Creating sunlight on demand is indeed the claim of US startup Reflect Orbital, who propose to use mirrors in orbit to reflect extra sunlight down to Earth.
The idea isn't to make the whole planet sunnier; only to increase the amount of time solar power farms can generate electricity each day.
The initial plan is for two satellites to be launched in 2026 as a proof of concept. These would have an 18m x 18m (59 x 59ft) deployable mirror and fly in low Earth orbit, around 600km (373 miles).
This would illuminate a 6km-diameter (3.73 miles) patch on the ground, with a brightness roughly equivalent to a full moon.
This is far too dim to generate solar power from, but the plan is to have lots of satellites all pointing in the same direction to overlap the beams: 5,000 of them by 2030 and more than 50,000 by 2035.
Under the most optimistic set of assumptions for the reflectivity and accuracy of the mirrors, this would approach the brightness of twilight for a handful of 6km-wide locations on the ground.
But this isn’t a constantly illuminated spot; the mirrors are travelling at 7.5km/s (4.66mi/s), so they can only illuminate the same place for a few minutes at a time. And since twilight still isn’t very bright, this would only be useful for solar farms whose local time is just after sunset or just before dawn.
Anywhere else, either the natural light is already bright enough not to need the boost, or the satellite is also in the dark.
It’s therefore somewhat unlikely that the economics of this venture will ever make sense, compared to simply building more solar capacity and battery storage here on the ground.
This article is an answer to the question (asked by Samantha Barker, Oxford) 'Could we create sunlight on demand?'
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