Give a stream of consciousness and then the final answer. Spacecraft operating in the inner Solar System usually rely on the use of photovoltaic solar panels to derive electricity from sunlight. In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermoelectric generators (RTGs) are used as a power source.

Answer this question: where do satellites in outer space derive their electrical energy from?
To answer the above question, the relevant sentence is: Spacecraft operating in the inner Solar System usually rely on the use of photovoltaic solar panels to derive electricity from sunlight.
So, the final answer is photovoltaic solar panels to derive electricity from sunlight.