This is a plutonium-driven device that produces power far more efficiently than the traditional Radioisotope Thermoelectric Generators (RTGs) used hitherto on space missions, such as on Cassini.
Although solar panels will work on spacecraft at that distance, the desire for sufficient energy to drive many instruments means any mission would really need to go with radioisotope thermal generators (RTGs) - solid state electrical generators powered by the heat of radioactive decay.