Chinese electric automaker BYD is about to outsell Tesla this year. Here's how it's winning the race against Elon Musk.

• China is the world's biggest market for electric vehicles.
• BYD is expected to overtake Tesla as the world's biggest EV maker when fourth-quarter data is released. 
• China's control of battery supply chains and its focus on charging networks has boosted EV sales.

China's economy may be spluttering, with growth faltering and big property developers collapsing, but one industry has continued to rev harder.