 kW on the ground, it produces 0.7 to 0.8 kW in the stratosphere, and about 1.36 kW at the geostationary orbit at 36,000 km where space solar power plants are located. Considering that electricity is produced 24 hours regardless of weather, latitude, or day and night, the efficiency of space solar power plants is more than ten times higher than on the ground. Most of the technologies required to build such space solar power plants have already been developed, so only scaling up, improving efficiency, and stabilization remain, which is also a positive factor. Choi Jun-min, a senior researcher at KARI's Future Innovation Research Center, said, "It is one of the technological alternatives to overcome the challenge of sufficiently supplying clean energy in the carbon-neutral era," adding, "If Korea installs a giant rectenna (receiving device) on the Demilitarized Zone and jointly utilizes it with North Korea, it will bring great benefits such as inter-Korean exchange, peace settlement, and mutual resolution of power issues."

◇ Countries Worldwide Have Joined In

The most advanced is the United States. The U.S. began research in the 1970s but stopped due to immature technology and lack of economic feasibility. However, it has accelerated rapidly since the 2000s, judging that conditions have greatly improved with advances in solar power generation and space launch vehicle technologies. The U.S. is already at the stage of experimenting with satellites that transmit and receive power. In June 2020, the U.S. Naval Research Laboratory launched the space solar power satellite (SPS-ALPHA) module into orbit to conduct actual solar power generation and radiative energy conversion. They are studying how well energy conversion and transmission occur in the space environment and how to solve heat generation problems. In April last year, the U.S. Air Force Research Laboratory (AFRL) started a pilot project for space solar power generation, planning to solve energy supply threats to isolated forward military bases through space solar power. NASA is also researching plans to launch a 5 GW-class giant space solar power satellite (SPS). It is an enormous size, 5 km wide and 15 km long. The ground receiving antenna is also being considered at a scale of 6.5 km wide and 8.5 km long. The U.S. Department of Defense developed the Wireless Solar Power Experimental Device (WISPER) and conducted experiments transmitting power using 35 GHz microwaves from a 600 km polar orbit to the ground.

Europe, which is active in carbon neutrality, is also entering space solar power. The UK launched the "UK Space Energy Initiative" last year, involving over 50 companies and research organizations including Airbus, Cambridge University, and satellite manufacturer SSTL, to begin full-scale research and development. The engineering company International Electric Company is already developing a space solar power satellite named "CASSIOPeiA."

Japan has been researching wireless power transmission technology since the 1990s and is pushing plans to launch space solar power satellites in the 2030s and supply 1 GW-class power from space around 2040. China is also at the forefront due to active government investment. Since 2014, China has been researching space solar power satellites (MR-SPS) and aims to commercialize them in the 2030s and install gigawatt-class space solar power facilities in the 2040s to supply power to the ground using microwaves or lasers.

Conceptual diagram of space solar power generation by the National Aeronautics and Space Administration (NASA).

◇ South Korea Lagging by Decades

South Korea began full-scale research by including space solar power generation in the 3rd National Space Development Promotion Plan in 2018. KARI presented a roadmap the following year to launch a "Korean-type space solar power satellite." The plan is to complete wireless power transmission technology, solar power generation and receiving equipment development, and high-capacity power management system construction between 2020 and 2025. Subsequently, related technologies will be demonstrated through small satellites by 2029, develop kilowatt-class by 2035, megawatt-class in the 2040s, and construct gigawatt-class space solar power plants for power supply after the 2050s.

The core technology of long-distance wireless power transmission is being vigorously developed by the Korea Electrotechnology Research Institute (KERI). By last year, KERI developed equipment that converts 4.8 kW power into microwaves and can transmit and receive at a distance of 110 meters and is currently testing it. In this process, they achieved results such as high-performance small transmission devices for wireless power transmission, including the world's highest-efficiency pre-matching power amplifier, ultra-high-frequency integrated devices, and high-capacity, high-efficiency receiving circuits based on new materials. They completed Korea's first outdoor wireless power transmission test station and implemented a 10 kW-class remote-linked transmission system. They also developed technology to track targets whose positions change in real time to transmit and receive power, and experiments on actual flying objects will be conducted within this year. They plan to complete the development of wireless power transmission technology for space power by 2025.

The problem lies in securing efficiency and safety in the power transmission and reception process. While major advanced countries achieve about 70-80% of received power compared to generated power, the equipment developed by KERI is known to be below this level. The RF wireless power transmission system developed by KAIST in 2019 also had only 20% efficiency at a 10-meter distance. Concerns about the safety of microwaves also need to be resolved.

Since space solar power involves complex technologies, various technical challenges exist. First, high-performance space launch vehicle technology is needed to transport materials, modules, and components for power plant construction to geostationary orbit. The U.S., Japan, China, and Europe all have launch vehicles, but South Korea will only be able to own launch vehicles regularly by 2030, even if the second Nuriho launch in June succeeds and the next-generation launch vehicle is safely developed. Especially, developing reusable, recyclable rockets using clean and low-cost fuels to minimize single-launch costs is essential. Along with wireless power transmission technology that guarantees efficiency and safety, high-efficiency and flexible solar cell manufacturing technology, unmanned artificial intelligence (AI) robot technology for assembly, and material technology for ultra-lightweight and ultra-strong structural construction must also advance.

Lee Sang-hwa, a senior researcher at KERI's Power ICT Research Center, explained, "The intensity of microwaves is not at a power level that cooks or melts materials; at its highest, it is several times the direct sunlight on a sunny day, and the edges of the receiving part are designed to be at a level that does not affect the human body," adding, "Technologies to monitor, adjust, and block the beam in real time to ensure it is accurately directed are also being developed, so there is no major safety issue. Technologies to improve efficiency, such as making the receiving antenna larger and lowering the operating frequency, are also under research."