Gigaton Potential
Three-quarters of our CO2eq emissions in 2016, 36 billion tons, came from energy generation. The good news is that we have pathways to electrify all but the hardest-to-abate sectors that use this energy. The bad news is that today only 32% of power is generated by renewables (incl. hydro, geothermal, and biomass). The technology needed to decarbonize the last ~50% is still in the demonstration or prototype phase. Terrestrial solar cannot close the gap alone; its seasonality and dependence on daylight mean you have to dramatically overbuild farms, sacrifice huge amounts of land, and rely on short- and long-duration energy storage.
Space-based solar power (SBSP) potentially offers a highly effective solution. By placing solar panels in space where the sun shines all the time and then beaming the energy to Earth, solar power is converted into a firm, dispatchable, and baseload-ready energy source. A lifecycle assessment shows that solar power only uses 40 g CO2eq/kWh compared to coal at 1,000 g CO2eq/kWh. Space solar has even lower1 emissions than terrestrial solar because of its higher productivity, making it a tangible option to decarbonize the rest of energy production.
What You Should Know
Sounds a bit like science fiction so far? Well, that’s because it is! Space-based solar power was first mentioned by Isaac Asimov in his 1941 short story titled “Reason”, portraying a space station that captures the sun’s energy and transmits it wirelessly to various planets. The basic premise has remained the same: solar panels are placed in space structures orbiting the Earth and wirelessly transmit energy back.
Proposals for wireless power transfer over long distances typically revolve around using microwaves from phased array antennas or concentrated light from lasers. Microwave power beaming from space is essentially done today; it’s how telecommunication satellites (e.g., Starlink) send signals to and from Earth. SBSP requires scaling up the low power levels used for communication to those meaningful for power transfer. Some SBSP proposals operate in the 2.45 GHz frequency spectrum, similar to your microwave oven or WiFi network, while others go up to 10 GHz or higher.
Benefits of space-based solar power compared to traditional terrestrial solar
Increased capacity factor: Solar farms only generate 20-30% of their peak power in a day, as most generation takes place around midday. Generation is also highest during the summer2. However, early evenings and winters are often when we need energy the most. To overcome the day/night cycle and seasonality, solar farms are often overbuilt to generate the average required most of the year, which leads to waste when we generate excess energy. Meanwhile, solar panels in space see the sun all the time and are not impacted by the Earth’s seasons. This dramatically increases the utilization of solar panels that, on Earth, would have sat idle for most of the day.
Limited storage required: The current solution to provide baseload power with solar and overcome the limited capacity factor is to both overbuild solar farms by 4-5x to capture the necessary energy and deploy costly storage (e.g., lithium-ion batteries) to store this energy for when it’s needed. The sun’s near 100% availability in space makes this unnecessary.
Lower land footprint: Powering the world with terrestrial solar requires 0.3% of the Earth’s area or roughly the size of New Mexico. Depending on the technology of the SBSP ground receiver, this required area could be dramatically reduced.
Geographic redirectability: Solar farms, wind turbines, and nuclear fusion plants are geographically fixed in one place on Earth. Expensive and lossy transmission means they can only power nearby cities, states, and countries. Since energy demand varies during the day, this means that they are not always utilized, which increases the cost of energy. An SBSP plant in geostationary orbit can see a third of the Earth, and nearly instantly redirect energy to any visible point that has a ground receiver. This means that one SBSP plant can supply Spain, New York, and San Francisco’s peak power demand without relying on any transmission infrastructure, leading to significantly higher utilization and cheaper economics.
SBSP delivers superior techno-economics
Some projections for baseload SBSP LCOE are as low as $30/MWh3, which is attractive for a renewable baseload generation technology under most future energy price scenarios. The main cost buckets are the solar modules, wireless transmitters, balance of plant (e.g., satellite structure, GNC), launch, and ground receivers. A solar module in space is at least 4-5x more economically productive than one on Earth due to the near 100% capacity factor.
Therefore, SBSP achieves cost parity so long as it’s no more than 4-5x more expensive to place the solar module in space. This provides SBSP with an all-in budget of $1,000-1,500/m2 of solar module4. Solar modules cost $80-140/m2 5 and launch costs $160-280/m2 6. This comfortably leaves $500-1,250/m2 for wireless transmitters, balance of the plant, and the ground receiver in the cost budget.
In reality, solar modules in space would be even more productive once you account for revenue maximization due to geographic redirectability and cost savings due to reduced overbuilding and storage requirements. Therefore, so long as the cost of placing it in space and receiving energy on the ground is around or less than 4-5x of the solar module’s cost, it makes more sense to launch the incremental solar module into space rather than install it on Earth.
Key Players
Several private and public organizations are working on SBSP, examples include:
Virtus Solis is a funded early-stage startup that is using a microwave transmission approach
Caltech received a $100M grant a decade ago to investigate space-based solar and conducted a demo of low-power transfer from space in 2023
SOLARIS is a European Space Agency (ESA) investigation that will lay the groundwork for an ESA decision on launching an SBSP program by 2025
JAXA is testing both microwave and laser-based power-beaming systems and has committed to a demo by 2025
Opportunities for Innovation
Size comparison between Burj Khalifa and CASSIOPeiA, an SBSP proposal that requires $20B in CapEx to get to the first 1-2GW plant. Recent proposals and startups are far more capital-efficient. Credit: Adapted from Frazer Nash
📡 Ground receivers for microwave technologies are diffraction-limited and have an inverse relationship between the space and ground antenna sizes for a given frequency. For example, at 100GHz, a 330m diameter antenna in space requires a 660m diameter antenna on the ground. Decreasing the space antenna size to a more manageable 30m diameter necessitates a huge 3.6km diameter ground receiver. This basic law of physics is a principle limitation of microwave technologies and requires investigating creative antenna solutions or alternatives to microwaves
🚀 Launch costs have declined dramatically over the past few decades from $65,400/kg for the Space Shuttle to $1,500/kg for SpaceX’s Falcon Heavy. They are expected to further decrease to <$400/kg and go as low as $10/kg (as claimed by Elon Musk) driven by Starship’s high cadence and reusability. Others working on low-cost reusable launchers are Blue Origin, Rocket Lab, and Relativity
🛰️ Satellite manufacturing costing a fortune is a myth that has been debunked by SpaceX’s Starlink telecommunications constellation due to mass automotive-style manufacturing and use of terrestrial components
🛠️ In-orbit assembly remains one of the biggest challenges as microwave SBSP structures are too large to launch into space fully assembled. This requires breakthroughs in space robotics, deployment structures, and automation AI
📻 Interference/jamming requires mitigation as microwave SBSP proposals occupy similar frequencies to terrestrial communication applications
🦺 Human, animal, and environmental safety risks due to microwave radiation must be thoroughly investigated and mitigated
💰Financing innovations in reducing capital expenditure and building business models with a focus on profitability are required to make SBSP startups attractive for venture capital financing. A parallel is nuclear fusion, where Commonwealth Fusion Systems recently raised $1.8B for an equally lucrative and risky energy generation venture.
Way Ahead
SBSP is a nascent technology with dramatic decarbonization potential if realized. The primary barriers to SBSP are regulatory, economic, and financial, rather than technological. The next step following Caltech’s work is a high-power wireless transfer demonstration from space to validate the concept's viability. In the medium term and without significant non-dilutive funding, SBSP players should consider pursuing intermediary business plans (e.g., in-orbit assembly) to develop the required technology and create venture capital-backable companies.
Absent fusion materializing over the next one to two decades, space-based solar power could be the only firm dispatchable baseload energy source that can take us to Net Zero by 2050. Watch out for public organizations and startups that are pursuing this lofty goal and opportunities to get involved.
Further Reads
Catalyst with Shayle Kann Beaming 24/7 solar… from space
The Wall Street Journal Beaming Solar Energy From Space Gets a Step Closer
The New York Times Looking to Space in the Race to Decarbonize
European Space Agency Frazer Nash and Roland Berger studies
1 A Starship launch conservatively generates 87 kg CO2eq/kg payload. This figure comes from dividing 208,172 MT CO2eq of 24 Starship launches by their 2,400 MT payload for all 24 launches. Assuming a solar cell weighs 1.76kg/m2, this results in 153 kg CO2eq for launch per square meter of solar, a 4-5x increase over NREL’s figure for terrestrial solar. Note that this is a massive oversimplification, and this illustrative calculation alone can be the subject of an academic paper. For example, this does not account for increases due to additional mass (e.g., cell substrate) and decreases due to the fact that Starship’s figures are based on NASA KSC GHG emissions in 2017 before significant decarbonization measures and that a space solar cell would create far fewer emissions due to not requiring a heavy metal structure. Further note that the 40 g CO2eq/kWh benchmark excludes carbon-intensive storage which traditional terrestrial needs to deliver firm energy and SBSP does not require
2 Summer sees higher solar output due to longer days and the sun’s higher position in the sky
3 The range of estimates varies widely based on different proposed approaches to SBSP (e.g., different microwave frequencies or even concentrated laser)
4 Solar panels installed cost ~$1/W. Assuming 1,361W/m2 peak solar radiation per unit area and 20% efficiency, it means that a square meter costs ~$270 and assuming 4-5x productivity increase in space leaves a budget of $1,000-1,500/m2
5 The module itself is 30-50% of the installed cost, which is $80-140/m2
6 A square meter of solar module weighs ~2kg. Therefore, the launch would cost $160-280 at a launch cost of $80-160/kg
About the Author
Abdullah Al-Shakarchi is an MBA candidate at Harvard Business School focused on green energy generation and storage startups. Before the MBA, Abdullah worked on early-stage energy and climate technology projects at X (fka. Google X) and was a management consultant at Bain & Company. Abdullah is trained as an electronic engineer and started his career doing hardware design for Formula 1 cars. In his free time, Abdullah enjoys cooking, traveling, sailing and is a private pilot.
The first paragraph feels less like reporting and more like a sales pitch. "Terrestrial solar cannot close the gap alone", I'm not an expert but from the specialized media I read, it really doesn't seem like we need to go to space to get enough renewables.