http://aheadoftheherd.com/Newsletter/2011/Rick-Mills-Cobalt-Is-the-King-of-Critical-Metals.htm

.................The U.S. Department of Energy says materials used in four clean energy technologies: wind turbines, electric vehicles, solar cells and energy efficient lighting, are critical now. The American Physical Society's Panel on Public Affairs and the Materials Research Society coined the term "energy critical element" to describe elements that are essential to one or more of the new energy-related technologies. The European Union commissioned a report that identified 14 materials critical to the EU.

Only four metals or element groups made all three lists: REEs, platinum group elements (PGEs), lithium and cobalt.................