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130                          Geothermal Energy: Renewable Energy and the Environment



                     Table 7.1
                     results of the Geothermal resource assessment for the Identified
                     sites in the western states showing the electrical power production
                     (in mw) at the 95% (95%) and 5% (5%) confidence Intervals and the
                     mean (mean), based on the monte carlo methods Used by williams
                     et al. (2008b)
                     state         number of sites  95%        mean        5%
                     Alaska            53           236        677        1,359
                     Arizona            2            4          26          70
                     California        45          2422        5404       9282
                     Colorado           4            8          30          67
                     Hawaii             1            84        181         320
                     Idaho             36            81        333         760
                     Montana            7            15         59         130
                     Nevada            56           515        1391       2551
                     New Mexico         7            53        170         343
                     Oregon            29           163        540        1107
                     Utah               6            82        184         321
                     Washington         1            7          23          47
                     Wyoming            1            5          39         100
                     Total            2.4.8.       3.6.7.5.    9.0.5.7.  16.,4.5.7.

                     Source:  Williams,  C.  F.,  Reed,  M.  J.,  Mariner,  R.  H.,  DeAngelo,  J.,  and  Galanis  Jr.,  S.  p.,
                           Assessment of Moderate- and  High-Temperature Geothermal Resources of the United
                           States, U.S. Geol. Survey Fact Sheet, 2008–3082, 2008.



            volumes, heat contents, and recovery factors for the various reservoirs and then used that data to
            generate estimates of the amount of electrical power that could be generated (Table 7.1). For the
            reservoir volumes and heat contents it was assumed that the distributions were  triangular, peaking
            at a most likely value and then decreasing linearly to either side of that value (Figure 7.7) for liquid
            dominated geothermal systems. For the recovery factors, it was assumed that the probability of any
            particular value was the same throughout the possible range, which was concluded to lie between
            0.08 and 0.2 for systems in which fracture permeability controlled the flow regime, and between
            0.1 and 0.25 for systems in which porous matrix permeability controlled the flow regime.
              Monte Carlo simulations were then carried out using the probability bounds and distributions
            for the various parameters for the individual sites. The results of the simulations for the known
            and identified geothermal resources (the “Reserve”) are presented in Table 7.1. The results for the
            undiscovered and enhanced geothermal systems (EGS, which is a geothermal resource discussed
            in Chapter 14) are presented in Table 7.2. In all cases, the results are presented as the electric power
            generation potential in megawatts.
              The results of the resource assessment provide perspective on the magnitude of the potential
            contribution geothermal energy could make to the power needs of the United States. If only the
            reserve is considered (Table 7.1 values), nearly 10 GW of power could be produced requiring no
            new discoveries, assuming the mean value for the estimate. If the mean values for undiscovered
            and EGS are added in (Table 7.2), the total power output could be more than 555 GW. For com-
            parison, total current installed generating capacity in the United States is approximately twice that
            amount.
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