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2 GeothermaZ Resources CounCi 1, TMSACZ'O'JS, VoZ. 3 September 1979 A NEW PERSPECTVE ON MAJOR GEOTHERMAL POWER R&D PROGRAMS T. W. Lawford* ABSTRACT This paper describes an innovative new method to evaluate the economic electric potential of the U.S. hydrothermal resource base, and the increase in this economic potential due to major R&D technical programs. This method first evaluates the electrical potential of the U.S. hydrothermal resource base by applying appropri - ate conversion efficiencies to the projected temperature distribution of the hydrothermal energy base. Economics are applied, and the well flow required to generate economical power at any given temperature is established. A well flow probability distribution establishes the probability that the required well flow can be achieved, and that probability establishes the fraction of the resource base at the given temperature which can economically be developed. EG&G daho, tic. daho Falls, daho denlilied resources L 2 '3 M f a 7 2 h 300- W E - W n m tl K l Jndiscovered resources 0 TOTAL THERMAL RESOURCE BASE The United States Geological Survey quantified the total hydrothermal resource base in Circular 790(l). Approximately 400 x 10l8 joules have been identified as recoverable thermal energy above 90 C. The temperatures and energy contents of the individual identified resources are also estimated. These individual resources were grouped by temperature category, and their energy contents summed for each category. An additional 2000 x lo1* joules of undiscovered resources above 9OOC are also projected by the USGS. The temperature distribution of the undiscovered portion of the resource base, for purposes of this analysis, is based upon the frequency distribution of the identified resources and the assumption that individual resource size is independent of temperature. Figure 1 shows the temperature distribution of the total identified and undiscovered resource base of 2400 x 10l8 joules above 90 C. Electrical Conversion Potential - n order to evaluate the electrical conversion Dotential of the recoverable thermal energy in the U.S. hydrothermal resource base, it is necessary to consider the effect of resource temperature on conversion efficiency. Figure 2 shows this re- Fig. 1 Resource temperalure (C) Temperature Distribution of Recoverable Hydrothermal Energy lationship for both dual-flash steam aod state of the art binary plants. The binary-plant cycles considered uti1 ize working fluids which range from dual-boiling propane cycles at the low end of the temperature range through isohutane cycles to pentane cycles at the high end of the temperature range. Representative parasitic power losses have been deducted over the temperature range. The electrical conversion potential for each resource temperature grouping is evaluated by fi rst converting the recoverable thermal energy in each temperature group to water produced at the wellhead, u ing the method described in USGS Circular 790('j. The total electrical energy in watt-hours which each temperature group of resources could support can then be evaluated directly from the product of the net brine effectiveness and the water produced at the wellhead. This is then converted to installed electrical capacity by assuming a 30-year plant life and 0.8 capacity factor. 361

3 ECONOMCS --r n a g 22- La- 1 te- te-! e- a- - The economics of geothermal power is then factored into this evaluation using generalized power generation costs developed as follows: Costs - Basic capital cost and performance f i s for the dual flash steam plants have been derived from a data base generated by the Geothermal Loan Guaranty Program. All capital costs have been escalated to 1978, fourth quarter. Fjeld system capital costs have been developed for each flowrate considered and for each resource temperature. Generalized power generation costs have been developed from the plant and field capital costs described above. The fixed portion of the power generation cost is evaluated using a 17% per year total fixed cost of capital, which is representative of most investor-owned utilities. A thirty year plant life and 80% capacity factor were also assumed. Operations and maintenance costs were added to the fixed costs to develop total power generation costs. Figure 4 is a composite curve of power generation cost for binary plants. Fig. 2 ReaWrc. lernpmlure ('G lnel * ' "a Brine Utilization Effectiveness ' O l eo Bo - \ - Fig. 3 Distribution of Electrical Capacity for Binary and Flashed Steam Plants Fig. 4 Cost of Geothermal Power-Binary P1 ants 4ell Flowrates - From Figure 4 and its equipment for dual flash steam plants, the well flowrate required to generate power at any specified cost for any given temperature can be established for either type plant. A preliminary estimate of the flowrates obtained from North America geothermal wells was made using data supplied b R. Schroeder of Lawrence Berkeley Laboratoryf3, 362

4 including the East Mesa, Heber, Niland, Raft River and Cerro Prieto KGRA's. Figure 5 plots and cumulative distribution of these well flowrates, and an additional distribution which assumes that 30% of the wells drilled were dry and not reported. Also shown in Figure 5 is a cumulative chi-square distribution used to represent this data in a smooth manner, which has been used as the basis for further calculations as described in this report. d Fig. 6 Distributions of Electrical Capacity for Binary Plants for 'Electricity Costing 60 Mills/Kwh or less (Nominal Well Flow, Nominal Plants) Fig. 5 Distribution of Well Flowrates However, two major technological barriers Economic Development of the Resource Base - to achieving this increment of installed capacity The fd exist. One is a shortage of available ground capability at a specified temperature (Figure 3) water for cooling tower makeup, and the second which can be developed at a given power generation is the incidence of corrosive.chemicals in the cost is the probability that a well flowrate geothermal bri ne which would requi re design equal to or greater than that required for that a1 ternatives to this problem; Removal 'of both power cost will be realized. Application of this economic fraction of the total electrical potential at a given temperature to the temperature distribution of the electrical potential, gives the total distribution of the economic power potential. is shown in Figure 6 for binary plants. EVALUATON OF MAJOR R&D PROGRAMS This With this background, the merits of each proposed major R&D program can be evaluated, in terms of additional installed capacity which will be made economical, and the amount of oil which that increment of installed capacity would displace. To simplify the logistics of these comparisons, 50 mills/kw-hr will be considered to be the going cost of competitive new power. Conversion Technology - Over the spectrum o f resource temperatures, the hydrothermal resource base usin dual-flash steam plants will support 45,000 MWqe) for 30 years at an 80% capacity factor, with power costs of 50 mills/kw-hr or less. The same resource base would support 86,000 Mbl(e) under the same conditions using current binary technology (Figure 6), an apnarent difference of 41,000 M!J(e), worth 15.4 x lo9 barrels of oil over the 30-year plant lifetime. barriers is necessary to achieve the projected advantage of 41,000 FW(e) instal led capacity for binary plan'ts, and should be considered to be the main thrust of the conversion technology program. mproved conversion-plant performance improves power generation costs by reducing the investment required for the well field, and also increases the potential output. from individual resources and the total resource base. The potential exists for a 20% improvement in plant performance, so thdt increment has been used as a goal over the spectrum of resource temperatures. Meeting this goal increases the economic power generation capacity from 86,000 MM(e) to. 111,000 MW(e) or 25,000 MW(e) for 30 years. is worth 9.4 x lo9 barrels of oil over the This 363

5 projected plant lifetime. Field System Technology - The flowrate -, 1 achieved from geothermal wells directly affects the number of wells needed for a specific plant. The Field System Technology Program is designed to increase the flowrate of wells by means of pumping and improved casing design for flashing wells. - Mulmum polmllal Study of a few specific geothermal wells for which data were available shows that geothermal well flow can nominally be doubled if a reliable pump can be developed. The value of increased well flow by pumping was determined by running through an analysis similar to that previously described using the projected improved well flows. This enhancement of well flowrates increases the economic potential of the resource base by 35,000 MW(e) for 30 years at 50 mills/kw-hr, and is worth 13 x lo9 barrels of oil. Well Stimulation - Well stimulation is another potential method to increase the average flow of geothermal wells. Hydrologists generally agree that we1 1 stimulation will greatly enhance the flow of poor producing wells, but will do little for the exceptionally high producing wells. On this basis, a well flow distribution was developed with a target of 60% improvement in the flow of the mean well and no improvement in wells with initial flowrates in excess of 550,000 lb/hr. Meeting the target for well stimulation will bring an additional 25,000 MW(e) into the economic range of 50 mill/kw-hr which is worth 9.4 x lo9 barrels of oi 1. Combination of All of the Program Elements - A separate analysis of the combination of all of the major R&D programs discussed was made. The results of this analysis are shown in Figure 7.. The combination of the technologies of all of the program elements results in an increase in the economically producable portion of the resource of 130,000 MW('e) for 30 years. This is worth a total of 44.8 x lo9 barrels of oil, or 3.7 times the present annual U.S. consumption. t also represents 85% of the total electric potential of the estimated U.S. hydrothermal resource base above 90 C. At 60 mills/kw-hr, 93% of the electric potential above 90 C can be realized. O Plan1 fla P 30 yr w Raaource lammm1um ('C) lntla 1'2 VUS Fig 7. Distributions of Electrical Capacity for mproved Binary Plants for Electricity Costing 60 Mills/kwh or less (stimulated wells and improved f i el d techno1 ogy ) REFERENCES Muffler, L. P. J. et al, 1979, Assessment of Geothermal Resources of the United States , Geol ogi cal Survey Ci rcul ar 790 Hol t, B. and Ghormley, E.L., November 1976, Energy Conversion and Economics - Case Studies, Schroeder, R., June 1976, Personal Communication to T. Lawford 364