Wind and the Mitigation of CO2 Emissions -- The Global Picture
Although Greenpeace's answer to wind-farm.org, Yes2Wind, includes a link to the Intergovernmental Panel on Climate Change (IPCC), I was not surprised to find almost nothing from IPCC about wind power. In one 1996 Technical Paper, "Technologies, Policies and Measures for Mitigating Climate Change," wind is discussed among other renewable sources. The study is interesting.
It examines seven areas of human activity that affect the emission of greenhouse gases, especially CO2. The main topics are buildings, transport, industry, and the energy supply itself to these three areas. Also of concern is agriculture, which accounts for only 5% of human CO2 release but 50% of CH4 and 70% of N2O; forests, the clearing and degradation of which in low latitudes adds 1.2-2.0 gigatonnes of carbon (GtC) to the atmosphere per year, while mid- and high-latitude forests remove 0.5-0.9 GtC/yr; and waste treatment, which adds carbon in the form of methane (CH4).
Of the 6 GtC released by human activity in 1990, 1.9 GtC was from buildings, 1.3 from transport, and 2.8 from industry. The paper discusses the many possibilities for reducing carbon emissions in each area as well as in energy production itself. For example, by simply improving energy efficiency in the design of buildings carbon emissions could be reduced 0.175-0.45 GtC/yr by the year 2010, and 0.25-0.70 GtC/yr by 2020.
Those figures are worth remembering when wind power is discussed. The potential use of wind energy is estimated to be 7-10 etajoules (EJ) per year by 2020-2025, which if accepted as a simple displacement of other energy sources represents 0.1-0.2 GtC/yr not emitted. This amount is less than half of what could be reduced by simple energy-efficiency improvements in building. Further, the amount of reduction is figured for a fossil-fuel-based energy system that reflects the years 1860-1990, when 218 GtC were released by the consumption of 10,249 EJ of fossil fuels, i.e., 0.02 GtC/EJ, most of which was coal and only some of which was for electricity (in the U.S., for example, electricity represented 39% of total energy consumption in 2002). By 2020-2025, many of the mitigating technologies and practices described in this study will likely have reduced the rate of carbon emissions from energy production and consumption, and electricity will likely be much "cleaner" than in the past. The electricity generation, therefore, that wind power will be displacing will not represent anywhere near as much carbon emission as this figure would suggest.
The IPCC paper claims a maximum potential wind resource worldwide of >130 EJ/yr. It also recognizes that, "Countries with large numbers of operating wind turbines sometimes experience public resistance to such factors as the noise of turbines, the visual impact on the landscape and the disturbance of wildlife." The potentials they recognize for other renewable sources are >130 EJ/yr for hydro (up from 21 in 1990), >1300 for biomass (up from 55 in 1990), >20 for the ocean (tides, waves, and thermal and salinity gradients), and >2600 for solar. The use of these sources, however, as with wind, is likely to be much lower: 35-55 EJ/yr by 2020-2025 from hydro, 72-137 from biomass, 2 from the ocean, and 16-22 from solar.
To put this in perspective, worldwide in 1990, 290 EJ were produced from fossil fuels (128 from oil, 71 from natural gas, 91 from coal), 19 from nuclear fuel, and 76 from renewable sources (21 from hydro, 55 from biomass, neglible amounts from others). The paper states that energy consumption has risen and is projected to rise steadily by 2% each year. The total 1990 production of 385 EJ will therefore need to be increased to 697 by 2020. The IPCC's generous projection of 7-10 EJ/yr of wind generation by 2020-2025 will represent 1%-1.4% of the total, perhaps 3%-4.3% of electricity production.
And what does 7-10 EJ of wind power mean physically? 1 EJ = 277.8 TW-h, and 1 MW of rated capacity in a wind turbine will theoretically produce 2,628 MW-h/yr (30% capacity factor). 7-10 EJ/yr therefore represents 1,945-2,778 TW-h/yr, or 740-1,057 GW of installed wind capacity, or 493,000-705,000 1.5-MW towers, a terrifying plan for generating a very small fraction of our electricity and reducing carbon emissions by an even much smaller fraction.
The IPCC paper is available as a 660-KB PDF file at www.ipcc.ch/pub/IPCCTP.I(E).pdf. A 2001 summary of continuing analysis -- in which efficiency in buildings, transport, and manufacturing is projected to account for more than 50% of emissions reduction -- is available as a 380-KB PDF file at www.ipcc.ch/pub/wg3spm.pdf. Tables from the new report [click here] continue to show wind's small potential contribution (its actual contribution is projected to be much less): potentially mitigating 2.0%-4.3% of projected carbon emissions from electricity generation by 2020, or about 0.7%-1.4% of carbon from all energy use.
-- Eric Rosenbloom