Wednesday, March 18, 2009

Zero Emissions?

The other day I ran across reports of a curious event, in which the Attorney General of the state of Vermont convinced Entergy, which owns or operates 11 of the nation's 104 active nuclear power plants, to back away from characterizing nuclear power as having zero emissions. Technically, of course, the AG was correct. However, as a reader reminded me, it is equally true that such unambiguously "green" energy sources as wind and solar power also entail emissions greater than zero--a fact that appeared not to trouble Mr. Sorrell. This situation highlights another important gap in the public debate over energy and the environment. The solution lies in better public education and clearer reporting of absolute and relative emissions, based on numerous studies detailing the lifecycle emissions of our various energy sources. We might also apply some common sense to this complex technical issue. Unfortunately, the resolution of the Vermont dispute leaves the public with the mistaken impression that, at least in terms of greenhouse gas emissions, nuclear power is not in the same league as our favored renewables.

The misunderstanding in the Green Mountain State reflects a common inconsistency in the way that we look at the emissions of energy sources. In the last few years it has become pretty routine, at least in the better-informed media, to report the emissions from fuels and the vehicles and stationary facilities that consume them on the basis not just of what comes out of a tailpipe or smoke stack, but by tallying all emissions from extraction and production through to end-use: a technique referred to as "well-to-wheels" analysis, or more generically as "lifecycle" analysis when no actual wheels are involved. Energy sources that don't burn fuels have often escaped this level of rigor and tended to be clumped together as zero-emission sources. That includes nuclear power, wind, solar, geothermal, and hydropower. All of these entail a modest level of "embodied" emissions associated with their construction or manufacture, including the direct and indirect emissions from the conversion of raw materials, machining and assembly of components, and transportation to their operating sites. Nuclear power is different in one respect, in that it also consumes a fuel, the production of which--though not its use--results in some emissions. That hardly justifies lumping nuclear power in with coal, oil and natural gas burners, and drawing a misleading distinction from the embodied emissions of other low-GHG energy.

A web search turned up numerous references that quantify the lifecycle emissions from all these electricity sources. A recent report to the International Energy Agency on electricity in Japan, for example, cited cradle-to-grave GHG emissions from nuclear power at 29 grams of CO2 per generated kWh, equal to those from wind power and roughly double those from geothermal and hydropower, but half the emissions from solar photovoltaic power (PV). By comparison, the lowest fossil fuel emissions in Japan come from combined-cycle gas turbine plants running on imported LNG. Those averaged 519 g/kWh. Then there's the study from the University of Wisconsin, which shows nuclear at 17 g/kWh, beaten only by wind and geothermal, but exceeded by every other renewable source. Finally, I was amused to find the website of the Windham Regional Commission in Vermont hosting a report from the Nuclear Energy Institute bracketing nuclear power between hydro and geothermal and lower than PV and biomass power.

Rather than seeking to highlight the inconsistency of a government official--cue Captain Renault, here--I'd like to propose the common-sense application of a two-tier standard to this problem. All energy and environmental decisions involving comparisons of different energy sources and devices, particularly when they result in money changing hands, should certainly be made on the basis of full and careful lifecycle analysis. For general discussion purposes, however--most likely including the ads that offended the group that appealed to the Attorney General of Vermont--the emissions from wind, solar, geothermal, hydroelectric and nuclear power are all so much lower than those from coal, oil and natural gas that it seems entirely reasonable to treat them as effectively zero. Perhaps Entergy should reconsider its retraction on this basis.

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