More than half of the world's population lives in cities, most of them overcrowded and polluted. Now the biggest city of them all wants to become what it calls a "smart energy city". Al Jazeera's Scott Heidler reports from Tokyo. - Subscribe to our channel: http://bit.ly/AJSubscribe - Follow us on Twitter: https://twitter.com/AJEnglish - Find us on Facebook: https://www.facebook.com/aljaze
