Solar power is the energy that comes from the Sun and is the most abundant source of energy that is converted into thermal or electric energy. Widely-used solar panels harness solar energy for domestic, commercial, or industrial use.

However, solar power on Earth is intermittent which makes it difficult at times to harness it. Scientists at the California Institute of Technology in Pasadena, California thought of harvesting solar power from space and beam it down to Earth via microwaves. They called this the Space Solar Power Project, which aims to provide solar power anywhere on Earth unaffected by either weather or time of the day.

 Caltech's Space Solar Power Project Made Possible By Billionaire's $100M Donation
(Photo: Wikimedia Commons)
Stanford and Oxford scientists have created novel solar cells from crystalline perovskite that could rival and even outperform existing silicon cells on the market today. The new design converts sunlight to electricity at efficiencies of 20 percent, similar to current technology but at much lower cost.

Anonymous Donor of $100M for SSPP Finally Revealed

SSPP researcher professor Harry Atwater said in a statement that solar energy is the most abundant energy resource in the world. But sunlight is only intermittent to Earth's surface, which makes it hard sometimes to harness solar power. The SSPP will hopefully overcome the intermittency for energy storage since harnessing solar power from space means it will be continuous and can be beamed anywhere in the world.

According to, the SSPP was able to take off the ground and has been running for nearly a decade ago thanks to the anonymous donation of over $100 million. On August 3, Caltech revealed these anonymous donors to be the real estate developer Donald Bren and his wife Brigitte.

Irvine Co. chairman Bren said that he had been studying the possible applications of space-based solar power for many years, which fueled his interest in supporting Caltech's SSPP in 2013. He believes that harnessing natural energy from the Sun will benefit everyone.

SSPP team members said that the Brens do not have any financial stake in the project or the technology that it develops. "It shows the magnitude of the generosity," SSPP co-director Ali Hajimiri said in the same statement that the university posted.

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Harvesting Solar Energy from Space

The SSPP has developed a technology that demonstrates prototypes that could convert sunlight into radio-frequency (RF) microwave energy and transmit usable power via a wireless steerable beam. Caltech said that the integration of solar power and RF into one element further reduces the weight and complexity of beaming down the energy to Earth. Its scheduled first space flight will be in 2023.

But Caltech's SSPP is not the only one that is planning to harvest solar power from space. According to, the US Air Force also plans to launch a power-beaming experiment to orbit in 2024 with their Photovoltaic Radio-frequency Antenna Module Flight Experiment (PRAM-FX).

The 12-inch-wide square is now aboard the unmanned US Space Force's X-37B space plane zooming around the Earth. PRAM-FX is designed to harvest solar energy and convert it to microwave power. 

The X-37B space plane is on its sixth flight mission which was launched on May 2020. It is still unclear when it will come down as the mission is highly classified, including its identity and purpose.

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Check out more news and information on Space Solar Power in Science Times.