Solar-electric propulsion has been used several times now in deep space missions. This question explores the scalability in comparison to Radioisotope thermoelectric generation or other nuclear-based sources.
Suppose a deep-space mission where smallsats needs to be placed at several distances from the Sun in circular orbits. Each requires 1 kW of electrical power (thermal management for the coldest orbits is done with separate radioisotope heating units).
Does solar-electric always win over RTGs in terms of mass? Below 1 AU it's almost certain that solar-electric power wins, but at what distance from the Sun would the cross-over point be where, roughly speaking the two types of power systems would be similar masses?
Reasonable extrapolation and estimation are fine, we don't need a design review. I'm just wondering if these points are in the asteroid belt or the Oort cloud.
Secondary (optional) part
If the power requirement were much lower, say 1 W or 10 W, would the crossover point be roughly the same? Or does the scaling of mass with output power behave very differently for one versus the other?
Just fyi Juno had to hibernate for 2.5 years because there wasn't enough sunlight near aphelion, and the really-deep-space probes all used RTGs.