3 ENERGY TECHNOLOGY IMPACTS ON CLIMATE Many different factors must be considered when determining the potential culpability of the widespread use of various energy technologies in causing climatic change. However, the potential for significant change in climate is a factor that cannot be ignored. This chapter contains a description of the potential contribution of various energy technologies to climatic change on a local and global scale. 3.1 COAL TECHNOLOGIES 3.1.1 Waste Heat Impacts A conventional coal-fired electric generating plant operates at a thermal efficiency of about 34%.This means that 3 joules of heat input are required for every joule of useful energy output. More efficient methods of coal-fired electrical generation are being developed, and one possible method is the combined-cycle system. A combined-cycle system can achieve a thermal efficiency of as much as 45%.This represents a saving of about 25% of the amount of energy input needed to generate a given amount of useful electrical energy by conventional coal-fired systems. Potential global waste heat impacts were discussed in Sec. 2.1.2. It appears that coal energy technologies will play a minor role in whatever global impacts could occur as a result of anthropogenic heat release. Table 3.1 compares current and future energy releases from coal-fired utilities in the United States to current and projected global energy releases. The contribution of U.S. coal use to global energy use is extremely small — 5% or less of the total. Given that the U.S. accounts for a third or more of the world's coal consumption, global consumption of coal as an energy source does not present a problem as far as waste heat is concerned, particularly because no noticeable effects on global climate are expected until the atmospheric thermal loading due to human activities reaches 3.4 x 10$ GW (10^-^ Btu/yr). Table 3.1 also indicates that use of more efficient coal technologies will not substantially reduce global energy use. Impacts of waste heat rejection on a local scale were described in Sec. 2.1.4. These potential impacts include increased fogging, cloud and
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