Is space solar power an expensive and risky dream? Or is it a viable way to combat climate change? Although beaming solar energy from space to Earth may eventually involve transmitting gigawatts, the process can be made surprisingly safe and cost-effective, according to experts from Space Solar, the European Space Agency and the University of Glasgow.
But we will need to go far beyond demo hardware and solve a number of engineering challenges if we are to develop this potential.
Space Solar Design
Beaming solar energy from space is nothing new; telecommunications satellites have been sending microwave signals generated by solar energy back to Earth since the 1960s. But sending useful amounts of energy is an entirely different matter.
“The idea [has] it’s been around for a little over a century,” Nicole Caplin, ESA’s deep space exploration scientist, said in a Physics World podcast. “The original concepts were really science fiction. It’s kind of rooted in science fiction, but then, since then, there’s been a trend of interest that comes and goes.”
Researchers are considering numerous space solar energy projects. Matteo Ceriotti, a senior lecturer in space systems engineering at the University of Glasgow, writes in The Conversation that many designs have been proposed.
The Solaris Initiative is exploring two possible technologies, according to Sanjay Vijendran, head of the Solaris Initiative at ESA: one that involves beaming microwaves from a station in geostationary orbit down to a receiver on Earth, and another that involves using huge mirrors in lower orbit , to reflect sunlight down onto the solar farms. He said he thinks both solutions are potentially valuable. Microwave technology attracted wider interest and was the main focus of these interviews. It has huge potential, although high frequency radio waves can also be used.
“You really have a 24/7 source of clean energy from space,” Viendran said. Power can be transmitted regardless of weather conditions due to the microwave frequency.
“One gigawatt power plant in space would be comparable to the first five solar farms on earth. A 1 gigawatt power plant can power about 875,000 households for a year,” said Andrew Glester, host of the Physics World podcast.
But we are not ready to implement something like that. “It’s going to be a big engineering challenge,” Caplin said. There are a number of physical obstacles involved in successfully building a solar power plant in space.
Using microwave technology, the solar array for an orbiting power plant that generates a gigawatt of power would need to be more than 1 square kilometer in size, according to a Nature paper by senior reporter Elizabeth Gibney. “It’s more than 100 times bigger than the International Space Station, which took a decade to build.” It will also have to be assembled robotically, since the orbiter will be unmanned.
Solar cells must be resistant to cosmic radiation and debris. They also need to be efficient and lightweight, with a power-to-weight ratio 50 times that of a typical silicon solar cell, Gibney wrote. Keeping the cost of these cells down is another factor that engineers must consider. Reducing losses during power transmission is another challenge, Gibney wrote. The energy conversion rate should improve to 10-15 percent, according to ESA. This will require technical progress.
Space Solar is working on a satellite design called CASSIOPeiA, which Physics World describes as looking “like a spiral staircase, with photovoltaic panels being the ‘steps’ and microwave transmitters – rod-shaped dipoles – being the ‘risers.'” has a spiral shape with no moving parts.
“Our system consists of hundreds of thousands of dish-sized power modules. Each module has a PV that converts solar energy into direct current,” said Sam Adlen, CEO of Space Solar.
“This constant power then drives the electronics to transmit the power … down to Earth from dipole antennas. This force in space is converted into [microwaves] and is beamed down in a coherent beam to Earth, where it is received by a rectifying antenna, converted back into electricity, and fed into the grid.
Adlen said robotic technologies for space applications, such as in-orbit assembly, are advancing rapidly.
Ceriotti writes that SPS-ALPHA, another design, has a large solar collector structure that includes many heliostats, which are modular small reflectors that can be moved individually. They concentrate sunlight on individual modules to generate power, which is then transmitted back to Earth by another module.
