Are Solar Energy Transmissions from Satellites the Next Frontier for Renewable Energy?

Earlier this month, the University of Caltech (United States) Space Solar Power Project’s (SSPP) hosted payload successfully demonstrated wireless energy transfer to satellite receivers in orbit. When those receivers were pointed toward Earth, the researchers at Caltech were also able to detect the payload’s energy transmissions. While Photovoltaic (PV) solar panels have long been used to collect solar energy for their satellite bus power supply, and beamforming used for Satellite Communications (SatCom), this is the first instance of solar energy being converted to microwave energy to power remote objects. In this way, the successful demonstration of Caltech’s Space Solar Power Demonstration One (SSPD-1) payload hosted on Momentus Space’s Vigoride spacecraft, represents a significant step toward making space power stations a reality.

Space power stations that use beamforming to dynamically allocate energy can offer immense value and benefits. As energy from the sun is essentially always available and dispatchable via space power stations, they offer unique benefits even over terrestrial solutions.

• Sustainable Solar Solution: One of the key advantages of space-based solar energy is greater solar irradiance. For terrestrial solar systems, the National Aeronautics and Space Administration (NASA) estimates that roughly 71% of total incoming solar energy is absorbed by the Earth’s atmosphere. Furthermore, terrestrial solar solutions are highly inefficient, operable mostly during clear days (i.e., no haze or cloud cover), and they require 10 acres (40,500 square meters) of solar panels to produce one Megawatt (MW) of electricity. Solar arrays deployed in space can generate about 8X more energy than land-based solutions.
• Uninterrupted Energy Supply: Another key advantage is the ability to deploy energy beams outside of localized energy supply infrastructure (i.e., terrestrial-based sources, such as oil- or gas-fired generators). This confers obvious advantages in scenarios where there is a grid collapse or power infrastructure that may be jeopardized, such as in natural disasters or warzones, enabling critical access to energy. Additionally, it may be possible to beam energy to non-terrestrial and terrestrial hybrid or Electric Vehicles (EVs) to top up on the required energy to make a trip or complete an operation. In these ways, space power stations could provide enhanced energy resilience, travel time optimization, and even save lives by providing uninterrupted energy delivery.
• Democratized Energy Access: The ability to deploy energy via beams outside of localized power infrastructure also has the potential to transform remote and rural communities without access to power. Developing energy infrastructure is expensive and can often leave many developing regions without enough access. In 2020, it was estimated that 940 million people did not have access to electricity for a minimum level of consumption—250 Kilowatt-Hours (kWh) per year for rural households and 500 kWh per year for urban households. For context, in 2020, the average Kilowatts (kW) for a house in the United States was 893 kWh per month or around 30 kWh per day. Access to energy is very limited to these communities and space power stations could potentially serve as an interim option, especially if installing energy infrastructure (i.e., long-distance power lines and localized power generators) is impossible or too expensive due to geography.

Although the technology of space power stations is technically feasible, one crucial aspect that must be addressed for its commercial viability is the economics. The SSPD-1 mission is planned for 6 months at a 500 Kilometer (km) altitude in a Low Earth Orbit (LEO), crucially using ultra-lightweight materials to keep the total payload weight under 50 Kilograms (kg). This translates to a remarkably low launch cost of US$750,000 for the payload. The long-term objective, however, is for each payload’s uncoiled PV solar panels to reach the size of a football field (about 5,400 square meters) with a weight of 150 kg, amounting to a new launch cost of US$2.5 million per payload, assuming current launch costs. With potentially hundreds of thousands of these needing to be deployed into Medium Earth Orbit (MEO) or Geostationary Orbit (GEO) to be able to supply the appropriate capacity, the economics and evolving challenges of security, space debris, and orbital regime regulations make the future of space solar power stations equivocal. In this way, a lower orbit in MEO would have the edge in terms of Levelized Cost of Energy (LCoE) and require multiple solar harvesters and multiple Earth-bound receivers to bring the estimated cost of energy down to US$1 to US$2 per kWh. In comparison, U.S. electricity currently retails for less than US$0.17/kWh. Scaled-up test payloads and energy transmissions will be important for demonstrating proof of concept, economic viability, and applicability in real-world scenarios with airplanes, inclement weather, and even other satellites passing the solution’s required Line-of-Sight (LOS).

Given the nascent stage of space solar power station technology, it is likely that commercial deployment for this technology will not come for another decade or two. This is largely attributed to the investment and regulatory hurdles that this technology will face. Below are some options that could help accelerate the delivery of this technology:

• Satellite-as-a-Service (SaaS): Considering that the SSPD-1 was a hosted payload, the Caltech team has already considered the economic benefits of leveraging the growing hosted payload model, integrating multiple independent payloads from different customers into the same satellite platform. Not only does this reduce the costs of not having to buy a satellite and all the services it requires, but allows Research and Development (R&D) teams to focus on delivering and improving the SSPD payload. Furthermore, this represents a significant market opportunity for the SaaS market, as increasing energy demands could help boost demand for hosting SSPD payloads. This business model could be a strong contender for reducing the Total Cost of Ownership (TCO) for space solar power stations and improving time to market.
• Standardized Satellite Bus: Another critical aspect of enabling improved economics is using a standardized satellite bus and even a standardized payload design. This would enable space solar power station operators to reduce the overall cost of satellite development and production by leveraging economies of scale and commercial off-the-shelf components. This would not only improve the economics of managing a fleet of space solar power stations, but also enhance time to market and modularity. This may also act as a catalyst for growth in the satellite manufacturing market to produce new standardized space solar power station bus and payloads for wide-scale deployment.
• Software-Defined Payload: One of the more critical aspects for enhancing flexibility and future-proofing satellites with space solar power station payloads is leveraging software-defined architecture. These digital transponders, amplifiers, and antennas allow for the optimization of onboard resources to repeatedly adjust to evolving business requirements, beam capacities, and shapes, effectively future-proofing satellites with longer operational lifetimes. Therefore, this would be a key technology to ensure that the missions of these satellites can be shifted and secured with the changing needs of their users.
• Post Quantum Cryptography (PQC): Security in satellites is an increasingly growing priority in the SatCom space and will prove invaluable to a space solar power sector. Satellite firmware analysis and reverse-engineering is challenging due to the large variety of Instruction Set Architectures (ISAs), plethora of software and custom-made components, and lacking documentation, but not impossible. The transition to standardized bus design and software-defined payloads increases the risk of firmware attacks to the payload (i.e., payload data handling) and from external attackers (ground stations and inter-satellite links to the bus). Furthermore, with attack-capable quantum computers on the horizon, satellites, which can be as old as 15 years old, could become attractive targets. There is precedence for future-proofing satellites with commercially accepted cryptographic algorithms, especially if those satellites serve to provide critical energy resources.
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