Industry Market Trends
The Damage Done, Part 4 -- Natural Gas, Green or Dirty?
December 27, 2011
So what about natural gas?According to the Natural Gas Supply Association,
Natural gas is the cleanest of all the fossil fuels ... [Compared with coal and fuel oil,] combustion of natural gas ... releases very small amounts of sulfur dioxide and nitrogen oxides, virtually no ash or particulate matter, and lower levels of carbon dioxide, carbon monoxide, and other reactive hydrocarbons.However, not everyone is so sanguine about the use of natural gas for power generation. As you can see from the EIA chart show here, the growth of gas supply in the U.S. is depending heavily on shale gas. This gas is being extracted largely using the controversial practice known as "fracking," or hydraulic fracturing. In June 2011, ThomasNet's Tracey Schelmetic (see "What's The Big Fracking Deal?" outlined some of the environmental concerns around fracking:
Fracking fluid can be made up of any combination of substances in liquid, gel, or foam form, with any number of chemical ingredients. Among the chemicals used in fracturing fluid is a cocktail of nasty substances that include known carcinogens, skin irritants, and endocrine disruptors - chemicals that affect the healthy function of human adrenal glands that govern development, growth, reproduction, and behavior in people and animals... Poisoning aside, fracking has also been implicated as the reason behind the "flammable water" phenomenon sometimes encountered in mining country in the U.S.: Tap water from the ground that is so contaminated with chemicals that it can literally catch on fire.The environmental impact of fracking is under study right now, so it might be a little early to try to quantify its effects. The U.S. Environmental Protection Agency (EPA) released a draft report in December 2011 after studying the effects of fracking on drinking water in a community in Wyoming. EPA's announcement about the report says,
EPA's analysis of samples taken from the Agency's deep monitoring wells in the aquifer indicates detection of synthetic chemicals, like glycols and alcohols consistent with gas production and hydraulic fracturing fluids, benzene concentrations well above Safe Drinking Water Act standards and high methane levels. Given the area's complex geology and the proximity of drinking water wells to ground water contamination, EPA is concerned about the movement of contaminants within the aquifer and the safety of drinking water wells over time.
Natural Gas and Human HealthAs I discussed in last week's article on coal, researchers have measured the health effects of energy sources by using a metric called the value of a statistical life (VSL), representing an attempt to assign a dollar value to a human life. If this very idea sends you in a rage, that's what the comment space below this article is for. Before you post your tirade, though, please keep your lid on and first read the explanation of VSL in last week's article. While VSL measures vary considerably, EPA uses a figure of $9.1 million for its studies. The National Academy of Sciences (NAS) uses a VSL of $6 million in its report, "Hidden Costs of Energy: Unpriced Consequences of Energy Production and Use." The NAS report is useful for our purposes, as it undertakes a survey of the environmental effects of all of the main energy sources. (Photo: Gas power plant, New Hampshire, U.S. Credit: Jim Richmond, CC BY-SA 2.0.)
Air Pollution From Gas-Fired Power PlantsNAS studied emissions-related damages of key pollutants for 498 power plants in 2005; the pollutants the researchers considered were sulfur dioxide (SO2), nitrogen oxides (NOx), fine particulates (PM2.5), and coarse particulates (PM10). These 498 were plants that generated at least 80 percent of their electricity from gas. They accounted for 71 percent of gas-generated electricity in the U.S. in 2005. The study calculated average annual damages of $1.49 million per plant. Damages at gas-fired plants were much lower than those at coal-fired plants. One reason is that gas plants tend to be much smaller than coal plants. However, they also do less damage per kilowatt-hour (kWh). On average, damages at gas plants are .16 cents ($.0016) per kWh, as opposed to 3.2 cents ($.032) for coal plants. However, the study notes that damages per kWh vary widely among plants. The 10 percent of plants with the highest damages account for 65 percent of damages from all 498 plants. The following chart outlines key figures about damage done by the four chief pollutants. This chart is similar to the one I showed in last week's article about coal:
|Pollutant||Mean Damages per Ton of Emissions (2007 $US)||Mean Damages per Kilowatt Hour (2007 $US)|
$.00018 (0.018 cents)
$.00230 (0.230 cents)
$.00170 (0.170 cents)
$.00009 (0.009 cents)
Natural Gas and Climate ChangeGreenhouse gas (GHG) emissions offer another means to compare the environmental effects of power generation. Carbon dioxide (CO2) is the GHG most often mentioned in discussions about human-caused global warming, but water vapor, methane, nitrous oxide, and ozone are also considered GHGs. For simplicity's sake, GHG emissions for electricity generation are usually wrapped all together in a single "carbon footprint" measure, expressed in "carbon equivalents" using the metric "gCO2eq/kWh." This stands for "grams of CO2-equivalent per kWh." (For more explanation of this metric, see the U.K. Parliamentary Office of Science and Technology's report, "Carbon Footprint of Electricity Generation.") A study by Benjamin K. Sovacool of the Vermont Law School is useful for comparing the carbon footprint of various power sources. (See "Valuing the greenhouse gas emissions from nuclear power: A critical survey," Energy Policy, 2008.) Sovacool estimates the lifecycle carbon footprint for natural gas power generation at 443 carbon equivalents. While high compared to nuclear, solar, and wind, that figure is less than half of the carbon footprint of coal. The following table shows how the various sources compare, according to Sovacool's research:
|Source/Technology||Lifecycle CO2 Equivalents (gCO2eq/kWh)|
|Solar Photovoltaic (PV)||32|
Given the growth of natural gas power generation, we can expect the CO2 impact to grow as well, as indicated in this EIA chart:Overall, then, we could say that by measures that are available, natural gas does a fair amount of environmental damage, but less than coal. That's why some observers have advocated using gas as an alternative to decrease reliance on coal, while power generation transitions to renewables over the coming decades. But do other power sources offer a less-damaging way to produce electric power? In coming weeks, we will go on to consider the environmental impacts of nuclear power, hydro, solar, and wind, asking our core question, How do we know what kind of energy is truly "green"?