shouldn't the recipe replace solar panels / accumulators?

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

RTGs are usually the most desirable power source for unmaintained situations that need a few hundred watts (or less) of power for durations too long for fuel cells, batteries, or generators to provide economically, and in places where solar cells are not practical.

Logically, I would agree. However, replacing the 100 Solar panel requirement with the RTG would reduce the raw material costs of the Satellite by a great deal, which seems to go against the intended vanilla friendly balance and also reduce the spirit of the Satellite as part of the "final boss" in Factorio.

I could make the RTG about as expensive as the 100 solar panels and accumulators but that seems a little excessive. My head canon is that the satellite uses both solar energy and nuclear energy (not unlike most bases!)!

1. you could replace some of the solar/accum and leave the LDS alone (my head canon is that LDS is the container, so adding RTG would mean MORE LDS, not less)
2. remove all the solar/accum and rebalance by adding more of the other ingredients (LDS, blue chips, radar, rocket fuel)

but it's not a big deal and balancing is arbitrary.