The energy pay-back time of a photo-voltaic module is between 1 and 3 years and this figure is coming down steadily

All the electricity demand of the world could be produced by a PV plant of 500 square miles in the Sahara dessert

in q3 of 2009, US company First Solar claimed to produce cheaper electricity with PV power plants than with coal fired ones

Current CO2 concentrations are roughly loading...  ppm (and counting).

Solar activity varies in short term cycles, but only very slightly impacting the useful radiation we receive at earth.

Source: Wikipedia