Thai billionaire entrepreneur Sarath Ratanavadi plans to merge his energy and telecoms companies in a new firm, which will be worth around $20.5 billion. Ratanavadi, with a net worth of $10.8 billion as of July 17, owns Gulf Energy Development, one of Thailand’s largest power producers by installed capacity. The businessman, number 5 on Forbes’ list of Thailand’s richest persons and number 200 on the Forbes Billionaires list, also owns Intouch Holdings, the conglomerate that owns Thailand’s most valuable mobile phone…