“The hard work and dedication of the brilliant scientists at Caltech have advanced our dream of providing the world with abundant, reliable, and affordable power for the benefit of all humankind.” — Donald Bren
A new documentary film highlights the ongoing efforts and breakthroughs of three Caltech professors in their quest to make space-based solar power a reality. In 2011, philanthropist Donald Bren provided a generous grant to Caltech which began the Space-based Solar Power Project. In 2023, the project, led by professors Harry Atwater, Ali Hajimiri, and Sergio Pellegrino launched the Space Solar Power Demonstrator into orbit, showcasing three technological advancements needed to make space-based solar power possible.
The Bright Harvest website details the story behind the Caltech Space-based Solar Power Project, along with ways to view the documentary.
Here’s a summary of “Astroelectricity: America’s national energy security imperative” by Mike Snead (The Space Review, September 22, 2025). You can read the full article here. Learn more about Mike at The Spacefaring InstituteTMhere.
Conclusions
Snead argues that space solar power–supplied astroelectricity is the only sustainable energy solution that is both large enough and practicable enough to enable America to replace its fossil carbon energy sources before depletion and avoid returning to energy insecurity. The scale of the energy transition is enormous, and only with strong government leadership, research, and early deployment of SSP can the U.S. ensure an orderly transition. To maintain national energy security, and protect future generations, Snead believes the development and deployment of astroelectricity must now be viewed as a strategic imperative.
Main Points
The U.S. currently depends heavily on fossil fuels: oil, natural gas, and coal supply about 70–80 Quads of the ~100 Quads of primary energy consumption as of 2019.
Technically recoverable oil and gas in the U.S. may last ~75 years at 2019 consumption levels, but with exports and growing use, the lifetime could be much shorter.
To transition (“go clean”) to sustainable energy, two criteria are key: (1) sufficient scale, and (2) a practicable, orderly implementation. Political or symbolic solutions will not suffice.
Of all sustainable energy sources, only a few are scalable to entirely replace fossil carbon fuels: intermittent wind, intermittent ground solar, baseload nuclear fission, and baseload space solar power (SSP), i.e. “astroelectricity.”
Assessment of wind power: Even if large areas are used, in average years wind might supply ~68 % of the needed intermittent power; in low wind years that drops sharply; public/land-use acceptance is a major constraint.
Ground solar farms: To meet the intermittent power need would require ~14 % of the U.S. contiguous land area—much of which overlaps with prime agriculture or unsuited terrain.
Nuclear fission: To supply all baseload power would require many times current nuclear capacity; breeder reactors bring proliferation risks; decommissioning, waste, natural disasters, and terrorism risks also loom large.
Astroelectricity (SSP): Collect sunlight in geostationary orbit, convert to electricity, beam to earth via radio/microwave, received by large rectenna farms. Supplies baseload power. Requires only a small fraction of U.S. land compared to terrestrial-only options.
For example: to supply ~80 % of baseload power via astroelectricity, about 4,339 GW continuous (GWc) would be needed from SSP, requiring ~182,000 km² land for rectenna/plant sites—< 3 % of the contiguous U.S. land area.
Glossary of Terms Used
BTU (British Thermal Unit) A unit of thermal energy defined as the amount of heat needed to raise one pound of water by one degree Fahrenheit. 1 BTU ≈ 1,055 joules. Used to measure the energy content of fuels like coal, oil, and natural gas.
BOE (Barrel of Oil Equivalent) A unit that expresses energy content in terms of a barrel of crude oil. One BOE = 5.8 million BTU of thermal energy. Useful for comparing different fuels on a common basis.
Quad (Quadrillion BTUs) A large-scale unit of energy equal to 1 quadrillion (10^15) BTUs. Commonly used to describe national energy consumption. For example, in 2019, the U.S. used about 100 Quads of primary energy.
GW (Gigawatt) A measure of power equal to 1 billion watts (10^9 W). Often used to describe the size of power plants or electricity generation capacity.
GWc (Gigawatts Continuous) A refinement of GW, meaning gigawatts of continuous power output, i.e., power delivered around the clock without interruption. Used to describe baseload capacity requirements for astroelectricity.
Technically Recoverable Resources The portion of identified oil, gas, or coal reserves that can be produced with existing technology and practices, regardless of market price.
Primary Energy Energy found in natural resources (like coal, oil, natural gas, wind, sunlight) before being converted into electricity, fuels, or heat for use by consumers.
Baseload Power The minimum level of continuous power demand that must be met by an energy system. Technologies that can deliver baseload (like nuclear or space solar power) are especially valuable for energy security.
Rectenna A large ground-based receiving antenna that converts microwave or radio wave transmissions from space solar power satellites back into usable electricity.
Space-based solar power, once a topic for science fiction, is gaining interest.
When The New York Times (NYT), a major US newspaper known to achieve 70 million unique monthly visitors, runs a positive article about the potential of space-based solar power (SBSP), that’s an indication that this clean energy game-changing technology is finally becoming part of the broader conversation.
Run as part of NYT’s Climate Forward event in its special section on climate change solutions, the article doesn’t break any news but does highlight the fact that advances in space launch technology by private companies have made the business case for SBSP much more viable in recent years.
I believe you will need to be a NYT subscriber to read the full article linked below:
After listening to Can Science Save Us?, a conversation with Sir Martin Rees on the Michael Schermer Show, I wrote both Dr. Schermer and Lord Rees with the intention of telling them about space-based solar power (SBSP), which was not mentioned in the podcast. As a result, I was invited to write an article about SBSP for the current issue of Skeptic Magazine v28.2: Energy Matters. My article, ‘It’s Always Sunny in Space,’ is reprinted here with permission from Skeptic Magazine.
This is the highest resolution image of the Sun’s full disc and outer atmosphere (the corona) ever taken, as seen by Solar Orbiter in extreme ultraviolet light from a distance of nearly 47 million miles. This stellar image is a mosaic of 25 photographs taken on March 7, 2022 by the high resolution telescope of the Extreme Ultraviolet Imager (EUI) instrument. An image of Earth is included for scale, in the upper right corner of the illustration.
A tremendous thermonuclear furnace, our Sun radiates about 134,000 terawatts (TW) of continuous power to Earth’s surface, about 7000 times more than the entire population of humankind consumes from all current sources of energy.
It’s Always Sunny in Space
Why space-based solar power is a viable source of energy.
by Rob Mahan
Advances in human civilization have always been fueled by the availability of excess energy in various forms. For the vast span of human history, energy from the Sun was converted to food and biomass by photosynthesis and expended in the forms of muscle power and fire. Energy from the Sun produced weather, and as a result, wind- and water power were eventually harnessed and converted into increased levels of societal organization.
When humans began to extract massive amounts of energy from plant-based fossil fuels—which originated millions of years ago, through photosynthesis driven by energy from the Sun—further technological complexity, economic surplus that freed increasing numbers from manual labor, and human population all exploded. Gasoline-powered, mass-produced automobiles represented freedom in the form of personal transportation. Electricity became an efficient way to deliver energy to homes and businesses, and eventually to power a global information network. Growth was good, and seemed unstoppable, at least to those with easy access to abundant energy.
More recently, science and rationality have led us to a stark realization. Year-over-year economic growth, driven by the ever-increasing consumption of finite natural resources to produce abundant energy and other goods, has proven unsustainable. Coupled with concerns about climate change resulting from the release of excessive carbon dioxide into the atmosphere, three broad future scenarios emerge:
Continue the current, unsustainable trend of natural resource extraction, energy consumption, and economic growth, and let natural processes dictate the next era in human history.
Based on current and past technologies, voluntarily and drastically reduce global energy consumption and revert much of humankind to the previous era of muscle, wind, and water power.
Develop new technologies and find cleaner, renewable, or unlimited forms of abundant energy, while becoming better stewards of the finite natural resources that remain.
If the third scenario is the most appealing to you—as it is to me—and almost all forms of energy harnessed by humankind throughout history originated with energy from the Sun, doesn’t it make sense to look directly to the source in our quest to find a clean, unlimited source of energy for all of humanity going forward?
What does “space-based solar power” mean?
Space-based solar power (SBSP) refers to the concept of collecting the Sun’s energy in space and then transmitting it to Earth for use as a baseload renewable energy source. This involves putting solar panels in orbit around the Earth to continuously collect energy from the Sun. The energy is transferred to receiving antennas (rectennas) on Earth as microwave or laser beams, converted to electrical energy, and then sent to consumers through the existing power distribution grid. The goal of SBSP is to provide practically unlimited clean energy that is not subject to weather conditions or night-day cycles; energy that is available 24/7/365, anywhere on the planet.
Before we delve into the details and challenges around space-based solar power, let’s take a brief step back in time to see how humanity got where we are today, and how we may soon be consuming the equivalent amount of energy in 150 billion barrels of oil every year.
How much energy is globally consumed by humankind?
It took the first three million years of evolution for the world population to reach one billion of us. Over the past 220 years, fueled by advances in medicine, nutrition, and a massive glut of cheap energy from the worldwide fossil fuel industry, the world population has exploded to over eight billion humans. The United Nations estimates that the world population will expand to over ten billion by the year 2100.1 In the developing economies of emerging nations, particularly in Asia, per capita energy consumption is increasing as people seek better lives for themselves and their families.
Driving—or driven by—economic and population growth, worldwide energy consumption also exploded over the past two centuries, and with it, energy-related carbon dioxide emissions. The Enerdata World Energy & Climate Statistics lists the 2021 global total energy consumption as 14,555 million tons of oil equivalent (Mtoe), or for comparison purposes, the equivalent of about 169,277 terawatt-hours (TWh) of electrical energy. For 2021, the global electricity generation is listed as 28,433 TWh of electrical energy, or about 16.8% of the global total energy consumption.2
A mid-range scenario presented in the Enerdata Global Energy & Climate Outlook 2050 assumes policies that will lead to a global temperature rise between …
A recent article in The Economist, 23 items of vital vocabulary you’ll need to know in 2023, was a fascinating list of new and not-so-new science and technology-related words / concepts that are starting to bubble up into everyday news stories and conversations. (If you have a free or paid account on The Economist website, or want to sign up for one, you can read or listen to the article linked above.)
The European Space Agency’s SOLARIS Space-based Solar Power Preparatory Programme, as mentioned in the referenced article
In good company with other vital new vocabulary such as passkeys and post-quantum cryptography, I am happy to note that Space Solar Power has been included near the bottom of the list. It’s exciting to see The Economist authors of this article state that the field of space solar power “… is experiencing a new dawn.”
Space solar power The idea of capturing energy in space using huge solar arrays attached to orbiting satellites, and then beaming it down to Earth as microwaves, has been around since Isaac Asimov proposed it in a science-fiction story in 1941. But the sums have never added up: launching things into space simply costs too much. That could change if launch costs fall far enough, or if new space-based manufacturing techniques emerge, such as mining asteroids for raw materials. And in a high enough orbit, a solar-power satellite could stay in sunlight around the clock, providing a clean, reliable source of power. The European Space Agency sponsored a ground-based demonstration in Germany in 2022 as part of a proposed scheme called Solaris. America, Britain, China and Japan are also funding research in the field, which is experiencing a new dawn.
By Martin Adams, Aryn Braun, Joel Budd, Tom Standage and Vijay Vaitheeswaran
ISS030-E-020039 (26 Dec. 2011) — This busy night time panorama was photographed by one of the Expedition 30 crew members from the International Space Station on Dec. 26, 2011. Comet Lovejoy streaks through the star-filled sky just to the right of center. The land mass is the coast of Chile, looking southeast, with several coastal cities in the capital city region near Santiago. A 28-mm focal length was used to record the image.
“I have often suggested that given humanity’s increasing and irreversible dependence on outer space for daily human needs, space will either be safe for all or for none.”
Nayef Al-Rodhan
The future of space based solar power is dependent on solving technical, financial and political issues. Could the security of outer space end up being the most difficult issue of all? Perhaps the collective need of all humankind for a virtually unlimited source of clean energy can be the catalyst for geopolitical agreement on a peaceful use of outer space.
The article, published in The Space Review and linked above, summarizes the current positions of the United States, our allies and our competitors in outer space. In a rather ominous summary, the author asks if space will ultimately be safe for all … or for none.
STS097-376-019 (7 December 2000) — A close-up view of the P6 solar array on the International Space Station (ISS), backdropped against the blackness of space and the Earth’s horizon. The P6 solar array is the first of eight sets of solar arrays that at the completion of the space station construction in 2006, will comprise the station’s electrical power system, converting sunlight to electricity.
C-SBSP has long believed that space-based solar power (SBSP) hardware should be manufactured in space, away from the deep gravity well of Planet Earth. Perhaps a cislunar application for SBSP will provide the impetus needed for the United States to develop the required space-based mining / refining, space-based manufacturing and space-based assembly technologies.
The article, published in Breaking Defense and linked above, explains how a novel satellite might just be an early consumer of space-based solar power.
The sixth mission of the X-37B Orbital Test Vehicle is scheduled to launch on May 16, 2020. As reported by Air Force Secretary Barbara Barrett, aboard will be an experiment from the the U.S. Naval Research Laboratory will transform solar power into radio frequency microwave energy which could then be transmitted to the ground. Link to the full U.S. Space Force article is below.
Ian Cash, of SICA Design Ltd, presented a new Solar Power Satellite (SPS) concept during the Space Solar Power Workshop of the IEEE WiSEE conference held in Montreal last month. Ian’s presentation is linked below. Special thanks to Elisa Shebaro of PowerSOL, who attended this conference and brought the CASSIOPeiA presentation to my attention.
The CASSIOPeiA Solar Power Satellite is “based on the principle of wavelength-scale modular integration of all major functions, from solar collection through to beam-formation.” With no moving parts, CASSIOPeiA’s patent-pending phased array permits beam steering through 360 degrees.
The ultralight helical structure maintains a constant solar collecting area directly facing the Sun. Stowed as an integrated and highly compact package, this concept offers “the enticing possibility of a fully functional SPS deployed as a single payload.” The full CASSIOPeiA white paper can be read here.
Dr. Seyed (Reza) A. Zekavat, Michigan Tech, and Darel Preble, Space Solar Power Institute, Georgia Tech, co-chair the Space Solar Power Workshop as part of the annual IEEE WiSEE Conference. Papers and presentations from recent Space Solar Power Workshops can be seen at the bottom of Dr. Zekavat’s faculty page, here.
“Trump Should Make Space-Based Solar Power A National Priority”
by Bruce Dorminey, contributor, Forbes.com
Image Credit: NASA
In a recent Forbes.com article, science journalist and author Bruce Dorminey argues for the current administration to make development and deployment of space-based solar power a national priority. Read the full article here.
If President Trump were to champion space-based solar energy as a means of delivering unlimited, renewable electricity from Earth orbit, it’s arguable that his administration could leave the U.S. and the world at large with a revolutionary new source of energy.
In this advocate’s opinion, one of the most important points Dorminey makes is that ” … the fledgling space-based solar power initiative needs cohesive leadership to actively plot goals and transform it into a workable industry.” The majority of SBSP supporters have thus far focused on engineering challenges, essential to the technical “how is it done” question of space-based solar power. Two other questions, the financial “who pays for it” and the political “who gets the credit or takes the blame” must also be answered for a complete solution.
With most complex problems, the level of difficulty usually increases from the technical solution to the financial solution to the often intractable political solution. A current, complex problem to illustrate this three-pronged approach might be the ongoing battle over national healthcare. (Have even one of the three questions truly been answered yet?)
To jumpstart a U.S.-led space-based power agenda, at least three in-depth proposals for federal legislation have already been put forward:
SunSat Corporation Charter – proposed by the Space Solar Power Institute’s (SSPI) Space Solar Power Workshop, led by Darel Preble at Georgia Tech
D3 Space Solar Proposal – Diplomacy, Development, and Defense (D3) Innovation Summit Pitch Challenge award-winning proposal by a team of scientists led by Dr. Paul Jaffe, spacecraft engineer at the U.S. Naval Research Laboratory (NRL)
Citizens for Space Based Solar Power 