At the closing bell, SCTY is down about 2.1%, while XYL is trading flat on the day Friday.
Lyndon Rive, a co-founder and former CEO for SolarCity, is leaving Tesla to start another company next year.
Bank of America/Merrill Lynch analyst John Murphy believes Tesla's acquisition of SolarCity will cause shares to sink.
SpaceX made history Thursday evening when it successfully launched a recycled Falcon 9 rocket into space.
The residential solar company said after the market closed Wednesday that it expects to post 325 megawatts of bookings in 2017.