Smokestacks, cooling towers, reactor domes and gas installations are defining features of our modern landscape. Each is a key component in electricity generation, but perhaps not for much longer. Sprinkled over every continent are the totems of a new era of power: wind turbines and solar energy collectors. So far they are few and far between, but that's about to change. Plans for huge solar power plants have been drawn up in the US, Spain and Portugal, and it seems barely a month goes by without a new wind farm springing up.