While on the surface of the Earth, society still struggles to adopt solar energy solutions, many scientists maintain that giant, space-based solar farms could provide an environmentally-friendly answer to the world’s energy crisis.
Only last week, we reported that China was planning to build the world’s first solar power station to be positioned in Earth’s orbit. Because the sun always shines in space, an orbital solar power station is seen as an inexhaustible source of clean energy.
“Above the Earth, there’s no day and night cycle and no clouds or weather or anything else that might obstruct the sun’s ray, so a constant power source is available,” said Ali Hajimiri, professor of electrical engineering at the California Institute of Technology and co-director of the university’s Space Solar Power Project.
Proposed space solar array SPS-ALPHA, image and concept courtesy John C. Mankins.John C. Mankins
Collecting solar power in space and wirelessly transmitting was first described by Isaac Asimov in 1941 in his short story Reason. In 1968, American aerospace engineer Peter Glaser published the first technical article on the concept – Power From The Sun: Its Future in the journal Science.
Space-based solar power attracted considerable attention in the 1970s as the necessary individual technical components – in essence, photovoltaic cells, satellite technology and wireless power transmission – were developed. Despite the concept being technically feasible, it was considered economically unrealistic at the time and research ultimately stalled.
“The idea seems to be going through a resurgence and it’s probably because the technology exists to make it happen,” said John Mankins, a former NASA scientist who was at the forefront of this field in the 1990s, before it was abandoned.
Aerospace engineer Peter Glaser first wrote about the idea in 1968.Science magazine
Global energy demands are only going to grow, says Hajimiri. The global population is expected to reach a staggering 9.6 billion by 2050, according to a United Nations report, so methods of generating large quantities of clean energy must be found. A space-based solar power system could provide energy to everyone, even in places that don’t receive sunlight all year round, like northern Europe and Russia.
In April of 2015, a research agreement between Northrop Grumman and Caltech provided up to $17.5m for the development of innovations necessary to enable a space solar power system. Three Caltech professors head up the project: joining Hajimiri were Harry Atwater and Sergio Pellegrino.
Caltech is just one institution working on developing this technology. We know that scientists at the Chongqing Collaborative Innovation Research Institute for Civil-Military Integration in China are constructing a facility to test the theoretical viability of the concept and plans to develop an orbital photovoltaic array were announced in Japan some time ago.
One of the biggest issues to overcome is that of getting an array of solar panels large enough to make the project viable into orbit. Early concept designs in the 1970s featured giant arrays that would’ve proved very difficult to actually get into orbit.
“The systems of the 70s for solar power satellites, the cost estimates suggested, at that time, that it might be as much as a trillion dollars to get to the first kilowatt hour because of the way the designs worked. Essentially a single satellite, a platform, an integrated, monolithic platform about the size of Manhattan,” said Mankins.
However, with SpaceX and Blue Origin slowly driving the cost of orbital delivery down, suddenly the concept seems a little closer to reality.
“Going to modular systems to allow mass production, I believe was the answer to how to get solar power satellite costs down to something more reasonable,” said Mankins.
The multi-rotary SPS (MR-SPS) concept is one with multiple independent solar sub-arrays used to point to the sun.NASA
Details of China’s proposed plans have not been made public, but most concept designs that exist today are based around an idea that the photovoltaic array is composed of a lightweight, deployable structure made of many smaller “solar satellites” that could easily connect together in space to form much larger array and “harvest sunlight.” Equally, this approach also makes assembly, maintenance and repair considerably easier.
“I’ve seen a presentation on what they [China] are presumably doing. I can’t guarantee that’s actually it, but it was by them, about the space solar system. What I’ve seen appears to be a conventional approach, which is similar to what people are currently contemplating,” said Hajimiri.
This completed array would orbit about 22,000 miles above the Earth and “beam” the energy back down to the surface. The photovoltaic array converts the sunlight into electricity, which in turn is converted into RF electrical power (microwaves) that are beamed wirelessly to ground-based receivers. These would take the form of giant wire nets measuring up to four miles across that could be installed across deserts or farmland or even over lakes.
A solar facility like this could generate a constant flow of 2,000 gigawatts of power, Mankins estimates, compared to the largest solar farm that exists today in Aswan, southern Egypt, that only generates in the region of 1.8 gigawatts.
It’s unlikely the solar array could be weaponized into a “death ray” like the one seen in Diamonds Are Forever.MGM/United Artists
An orbiting solar array, collecting and storing massive amounts of energy that’s beamed to the surface… You’d be forgiven for thinking this could be the plot of a James Bond movie, if this array was somehow weaponized.
Thankfully, that’s not how it works.
“The energy densities will not exceed what you normally would get. It would definitely not exceed what you get from the sun,” said Hajimiri.
The microwaves that transmit the energy to the surface would be at the so-called non-ionizing radiation frequency. “What that means is that the frequencies are such that unlike x-rays, these are the frequencies at which their photons don’t have enough energy to induce chemical change, like that ultraviolet or x-rays do,” said Hajimiri.
“I’ve been working on wireless power transmitters that would operate in the microwave frequency range, between about 2 gigahertz and 8 gigahertz, roughly. Wavelengths on the order of 10 to 2 inches. Those wavelengths of electromagnetic radiation can pass through the Earth’s atmosphere, including clouds and weather, without interruption, without interference.”
However, Mankins expects there might still be some problems. “There’s always the geopolitics issue. Because when you’re at an equatorial orbit, geostationary Earth orbit, you can see a great deal of the Earth below you. For me, it’s challenging to envision how there would ever be agreement to allow such a thing.”
The team at Caltech have successfully tested their proof of concept on the ground, their photovoltaic prototypes demonstrated they can collect and wirelessly transmit 10 gigahertz of power, so the next step is to perform scaled down experiments in space.
The biggest challenge is to reduce the mass as much as possible without sacrificing efficiency. Of course, that would also help reduce cost, which is probably still the biggest hurdle.
“Hopefully, we’ll be able to test it in space within a couple of years,” said Hajimiri.
“Space solar power would transform our future in space and could provide a new source of virtually limitless and sustainable energy to markets across the world,” said Mankins. “Why wouldn’t we pursue it?”
John Mankins has written a book called The Case for Solar Power, which is available on Amazon.