In a Twitter exchange today, Tesla CEO Elon Musk said the company will likely add solar charging technology to the roofs of future all-electric cars. “We will probably offer that as an option,” Musk wrote in the Twitter exchange with Tesla enthusiasts. In answer to one enthusiast who doubted the value and charging capacity of photovoltaics on a car roof, Musk said the solar technology could come in the form of “a deployable solar shield…