ating margin of 26.2%. Consequently, some of this margin can be applied to subsequent growth needs, depressing the growth curve. Figure 2-3 shows variation of this margin with time. 18% is generally considered by utilities to be desirable: the margin was 16.6% in 1969 when reductions and curtailments occurred. Fig. 2-3. U.S. Capacity Margin Table 2-1. 1968 U.S. Energy Consumption Patterns by End Use Some authors have forecast and/or recommended very low or even zero energy growth rate. Hannon (2) recommends a more labor intensive economy, i.e. one in which, in essence, human muscles perform rather than electric motors, thereby making more (lower paying) jobs. One factor is the growing labor pool resulting from population growth; if the birth rate instantly dropped to zero, the labor pool would still increase in size for two decades. A more middle-of-the-road view is that energy growth is essential to economic health. Federal Energy Administrator Zarb has recommended a 3.5% to 4.5% installed capacity growth rate for 1975 to 1985 (6). This range was plotted in Figure 2-2. The actual growth rate for 1975 was 3.0% (8). It is possible for national energy consumption to remain constant while the amount of electricity generated increases. In 1968 the U.S. Energy Consumption was as shown in Table 2-1 (from 3). In 1968, 21.2% of the energy expended went to produce electricity. The last column shows a potential of 70.7% utilization without significant changes in energy use technology; for example, electricity could be used for all process heat.
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