Bibliography 1.         Energy and the Enviroment-by Robert A. Ristinen, Jack J Kraushaar, copryright 1999 John Wiley and Sons, Inc.   2.         World book  Encyclopedia ,Cdrom, 2001.   3.         How Things Work, by Peter R. Crabb, copyright 1998 McGraw-Hill Irwin.   Web Sites Used http://greennature.com/article1546.html http://www.ott.doe.gov/hev/concept.html      6.  http://www.npga.org/i4a/pages/index.cfm?pageid=623