RESEARCHERS at the California Institute of Technology (Caltech) are making renewable energy history by sending solar panels into space to harvest our sun’s energy from orbit.
On January 3, researchers at Caltech successfully launched the Space Solar Power Demonstrator (SSPD), a prototype spacecraft designed to gather the sun’s energy without the atmosphere and day-night cycle getting in the way. The spacecraft will send this energy back to Earth using wireless transmission.
Solar panels on Earth work by converting sunlight directly into electric power using the photovoltaic effect. Here, photons knock electrons off the atoms in the silicon photovoltaic cells, generating a flow of electricity. Energy can also be gathered from sunlight using concentrated solar power (CSP), which uses mirrors or lenses to concentrate sunlight to extreme heat to eventually make steam, which is converted into electricity by a turbine.
In 2021, solar power generated 4 percent of the world’s electricity.
However, one major drawback of solar power on earth is that it can only gather energy during the day, and efficiency is affected by seasons and cloud cover. In space, these issues could be avoided.
The SSPD consists of three sections, each of which will perform a separate experiment. The first is DOLCE (Deployable on-Orbit ultraLight Composite Experiment), which will test the deployment of modular spacecraft. DOLCE measured 6 by 6 feet, and will test the mechanisms required to eventually release a kilometer-scale constellation of spacecraft. Another experiment is ALBA, which will test which of 32 different types of photovoltaic (PV) cells are the most effective in space, and the last is MAPLE (Microwave Array for Power-transfer Low-orbit Experiment), which will test the transmission of energy using microwaves.
However, there are some major milestones to pass in order for this nascent technology to become functional.
“To me, the major challenge is indeed to get the power back to Earth without huge losses or other problems (like beams coming down in places where they are not wanted),” Kevin E. Trenberth, a climate scientist and Distinguished Scholar at the National Center for Atmospheric Research, told Newsweek.
“This should not be a problem in space, where there is no air, but as soon as air atoms (charged atoms in the ionosphere) and molecules get in the way, scattering takes place.”
Trenberth said that the worst problems are most likely to be with water vapor, as it absorbs sunlight and produces some local heating. This cuts down on the transmission and its efficiency.
“Some parts of the Earth, such as the subtropics, have less water vapor and provide windows of sorts but I do not know how those can be targeted or used productively on a rotating planet. Now this can be partly avoided by changing the solar energy into microwave energy that can be transmitted more readily through the atmosphere unless raindrops or particles get in the way. Microwave towers are used on the surface to beam energy over distances of 10 miles or so, not hundreds of miles,” he said.
“A big problem is that the beam spreads out and does not stay focused. More focus is achieved with huge antennae, but even then huge receivers would also be needed. Laser power beams could be used in space but not in the atmosphere.”
Even if the technology is found to work, some don’t think that it will catch on.
“I find it very difficult to imagine how this approach could ever compete with ground-based PV, even when storage costs are included to provide 24-hour supply,” Thomas White, a solar cell scientist and associate professor at Australia’s University of Sydney, told Newsweek.
“Even with some very optimistic assumptions about future technology development, [a recent cost-benefit analysis commissioned by the European Space Agency] came up with a potential levelized cost of electricity (LCOE) of 3.8 – 10.6 Euro cents/kWh by 2045. Ground-based PV LCOE is already around 3c/kWh, and getting cheaper every year, so it will be far below this price by 2045. The cost of storage is also coming down rapidly.”
White said that the space-based solar cells, if they are successful, would have to compete with existing technology that is well-understood, proven in the field, already one of the cheapest forms of electricity generation and following a very predictable cost-reduction path.
“While we should be considering a wide range of strategies to achieve net-zero emissions as rapidly as possible, I am yet to see a compelling argument for space-based solar power being one of these,” White said.
The testing of SSPD will take a long time, although the team hopes to have a full assessment of its performance within a few months.
“No matter what happens, this prototype is a major step forward,” Ali Hajimiri, Caltech’s Bren Professor of Electrical Engineering and Medical Engineering and co-director of SSPP, said in a statement.
