If your solar system sends any excess power to the grid (i.e. your electric utility company) we can probably rule out problems with the 60Hz waveform as there are rather stringent rules governing that. So far, we have seen no documented issues with solar power and X10.
There were documented problems with Echelon Smart Meters used in one Duke Energy region in suburban Cincinnati. I don't recall any proven problems with other meters or even with the Echelon meters in other regions (e.g. I live in Northern Kentucky about halfway between downtown Cincinnati and the Greater Cincinnati International Airport and my Duke Energy supplied Echelon meter has not caused me any X10 problems.)
Details on your X10 hardware might prove helpful. Also, what solar company? What electric utility? What Smart Meter?