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Breakthrough barium titanate solar panels are 1000x more powerful than existing panels
(www.thebrighterside.news)
everything about energy production
It's not a measure of efficiency per se, but efficiency is a limiting factor:
In order for a solar panel to put out 1000x more power, the baseline you're comparing it to must be at most 0.1% efficient, because otherwise the new thing would have greater than 100% efficiency and that isn't possible.
And that's a purely thermodynamic argument. The actual limit for solar efficiency is likely less.