Harvesting solar energy in orbit and beaming it down to Earth is a decades-old idea. Now, a raft of companies say they could finally make it a reality.

At an American football stadium in Florida last March, an unusual test took place. Here, it wasn't footballs being thrown, but beams of light across the length of the pitch. The concentrated streaks of light lasted for a few minutes, fired from an emitter on one side of the field in the Jacksonville Jaguars' stadium and collected on a screen on the other.

The light was collected from the Sun and them beamed out by large lenses on the field like a magnifying glass, each about 1.2m (4ft) tall. "We had to get up a ladder to pull the cover off," says Andrew Rush, president and chief executive of the Florida-based company Star Catcher that carried out the test.

The goal? To see if beaming sunlight across space to power satellites was feasible.

"We knew some folks at the Jaguars and we thought this would be a cool thing to do," says Rush. "We beamed 100 watts about 105m [345ft]."

Star Catcher is one of several companies around the world developing space-based solar power technologies, a concept that has languished in a grey area between science fact and science fiction for decades. The idea is to provide Earth with abundant clean energy by capturing sunlight in space and beaming it to the ground or other satellites.

Solar panels on terra firma are, by contrast, limited by the atmosphere, the weather and Earth's day-night cycle. These all affect how much sunlight those panels can soak up, filtering out varying amounts of the Sun's radiation before it can reach ground level. But in space, it is possible to collect sunlight almost around the clock at much higher efficiencies.

"I remember telling my father about this and he thought I was a bit bonkers," says David Homfray, co-founder and chief technology officer of UK firm Space Solar. But multiple countries, including the UK, US, Japan and China are now investing in the technology.

"Space-based solar power makes the energy transition work," argues Homfray, noting that some estimates claim it could supply up to 80% of Europe's renewable energy needs.

This is largely due to the higher power density – more than 10 times higher – that space-based solar has compared to those based on the Earth's surface – it can convert far more of the Sun's energy into electricity.

And yet realising it is no mean feat.

It would likely require enormous satellite constellations, which might be controversial, difficult to operate safely and require a significant number of rocket launches to construct. Plus, there are cheaper and easier forms of renewable energy that could come online far quicker – which is important given the need to replace fossil fuels with greener alternatives if the world is to have any hope of bringing global warming under control.

Even so, there are some who believe the rewards for building solar power stations in space will come to far outweigh the drawbacks. The US military, for example, is very keen on a technology that will allow it to beam energy to anywhere in the world on demand, helping to overcome one of the major problems faced on modern battlefields, but it could be equally as useful in the aftermath of disasters or for rural communities.

Space-based solar power works much like solar on Earth – panels convert sunlight into electricity – but with one huge advantage: they're above the atmosphere. This means those panels can collect sunlight that hasn't been filtered through the gas and clouds that cloak our planet. The atmosphere reflects around 30% of the energy that reaches our planet while it absorbs around a quarter before it even reaches the Earth's surface. Space-based solar panels can avoid this effect, but can remain in near-constant sunlight if placed in the right orbit.

Once collected, this power can be transmitted to Earth as microwaves or laser beams, and captured by large ground antennas that convert it back into usable electricity. To make economic sense, however, each satellite must generate and beam immense amounts of power at gigawatt scale, requiring massive arrays assembled in orbit.

US science-fiction author Isaac Asimov first wrote about tapping solar energy from space in 1941,

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