Space-Based Solar Power: The Future of Renewable Energy
By: Joanna Chi
Tags: Space Exploration, Renewable Energy, Space, Solar Power, Solar Energy

Image from NASA

At some point, we’ve probably all been reminded to not waste our energy — literally. Turn off the lights when you leave the room. Don’t leave the fan running if you aren’t hot. Make sure your air conditioning isn’t freezing when it’s 100 degrees outside.

It’s a common mindset for many people to conserve as much energy as possible, and rightfully so: in 2019, fossil fuels comprised about 84% of the world’s energy consumption. And according to BP, a multinational oil company, our planet can only provide oil for about 50 more years and coal for 100 given the current energy demand.

Despite our insatiable appetite for oil and coal, renewable resources exist in abundance, waiting to be harnessed. Take solar power, for instance — more solar energy reaches the earth in an hour than all of humanity uses in a year, yet only 1.11 percent of our energy consumption in 2019 was derived from solar power.

Global energy consumption by source (BP Statistical Review of World Energy, visualized by Our World in Data).

The sun has an enormous potential to power our entire planet, but its energy is barely being harnessed! As deadlines regarding our use of fossil fuels continue to emerge, scientists are directing some of their research toward moving solar power off of Earth’s surface. By targeting issues such as efficiency and accessibility, we may be able to invest in space-based solar power (SBSP), saving the future of our planet.

Solar Power Should Work, But it Doesn’t

At first glance, harnessing the sun’s energy seems like an easy choice to make. Unlike fossil fuels, solar power does not emit the greenhouse gases that are accelerating global warming. Competition for water resources and farmland, which has been a growing concern in oil fracking, is also a non-issue when considering solar power.

From a political perspective, solar power is also one of the safest sources of alternative energy. Tensions over the rights to existing oil and coal have given way to violent conflicts between different nations. If we defaulted to solar power instead, conflicts over nonrenewable resources might be resolved. Solar power centers would be both structurally and politically sound.

Implementing solar power as an environmentally and politically low-risk system sure sounds nice, but our current methods of harnessing solar energy are disappointingly inefficient. As with any system that looks too good to be true, we need to analyze the current roadblocks to efficient solar power.

Obstacles to Earth-Based Solar Power

When we think of the word “inefficient” in relation to solar energy, our minds might immediately begin questioning the efficacy of solar grids themselves. However, the root of the problem actually begins before sunlight even reaches Earth’s surface.

According to NASA, roughly 29% of the sun’s energy is reflected back by Earth’s atmosphere and dissipates into space. On top of this, an additional 23% of solar energy is absorbed by water vapor, ozone, and dust while it travels through the atmosphere. In the end, only 48% of the solar energy that reaches our planet actually makes it to the surface in the first place.

Image taken from NASA Earth Observatory

Due to the obstacle known as our atmosphere, solar grids on Earth are working with less than half of the energy that originally reached our planet. What’s worse, current solar panels max out at about 22% efficiency in non-laboratory conditions. This means that on a sunny day, at maximum efficiency, an Earth-based solar grid would only be able to convert 10 to 11 percent of the Sun’s energy into usable energy. And to top it all off, solar panels are severely constricted by limited daylight hours, bad weather, and inefficient transportation. All of these factors combined absolutely crush the viability of terrestrial solar power as our main source of energy.

This begs the question: who on Earth would still try to use solar power?

The answer? In the future, anyone may have access to energy generated by solar power! We just need to move our technology off of the surface and into space.

The Reasoning Behind Space-Based Solar Power

Space-based solar power (SBSP) is fairly self-explanatory: it’s the concept of collecting solar power in space via satellite solar panels, then distributing it to Earth. Once we escape Earth’s atmosphere, we also escape the terrestrial constraints on solar power. We no longer need to worry about solar energy not reaching us — according to the European Space Agency (ESA), sunlight is up to 11 times more intense outside of the atmosphere. Satellite solar panels would have access to more energy than the human race could ever use.

Furthermore, satellite panels would be free from bad weather, as well as the nighttime. They also wouldn’t be limited by a lack of sunlight in the winter, since satellites would not be restrained by the tilt of Earth’s axis. In space, solar panels would be able to beam energy to any location on Earth, so countries using SBSP would only need to launch their satellites to the optimal position for orbit.

Illustration of a solar satellite beaming energy to Earth (Futurism).

With this encouraging information in mind, there are just a few key components that would be needed to actually build and implement satellite solar panels.

Requirements for SBSP

To make space-based solar power feasible on a global scale, there are two main technologies that we need. First, the launch vehicles to get materials into space need to be low-cost and eco-friendly. Most of the rockets that are currently used to deliver payloads are expendable, and they are extremely expensive and prone to causing pollution. As such, reusable rockets are vital to a sustainable SBSP model. Several private companies, including SpaceX, are in the process of developing cheaper, reusable rockets.

Once we have the means to launch parts into space, the second facet of building satellite solar panels centers around the in-orbit construction of solar satellites. To collect the amount of energy that we need, satellite solar panels will need to be much larger than even the ISS, making them the largest spacecraft ever built. Luckily, satellite solar panels will also be much simpler to build than the ISS, as they would be built from many identical parts.

Solar panels on the ISS cover about 2.5 square km — some SBSP satellites would be over twice this size.

In the long term, investments into space infrastructures such as asteroid mining may allow the construction of spacecraft to be completely removed from Earth, which would require only the energy receiving centers of SBSP to be built on Earth. For now, though, the main technologies needed to build satellite solar panels can be found on Earth, and they are reasonably attainable within the next few decades.

Types of Solar Satellites

According to researchers at the U.S. Energy Department, two types of satellites would be viable for SBSP: microwave-transmitting satellites and laser-transmitting satellites. Both of these types of satellites would consist of solar collectors, reflectors, and a transmitter. Reflectors, which are basically large inflatable mirrors, would direct radiation to the small panels known as collectors, which would then convert the solar energy into either a microwave or laser to beam down to Earth. Receiving stations back on Earth would collect, store, and distribute the energy.

Microwave-Transmitting Satellites

The larger of the two models for solar satellites, microwave-transmitting satellites would consist of huge solar reflectors that direct solar energy into the center of the satellite, where energy is then beamed to Earth as a microwave transmission. Microwave-transmitting satellites would orbit Earth in geostationary orbit (GEO) at a height of around 21,700 miles (35,000 km) — a little less than one-tenth of the distance to the Moon.

Image from the Department of Energy

These satellites would be constructed on a huge scale, with solar reflectors that weigh more than 80,000 metric tons and up to 3 km (1.9 miles) in diameter. With their massive size, microwave-transmitting satellites would be able to generate gigawatts of energy, which would be capable of powering major U.S. cities. Since the wavelength of microwaves is relatively long on the electromagnetic spectrum, the transmissions from one of these satellites would only be as intense as bright sunlight, making this mode of transmission extremely safe.

On the downside, microwave-transmitting satellites would be expensive to launch, assemble, and operate, with estimates ranging in the tens of billions of dollars. Roughly 40 to 100 launches would be necessary to get all of the materials into GEO due to the large size of the satellites. Furthermore, the size of receiving centers on Earth would need to be scalable to the size of the satellites in space — about 3 to 10 km (1.9 to 6.2 miles) in diameter. Tracts of land that large would be difficult to develop and maintain.

Laser-Transmitting Satellites

The second type of solar satellite, laser-transmitting satellites, would only be about 2 meters in diameter. To transmit energy back to Earth, they would use a diode-pumped alkali laser. The laser would be about as large as a kitchen table and would beam energy to Earth at over 50% efficiency, which is remarkably high compared to the current efficiency of solar power.

Image from the Department of Energy

Due to their small size, laser-transmitting satellites would be launched in groups into low-Earth orbit (LEO) about 400 km (250 miles) into space. With a single launch per satellite, these satellites would significantly reduce the costs and risks, as well as the time frame, of production compared to microwave-transmitting satellites. Estimates of costs for laser-transmitting satellites range from $500 million to $1 billion, which is drastically cheaper than the cost of microwave-transmitting satellites.

However, laser-transmitting satellites are comparably less powerful than microwave-transmitting satellites, as each laser-transmitting satellite would only generate about 1 to 10 MW of power. Even when launched in fleets, the energy production of laser-transmitting satellites would probably be unable to match that of microwave-transmitting satellites. As a result of their decreased power, these satellites would experience some difficulties beaming energy through heavy clouds and rain. There are also concerns about the militarization of space using high-powered lasers, but this could be avoided by limiting the direction in which a laser satellite could direct its power.

Implications of SBSP

If SBSP were to be implemented on a global scale, it could resolve not only energy issues but also multiple social and political conflicts. In the present day, many countries depend on other nations for fossil fuels, and the limited supply of oil and carbon has caused violent international conflicts. Abundant solar energy would provide energy independence to nations that currently rely on imported oil. Without having to worry about conflict over nonrenewable energy, countries could reallocate their resources to further developing different parts of their infrastructure.

Additionally, since SBSP can be exported to virtually anywhere on the globe, it could be used to resolve a variety of problems on the local scale. For example, SBSP would generate enough energy to desalinate seawater, which could provide millions of people with access to clean water.

Solar power is already improving day-to-day energy needs in remote areas, but SBSP could exponentially increase access to energy (image from Reuters).

Although it seems like we are a long way off from a sustainable future, space-based solar power is closer to our grasp than we think. SBSP has the potential to be a sustainable, safe source of power that could save the future of our planet from global warming. By prioritizing sustainable construction methods and distribution over the easy route of relying on fossil fuels, the future of Earth’s energy could lie in space-based solar power.

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