According to Leveen, Bloom's fuel cells on average emit 884 pounds of CO2 per megawatt-hour (mWh) of electricity produced. While that's not a bad reduction compared to 2,249 pounds for a coal-fired plant, it's not a whole lot less than 1,135 for an existing natural gas plant.
But get this: It's more than the 730 pounds per mWh of modern combined cycle natural gas plants made by the likes of GE, Siemens and Mitsubishi, according to the report.
How does a Bloom fuel cell get involved with CO2 in the first place? The clue is in the name: fuel cell. A Bloom Box makes electricity by sending, whadya know, fossil fuel - natural gas - on a journey between a cathode and an anode (fuel cells make electricity in a manner similar to a battery; unlike a battery, they generally can't store electricity).
Like solar, wind, geothermal and all those other clean renewables that each have their dirty sides, we are reminded again that green comes in shades.