1. Homewyse, http://www.homewyse.com/costs/index.html , 2013
2. P. Stackhouse, NASA, http://eosweb.larc.nasa.gov/cgi-bin/sse/grid.cgi?email=skip@larc.nasa.gov , 2013
3. EIA, http://www.eia.gov/totalenergy/data/annual/showtext.cfm?t=ptb0105 , 2012
4. G. Barbose, N. D. S. Weaver, R. Wiser, Tracking the Sun V: An Historical Summary of the Installed Price of Photovoltaics in the United States from 1998 to 2012 (LBL Report), LBNL-6350E http://emp.lbl.gov/sites/all/files/lbnl-6350e.pdf , 2013
5. CIA, http://www.cia.gov/library/publications/the-world-factbook/fields/2195.html , 2013