Renewable sources of electricity may be not consistent, but they are highly predictable. Smartly combining them through a smart grid with efficiency measures makes it possible to compensate intermittence effectively. On the other hand, traditional sources of electricity, like coal and nuclear, have 10-12% downtime, which may happen unpredictably.
Just to put things into perspective: the greenest kWh is the one which has not been used.
This video was re-recorded by Rocky Mountains Institute (RMI) to serve the energy community until its original version, delivered in the TED All-Stars session in Vancouver on 18 March 2014, is posted at ted.com. Copyright (c) 2014 Rocky Mountain Institute.