The additional weight of solar panels (heavy, if you're getting 20%+ efficient panels) replacing thin, lightweight aluminum panels will drive the efficiency of the Tesla probably below 3.0mi/kWh.
The solar panels would be an extra 100 kg, and that's just using the mass of the whole panel (in reality there would be some savings since the aluminum frame could be reused). I'm using the mass here, which is ok because "high efficiency" monocrystalline panels don't really weigh any more than regular efficiency panels. Silveo (aka SolarCity aka Tesla) will be making 23% efficient panels in their Buffalo factory.
Call it generously 200 kg with wiring and electronics. That's like carrying a couple extra passengers. Are you suggesting that a 9% increase in mass could cause a 14% increase in energy consumption? Especially since none other than Elon Musk has stated that the partial derivative of mass vs energy consumption isn't very strong...
I don't think solar cars are a great idea, but let's not use bogus arguments here.