[jjtheblunt]

Is solar the only source of power on long spacecraft journeys, like that of Voyager and so on?

[lukan]

No, Voyager uses a radioactive battery. The sun is already way too far away for Voyager, to provide enough energy.

[thinkcontext]

Voyager doesn't use solar power since its incredibly faint as you get further from the Sun. It uses the heat from the decay of radioactive plutonium to generate electricity.