Can high-efficiency solar cells power satellites?
With the arrival of a new batch of robotic expeditions, the observation of the space world may now focus on Mars, but later this year, NASA's ambitious "Lucy" mission will be snatched away Some limelight. On October 16th, Lucy launched into space for more than 10 years. She will go to the Troy Islands, a distant asteroid in Jupiter's orbit.
Most previous exploration of the outer solar system relied on expensive radioisotopes thermoelectric generators, such as the Voyager and New Horizons probes. Instead, Lucy carried a pair of solar panel arrays. They unfold like huge hand fans, each array 6 meters (20 feet) in diameter. Going beyond Jupiter's orbit will make Lucy farther from the sun than any previous solar panel - the previous record was Juno, which is currently in Europa's orbit.
Katie Oakman, Lucy's head of spacecraft structure and agency, said that the current "extreme power demand" is "the key to why solar panels are so huge and amazing."
This means advancing light volume research from different directions to focusing on the development of solar energy for the earth. Although cheap silicon photovoltaic cells provide the fuel for the planet's clean energy transition, space solar energy must rely on other types of solar panels. This means that space-based solar panels face severe temperature fluctuations between extreme cold and high temperatures. And this sunlight is different: for example, it has more ultraviolet rays than what we see on the ground.
There is another danger in space: ionizing radiation. Solar panels in the Earth’s orbit may face the vortex of the Van Allen belts, while solar panels elsewhere may need to withstand the solar wind. Over time, this radiation can erode the efficiency of solar cells. A solar cell has been operating in a geosynchronous orbit for 15 years and is about 36,000 kilometers (22,000 miles) high, and its effectiveness will drop to about 80%.
Early satellites in the 1950s and 1960s used silicon photovoltaic cells. But designers soon began to study so-called multi-junction (MJ) III-V solar cells, which are made of multiple layers of materials, each layer of material absorbing light of a different wavelength. MJ batteries are more efficient, more resilient under non-terrestrial conditions in space, and lighter.
"For these reasons, the aerospace industry has been using III-V solar cells for quite some time," said Ryan, a scientist at the National Renewable Energy Laboratory (NREL) in Denver's Suburban Surgery, Golden City, Colorado. France said.
NREL has taken the lead in launching the MJ III-V battery in the past few decades. Recently, researchers have pushed the MJ battery to a milestone of 50% efficiency. Most MJ cells consist of three layers, but in 2020, NREL researchers proposed a six-junction cell that has an efficiency of 47% under concentrated sunlight, which is better than silicon photovoltaic cells.
However, on the earth, MJ cells face an economic obstacle: the low cost and overwhelming market dominance of silicon photovoltaic cells, together, make the commercialization of MJ cells a struggle. Since 1980, the price of silicon cells has fallen by 60 times, and this decline shows almost no sign of stopping.
So far, MJ batteries are mainly used for concentrating solar energy, using mirrors or lenses to focus and enhance sunlight on solar panels. This has produced impressive efficiency data, but it cannot compete with cheap silicon outside of the laboratory.
But NREL researchers have now shifted their attention from the 50% performance index to reducing the cost of MJ batteries. "The more we reduce costs," France said, "we may have more markets." They hope to pave the way for new applications for MJ batteries, although it is unclear what these applications might be.
But cheaper solar cells will undoubtedly benefit space applications in turn. Oakman believes that solar panels like Lucy have a place in the future of mankind, especially near Jupiter, where the temperature and light levels are much lower than those near Earth.
"If we want to continue to launch spacecraft into the outer solar system," she said, "then I think there are various opportunities to use this design in the future."