Tesla says it will build 500K cars a year by end of 2018; can it?

When Tesla Motors CEO Elon Musk said two years ago that the electric-car maker planned to be building half a million cars a year by the end of 2020, it seemed an ambitious stretch goal. When he said on last week's quarterly earnings call that the company was pulling that goal two years ahead to 2018, you can almost hear the gasps. That means that...