Alternative Energy Letdowns

From 60 Second Science:

As the call for a clean-energy savior—to wash away our fossil-fuel sins—grows louder, the number of questionable candidates swells. Should we be looking to photovoltaic or fusion? Turbines or tides? With thanks to readers who responded to our Twitter call for favorite alt-energy duds, here's a roundup of five ideas that may one day succeed, but aren't going to save the globe from a climate calamity anytime soon. Find out what they are...