[hwillis]

The earth is actually a pretty big heat source in space. Solar radiation is a point source, so you can orient parallel to the rays and avoid it. The earth takes up about half the sky and is unavoidable. The earth also radiates infrared, the same as your radiators, so you can't reflect it. Solar light is in the visible spectrum so you can paint your radiators to be reflective in visible wavelengths but emissive in infrared.

Low satellites are still cooler in the Earth's shadow than they would be in unshadowed orbits, but higher orbits are cooler than either. Not where you'd want to put millions of datacenters though.