Europeans from Portugal to Finland are being treated this morning to a partial eclipse of the sun, which is also visible in parts of north Africa and the Middle East. (Totality, where the moon completely covers the sun’s disc, is visible only from a few North Atlantic and Arctic islands.) But while most people hope for clear skies, the operators of Europe’s power grids have been praying for cloud, to minimise the impact on the level of solar-power output. Europe generates 100 times as much solar electricity (4% of peak demand) as in 1999, when the previous eclipse occurred; engineers have been preparing for this one for more than a year, and issuing warnings of potential disruption as power levels seesaw. It sounds like the Millennium Bug all over again. But, as in that case, disaster seems unlikely—not least because skies are cloudy across much of Europe.