BYD, the Chinese electric-vehicle maker backed by Warren Buffett, is taking some of the zing out of the red-hot renewable energy sector. Investors are concerned that some bets in the green energy segment have become crowded, while others say that price gains are unsustainable. The Shenzhen-based carmaker slumped 8.5 per cent for the week ended July 15 in Hong Kong, posting the biggest decline for the five-day period since the end of March. The sell-off wiped out HK$77.5 billion (US$9.9 billion) from BYD’s market capitalisation that exceeded HK$1 trillion last month. One direct trigger for the sudden sell-off was due…