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Illustration by Chen Wu

In 2023, Caltech’s space solar power prototype demonstrated its ability to wirelessly beam power through space and direct a detectable amount of energy towards Earth for the first time. The recent £4.3 million investment by the UK government, China's ambitious Chasing the Sun project and the US Air Force's plan for a power-beaming demonstrator from low Earth orbit collectively underscore the global attention on the potential of space-based solar power. Could 2024 be a pivotal year for space-based solar power to spark an energy revolution?

Beam us down, Scotty: space solar power straight to Earth video still

Last year marked the centenary of Russian theorist Konstantin Tsiolkovsky proposing what seemed like a flight of fancy: deploying mirrors in space to concentrate sunlight onto Earth with such power that it could boil 10 large cups of coffee in just two minutes. The idea was so intriguing that it inspired Isaac Asimov to feature it in his 1941 short story, Reason. Fast forward to today and what was once a fictional idea is now becoming a reality.

The technology, known as space-based solar power, collects energy from the Sun using panels on satellites and beams it safely back to Earth. It's no longer a quirk of the imagination but a serious subject of scientific and governmental interest.

24-hour solar power

Why look to the stars for energy when the cost of ground-based solar power has dropped nearly 90% over the last decade? Facing the urgent need to achieve net zero emissions, we're confronted with a stark reality that global energy use is expected to rise by nearly 50% by 2050. Ground-based solar power, while increasingly affordable, struggles with being intermittent as weather or night can interrupt sunshine.

Intermittency poses challenges for grid operators, who need to balance meeting higher demand after sunset and curtailing excess daytime output. A striking example is the 'duck curve' in California, showing a deepening daily mismatch between supply and demand from 2015 to 2023: abundant solar energy during the day but insufficient levels at night. The issue was particularly pronounced in 2023, when solar energy output from stations in New England dropped by 56% in a week due to wildfires. In contrast, space solar power offers a consistent, uninterrupted and unlimited supply, mitigating these terrestrial challenges.

Space solar power involves equipping satellites with solar panels and positioning them thousands of miles above Earth. These panels continuously capture sunlight which is then converted into low-intensity microwaves. This method has been proven to be safe to humans and many sorts of wildlife. The microwaves are beamed through Earth's atmosphere and received by ground-based antennas. Here, it is transformed back into electricity and sent to the power grid. The potential of a single satellite in this system is immense, capable of delivering as much as 2GW of carbon-free power – enough to sustain a city of two million people around the clock.

A crucial factor in the growing excitement around space-based solar has been the dramatic reduction in launch costs, thanks to reusable rocket vehicles like SpaceX's Falcon Nine, which have cut launch costs by approximately 90%. Space solar power is projected to be cheaper than nuclear or biomass energy by 2040. While it is likely to be more expensive than conventional solar or wind, it avoids the problem of irregularity.

Making space-based solar power a reality

Debate over the feasibility of space solar power continues, echoing similar concerns from the 1970s when it first gained attention but was ultimately sidelined due to high costs. The next step in advancing space-based solar power to a scalable level involves tackling the infrastructure challenge. While estimates vary considerably, according to some sources, for effective power beaming, each satellite needs to span at least one kilometre. Under these assumptions, the complementary ground-based receiving station needs a footprint more than ten times larger to efficiently capture the diffused microwaves from space. The precision of energy transmission, infrastructure requirements and scalability are key factors that need close observation in the near future to determine the viability and practical application of space solar power on a larger scale. Just as significant research and investment have led to major advances in ground-based solar power, such as increased efficiency, similar efforts could address the infrastructure challenges of space-based solar power.

In the next year or two, improving transmission precision will be important for determining the progress of space solar power. Japan plans to precisely transmit solar energy from space by 2025. This involves accurately beaming microwaves from a fast-moving satellite in low orbit to a ground receiver. The forthcoming European Space Agency's business case presentation to the EU represents another signal to watch for market readiness of this technology.

As we navigate this exciting yet challenging path, space-based solar power represents more than a technological breakthrough. It is a revolution in how we produce energy, potentially, in the long run, offering a future where clean and constant power is no longer a fiction but a reality for all.