What are the challenges the world faces in the transition to renewable energy – and what are the possible solutions? The BBC's Carl Nasman learns about the US' first 100% renewable-powered city; the world’s largest solar farm; and the research project literally getting energy from thin air. This is episode three of Future Earth, a series exploring today’s most important developments in climate science and sustainability. For more climate news and hopeful developments, subscribe to the Future Earth newsletter here: https://cloud.email.bbc.com/FutureEarth_Newsletter_Signup? 00:00 Sealing off abandoned oil wells 05:47 World's largest solar farm 11:00 America's first 100% renewable energy city 14:37 Decarbonising aviation 21:19 Sand batteries 22:22 Harnessing subway heat #FutureEarth #Climate #BBCNews