A worker walks by electrochromic windows that are beginning to darken at the seams at the U.S. National Renewable Energy Laboratory Research Support Facility (RFS) in Golden, Colorado September 4, ... more 
A worker walks by electrochromic windows that are beginning to darken at the seams at the U.S. National Renewable Energy Laboratory Research Support Facility (RFS) in Golden, Colorado September 4, 2013. The "dynamic windows" change color to modulate interior temperatures and lighting. The 800 occupants of the RFS building consume only the amount of energy generated by renewable power on and near the building. REUTERS/Rick Wilking (UNITED STATES - Tags: ENVIRONMENT ENERGY) less 
1 / 29
Reuters | Photo By RICK WILKING / REUTERS
Mon, Sep 9, 2013 12:44 PM EDT