[keenans]

Part of the BusinessWeek article on Bloom from last December discusses emissions: "Though the technology consumes hydrocarbons, Sridhar says, it doesn't involve carbon-releasing combustion, so it emits only about half the greenhouse gases of conventional energy sources."

http://www.businessweek.com/globalbiz/content/dec2009/gb2009...

[Devilboy]

The carbon has to go somewhere! If it's not being converted to CO2 then what are they doing?

[teilo]

Please guys, read more carefully. He never claims that it releases "no emissions". He never said that it releases "no carbon". He said that it does not involve "carbon-releasing combustion". He specifically says that it releases about "half the emissions" of combustion, so there ARE carbon emissions. Nothing magically dissapears. There is less heat loss than with combustion reactions. Less heat loss = more energy density = less emissions per kW. This is fuel-cell 101.

His exact quote: "The ceramic core acts as an electrode. At high temperatures, a hydrocarbon fuel, ethanol, biodiesel, methane, or natural gas on one side of the cell attracts oxygen ions from the other. As the ions are pulled through the solid core, the resulting electrochemical reaction creates electricity. Though the technology consumes hydrocarbons, Sridhar says, it doesn't involve carbon-releasing combustion, so it emits only about half the greenhouse gases of conventional energy sources."

[mbrubeck]

Also: "eBay's boxes run on bio-gas made from landfill waste, so they're carbon neutral" - so at least in this case, they specifically say there are emissions, but the net emissions are zero because if they weren't using it as fuel, the same amount of carbon would eventually be released into the atmosphere as the waste degraded.

[Devilboy]

I still don't see where the carbon is going in this process. If it's not emitted as CO2 then what?

[anthonyb]

Fuel cells can be more efficient than just burning stuff (aka. combustion) so that's where the lower CO2 comes from - it's not a magic energy machine.

Look at dandelany's posts for the technical details.

[teilo]

The carbon is being vented. Just a lot less of it than the equivalent in combustion systems. Why less? Because fuel cells have a lot less heat loss, and so that means more electricity for the same amount of fuel. "Half the emissions" is relative to the amount of energy produced, not the amount of fuel put into it.

[dandelany]

"it doesn't involve carbon-releasing combustion"

The key here is to read this sentence with the emphasis on combustion. The reaction still releases carbon in the form of CO2, but it does not do so through combustion, a much less efficient process.