> Either the satellite is geostationary and doesn't have 24h / 24h sun exposure as energy source.

Due to the Earth's axial tilt [1], geostationary orbits generally have 24 hour sun exposure, except for a few minutes a day around the equinoxes [2].

[1] https://en.wikipedia.org/wiki/Axial_tilt

[2] https://www.nesdis.noaa.gov/our-satellites/currently-flying/...