The vagaries of the weather here on earth and the nightly blackout limit the power we can get from solar energy. But this energy could take on a whole new dimension if it can be captured in space 24 hours a day by gigantic stations and transmitted to earth.

In the face of limited fossil resources (oil, gas and coal), rising demand for electricity (projected to double by 2050) and serious environmental concerns (global warming), the most sustainable of the alternative energies currently available to our planet is the sun. The lure of this almost inexhaustible energy source, with reserves estimated at four to five billion years, has stimulated very strong growth: worldwide, solar-generated electricity has grown by an average of 35% annually since 1998. A self-fulfilling prophecy? Perhaps. But already, scientists are coming up with the solutions that will completely do away with the limits – especially intermittent sunshine – to capture this energy on earth. And they’ve found the place with just the right conditions: space.

Shades of science fiction

It is not a new idea. The earliest interstellar adventures of science fiction were already on to it. But it was Dr. Peter Glaser, an American scientist, who formalized the concept of space-based solar power (SBSP) in 1968. It involves transmitting several gigawatts of energy from space to earth via microwaves using geosynchronous satellites equipped with solar collectors. The concept keeps resurfacing every ten years or so, triggering assessments by various businesses and institutions, mostly American, such as the US Department of Energy, NASA, Raytheon, Lockheed Martin and Boeing. Despite all the resources available, the various technical solutions considered have never sparked joint programs, for lack of a real commitment to cooperation. A think tank expert who works for the Pentagon explains it this way: “The problem is that the DOE does not work on space, and NASA works on space but not on energy!” Today, the required funding will likely have to come from international cooperation. A number of private companies have recently been created to begin the process of raising funds and pooling the necessary capabilities. The goal is to develop mature, economically viable technologies for commercial deployment in around 2030.

A sustainable energy with considerable appeal

If Dr. Glaser’s concept is to be possible in the short term, it will be thanks to technological advances. Radio-wave transmitters, lasers and photovoltaic materials have all made major strides in forty years, while the conquest of space is opening up prospects for the installation of large solar energy capture stations in orbit. The international scientific community now recognizes the advantages of such stations, and several concepts abound. Solar energy captured in space could be transmitted to earth to generate clean, reliable, high-quality electricity. Since it is available 24 hours a day, 365 days a year, there would be no need to store the electricity, increasing its appeal as an alternative energy source in areas with no local source of primary energy production. Countries without enough demand or the infrastructure to justify nuclear power or renewable energies could be quite interested in the "direct-fromspace" solar power option. But the very high costs of acquiring the necessary infrastructure, both on land and in space, make it likely that international financing will have to be provided and the resulting energy shared. Space-based solar-generated electricity could also offer developing countries several benefits. They would no longer have to turn to fossil fuels, which cause pollution and are expensive to extract and use, to achieve fast, widespread electrification on a large scale, thereby dramatically improving living standards for their citizens. Just a few of the benefits: irrigation could be expanded, energy supplied to schools and hospitals, hygiene standards improved, especially in the area of water treatment, and food reserves more reliably conserved.

Frequencies similar to household systems

The two technologies chosen to transmit energy from space to earth have their pros and cons, though the advantages largely outweigh the disadvantages in each case. Both technologies are capable of transmitting a large amount of power over very long distances with very little power loss.

Produced by a combination of mirrors and photovoltaic panels, the microwaves sent from space are at frequencies of 2 to 8 GHz (several projects have settled on 5.8 GHz), which are within the range of frequencies used in the home: internet, television, microwave ovens, cell phones, etc. The spacebased solar power concept is very efficient: energy losses are less than 2%, and it has no health effects. Another promising technology, developed more recently, involves transmitting captured solar energy by laser beam. Rather than putting photovoltaic panels into orbit, the satellite is covered with special ceramic tiles made with chromium and neodymium, which act like high-power diodes to transmit solar energy to a laser amplifier.

The amplifier transmits a laser beam to a photovoltaic panel on earth, which generates electricity.

Installing collectors on the moon?

Then there are the much longer-term lunar projects, some 300,000 kilometers from earth. That’s the destination of programs that seek to restart human travel to our natural satellite. Photovoltaic collectors made with lunar materials would be placed on a fixed base on the two quarters of the moon’s visible surface, which alternate in being lit up by the sun, and would send a microwave beam to earth. But microwave transmission is only possible when the moon is in direct alignment with the land-based receiving station. Collectors orbiting the moon or the earth must be able to fill this role the rest of the time.

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The space-based solar energy collection system consists of the space component itself (space infrastructure, including the satellite, mirrors, solar panels, etc.), the transmission process (microwaves or laser beam) and the land-based component (receiving antenna).