By Rajat Sharma
The Sun never sets in space. The idea of harvesting solar energy via power-beaming satellites has therefore long intrigued researchers looking for ways to feed an energy-ravenous Earth. That reflection has fomented for decades but is now garnering new looks all over the world: Technologists in the U.S. and China, experts in Japan and researchers within the European Space Agency and the United Kingdom Space Agency are all working to make space-based solar power a reality.
It sounds like science fiction: giant solar power stations floating in space that beam down enormous amounts of energy to Earth. And for a long time, the concept – first developed by the Russian scientist, Konstantin Tsiolkovsky, in the 1920s – was mainly an inspiration for writers. A century later, however, scientists are making huge strides in turning the concept into reality. The European Space Agency has realized the potential of these efforts and is now looking to fund such projects, predicting that the first industrial resource we will get from space is “beamed power”. Climate change is the greatest challenge of our time, so there's a lot at stake. From rising global temperatures to shifting weather patterns, the impacts of climate change are already being felt around the globe. Overcoming this challenge will require radical changes to how we generate and consume energy. Renewable energy technologies have developed drastically in recent years, with improved efficiency and lower cost. But one major barrier to their uptake is the fact that they don't provide a constant supply of energy. Wind and solar farms only produce energy when the wind is blowing or the sun is shining – but we need electricity around the clock, every day. Ultimately, we need a way to store energy on a large scale before we can make the switch to renewable sources.
High Earth Orbit is a great place for a Solar Farm- the sun never sets and clouds never form, but to generate a meaningful amount of electricity, most past designs were unrealistic, unaffordable and massive. Engineers depicted giant truss structures, usually measured in kilometers or miles, to which photovoltaic panels or mirrors were attached, absorbing or concentrating sunlight to convert to direct current, then transmit it to the ground via laser or microwave beams, Hundreds of Rocket launches might be needed to build a Single Installation, It was technology too big to succeed.
How does it work?
Self-assembling satellites are launched into space, along with reflectors and a microwave or laser power transmitter. Reflectors or inflatable mirrors spread over a vast swath of space, directing solar radiation onto solar panels. These panels convert solar power into either a microwave or a laser, and beam uninterrupted power down to Earth. On Earth, power-receiving stations collect the beam and add it to the electric grid.
The two most commonly discussed designs for SBSP are a large, deeper space microwave transmitting satellite and a smaller, nearer laser transmitting satellite
Microwave Transmitting Satellites
Microwave transmitting satellites orbit Earth in geostationary orbit (GEO), about 35,000 km above Earth's surface. Designs for microwave transmitting satellites are massive, with solar reflectors spanning up to 3 km and weighing over 80,000 metric tons. They would be capable of generating multiple gigawatts of power, enough to power a major cities in India.
The long wavelength of the microwave requires a long antenna, and allows power to be beamed through the Earth's atmosphere, rain or shine, at safe, low intensity levels hardly stronger than the midday sun. Birds and planes wouldn't notice much of anything flying across their paths.
The estimated cost of launching, assembling and operating a microwave-equipped GEO satellite is in the tens of billions of dollars. It would likely require as many as 40 launches for all necessary materials to reach space. On Earth, the rectenna used for collecting the microwave beam would be anywhere between 3 and 10 km in diameter, a huge area of land, and a challenge to purchase and develop.
Laser Transmitting Satellites
Laser transmitting satellites, as described by our friends at LLNL, orbit in low Earth orbit (LEO) at about 400 km above the Earth's surface. Weighing is less than 10 metric tons, this satellite is a fraction of the weight of its microwave counterpart. This design is cheaper too; some predict that a laser-equipped SBSP satellite would cost nearly $500 million to launch and operate. It would be possible to launch the entire self-assembling satellite in a single rocket, drastically reducing the cost and time to production. Also, by using a laser transmitter, the beam will only be about 2 meters in diameter, instead of several km, a drastic and important reduction.
To make this possible, the satellite's solar power beaming system employs a diode-pumped alkali laser. First demonstrated at LLNL in 2002 — and currently still under development there — this laser would be about the size of a kitchen table, and powerful enough to beam power to Earth at an extremely high efficiency, over 50 percent.
While this satellite is far lighter, cheaper and easier to deploy than its microwave counterpart, serious challenges remain. The idea of high-powered lasers in space could draw on fears of the militarization of space. This challenge could be remedied by limiting the direction that which the laser system could transmit its power.
At its smaller size, there is a correspondingly lower capacity of about 1 to 10 megawatts per satellite. Therefore, this satellite would be best as part of a fleet of similar satellites, used together.
You could say SBSP is a long way off or pie in the sky (puns intended) — and you'd largely correct. But many technologies already exist to make this feasible, and many aren't far behind. While the Energy Department isn't currently developing any SBSP technologies specifically, many of the remaining technologies needed for SBSP could be developed independently in the years to come. And while we don't know the future of power harvested from space, we are excited to see ideas like this take flight (okay last pun, I promise).
Benefits of Space
There are many advantages to this. A space-based solar power station could orbit to face the Sun 24 hours a day. The Earth's atmosphere also absorbs and reflects some of the Sun's light, solar cells above the atmosphere will receive more sunlight and produce more energy. But one of the key challenges to overcome is how to assemble, launch and deploy such large structures. A single solar power station may have to cover as much as 10 sq km (4.9 sq miles) – equivalent to 1,400 football pitches. Using lightweight materials will also be critical, as the biggest expense will be the cost of launching the station into space on a rocket.
We are currently reliant on materials from Earth, but scientists are also considering using resources from Space for manufacturing such as Materials
Found on the Moon.
One proposed solution is to develop a swarm of thousands of smaller satellites that will come together and configure to form a single, large solar generator. In 2020, researchers at the California Institute of Technology outlined designs for a modular power station, consisting of thousands of ultra light solar cell tiles. They also demonstrated a prototype tile weighing just 280g per square meter, similar to the weight of card. Recently, developments in manufacturing, such as 3D printing, are also being investigated for their potential in space power. At the University of Liverpool, we are exploring new manufacturing techniques for printing ultra light solar cells on to solar sails. A solar sail is a foldable, lightweight and highly reflective membrane capable of harnessing the effect of the Sun's radiation pressure to propel a spacecraft forward without fuel. We are exploring how to embed solar cells on sail structures to create large, fuel-free power stations.
The possibilities don't end there. While we are currently reliant on materials from Earth to build power stations, scientists are also considering using resources from space for manufacturing, such as materials found on the Moon. But one of the major challenges ahead will be getting the power transmitted back to Earth. The plan is to convert electricity from the solar cells into energy waves and use electromagnetic fields to transfer them down to an antenna on the Earth's surface. The antenna would then convert the waves back into electricity. Researchers led by the Japan Aerospace Exploration Agency have already developed designs and demonstrated an orbiter system which should be able to do this. There is still a lot of work to be done in this field, but the aim is that solar power stations in space will become a reality in the coming decades. Researchers in China have designed a system called Omega, which they aim to have operational by 2050. This system should be capable of supplying 2GW of power into Earth's grid at peak performance, which is a huge amount. To produce that much power with solar panels on Earth, you would need more than six million of them. Smaller solar power satellites, like those designed to power lunar rovers, could be operational even sooner. Across the globe, the scientific community is committing time and effort to the development of solar power stations in space. Our hope is that they could one day be a vital tool in our fight against climate change.
