"In the 1970s, manufacturing a solar cell required about as much energy as the cell could produce over its 20-year lifetime, so using solar power provided little if any energy gain. Also, as recently as 10 years ago, total emissions from solar cells were about twice what the new study shows."
-- Science News Online, Week of March 1, 2008; Vol. 173, No. 9 , p. 133
http://www.sciencenews.org/articles/20080301/fob5.asp
The pay back time now is only 1 to 3 years