http://www.ck12.org Chapter 3. Making A Difference
See Quayle and Changery (1981).
Geothermal power in 1995.Freeston (1996).
Energy crops.See Rogner (2000) for estimates similar to mine.
Further reading:Naturemagazine has an 8-page article discussing how to power the world (Schiermeier et al., 2008).