On September 2, 2025, the California Institute of Technology, or CalTech, announced (according to Morning View) that they have reached another milestone in space solar technology. The new milestone is the beaming back of collected solar energy from space wirelessly to Earth. My source may be confused since they first achieved this in the 2023 tests. It is unclear if anything new actually occurred in 2025 aside from more funding being secured. I wrote about space solar in June 2023, noting CalTech’s previous success at beaming energy from space to Earth. Previous milestones achieved in CalTech’s project include developing a lightweight, deployable structure for the solar power satellite and improving the efficiency of wireless energy transfer.
According to Morning View:
“Caltech’s recent demonstration of wireless power
transmission marks a monumental step forward in the field. During the test, a
small, lightweight module was deployed in space. This module successfully
collected solar energy, converted it into microwaves, and beamed it wirelessly
to a receiver on Earth.”
“This breakthrough has far-reaching implications. It
validates the feasibility of space solar power and brings us a step closer to
realizing its full potential. It also opens up new avenues for research and
development in related areas, such as wireless energy transfer and power
beaming technology.”
“Startup AetherFlux has played a significant role in the
advancement of Caltech’s project. They’ve been instrumental in developing the
technology for wireless power transmission and have also contributed to the
design and deployment of the space module.”
“Recently, AetherFlux secured a funding of $50 million.
This funding is expected to greatly accelerate the project’s progress, enabling
further research and development, and possibly even the deployment of a
full-scale power-beaming satellite in the near future.”
Below are some figures from a 2022 paper about CalTech's project.
Space solar has the advantage
over earth solar that there are no clouds to block the sun and there is no
night to hide the sun. There are also no seasons to limit sun time. Thus, it
would be a 24/7/365 power source.
According to an article in PV
Magazine:
“Beaming solar power from space may seem like science
fiction, but it has been proven in the field. In 2023, Caltech launched the
Space Solar Power Project (SSPD).”
“The SSPD deployed a constellation of modular spacecraft
equipped with solar to collect sunlight, convert it to electricity and then
wirelessly transmit the electricity over long distances wherever it is needed.”
“Wireless power transfer was demonstrated by Microwave
Array for Power-transfer Low-orbit Experiment (MAPLE), developed at Caltech.
MAPLE includes lightweight microwave power transmitters driven by custom
electronic chips that were built using low-cost silicon technologies. It uses
the array of transmitters to beam the energy to desired locations.”
“Caltech researchers estimate that solar from space
could yield eight times more power than solar panels at any location on Earth’s
surface.”
AetherFlux obtained about $60
million in funding in April 2025, including some from Bill Gates’ Breakthrough
Energy ventures. AetherFlux “seeks to
build small, portable ground stations about 5 to 10 meters in diameter to bring
electricity to remote locations. It said the project has applications in
military operations and disaster relief, where ground wire transmission is not
feasible.”
The latest news I could
find about the project linked to CalTech is in an April 2024 article in IEEE
Spectrum. While space solar has been and is being proven to be technologically
feasible, it may never be economically feasible, unfortunately. The 2023
demonstration involved launching a lightweight space satellite that unfurled
the solar array like a sail. It was successful and successfully beamed energy
down to Earth that was collected by a microwave receiver. The lightweight
satellite launch could have positive implications for communications
satellites, which are typically bulkier and heavier.
IEEE Spectrum interviewed the
project’s co-founder, Ali Hajimiri, in April 2024. He noted that new solar cell
designs were being pursued. In space, there is no water vapor or air oxidation,
but there is radiation that can cause damage. Perovskites can work well in
space. Hajimiri noted:
“Cells made with thin films of perovskites or
semiconductors like gallium arsenide, cells that use quantum dots, or use
waveguides or other optics to concentrate the light. Many of these cells show
very large promise. Very thin layers of gallium arsenide, in particular, seem
very conducive to making cells that are lightweight but very high performance
and much lower in cost because they need very little semiconductor material.”
Regarding the lightweight
satellite solar arrays, Hajimiri noted:
“Our idea is to deploy a fleet of these sail-like
structures that then all fly in close formation. They are not attached to each
other. That translates to a major cost reduction. Each one of them has little
thrusters on the edges, and it contains internal sensors that let it measure
its own shape as it flies and then correct the phase of its transmission
accordingly. Each would also track its own position relative to the neighbors
and its angle to the sun.”
Below is more copied from the
interview, including discussion of some difficult challenges to be overcome:
From your perspective as an electrical engineer, what are
the really hard problems still to be solved?
Hajimiri: Time synchronization
between all parts of the transmitter array is incredibly crucial and one of the
most interesting challenges for the future.
Because the transmitter is a phased array, each of the million little antennas
in the array has to synchronize precisely with the phase of its neighbors in
order to steer the beam onto the receiver station on the ground.
Hajimiri: Right. To give you a sense
of the level of timing precision that we need across an array like this: We
have to reduce phase noise and timing jitter to just a few picoseconds across
the entire kilometer-wide transmitter. In the lab, we do that with wires of
precise length or optical fibers that feed into CMOS chips with photodiodes built into them. We have some
ideas about how to do that wirelessly, but we have no delusions: This is a long
journey.
What other challenges loom large?
Hajimiri: The enormous scale
of the system and the new manufacturing infrastructure needed to make it is
very different from anything humanity has ever built. If I were to rank the
challenges, I would put getting the will, resources, and mindshare behind a project
of this magnitude as number one.
Again, the bottom line is
that while successful experiments are ongoing and have the ability to improve
results, there is a wide divide between technological success and economic
feasibility. Space solar will likely remain a novelty experimental pursuit that
will improve incrementally, but likely won’t be widely deployed unless some
significant improvements in economic feasibility occur.
References:
Solar
energy beamed from space—Caltech’s orbital breakthrough today. Alexander Clark.
Morning Overview. September 2, 2025. Solar
energy beamed from space—Caltech’s orbital breakthrough today
Space
Solar: Orbital Solar Panels on Satellites Beaming Energy to Earth Via
Microwaves: Japan Plans to Deploy an Orbital Solar Array By 2025 and Caltech
Demonstrates Wireless Power Transfer from Space to Earth. Kent Stewart. Blue
Dragon Energy Blog. June 6, 2023. Blue
Dragon Energy & Environmental Blog 2.0: Space Solar: Orbital Solar Panels
on Satellites Beaming Energy to Earth Via Microwaves: Japan plans to Deploy an
Orbital Solar Array By 2025 and Caltech Demonstrates Wireless Power Transfer
from Space to Earth
The
Caltech Space Solar Power Project: Design, Progress, and Future Direction. March
2022. Conference: 2022 IEEE European Conference on Antennas and Propagation
(EuCAP)At: Madrid, Spain. Authors: A Fikes, M Gal-Karziri, E Gdoutos. Michael
Kelzenberg. California Institute of Technology. (PDF)
The Caltech Space Solar Power Project: Design, Progress, and Future Direction
Space-to-earth
solar transmission startup Aetherflux raises $50 million. The California-based
company plans to transmit energy from satellites to ground stations. Ryan
Kennedy. PV Magazine. April 4, 2025. ‘Solar
bump’ breakthrough unlocks 80% more electricity from US data centers
Caltech’s
SSPD-1 Is a New Idea for Space-Based Solar Ali Hajimiri on boosting an
energy-beaming system from the lab to orbit. April 11, 2024. W. Wayt Gibbs is a
Contributing Editor for IEEE Spectrum. Caltech’s SSPD-1 Is a
New Idea for Space-Based Solar - IEEE Spectrum
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