In 2009, Dr. Richard Perez, an atmospheric scientist specializing in solar energy at the University of Albany, in New York, compared the world's annual energy consumption with its available fossil, nuclear, and renewable energy resources. The volume of each of the four "finite energy" spheres, above, represents the total recoverable energy reserves in terawatt-years (TWy), while the volume of the remaining "renewable energy" spheres represents yearly potential in terawatt-years. One of Perez's sun facts: The world's available solar energy exceeds its energy consumption by a factor of 1,200.