FAQ: Frequently Asked Questions on Space-Based Solar Power

Why is the SOLARIS preparatory programme being proposed now?

The increasing urgency of the need to resolve the climate and energy crises means that all potential technological solutions should be investigated. Previous SBSP studies by ESA and other international agencies have found no principal technical showstoppers but prohibitive challenges to make the concept economically viable due to high the launch costs and engineering challenges at that time. The substantial reduction in both launch cost and space hardware development costs in the past decade, warrants a thorough re-assessment of the viability of the concept. 

Would the SOLARIS technology development investments be useful for other applications?

Yes. The proposed developments made to the key technologies for SBSP have other cross-application benefits and use cases. For example, photovoltaic and power conversion efficiency, on-orbit manufacturing, assembly, and servicing, and deployable antenna developments would be useful to a wide range of space applications. Developments made in wireless power transmission technology (WPT) could also contribute to stimulating the terrestrial WPT market or the use of WPT to enable lunar or Martian exploration activities.

ECONOMIC & TECHNICAL

How does SBSP compare with terrestrial solar? 

SBSP would not compete with terrestrial solar power plants but complement them. Unlike terrestrial solar power plants, SBSP would provide continuous, stable, baseload (non-intermittent) power to an electrical grid similar to nuclear, hydro, coal and gas power plants.

The areas dedicated to receiving the power transmitted from the orbiting power generation satellites, could be on land or on sea and are expected to be usable in parallel for other applications, such as agriculture or combined with a utility scale ground-solar or wind farm, thus potentially allowing to maximise the generation of power from areas that have already been set aside for renewable power generation purposes.

How can SBSP be competitive with terrestrial renewables (e.g., solar, wind), when the cost of renewables is falling rapidly and given the typically high costs of launch and space hardware?

This question is at the heart of the two cost benefit studies commissioned by ESA, the results of which are available online in full. These studies assessed the economic and technical benefits of investing in the enabling technologies needed to realise large scale SBSP scenarios, and compared them to other energy sources, taking into consideration future market needs and technology forecasts.  They conclude that due to the nature of the electricity provided by SBSP (“baseload” power), SBSP doesn’t compete with intermittent renewables, but rather could serve a complementary role to terrestrial intermittent renewables, helping to provide stability and reliability to the grid. It therefore needs to be compared to other baseload sources like nuclear, carbon and gas with carbon capture technology or very large-scale deployment of storage solutions. The studies conclude based on the current available information that SBSP could contribute to a future diverse CO₂ neutral energy mix that has a high proportion of intermittent renewables, despite being more expensive than them. The IEA Net Zero 2050 roadmap demonstrates clearly that terrestrial wind and solar needs to expand rapidly, but even with the hoped-for availability by then of new storage solutions, the energy mix in 2050 still foresees some significant capacity from baseload and dispatchable sources to provide flexibility and reliability.

Wouldn’t the system losses of energy across the full SBSP concept from solar in space to microwaves and back to electricity on the ground be so great as to make it unviable?

Power will be lost at each energy conversion step in the chain as there are no steps that can be 100% efficient. Therefore, much of the energy gathered in orbit will be lost along the way. However, the Sun’s energy is free, continuous and more intense in space and both studies confirm earlier results that show that as long as the aggregate losses are not exceeding 85 to 90%, the remaining energy received at Earth could still be sufficient to make it a worthwhile and economically viable proposition. To achieve the required level of end-end efficiency (i.e., approximately 10-15% of the power falling on the panels of the satellite should be delivered into the grid), significant advances are required in several conversion technologies beyond the current state of the art. While these appear theoretically possible, they still need to be demonstrated with actual hardware development and testing. This is one of the key technical challenges for SBSP, and the main objective of SOLARIS which addresses the cost and availability at scale of components such as highly efficient, lightweight photovoltaic panels, or next generation high power RF amplification.  

SAFETY & ENVIRONMENTAL

How will the energy beam interact with Earth’s atmosphere? Will it significantly heat the atmosphere?

At any energy conversion step, some power is lost in the process, typically in form of heat. A number of atmospheric interaction effects have been discussed within the technical literature, for example ohmic heating owing to microwave frequency excitation of the ionosphere. Such phenomena have not been demonstrably shown or conclusively examined, especially in the context of the natural variability of our atmosphere. Understanding how the energy beam would interact with the atmosphere is one of the technical uncertainties that would be addressed within the SOLARIS exploratory programme. SBSP has use cases in exploration scenarios, such as Lunar power beaming, where the absence of an atmosphere negates this concern directly.

Isn’t adding additional energy into the Earth’s environment through SBSP going to warm the planet more rather than help mitigate global warming?

No, it is not. The Sun shines about 170,000 TW of power onto the Earth continuously, with about 70% of it absorbed by the atmosphere and the surface and about 30% of it reflected back into space. Even if we were to deploy 1000 Solar Power Satellites, each beaming 2GW of power down to Earth, that would be adding only 0.001% additional energy on top of the solar insolation. The solar output itself varies by a factor of 100 more than that or about 0.1% over its 11-year cycle.

More importantly, one of the main benefits of deploying SBSP, especially in the nearer term, is to allow an accelerated displacement of fossil-fuel powerplants, thereby reducing the total CO₂e emissions and contributing to mitigating global warming.

Would the beam be safe?

Most SBSP system architectures use microwave frequencies to achieve wireless power transfer back to Earth. Microwaves operate at a frequency that is too low for cellular stimulation, meaning it is non-ionising and energy absorption and subsequent tissue heating is the major mechanism for interaction with living things. Microwaves are widely used in technology today; applications using low power density microwaves are operating all around us, like mobile networks or wi-fi, other technologies use much higher powers, like microwave ovens. The European Commission’s Scientific Committee on Emerging and Newly Identified Health Risks concluded that “the results of current scientific research show that there are no evident adverse health effects [of EMF exposure] if exposure remains below the levels recommended by the EU legislation”.

Current SBSP designs have a maximum power density in the centre of the beam of approximately 250 W/m2 (as a reference point you would encounter 1000 W/m2 from the sun when standing at the equator of the Earth at noon). The power density would drop significantly towards the outside of the beam, reaching below 10 W/m2 at the beam edge. The EU sets the safe exposure limit to microwaves at 50 W/m2; while access to the central beam region in the ground rectenna station would be restricted (just as access is restricted to most industrial energy facilities), the outer region of the beam is likely to be safely used for dual purpose, such as crop production.

Even though the power densities being discussed are relatively low and would not exceed safe human exposure limits in the areas surrounding the ground station, studying any potential health risks is obviously of upmost importance and would be addressed early in the SOLARIS preparatory programme. Further, the impact of SBSP on fauna and flora localised around the ground station, or avian species passing through the beam, would also be examined in depth.

Would the beam be dangerous if it wasn’t pointing at the right place on Earth?

The system would be designed in a way that by design the peak power density could not exceed levels  at which it could be a threat to property or living beings. Regardless, redundant safeguards would be in place to prevent misalignment of the beam and ensure the power is shut off when not aligned correctly with the ground station, for example interlocked pilot beams from the ground station to the satellite would allow for precise steering and control. As with any large infrastructure project, multiple layers of defence and automated responses would be in place to prevent any harmful external attack.

Will SBSP interfere with other space uses or airplanes?

An SBSP radio frequency (RF) band would likely have to be allocated by the ITU (International Telecommunication Union); frequency management is a standard practice for avoiding interference between different technologies that utilise RF. Even still, the potential for interference with technology on the ground or in the air (for example airliners or other satellites), even at the low-density power levels that are envisaged, cannot be excluded at this stage and would need to be investigated through analysis and testing as part of early SBSP viability studies.

Will SBSP generate light pollution?

A sufficiently large, fully realised SBSP installation on the order of GW generation would likely be visible, like a star in the night sky, owing to the large arrays of solar photovoltaic panels. However, even though a SBSP station would be larger than any current satellite, its location in GEO (Geostationary Orbit ~36,000 km from Earth) would make it appear very small in the sky. For example, the International Space Station (ISS) is 108 metres wide and orbiting just ~400 km above Earth’s surface; if the ISS was in GEO, it would have to be approximately 10 km wide to appear the same size on Earth as we see it now. Smaller, demonstration satellites or smaller installations would not have an appreciable brightness beyond what is currently observable at GEO locations. Any LEO satellites flown to demonstrate SBSP would have negligible apparent magnitudes.

Will SBSP be affected by or contribute to the issue of space debris?

Solar Power Satellites, given their size, would be at risk of an increased frequency of interactions with orbital debris (though this is much reduced in GEO compared to lower orbits) and micrometeoroids. Strategies for how to deal with this (as well as other environmental hazards such as solar flares) will need to be investigated during future phases of study.

The European Space Agency has its own ESA Policy on Space Debris Mitigation, projects with the UN Space Sustainability Guidelines and ESA’s Space Debris Mitigation requirements. To ensure ESA leads by example on the topic of space sustainability, Director General Josef Aschbacher is proposing a Zero Debris approach for ESA missions, to be implemented by 2030. This Zero Debris Approach entails a more sustainable strategy for space operations and End of Life, boosting the disposal success rate from the protected regions and encouraging removal actions in the case of failed disposal. European large system integrators are also seeing Management of End of Life as one of the main drivers for the evolution of their platforms.  

What is the end-to-end environmental impact of implementing SBSP?

A major benefit of SBSP, is that it could contribute to accelerating the transition to Net Zero by displacing fossil-fuel sources of electricity generation. The manufacturing and deploying of SBSP will have an environmental impact, and it will be critical to quantify the projected impact and assess the associated carbon or energy payback time (how many years before the system has a net positive environmental impact). Naturally it would only make sense if SBSP saves a lot more CO₂e emissions on Earth during its operational life than the emissions it created during its production and launch and operations. Part of SOLARIS would be to investigate this question in-depth, assessing not only carbon emissions but all potentially harmful pollutants that could be generated throughout the system lifetime, including material production, manufacture, transport, integration, launch, orbit transfer and station-keeping, operations and finally decommissioning. Recent work indicates that SBSP would have life-cycle CO₂e emissions that are much lower than fossil fuel power sources that it would replace. Demonstrating that the deployment of SBSP systems will have a net positive impact on Earth’s environment long-term will be pivotal to the viability of SBSP.