Tesla Motors Inc. began delivering its new Model X sport utility vehicle at the end of September. But production challenges means Model X deliveries will be slow to take off this year. This means Tesla will rely on the Model S electric sedan more heavily than expected to meet its sales goals for the year. Tesla will need to deliver nearly 17,000 cars in the last three months of the year to meet its 2015 minimum sales goal of 50,000 units. Ben Kallo, an energy technology analyst at Baird Equity Research, estimates Tesla will more than hit that goal.