By the beginning of 2022, a number of space agencies, particularly the ESA, NASA, and JAXA, had announced their desire to resume research in the field of space-based solar power (SBSP). The accumulation of energy in orbit and its subsequent transmission to Earth using microwave radiation may be the future of alternative energy. However, before this can be done, aerospace engineers will need to solve several technical challenges.
We examine here the viability and cost effectiveness of SBSP, and how this technology can help humanity in the future to completely abandon the use of fossil fuels.
What are the types of orbital power plants
The process of harnessing solar power from space relies on the use of solar energy satellites (Solar Power Satellites, SPS) equipped with arrays of photovoltaic cells.
The light captured by the space satellites’ solar panels generates electricity, which is subsequently converted into high-intensity microwave radiation and transmitted to special receiving microwave antennas (rectennas) installed on Earth. There, the microwaves are converted back into electricity and distributed to end users via power lines.
In order to transmit power wirelessly down to Earth, SPS satellites can use both laser and microwave emitters. It is assumed that solar satellites using microwave radiation will be able to operate at an altitude of no more than 35,000 km (MEO), while laser SPSs will operate much lower, at altitudes of about 400 km above the Earth (LEO).
Since laser solar power satellites are much smaller than microwave ones, they will be much cheaper to launch. A noticeable disadvantage here is their dependence on clear weather to transmit power, since their laser beams can be scattered by clouds and rain. The energy production of one laser SPS can be from 1 to 10 MW, which would be enough to meet the energy needs of small installations, such as lunar or Martian orbital stations and ground bases.
Microwave SPSs can generate significantly more power – up to 1 GW of electricity – enough to power a medium-sized city. Unlike with laser SPS technology, microwave power transmission does not vary based on weather conditions, because their high-frequency waves easily pass through dense clouds with little or no loss of energy.
However, there are of course significant disadvantages to microwave solar power satellite technology, mainly including the enormous size of both the space solar power plants in orbit themselves and the receiving equipment located on Earth. Thus, to achieve power generation of 1 GW, the diameter of the wave receiver on Earth must be several kilometers.
In addition, the launch of such massive objects is not yet feasible. This means that the microwave solar orbital power plants will have to be assembled and will require the deployment of hundreds of space-launched composite modules, which will also need to be assembled in orbit. Given that the installations will be orbiting 35,000 km above the Earth, maintenance and repair of these power plants would currently be virtually impossible. However, the energy efficiency that microwave SPSs would generate still far exceeds the existing difficulties, and work on them continues, and with an increasing number of contributors.
What are the main advantages of space-based solar power satellites
In comparison with ground-based solar panels, the process of converting solar radiation into electrical energy in orbit has the following advantages:
- The absence of the earth’s atmosphere, which absorbs and scatters from 30 to 50% of solar radiation entering it. In space, this problem does not exist, and the intensity of solar radiation in the vacuum of space is approximately 10 times higher than on Earth. This directly affects the amount of space based solar power that panels can generate in orbit.
- Nearly round-the-clock operation: ground-based solar panels are ineffective at night and in cloudy weather. Solar energy satellites would not have this problem, and will be able to receive and convert sunlight into electricity 24 hours a day (except for the few minutes per day when the Earth passes between the SPS satellite and the Sun).
- Space solar panels can always be directed directly at the Sun, thus ensuring the maximally efficient absorption of solar radiation. This will allow the satellites to generate and transmit more electricity to Earth.
- SPS satellites can transmit to receiving stations located in different parts of the world. This feature can reduce the cost of transporting electricity to zero. It would no longer be necessary to transmit electricity through kilometers of power lines – the satellite would only need to be pointed at the desired receiving station on Earth, thus allowing energy to be received directly where it is used.
- Environmentally-friendly electricity – the use of space based solar power technology would take fossil fuels and greenhouse gas emissions out of the electricity generation equation. The development of orbital solar power plants can minimize the level of carbon emissions into the atmosphere, and in the distant future will allow us to completely abandon power plants that burn fossil fuels. To fight global warming, solar energy provides the best, safest means of generating electricity.
The ongoing downward trend in the price of launching satellites into orbit can help significantly drive the emergence of space-based solar power plants in the next 10 years. However, in order for this to become feasible, a number of serious engineering problems must be solved.
Major Engineering Challenges: Conversion Losses and Safety
Before the first space-based power plants can be put into orbit, engineers and designers will first have to solve some rather difficult technical problems. First of all, there is the problem of converting electrical energy into microwave or laser radiation. The process of energy conversion is not 100% efficient, and entails losses in the power of the electricity sent to the Earth. At the same time, at the moment the microwave radiation reaches the receiving equipment on Earth, the conversion must be performed again (from microwave radiation to electricity), which will again entail power losses. These energy losses are the chief obstacle to implementing ambitious space based solar power projects.
In addition to resolving the energy conversion problem, engineers from space based solar power companies will need to work out a comprehensive protocol for orbital safety when using SPS. Strong microwave radiation can affect the operation of aircraft, which could accidentally pass through satellites’ microwave beams. And while this issue can be realistically solved through proper air traffic control, the problem of tracking and disposing of orbital debris remains acute and unsolved. The collision of a space solar power plant with meteorites or other orbital debris could deflect a satellite’s microwave beam and direct it to areas on the Earth’s surface that are not equipped to receive it.
There are a number of initiatives intended to help address the issue of cleaning up space junk, including an ESA-funded project. The ClearSpace-1 spacecraft is designed to collect and dispose of orbital debris. In 2025, it will attempt to capture and launch into the atmosphere the second payload stage left behind by the Vega rocket in 2013. The project is working on an $86 million budget.
In addition to orbital garbage collectors, initiatives are being considered to deflect the orbit of space debris using laser installations located on Earth. If space debris can be reliably detected early, their trajectories calculated, and methods developed to prevent their collision with SPSs, it will be possible to achieve a sufficient level of safety for space-based solar power plants.
Last but not least of space-based solar power disadvantages, as described above, is the problem of orbital solar power plants’ massive size. The area of one microwave SPS can be approximately 10 square kilometers. The construction of such gigantic engineering structures will require durable but ultra-light materials that can be launched into orbit in stages, by launching constellations of satellite modules from which a power plant can subsequently be built. Another possible alternative would be to 3D print individual power plant modules in orbit and subsequently assemble them where they are manufactured. Such innovations, if successfully realized, could significantly reduce the cost of building space solar power plants, even consolidating everything into a single launch — that of an orbital 3D printing station.
As you can see, the issue of profitability of SBSP technology today rests on the cost of launching, composite materials, construction, and maintenance of these power plants in space. If humanity can get closer in the near future to solving the problems discussed above, and the volume of orbital energy generated can exceed that of ground-based solar power plants, space solar power technology will earn itself the go-ahead. Space companies around the world are already working on this.
The experience of the world’s space agencies and the future of SBSP technology
The European Space Agency launched an initiative in early 2022 to revive research on orbital solar power generation. This resulted in a campaign by the ESA soliciting ideas for clean space-based energy. During the campaign, 85 applications were considered, of which 13 ideas were selected for further funding. In particular, the campaign touched upon the main issues of SBSP related to new concepts for space power plants to supply energy to Earth, as well as to future lunar and Martian bases.
The UK is also interested. According to a report by The Times, the British government is currently considering allocating £16 billion to space-based solar power development as part of the country’s Net Zero initiative aimed at developing low-carbon energy.
In the USA, the Space Solar Power Project is already developing high-efficiency solar panels, as well as new technologies for converting electrical energy into microwave radiation.
The Australian space sector is also interested in the development of solar power from space. Solar Space Technologies is developing its SPS-Alpha system, which consists of many components that must be launched and subsequently assembled in orbit. By 2027, we should see the first version of SPS-Alpha helping to contribute to Australian energy security.
A group of specialists from JAXA (the Japan Aerospace Exploration Agency) has already developed a theoretical framework for orbiting space solar systems that will be able to convert energy into wave radiation with a minimum loss of energy. With proper funding, the project could become a reality in the next decade.
Chinese aerospace experts are developing their own SSPS (Space Solar Power System, analogous to SBSP) concept, called OMEGA. It consists of four main elements: a spherical solar collector, an array of hyperboloid photovoltaic (PV) cells, a power control and distribution system (PMAD), and a microwave transmission antenna. OMEGA is a very long-term prospect and is not set to appear in Earth orbit until 2050 at the earliest. However, it is obviously worth anticipating, as it is expected that the Chinese space solar power plant will be able to generate and transmit up to 2 GW of electricity to Earth, which is currently equivalent to the output of around 6.25 million ground-based solar panels.Today, space-based solar power technology is still in the infancy of its journey, but the growing demand for energy resources (which is projected to increase by 50% by 2050), and the issue of climate change is prompting many space agencies and private companies to intensify their efforts in this direction. By the middle of this century, we will see the first practical results of this work, which has every chance of becoming a leading alternative energy solution in the future.