Solar eclipse

[AstroPawian]

Hi guys this is solar eclise in ksp ??

 

[The Aziz]

Yes, happens every few days since Mun and Kerbin have no inclination.

[Snark]

As you may have noticed, it doesn't actually make anything dark (KSP doesn't model planetary shadows like that).  I see from your screenshot that you're running some visual F/X mods (I'm guessing SVE, at least.  Maybe Scatterer too?)  Some of those mods actually do add some eclipse effects so you actually do get a shadow-darkness effect on your ship (it's hard for me to tell from your screenshot whether you're getting that).  But the stock game doesn't.

However, regardless of visual F/X, an eclipse does prevent your solar panels from generating any electricity.  It may look like your vessel's in sunlight, but there's no electric power.

So, for anyone who has ever had a vessel that suddenly and unexpectedly runs out of electricity, and you thought, "what the hell?  I've got solar panels in sunlight!  Why are they not generating any power?!", that could be the reason.  This can happen any time you're in body A's SoI and the sun gets blocked by nearby body B.

This tends to happen especially often when you're visiting Jool's moons, for example, simply because Jool is so huge that the eclipses are frequent and long.