What's the key to using alternative energy, like solar and wind? Storage, so we can have power on tap even when the sun's not out and the wind's not blowing.
In this talk MIT professor Donald Sadoway takes to the blackboard to show us the future of large-scale batteries that store renewable energy.
As he says: "We need to think about the problem differently. We need to think big. We need to think cheap."
Donald Sadoway is named one of world's most influential people by Time magazine