A wind farm in Montezuma Hills, about 40 miles northeast of San Francisco. California is considering proposals to, among other things, derive half the state's electricity from renewable sources. Carl Costas/CALmatters hide caption

itoggle caption Carl Costas/CALmatters

There are about 400,000 greater sage grouse left on the landscape, spread across 11 Western states, from California to North Dakota. That's a fraction of what their numbers were just a century ago. Tom Koerner/U.S. Fish and Wildlife Service hide caption

itoggle caption Tom Koerner/U.S. Fish and Wildlife Service

An aerial view of Tokyo Electric Power Co.'s tsunami-crippled Fukushima Dai-ichi nuclear power plant, on March 11. Kyodo/Reuters/Landov hide caption

itoggle caption Kyodo/Reuters/Landov

A thermoelectric PowerCard like this one can be used to convert waste heat into an electric power source, Alphabet Energy says. Alphabet Energy hide caption

itoggle caption Alphabet Energy

"Physics tells you what you can and can't do. If you know the physics anything else is possible." — Taylor Wilson James Duncan Davidson/TED hide caption

itoggle caption James Duncan Davidson/TED