http://www.energy.ca.gov/education/story/story-html/chapter09.html

http://www.eren.doe.gov/erec/factsheets/rnwenrgy.html

/26366/text/alternative/solar.html

http://www.eren.doe.gov/roofus/solarpanels.html

Holt, Rinehart and Winston, Publishers [1986] Holt Science