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Energy analysis of electricity supply and energy conservation options
ENERGY ANALYSIS OF ELECTRICITY SUPPLY AND ENERGY CONSERVATION OPTIONSt
DAVID A. PILATI Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL 61801,U.S.A (Received 20 July 1976) Abstract-A methodology is developed to compute the total energy requirements for electricity-generating systems using an input-output model that explicitly accounts for the physicalflow of energy. The capital and operating requirements of 16 separate energy supply facilities are used to evaluate the total energy required by 9 alternative means of producing and delivering electricity. Evaluated electricity-generating systems rely on either fossil or nuclear energy as their fuel source. Energy payback periods are computed based on an equivalent electricity basis. These results are compared to a number of alternative capital investments to reduce energy demand. In general, the conservation options return their energy requirements sooner than the supply alternatives.
INTRODUCTION
The Federal Non-Nuclear Energy Research and Development Act of 1974 states that “the potential for production of net energy by the proposed technology at the stage of commercial application shall be analyzed and considered in evaluating proposals”. This concern for net energy analysis was first discussed by Odum’ and later applied to nuclear generating systems by Chapman and Mortimer.’ Recently Gilliland3 has elaborated on the policy implications of such analyses. Net energy is loosely defined as the difference between energy benefits (as output or savings) and requirements of an energy supply or conservation development. Because of the embodied energy in all goods and services, energy requirements for all inputs must be included. The net energy yield of a supply development is then the difference between its lifetime energy production and the total energy required to construct and operate it. Similarly, a home insulation program saves energy by reducing space heating and cooling requirements but requires energy to manufacture, transport, market and install the insulation. While the concept of net energy would be straightforward in a single energy economy, this is not the case. Because of (at the least) energy conversion losses, a Btu of coal is not the same as a Btu of electricity. On a Btu basis, society values electricity more than fossil fuels. This paper evaluates the total energy needed to build and operate a complete system that ultimately produces and delivers electricity. Energy requirements for each system are converted to the equivalent electricity that could have been produced if these requirements were diverted to produce electricity through existing systems. Table 1 identifies the 9 electricity generating systems considered. There are three methods for evaluating total energy needs: process analysis, input-output analysis or a hybrid of these methods. Process analysis consists of tracing production inputs back through the economy in a step-wise fashion to calculate the energy requirements of each input. Clearly this analysis must be truncated because of the infinite number of steps that would ultimately be involved.’ Input-output analysis uses a linear model of the economic system providing a computationally efficient means of calculating the indirect contributions from various industries in the output of a specific industry. This method has been extended to evaluate the embodied energy of goods and services for the latest year that the extensive economic data are available, 1%7.5 A hybrid analysis using a single process analysis step and then applying the input-output technique is employed here. Therefore, the total energy requirement of a power plant is found by summing the embodied energy of the individual items needed for its construction and operation. tThis work was supported by the National Science Foundation. ffiY
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D. A. PILATT Table 1. Electricity-generating system definitions
Resource base Coal
Natural gas Crude oil Nuclear
System ID
CM-CFPP CM-CG-NGU-GFPP CM-CCC CM-SRC-CFPP GP-NGU-GFPP CO-LGR-OFPP SO-LGR-OFFP LWR HTGR
System definition Coal Mine + Coal Fired-Power Plant Coal Mine + Coal Gas&cation + Natural Gas Utility + Gas-Fired Power Plant Coal Mine+Coal Combined Cycle Power Plant Coal Mine -+Solvent Refined Coal + Coal-Fired Power Plant Gas Production + Natural Gas Utility + Gas-Fired Power Plant Crude Oil Production --*Low Gas Refinery -, Oil-Fired Power Plant Oil Shale Mine/Retort + Low Gas Refinery + Oil-Fired Power Plant LWR Fuel Mining/Processing+ LWR Power Plant HTGR Fuel Mining/Processing + HTGR Power Plant
System boundary selection presents problems on both the macro- and micro-scale. On the macro-scale, some suggest the appropriate boundary should include the entire ecosystem.’ Another issue is whether to treat the technology marginally, separate from the existing economic system or incorporate the technology into an analytical economic system before analysis. In essence, these possibilities depend on the interpretation of “potential” as found in the law. The analyses described in this paper evaluate the potential for producing net energy at the margin, as the technology becomes commercially available. The analyst must then decide on the precise system boundary for the technology investigated. For example, are transportation requirements, research and development costs and pertinent regulatory commissions to be included in the technology’s cost? Are secondary products counted as output and are self-use requirements internalized? For some analyses, results can vary dramatically depending on how these questions are answered. For example, the net energy ratio (energy output/energy input) of shale oil has been found to differ by over a factor of ten depending on the choices of system boundary.6 For comparison purposes, consistency must be maintained. Assumptions for the present analysis are discussed in a later section. Data for facilities that are not in commercial operation obviously present unknown uncertainties. The results presented here relied on a number of data sources for the process-analysis step. A comparison of results for one electricity system using different source data is given. Differences in resulting energy requirements demonstrate a need for consistent data as well as methodology.
METHOD
An electricity-generating system consists of several facilities to extract the energy resource from the earth, process it, and ultimately produce and distribute electricity. Figure 1 is a schematic representation of a series of facilities defining a complete electricity-generating system. The initial facility in a system is typically a mine or well that extracts the direct-energy resource consumed by the system. The n th facility is the electricity-generating facility such as a nuclear power plant. Intermediate facilities represent fuel processing, distribution or conversion facilities. As shown in Fig. 1, the system boundary encompasses the transmission and distribution of electricity to the final user. Transmission-line losses and other electricity requirements of the final facility in each system are assumed to be supplied by the system itself. Therefore, the delivered electricity will be somewhat less than that generated. Due to lack of data, capital requirements for
CAPITAI. AND OPERATING REOUIREMENTS FOR SYSTEM
SVS’TEM BOUNDARY
Fig. 1. Schematic diagram of electricity-generating system.
Energy analysis of electricity supplyandenergyconservation options
3
transportation infrastructure (e.g. railroads and transmission lines) and vehicles are incomplete. However, all transportation operating requirements and the capital requirements of natural gas distribution (natural gas utility in Table 1) are included. Figure 2 is a more detailed schematic representation illustrating the requirements for a generalized system. In the figure, Ci represents a vector of annual capital requirements per unit output of facility i, OPi represents a vector of annual operating requirements (other than direct fuel requirements) per unit output of i, qi is the energy conversion efficiency of the ith facility, and e is a vector of input fuel energy from the earth to the initial facility.
Fig. 2. Schematic diagram of system capital and operating requirements.
Energy required to produce a bill of goods is obtained from input-output analysis. A matrix of energy coefficients, ~(6 x n), is obtained to give the energy (coal, crude oil and gas, refined petroleum, electricity, natural gas and total primary) embodied in each dollar of output for an economic sector, where n depends on the degree of industry aggregation in the analysis (depending on the data, n has values of 90, 101 or 357). Therefore, the energy required to produce the material requirements for the system is evaluated by using existing technology. The capital energy requirements for constructing a system is then
Z(J!,$*g*ci+g*c,.
(1)
Similarly, annual energy requirements for operating the system become
Fuel energy removed from the earth.
First n - 1 facilities
Final facility
The capital and operating data for the 16 separate facilities come from a number of sources. Data for the capital requirements are from Bechtel,’ MITRE’ and Battelle.9 All nuclear fuel-processing energy requirements are from Chapman and Mortimer’ and industry data for nuclear fuel loadings. (In Ref. 2, process analysis is used to evaluate the energy requirements of nuclear fuel processing. This procedure circumvents the problems associated with using input-output results for the “industrial chemicals” sector to characterize nuclear fuels.) Other operating requirements are from Bullard and Herendeen5 Bullard” and MITRE.’ All power plants are assumed to operate with capacity factors of 0.80. (For further details, see Pilati and Richard.“) RESULTS
AND DISCUSSION
The total energy needed to build and operate the 9 systems is presented in Table 2. Energy requirements are separated into coal, crude (oil and gas) and total primary. Primary energy is defined as the sum of coal, crude (oil and gas), and the fossil fuel equivalent of electricity
0.18 0.35 0.14 (0.33Y 0.27 0.39 0.70 0.30 0.31 0.50
Coal 0.27 0.56 0.21 (0.46) 0.41 0.67 1.26 0.48 0.35 0.56
Crude 0.47 0.95 0.36 (0.84) 0.71 1.09 2.02 0.81 IO.53 (0.74) 17.13 (1.17)
Primary
Crude Primary
Coal Crude
Primary
Lifetime (Other than fuel) (BtulBtu total output)
3.12 0.09 3.21 0.04 0.09 0.13 5.06 0.25 5.32 0.25 0.06 0.32 2.54 (2.55)0.03 (0.04)2.58 (2.60)0.02 (0.02)0.03 (0.04)0.05 (0.07) 5.29 0.45 5.74 0.05 0.45 0.50 0.05 3.46 3.52 0.05 0.37 0.44 3.70 3.81 0.62 0.09 0.09 0.73 5.20 0.08 5.30 0.08 0.58 0.68 0.09 0.09 4.23 0.09 0.21 0.09 0.09 0.08 4.45 0.09 0.08 0.19
Coal
Lifetime (Including fuel) (Btu/Btu total output)
“A 25-year lifetime is assumed for all facilities. (This may be overly optimistic for oil wells. If so, their energy requirements are underestimated.) Fuel requirements are considered to be all energy entering the initial facility from the ground. Several facilities actually use some of this energy to satisfy part of their operating requirements. bResults in parenthesis result when Bechtel’ construction requirements for the low Btu coal gasification facility are used instead of MITRE’s.’ ‘Non-fuel related primary energy requirements in parenthesis.
CM-CFPP CM-CG-NGU-GFPP CM-CCC CM-SRC-CFPP GP-NGU-GFPP CO-LGR-GFPP SO-LGR-GFPP LWR HTGR
System ID (from Table I)
Capital (Btu/Btu annual output)
Table 2. Comparisons of energy requirements for nine electricity-generating systems
e
s
Energy analysis of electricity supply and energy conservation options
produced by non-fossil sources. Requirements are given for construction and 25 years of operation, Data limitations and conceptual questions concerning appropriate discount rates have precluded consideration of the energy requirements of system decommissioning or the safeguarding of nuclear wastes. Nuclear fuel is considered a primary energy source equivalent to the fossil fuel that would have been required by fossil-electric systems to produce the nuclear-generated electricity. The results for the coal combined-cycle system demonstrate the problems associated with data sources. Capital costs for low Btu coal gasification per unit output from Bechtel’ are about six times those from MITRE.’ The early stage in development of the Texaco gasification facility, compared to the proven Lurgi process should explain some, but possibly not all, of the disparity. Under these circumstances, the results using the proven Lurgi process (Bechtel) are probably the most reliable. Lifetime non-fuel energy requirements for the oil-electric system (onshore oil well, refinery and oil-fired power plant) are higher than for any other system. This result illustrates a basic fact underlying the need for energy analysis: as nonrenewable resources become scarcer, it requires more and more energy to get them out of the ground. For example, capita1 costs for onshore wells assume 3 dry holes for every 4 wells drilled in the contiguous states.’ Figure 3 graphically compares the energy inputs and outputs over time for oil-electric and light water reactor systems that deliver 20 trillion Btus of electricity per year. Delivered electricity is plotted above the axis while total primary energy requirements are plotted below. The very high capital costs for onshore oil is obvious when one realizes that wells are being drilled during only the last two years of the 5-year construction period. The fuel and non-fuel primary energy requirements are separated for the light water reactor. Unlike fossil systems, nuclear systems require a substantial capital investment in fuel requirements for the initial core.
:
“T
ENERGY INPUT I-) AND OUTPUT IN TRILLION BTUS, FOR SYSTEM OIL-ELECTRIC ONSHORE WELLS
(+) i
T
ENERGY INPUT (-1 IN TRILLION BTUS, LWR
AN0 OUTPUT (+I FOR SYSTEM
35 0 --4
Fig. 3. Oil-electric
and light water reactor energy inputs (primary)
and outputs (electricity)
over time.
An energy-supply system is a net energy sink until the capital and some operational energy requirements are repaid by the system. Table 3 gives the non-fuel energy payback times for two cases: (1) the time required to repay the total primary requirements (other than fuel) with electricity on a Btu basis and (2) the time required to repay the electricity that could have been generated and delivered by diverting the non-fuel energy requirements to existing electric generating systems.” Because society values electricity more highly than primary fuel on a Btu basis, the second comparison is more valid. However, a better method for comparing energy requirements to benefits might be based on the function of the energy end-use. For example, if homes now heated by oil were converted to electric heat using oil-electric generation, the oil requirements for heating homes would increase.‘* All systems repay their sunk equivalent electricity inputs in less than two-thirds of a year. It
D. A. PILATI
6
Table 3. Energy-payback times [year(s)]
SuPPLY system CM-CFPP CM-CG-NGU-GFPP CM-CCC CM-SRC-CFPP GP-NGU-GFPP CO-LGR-GFPP SO-LGR-GFPP LWR HTGR
Electricity for primary 0.54 1.32 0.37 (0.87) 1.35 1.81 5.71 2.31 0.90
1.37
Electricity for potential electricity 0.13 0.26 0.09 (0.22) 0.21 0.31 0.62 0.25 0.20 0.32
Conservation Option Clock-actuated thermostat Full-size autos + Subcompact Full-size autos + Compact Home insulation Storm windows
Primary for Primary 0.11 (O.lS)b 0.12 0.17 0.25 1.77
“Results using Bechtel data for low Btu coat gasification facility in parentheses. ‘Setback from 68-55°Fat night. (Setback from 68-6O”Fat night.) Based on dollar costs and energy savings from Pilati.” ‘Auto turnover, insulation and storm window results are from Putnam.” Auto turnover costs are capital requirements to completely retool assembly lines.
should be noted that these results are very sensitive to the capacity factor of 0.80 assumed for all power plants. If actual capacity factors were 0.50, payback times would be increased by over 60%. The conventional coal-electric system requires the shortest repayment period. However, the repayment time for this system would probably be increased the most if all transportation capital-requirements were included. This analysis is static and appropriate only for marginal, as opposed to average, technologies. At high growth rates, feedback from new (and perhaps less efficient) technologies become significant and must be imbedded in a dynamic input-output formulation. For example, the electricity required to generate electricity would increase if there is expansion of nuclear power plants because of fuel enrichment requirements. The effect of this activity is to increase the payback periods derived here. To insure a positive net energy yield for expanding systems, longer payback periods can be compensated for by shorter construction times.” Under the equivalent electricity accounting scheme (Table 3), doubling times of less than 4 years for either the energy-intensive oil+lectric system or nuclear power plants (LWR) would result in net deficits. However, exponential system expansion rates may not be realistic. Many energy conservation schemes also require an energy investment. It is, therefore, instructive to compare their repayment periods with supply developments. Table 3 also includes the repayment period for a number of conservation programs: ceiling insulation, storm windows, conversion to smaller cars, and clock thermostats (a device that automatically lowers nighttime temperatures-a technical fix to a behavioral option). Except for storm windows, the conservation options return their primary energy investment sooner than any of the supply systems. If all transportation capital-requirements were included in the supply analysis, the advantage of conservation would be even greater. CONCLUSIONS
Net energy concern for energy supply programs can be raised in two instances: (1) When the energy required to produce leaner resources becomes prohibitive and (2) when the total energy system grows too rapidly. A single electricity-generating system is a net energy sink until sometime after it commences operation. For the equivalent electricity accounting procedure, all (static) systems have a positive net energy yield in less than two-thirds of a year. Dwindling supplies of crude oil in the U.S. result in the conventional oil-electric system requiring the longest repayment time. Programs for rapid expansion of energy supply may result in net energy deficits until the growth rate slows. Longer construction times of particular systems can aggravate this problem. For system doubling-times of less than 4 years, neither oil-electric @year construction period and 0.62 year for repayment) nor conventional nuclear power (Pyear construction period and 0.20 year for repayment) can repay their energy requirements. However, prolonged exponential growth rates are probably unrealistic.
Energy analysis of electricity supply and energy conservation options
7
From an energy point of view, conservation is comparable to new supplies. In general, conservation options repay their energy requirements sooner than supply alternatives (Table 3). Compared to the supply options, they can become operational in a shorter period of time. Therefore, if a premium is placed on rapid energy independence, conservation would be especially advantageous. Several other comparisons between conservation and supply developments deserve mention. Thus far, discussion has centered on energy inputs and benefits: because of differences between energy dollar costs and prices, the conservation options included here should be more economically desirable than they are energetically.” Longer lead times required by supply developments would penalize them economically if discounting were included. However, many conservation programs must be undertaken by the homeowner of small businessman who might be lacking in adequate information and technical expertise. Contrasted to the energy industry, these individuals also find it more difficult and costly to raise the necessary capital. Policy decisions to assist energy suppliers (such as an Energy Independence Authority) should be properly balanced by similar conservation programs. Otherwise, the energy supply-demand imbalance may not be reduced in a resource-efficient manner. REFERENCES 1. H. T. Odum, Energy, ecology and economics. Am&o, Z(6), 220-227 (1973). 2. P. F. Chapman and N. D. Mortimer, Energy Inputs and Outputs for Nuclear Power Stations. Open University Report ERG 005, Milton Keynes, Buckinghamshire, U.K., Dec. 1974. 3. M. W. Gilliland, Science 189, I051 (1975). 4. R. W. Berry and M. F. Fels, The energy cost of automobiles. Bulletin of Atomic Scientists-Science and Public Aflairs, Dec. 1973. 5. C. Bullard and R. Herendeen, Proc. IEEE 63, 484 (1975). 6. C. E. Clark and D. C. Varisco, Net energy and oil shale. In In Situ Recovery of Shale Oil, Report NSF-RA-N-75-001, (Edited by S. S. Penner), pp. 345-372. U.S. Government Printing Office, Washington, DC., Aug. 1975. 7. M. Carasso et al., The Energy Supply Planning Model, Vols. l-3. Bechtel Corporation, Energy Systems Group, San Francisco, CA, July 1975. 8. J. Just et al., New Energy Technology Coeficients and Dynamic Energy Models. (2 volumes), MITRE report MTR-6810. McLean, VA, Jan. 1975. 9. C. Chilton and W. Fisher, An Ex Ante Capital Matrix for the United States. 1970-1975,Battelle Memorial Institute. Columbus, OH, Mar. 1971. IO. C. Bullard, An Input-Output Model for Energy Demand Analysis. CAC Document No. 146, Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL, Jan, 1975. 11.D. A. Pilati and R. Richard, Total Energy Requirements for Nine Electricity-Generating Systems. CAC Document No. 165, Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL, Aug. 1975. 12. P. F. Chapman, Energy Policy 3. 285 (1975). 13. D. A. Pilati, The Energy Conseruafion Potenfial of Winter Thermostat Reduction and Night Setback. Oak Ridge National Laboratory Report ORNL-NSF-EP-80, Oak Ridge, TN, Feb. 1975. 14. D. E. Putnam, Energy Benefitsand Co&. Housinglnsulation and the UseojSmaller Cars.CAC Document No. 173.Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL Aug. 1975. 15. C. Bullard, Energy Costs, Benefits and Net Energy. CAC Document No. 174, Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL Aug. 1975.
DAVID A. PILATI Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL 61801,U.S.A (Received 20 July 1976) Abstract-A methodology is developed to compute the total energy requirements for electricity-generating systems using an input-output model that explicitly accounts for the physicalflow of energy. The capital and operating requirements of 16 separate energy supply facilities are used to evaluate the total energy required by 9 alternative means of producing and delivering electricity. Evaluated electricity-generating systems rely on either fossil or nuclear energy as their fuel source. Energy payback periods are computed based on an equivalent electricity basis. These results are compared to a number of alternative capital investments to reduce energy demand. In general, the conservation options return their energy requirements sooner than the supply alternatives.
INTRODUCTION
The Federal Non-Nuclear Energy Research and Development Act of 1974 states that “the potential for production of net energy by the proposed technology at the stage of commercial application shall be analyzed and considered in evaluating proposals”. This concern for net energy analysis was first discussed by Odum’ and later applied to nuclear generating systems by Chapman and Mortimer.’ Recently Gilliland3 has elaborated on the policy implications of such analyses. Net energy is loosely defined as the difference between energy benefits (as output or savings) and requirements of an energy supply or conservation development. Because of the embodied energy in all goods and services, energy requirements for all inputs must be included. The net energy yield of a supply development is then the difference between its lifetime energy production and the total energy required to construct and operate it. Similarly, a home insulation program saves energy by reducing space heating and cooling requirements but requires energy to manufacture, transport, market and install the insulation. While the concept of net energy would be straightforward in a single energy economy, this is not the case. Because of (at the least) energy conversion losses, a Btu of coal is not the same as a Btu of electricity. On a Btu basis, society values electricity more than fossil fuels. This paper evaluates the total energy needed to build and operate a complete system that ultimately produces and delivers electricity. Energy requirements for each system are converted to the equivalent electricity that could have been produced if these requirements were diverted to produce electricity through existing systems. Table 1 identifies the 9 electricity generating systems considered. There are three methods for evaluating total energy needs: process analysis, input-output analysis or a hybrid of these methods. Process analysis consists of tracing production inputs back through the economy in a step-wise fashion to calculate the energy requirements of each input. Clearly this analysis must be truncated because of the infinite number of steps that would ultimately be involved.’ Input-output analysis uses a linear model of the economic system providing a computationally efficient means of calculating the indirect contributions from various industries in the output of a specific industry. This method has been extended to evaluate the embodied energy of goods and services for the latest year that the extensive economic data are available, 1%7.5 A hybrid analysis using a single process analysis step and then applying the input-output technique is employed here. Therefore, the total energy requirement of a power plant is found by summing the embodied energy of the individual items needed for its construction and operation. tThis work was supported by the National Science Foundation. ffiY
Vol. 2. No. I-A
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D. A. PILATT Table 1. Electricity-generating system definitions
Resource base Coal
Natural gas Crude oil Nuclear
System ID
CM-CFPP CM-CG-NGU-GFPP CM-CCC CM-SRC-CFPP GP-NGU-GFPP CO-LGR-OFPP SO-LGR-OFFP LWR HTGR
System definition Coal Mine + Coal Fired-Power Plant Coal Mine + Coal Gas&cation + Natural Gas Utility + Gas-Fired Power Plant Coal Mine+Coal Combined Cycle Power Plant Coal Mine -+Solvent Refined Coal + Coal-Fired Power Plant Gas Production + Natural Gas Utility + Gas-Fired Power Plant Crude Oil Production --*Low Gas Refinery -, Oil-Fired Power Plant Oil Shale Mine/Retort + Low Gas Refinery + Oil-Fired Power Plant LWR Fuel Mining/Processing+ LWR Power Plant HTGR Fuel Mining/Processing + HTGR Power Plant
System boundary selection presents problems on both the macro- and micro-scale. On the macro-scale, some suggest the appropriate boundary should include the entire ecosystem.’ Another issue is whether to treat the technology marginally, separate from the existing economic system or incorporate the technology into an analytical economic system before analysis. In essence, these possibilities depend on the interpretation of “potential” as found in the law. The analyses described in this paper evaluate the potential for producing net energy at the margin, as the technology becomes commercially available. The analyst must then decide on the precise system boundary for the technology investigated. For example, are transportation requirements, research and development costs and pertinent regulatory commissions to be included in the technology’s cost? Are secondary products counted as output and are self-use requirements internalized? For some analyses, results can vary dramatically depending on how these questions are answered. For example, the net energy ratio (energy output/energy input) of shale oil has been found to differ by over a factor of ten depending on the choices of system boundary.6 For comparison purposes, consistency must be maintained. Assumptions for the present analysis are discussed in a later section. Data for facilities that are not in commercial operation obviously present unknown uncertainties. The results presented here relied on a number of data sources for the process-analysis step. A comparison of results for one electricity system using different source data is given. Differences in resulting energy requirements demonstrate a need for consistent data as well as methodology.
METHOD
An electricity-generating system consists of several facilities to extract the energy resource from the earth, process it, and ultimately produce and distribute electricity. Figure 1 is a schematic representation of a series of facilities defining a complete electricity-generating system. The initial facility in a system is typically a mine or well that extracts the direct-energy resource consumed by the system. The n th facility is the electricity-generating facility such as a nuclear power plant. Intermediate facilities represent fuel processing, distribution or conversion facilities. As shown in Fig. 1, the system boundary encompasses the transmission and distribution of electricity to the final user. Transmission-line losses and other electricity requirements of the final facility in each system are assumed to be supplied by the system itself. Therefore, the delivered electricity will be somewhat less than that generated. Due to lack of data, capital requirements for
CAPITAI. AND OPERATING REOUIREMENTS FOR SYSTEM
SVS’TEM BOUNDARY
Fig. 1. Schematic diagram of electricity-generating system.
Energy analysis of electricity supplyandenergyconservation options
3
transportation infrastructure (e.g. railroads and transmission lines) and vehicles are incomplete. However, all transportation operating requirements and the capital requirements of natural gas distribution (natural gas utility in Table 1) are included. Figure 2 is a more detailed schematic representation illustrating the requirements for a generalized system. In the figure, Ci represents a vector of annual capital requirements per unit output of facility i, OPi represents a vector of annual operating requirements (other than direct fuel requirements) per unit output of i, qi is the energy conversion efficiency of the ith facility, and e is a vector of input fuel energy from the earth to the initial facility.
Fig. 2. Schematic diagram of system capital and operating requirements.
Energy required to produce a bill of goods is obtained from input-output analysis. A matrix of energy coefficients, ~(6 x n), is obtained to give the energy (coal, crude oil and gas, refined petroleum, electricity, natural gas and total primary) embodied in each dollar of output for an economic sector, where n depends on the degree of industry aggregation in the analysis (depending on the data, n has values of 90, 101 or 357). Therefore, the energy required to produce the material requirements for the system is evaluated by using existing technology. The capital energy requirements for constructing a system is then
Z(J!,$*g*ci+g*c,.
(1)
Similarly, annual energy requirements for operating the system become
Fuel energy removed from the earth.
First n - 1 facilities
Final facility
The capital and operating data for the 16 separate facilities come from a number of sources. Data for the capital requirements are from Bechtel,’ MITRE’ and Battelle.9 All nuclear fuel-processing energy requirements are from Chapman and Mortimer’ and industry data for nuclear fuel loadings. (In Ref. 2, process analysis is used to evaluate the energy requirements of nuclear fuel processing. This procedure circumvents the problems associated with using input-output results for the “industrial chemicals” sector to characterize nuclear fuels.) Other operating requirements are from Bullard and Herendeen5 Bullard” and MITRE.’ All power plants are assumed to operate with capacity factors of 0.80. (For further details, see Pilati and Richard.“) RESULTS
AND DISCUSSION
The total energy needed to build and operate the 9 systems is presented in Table 2. Energy requirements are separated into coal, crude (oil and gas) and total primary. Primary energy is defined as the sum of coal, crude (oil and gas), and the fossil fuel equivalent of electricity
0.18 0.35 0.14 (0.33Y 0.27 0.39 0.70 0.30 0.31 0.50
Coal 0.27 0.56 0.21 (0.46) 0.41 0.67 1.26 0.48 0.35 0.56
Crude 0.47 0.95 0.36 (0.84) 0.71 1.09 2.02 0.81 IO.53 (0.74) 17.13 (1.17)
Primary
Crude Primary
Coal Crude
Primary
Lifetime (Other than fuel) (BtulBtu total output)
3.12 0.09 3.21 0.04 0.09 0.13 5.06 0.25 5.32 0.25 0.06 0.32 2.54 (2.55)0.03 (0.04)2.58 (2.60)0.02 (0.02)0.03 (0.04)0.05 (0.07) 5.29 0.45 5.74 0.05 0.45 0.50 0.05 3.46 3.52 0.05 0.37 0.44 3.70 3.81 0.62 0.09 0.09 0.73 5.20 0.08 5.30 0.08 0.58 0.68 0.09 0.09 4.23 0.09 0.21 0.09 0.09 0.08 4.45 0.09 0.08 0.19
Coal
Lifetime (Including fuel) (Btu/Btu total output)
“A 25-year lifetime is assumed for all facilities. (This may be overly optimistic for oil wells. If so, their energy requirements are underestimated.) Fuel requirements are considered to be all energy entering the initial facility from the ground. Several facilities actually use some of this energy to satisfy part of their operating requirements. bResults in parenthesis result when Bechtel’ construction requirements for the low Btu coal gasification facility are used instead of MITRE’s.’ ‘Non-fuel related primary energy requirements in parenthesis.
CM-CFPP CM-CG-NGU-GFPP CM-CCC CM-SRC-CFPP GP-NGU-GFPP CO-LGR-GFPP SO-LGR-GFPP LWR HTGR
System ID (from Table I)
Capital (Btu/Btu annual output)
Table 2. Comparisons of energy requirements for nine electricity-generating systems
e
s
Energy analysis of electricity supply and energy conservation options
produced by non-fossil sources. Requirements are given for construction and 25 years of operation, Data limitations and conceptual questions concerning appropriate discount rates have precluded consideration of the energy requirements of system decommissioning or the safeguarding of nuclear wastes. Nuclear fuel is considered a primary energy source equivalent to the fossil fuel that would have been required by fossil-electric systems to produce the nuclear-generated electricity. The results for the coal combined-cycle system demonstrate the problems associated with data sources. Capital costs for low Btu coal gasification per unit output from Bechtel’ are about six times those from MITRE.’ The early stage in development of the Texaco gasification facility, compared to the proven Lurgi process should explain some, but possibly not all, of the disparity. Under these circumstances, the results using the proven Lurgi process (Bechtel) are probably the most reliable. Lifetime non-fuel energy requirements for the oil-electric system (onshore oil well, refinery and oil-fired power plant) are higher than for any other system. This result illustrates a basic fact underlying the need for energy analysis: as nonrenewable resources become scarcer, it requires more and more energy to get them out of the ground. For example, capita1 costs for onshore wells assume 3 dry holes for every 4 wells drilled in the contiguous states.’ Figure 3 graphically compares the energy inputs and outputs over time for oil-electric and light water reactor systems that deliver 20 trillion Btus of electricity per year. Delivered electricity is plotted above the axis while total primary energy requirements are plotted below. The very high capital costs for onshore oil is obvious when one realizes that wells are being drilled during only the last two years of the 5-year construction period. The fuel and non-fuel primary energy requirements are separated for the light water reactor. Unlike fossil systems, nuclear systems require a substantial capital investment in fuel requirements for the initial core.
:
“T
ENERGY INPUT I-) AND OUTPUT IN TRILLION BTUS, FOR SYSTEM OIL-ELECTRIC ONSHORE WELLS
(+) i
T
ENERGY INPUT (-1 IN TRILLION BTUS, LWR
AN0 OUTPUT (+I FOR SYSTEM
35 0 --4
Fig. 3. Oil-electric
and light water reactor energy inputs (primary)
and outputs (electricity)
over time.
An energy-supply system is a net energy sink until the capital and some operational energy requirements are repaid by the system. Table 3 gives the non-fuel energy payback times for two cases: (1) the time required to repay the total primary requirements (other than fuel) with electricity on a Btu basis and (2) the time required to repay the electricity that could have been generated and delivered by diverting the non-fuel energy requirements to existing electric generating systems.” Because society values electricity more highly than primary fuel on a Btu basis, the second comparison is more valid. However, a better method for comparing energy requirements to benefits might be based on the function of the energy end-use. For example, if homes now heated by oil were converted to electric heat using oil-electric generation, the oil requirements for heating homes would increase.‘* All systems repay their sunk equivalent electricity inputs in less than two-thirds of a year. It
D. A. PILATI
6
Table 3. Energy-payback times [year(s)]
SuPPLY system CM-CFPP CM-CG-NGU-GFPP CM-CCC CM-SRC-CFPP GP-NGU-GFPP CO-LGR-GFPP SO-LGR-GFPP LWR HTGR
Electricity for primary 0.54 1.32 0.37 (0.87) 1.35 1.81 5.71 2.31 0.90
1.37
Electricity for potential electricity 0.13 0.26 0.09 (0.22) 0.21 0.31 0.62 0.25 0.20 0.32
Conservation Option Clock-actuated thermostat Full-size autos + Subcompact Full-size autos + Compact Home insulation Storm windows
Primary for Primary 0.11 (O.lS)b 0.12 0.17 0.25 1.77
“Results using Bechtel data for low Btu coat gasification facility in parentheses. ‘Setback from 68-55°Fat night. (Setback from 68-6O”Fat night.) Based on dollar costs and energy savings from Pilati.” ‘Auto turnover, insulation and storm window results are from Putnam.” Auto turnover costs are capital requirements to completely retool assembly lines.
should be noted that these results are very sensitive to the capacity factor of 0.80 assumed for all power plants. If actual capacity factors were 0.50, payback times would be increased by over 60%. The conventional coal-electric system requires the shortest repayment period. However, the repayment time for this system would probably be increased the most if all transportation capital-requirements were included. This analysis is static and appropriate only for marginal, as opposed to average, technologies. At high growth rates, feedback from new (and perhaps less efficient) technologies become significant and must be imbedded in a dynamic input-output formulation. For example, the electricity required to generate electricity would increase if there is expansion of nuclear power plants because of fuel enrichment requirements. The effect of this activity is to increase the payback periods derived here. To insure a positive net energy yield for expanding systems, longer payback periods can be compensated for by shorter construction times.” Under the equivalent electricity accounting scheme (Table 3), doubling times of less than 4 years for either the energy-intensive oil+lectric system or nuclear power plants (LWR) would result in net deficits. However, exponential system expansion rates may not be realistic. Many energy conservation schemes also require an energy investment. It is, therefore, instructive to compare their repayment periods with supply developments. Table 3 also includes the repayment period for a number of conservation programs: ceiling insulation, storm windows, conversion to smaller cars, and clock thermostats (a device that automatically lowers nighttime temperatures-a technical fix to a behavioral option). Except for storm windows, the conservation options return their primary energy investment sooner than any of the supply systems. If all transportation capital-requirements were included in the supply analysis, the advantage of conservation would be even greater. CONCLUSIONS
Net energy concern for energy supply programs can be raised in two instances: (1) When the energy required to produce leaner resources becomes prohibitive and (2) when the total energy system grows too rapidly. A single electricity-generating system is a net energy sink until sometime after it commences operation. For the equivalent electricity accounting procedure, all (static) systems have a positive net energy yield in less than two-thirds of a year. Dwindling supplies of crude oil in the U.S. result in the conventional oil-electric system requiring the longest repayment time. Programs for rapid expansion of energy supply may result in net energy deficits until the growth rate slows. Longer construction times of particular systems can aggravate this problem. For system doubling-times of less than 4 years, neither oil-electric @year construction period and 0.62 year for repayment) nor conventional nuclear power (Pyear construction period and 0.20 year for repayment) can repay their energy requirements. However, prolonged exponential growth rates are probably unrealistic.
Energy analysis of electricity supply and energy conservation options
7
From an energy point of view, conservation is comparable to new supplies. In general, conservation options repay their energy requirements sooner than supply alternatives (Table 3). Compared to the supply options, they can become operational in a shorter period of time. Therefore, if a premium is placed on rapid energy independence, conservation would be especially advantageous. Several other comparisons between conservation and supply developments deserve mention. Thus far, discussion has centered on energy inputs and benefits: because of differences between energy dollar costs and prices, the conservation options included here should be more economically desirable than they are energetically.” Longer lead times required by supply developments would penalize them economically if discounting were included. However, many conservation programs must be undertaken by the homeowner of small businessman who might be lacking in adequate information and technical expertise. Contrasted to the energy industry, these individuals also find it more difficult and costly to raise the necessary capital. Policy decisions to assist energy suppliers (such as an Energy Independence Authority) should be properly balanced by similar conservation programs. Otherwise, the energy supply-demand imbalance may not be reduced in a resource-efficient manner. REFERENCES 1. H. T. Odum, Energy, ecology and economics. Am&o, Z(6), 220-227 (1973). 2. P. F. Chapman and N. D. Mortimer, Energy Inputs and Outputs for Nuclear Power Stations. Open University Report ERG 005, Milton Keynes, Buckinghamshire, U.K., Dec. 1974. 3. M. W. Gilliland, Science 189, I051 (1975). 4. R. W. Berry and M. F. Fels, The energy cost of automobiles. Bulletin of Atomic Scientists-Science and Public Aflairs, Dec. 1973. 5. C. Bullard and R. Herendeen, Proc. IEEE 63, 484 (1975). 6. C. E. Clark and D. C. Varisco, Net energy and oil shale. In In Situ Recovery of Shale Oil, Report NSF-RA-N-75-001, (Edited by S. S. Penner), pp. 345-372. U.S. Government Printing Office, Washington, DC., Aug. 1975. 7. M. Carasso et al., The Energy Supply Planning Model, Vols. l-3. Bechtel Corporation, Energy Systems Group, San Francisco, CA, July 1975. 8. J. Just et al., New Energy Technology Coeficients and Dynamic Energy Models. (2 volumes), MITRE report MTR-6810. McLean, VA, Jan. 1975. 9. C. Chilton and W. Fisher, An Ex Ante Capital Matrix for the United States. 1970-1975,Battelle Memorial Institute. Columbus, OH, Mar. 1971. IO. C. Bullard, An Input-Output Model for Energy Demand Analysis. CAC Document No. 146, Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL, Jan, 1975. 11.D. A. Pilati and R. Richard, Total Energy Requirements for Nine Electricity-Generating Systems. CAC Document No. 165, Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL, Aug. 1975. 12. P. F. Chapman, Energy Policy 3. 285 (1975). 13. D. A. Pilati, The Energy Conseruafion Potenfial of Winter Thermostat Reduction and Night Setback. Oak Ridge National Laboratory Report ORNL-NSF-EP-80, Oak Ridge, TN, Feb. 1975. 14. D. E. Putnam, Energy Benefitsand Co&. Housinglnsulation and the UseojSmaller Cars.CAC Document No. 173.Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL Aug. 1975. 15. C. Bullard, Energy Costs, Benefits and Net Energy. CAC Document No. 174, Center for Advanced Computation, University of Illinois at Urbana-Champaign, Urbana, IL Aug. 1975.