Think globally, bake locally.
That could become the mantra in the power industry if technologies like solid oxide fuel cells – like the one proposed today in a paper from MIT – can one day move into production. The MIT fuel cell, which only exists as a design currently, would take methane from a pipeline and, in a multi-stage process, chemically crack it into electricity, heat, carbon dioxide and water. The electricity would get delivered to customers while the waste heat would get fed back into the fuel cell to provide energy to run the chemical reactions.
Overall, the system should be around 70 percent to 77 percent efficient, according to postdoctoral associate Thomas Adams. That high number is what makes fuel cells so appealing. Utilities now convert methane into electricity by burning natural gas in turbines and recovering the waste heat to drive the initial reactions. While efficient, combined cycle plants generally are 40 percent to 60 percent efficient, including the losses that invariably occur when transporting power.
Panasonic and ClearEdge Power have recently released methane fuel cells for homes in, respectively, Japan and the U.S. that are around 80 percent efficient when heat and electrical power are both consumed. The heat doesn't get re-submitted to the fuel cell: It heats the household water. (Delivering natural gas to a home or office and then burning it there would be the most efficient way to obtain energy, but then you'd have to swap out electric lights for gas lamps and lots of fire hazards.)
Secretive Bloom Energy, which has raised $350 million in venture funds and has been working on launching its first product since nearly the beginning of the decade, will allegedly soon release a 25-kilowatt fuel cell that runs on natural gas.
Arguably, fuel cells can serve as energy storage devices because the gas can sit in canisters until reactions are required.
An array of the MIT fuel cells could be made from existing components and produce a few hundred kilowatts of power. Adams is currently seeking funds to build a prototype array capable of generating a 100 kilowatts or so of power.
The MIT fuel cell would generate carbon dioxide, but there is another plus, assuming carbon capture can become economical. Unlike the gas mixture from conventional power plants, the gas from the fuel cell would almost be pure carbon dioxide. It wouldn't have any nitrogen, which can be expensive and energy intensive to eliminate.
How does Adams' fuel cell work? From a very high level, methane (CH4) is mixed with air at high temperatures. The methane breaks down into hydrogen and carbon monoxide. Meanwhile, the oxygen from the air absorbs free electrons and then passes through a solid electrolyte. When the ionized oxygen meets the gases, the electrons are freed and delivered to a circuit.
"It's not really right to call the solid electrolyte a membrane in the traditional sense of the word," he said.