Today, we look at three extraordinary stocks that have investors bewildered by incredible surges in share prices as well as off-the-charts volatility. Shares of Plug Power (NASDAQ:PLUG), a manufacturer of fuel-cell systems, have appreciated 3,200% over the past year. With such a rapid rise and heavy media coverage, investors are wondering if the business fundamentals warrant such price appreciation, or are we in a fuel cell bubble? The exuberance and volatility are not exclusive to Plug Power; FuelCell Energy (NASDAQ:FCEL) and Ballard Power Stations (NASDAQ:BLDP) are also along for the ride. Today, we answer a question from a Foolish reader wondering, "How do you identify a bubble"? 


This segment is from Tuesday's edition of "Digging for Value," in which sector analysts Joel South and Taylor Muckerman discuss energy and materials news with host Alison Southwick. The twice-weekly show can be viewed on Tuesdays and Thursdays. It can also be found on Twitter, along with our extended coverage of the energy and materials sectors: @TMFEnergy..

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.