It has long been known the U.S., and California in particular, have been driving forces behind the demand for Tesla Model S and Model X vehicles.

What has never been clear is exactly how much of the automaker's sales come from its home market. Tesla's policy has been, and still remains, that it doesn't break down sales by market.

But a new report by Moody's gives us a glimpse into just how important the U.S. is to Tesla. Moody's, citing company reports and registration data from Polk, says Tesla dominates the EV market in the U.S., selling 45 percent of all electric vehicles in the first half of this year.

That is well ahead of General Motors, which had 16 percent of the domestic market thanks to its Chevy Bolt.