Although the issues of climate change and crude oil have received plenty of media coverage over the past decade, scientists have been working for over a century to develop technology capable of replacing conventional fuels with renewable energy.
You could even argue that society has attempted to harness renewable energy since ancient times. Over the past 138 years, Popular Science has seen engineers adapt Dutch windmills into wind turbines, water mills into commercial tidal power facilities, and Roman hot spring-powered underfloor heating systems into geothermal electric power plants.
Going by the illustrations in our archives, however, most early prototypes of those facilities only vaguely resemble today's wind farms and solar power plants.
There were plenty of things engineers got wrong, of course: for instance, windmills atop the Empire State Building would not meet Manhattan's power demands, and marine kelp farms would not immediately be recognized as a profitable source of clean fuel. But if there's one thing everyone did right, it was acknowledging that the transition from conventional fuels to renewable energy would require an extraordinary amount of vision and risk-taking. Experimental projects would be expensive -- the Putnam-Smith wind turbine, for example, cost its manufacturer more than US$1.25 million dollars, and the structure was dismantled after operating for only four years.
Despite the setbacks, engineers have only developed more efficient ways to harness our natural resources. The Putnam-Smith wind turbine might have closed, but just last month, the world's largest offshore wind farm opened in Great Britain.
Renewable energy technology still has a ways to go, so in the meantime, click through our gallery to see where it's already been.