Geostationary orbit is 36,000 km above the earth surface. The earth is 12,000 km in diameter. The sun is 150 MILLION km away. The about of time the something in geo-stat stays in earth's shadow is tiny.
Imagine a base runner in baseball after a home run. Spends half the time on the far side of the pitcher from the homeplate umpire, but he is only occluded from the homeplate umpire by the pitcher for a very short amount of time. That's (very!!) roughly the scales involved here.
Not only that, but thanks to the fact that the Earth's rotation (and thus the plane of the equator) is tilted off of the orbital plane, even equatorial satellites far below geosynchronous orbit will only pass through the Earth's shadow at all close to the equinoxes (twice a year). Most of the time, you have eternal sunshine throughout an orbit. It's as though the metaphorical baseball player takes a flying leap so that the umpire can see him over the pitcher's head.
Imagine a base runner in baseball after a home run. Spends half the time on the far side of the pitcher from the homeplate umpire, but he is only occluded from the homeplate umpire by the pitcher for a very short amount of time. That's (very!!) roughly the scales involved here.