I was on travel last week. I find intriguing the application of solar, wind, geothermal, hydroelectric, and tide power generation on an industrial scale. In the meridian of a highway near the Denver airport they have an array, which I took a photo of.
Solar Power Generation
It seems solar and wind are becoming quite practical as a matter of dollars and cents, even without having internalized the externalities of various power generation sources. From Richard Stevenson ("First Solar: Quest for the $1 Watt", IEEE Spectrum, V. 45, N. 8 (August 2008): 26-31), I learn to be competitive for off-peak power generation, solar cells need to be priced to generate electricity at $1 per watt. Apparently, a number of companies are developing competing technologies that may attain this goal in a couple of years.
Disclaimer: In mentioning First Solar and their Cadmium Telluride (CdTe) technology, I am "talking my book" - a phrase I learned from D-Squared - in a small way.