The high-profile roll-out of the highly secretive Bloom Box fuel cell, on CBS’s 60 Minutes in February, ushered in a new round of excitement about fuel cells.Fuel cells have been around for over 50 years. They are, in essence, chemical batteries that churn out electricity as long as a fuel, such as hydrogen or natural gas, is fed in at the other end. They have been a mainstay of power generation in NASA’s space program for decades and have slowly been making inroads for more earthly applications.While President George W. Bush and many others have touted hydrogen fuel cells as the “energy source of the future,” a fuel cell is not an energy source at all, but rather a device that converts a fuel into electrical energy–and it does so quite efficiently and cleanly.One of the problems with most fuel cells is that they require pure hydrogen for their operation, and hydrogen is a difficult material to store and transport. Being our lightest element, hydrogen has to be compressed to achieve a reasonable power density, so you’re usually dealing with very high pressures in storing it. Compressed hydrogen is explosive and can be quite dangerous.What Bloom Energy has created with its Bloom Box, according to CEO K.R. Sridhar, Ph.D., is a novel fuel cell that doesn’t rely on rare-earth elements, such as platinum (as do most other fuel cells) and does not require pure hydrogen for its operation. The company makes thin ceramic wafers out of quartz sand, coats the wafers on both sides with special proprietary materials, and stacks these with layers of an affordable metal alloy between. A four-inch stack of these layered cells and metal will generate one kilowatt (kW) of power when a hydrogen-rich fuel, such as natural gas, and oxygen are forced through it. Sridhar claimed on 60 Minutes that two of these stacks could power a typical American home, while a single stack could power four homes in his native India.Dr. Sridhar is a physicist who previously led NASA’s efforts to develop a system to generate oxygen for a mission to Mars. When that project was eliminated, he kept working on his invention, but reversed the process to create a “solid-oxide” fuel cell. In this process, oxygen is used rather than produced and electricity is generated. His work has been financed, starting in 2002, by about $400 million, most prominently from the venture capital firm Kleiner, Perkins, Caufield & Byers (famous for recognizing the potential of–and funding–such Silicon Valley success stories as Netscape, Amazon, and Google). Until February, though, the Bloom Energy’s technology was shrouded in secrecy. The February 21 edition of 60 Minutes removed that veil of secrecy with great fanfare.The first commercial Bloom Boxes were installed at a Google facility in late 2008, and test installations have now been completed for WalMart, eBay, FedEx, Staples, and more than a dozen other companies. Most of these fuel cells are powered by natural gas, though the units at eBay’s headquarters–enough to provide 15% of the power needs–use landfill gas (a mix of methane, carbon dioxide, and other gases). These 100 kW units cost $750,000, or 7,500/kW of capacity, which is not a bargain in today’s distributed-generation market–but costs are expected to drop as production scales up. We’ll see how that goes.According to an article in Greentech Media, The Bloom Box is 56% efficient, which is far higher than most natural gas generators, but waste heat is not captured, as it is from some competing fuel cells–a number of which have been around for years.The Bloom Box isn’t the only “second-generation” fuel cell to come along recently (though it is certainly the most prominent). The Freemont, California company Oorja Protonics, makes methanol fuel cells that are initially being sold as power supplies for electric forklifts. Their OorjaPak Model III holds five gallons of liquid methanol (a type of alcohol) that will power a small forklift for two 8-hour shifts and can be refueled in about a minute–while standard electric forklifts can take up to four hours to recharge batteries.Some of these other fuel cell manufacturers are actively pursuing the combined heat and power (CHP) market, in which both electricity and useful heat are being delivered. While the Oorja fuel cell is only 35-37% efficient, according to Greentech Media, by capturing the waste heat, overall efficiency can be boosted to 70-75%. Panasonic and ClearEdge Power offer residential-scale CHP fuel cells with overall efficiencies of 80% and nearly 90%, respectively, according to the same article.I am excited about fuel cells as energy conversion systems that cleanly and efficiently produce electricity (and often heat) from an energy input, such as natural gas. We need to remember, though, that these are not renewable energy systems–since they have to have a fuel source–and they are not likely to revolutionize our power generation infrastructure quickly. But if they can generate electricity from natural gas and other hydrogen-rich fuels more affordably and more efficiently than other generation sources, they can be an important part of the many-faceted energy future we need.I invite you to share comments on this blog. Are fuel cells going to be the next great thing to come along?— Alex Wilson is the executive editor of Environmental Building News and founder of BuildingGreen, LLC. To keep up with his latest articles and musings, you can sign up for his Twitter feeds.