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Scenario analysis for sustainable development considering CO2 disposal
Energy Convers. Mgrat Vol. 34, No. 9-11, pp. 799--806, 1993
0196-8904/93 $6.00+ 0.00 Copyright © 1993PergamonPress Ltd
Printed in Great Britain. All fights reserved
Scenario Analysis for Sustainable Development Considering CO2 Disposal Ryuji Matsuhashi, Fukashi Watanabe and Hisashi lshitani
Department of Mineral Development Engineering, Faculty of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
ABSTRACT Depletion of the fossil fuels and climate change caused by the greenhouse effect is threatening the sustainable development of mankind. Since the CO 2 produced by burning fossil fuels is the dominant source of anthropogenic greenhouse gas emissions, CO 2 disposal is expected to be an effective option for mitigating climate change. However, if we took the option of CO 2 disposal and continued relying on fossil fuels, it could not be the sustainable use of energy resources. Therefore we need some theoretical framework for realizing the sustainable development. In this paper, we have developed a model to demonstrate the way of sustainable use of energy resources under constraints on CO 2 emissions. Computed results have shown that present energy system based on fossil fuels shifts to the system based on renewable resources in the ultra-long term with appropriate incentives. 032 disposal plays an important but a transitional role in this analysis.
KEYWORDS Sustainable development; fossil fuels; CO 2 disposal; renewable resources; photovoltaics.
INTRODUCTION Climate change caused by the greenhouse effect could be a serious threat to mankind, although it is quite uncertain how climate change damages to the human society. Since the CO 2 produced by burning fossil fuels is the dominant source of anthropogenic greenhouse gas emissions, CO 2 disposal is expected to be an effective option for mitigating climate change. However, if we took the option of CO 2 disposal and continued relying on fossil fuels, it could not be the sustainable use of energy resources. Therefore we need some theoretical framework for realizing the sustainable development. Concerning this, Word Bank economist Herman Daly (Meadows et al., 1991) has proposed three principles, by which we could maintain the sustainable development in the"~--arth'ssystem as follows. 1. For a renewable resource -soil, water, forest, fish- the sustainable rate of use can be no greater than the rate of regeneration. For example, fish are harvested sustainably when they are caught at a rate that can be replaced by the remaining fish population. 2. For a non-renewable resource - fossil fuel, high-grade mineral ore - the sustainable rate of use can be no greater than the rate at which a renewable resource, used sustainably, can be substituted for it. For example, an oil deposit would be used sustainably if part of the profits from it were systematically invested in solar collectors or in tree planting, so that when the oil is gone, an equivalent stream of renewable energy is still available. 3. For a pollutant the sustainable rate of emission can be no greater than the rate at which that pollutant can be recycled, absorbed, or rendered harmless by the environment. For example, sewage can be put into a stream or lake sustainably at the rate at which the natural ecosystem in the water can absorb its nutrients. In particular, the principle 2 is remarkable for sustainable use of energy resource. T h e r e f o r e we have developed the model to demonstrate the energy scenario for sustainable development of mankind based on ~.-H
799
800
MATSUHASHIet
aL:
SUSTAINABLEDEVELOPMENT CONSIDERING CO2 DISPOSAL
the principle 2. We have demonstrated three types of energy scenarios under constraints on CO 2 emissions in the ultra-long t6rm in this paper. In Scenario 1, the model determines the share of each energy resource under given demands of the whole world to minimize total primary energy. In Scenario 2, the objective function is not a total primary energy, but a cost-equivalent index, which is thought to reflect the actual economic criteria of the world. We explain the cost-equivalent index in the chapter of RESULTS OF SIMULATION. in Scenario 3, objective function is the same as that of Scenario 2, but is different in the point that part of the fossil fuels consumed are systematically invested in renewable energy technologies such as photovoltaics according to the principle 2. In other words, we have demonstrated in the scenario 3 that conventional energy system based on fossil fuels shifts to the sustainable system based on renewable energy system with appropriate incentives. Scenario 3 has also indicated that CO 2 disposal could play a significant but a transitional role for reducing global CO2 emissions.
ULTRA-LONG TERM ENERGY MODELS Basic Framework As mentioned above, we have developed the models to represent three types of scenarios. Basic structures and assumptions of the models are described as follows. (1) The models have 60 time periods, and each time period has time length of 5 years. Thus the time horizon of these models are 300 years ahead from now. In each time period, the model determines shares of different energy resources and technologies to minimize the objective function in each scenario. We simulate energy system by minimizing the objective function in each time period repeatedly for 60 times. A linear programming method is used to optimize an energy system in each time period. (2) In Scenario 1, the model determines the share of each energy resource under given demands of the whole world to minimize total primary energy. We estimate the total primary energy including that required to construct capital plants. In Scenario 2, the objective function is not a total primary energy, but the cost-equivalent index, which is thought to reflect the actual economic criteria of the world. In Scenario 3, objective function is the same as that of Scenario 2, but is different in the point that part of the fossil fuels consumed are systematically invested in renewable energy technologies such as photovoltaics. Technical Assumptions Next we describe on technical assumptions of the models. (1) Four kinds of fossil fuels ( coal, oil, natural gas and oil shale ) are considered. Unconventional oil such as Orinoco-Tar is included in oil, and the energy required to extract Orinoco-Tar is assumed to be higher than conventional oil. (2) Photovoltaics is selected as a representative of renewable energy technologies, since it is most abundant and promising renewable energy technologies. Both fossil fuels and electricity is permitted to fabricate photovoltaics. (3) Nuclear energy is not considered in this model, since it has much uncertainty in social acceptance problem and it has also ,serious problem of nuclear proliferation. (4) It is almost impossible to incorporate all possible technologies in 300 years in these models. Therefore we drastically simplified the model and incorporated the necessary minimum number of technologies. Recovery and disposal of CO 2 is assumed to be available in power generation and in coal gasification. (5) We classify final energy demands into two types, i.e. heat sector and electricity sector. Each energy demand is assumed to increase linearly. Generated electricity is not only used in the electricity sector, but also in the heat demand sector. (6) Constraints on CO 2 emissions is assumed to be 50% higher than present global CO 2 emissions produced by burning fossil fuels. (7) As accumulated production of each fossil fuel increases and the fuel begins to be depleted, more energy is required to extract the fuel. This relationship is expressed in the following equation.
(i) a {1 + exp(b x stat / URES - c)} URES : Ultimate reserves of a resource; stat : Accumulated production of a resource; a,b,c : Constan~ ef£i =
On the other hand, the energy balance (ratio of output energy to the energy required to construct photovoltaics) increases, as annual production of solar cells expands. This relationship is expressed in
MATSUHASHI et
al.:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
801
the equation (2). eff.5 =
d
(2)
{1 + e x p ( - e x sout / f)} sout : Annual production of solar cell; d,e,f : Constants Initial energy balances of fossil fuels and of solar energy (photovoltaics) are shown in table. 1. Those values were estimated by bottom up method accounting all materials required in those technologies. Table 1. Energy balances of energy resources.
Heat Electricit)
Coal
Oil
Gas
Shale
19.5
23.7
6.8
7.5
6.5
8.0
2.2
2.7
Solar 1.3
(8) Energy flow diagrams of the models are depicted in fig. 1. inv3.i
I
I 0utll,i
inv2.i inv5,i
0utl.5 inv4.i 0ut21
0ut22 C02 dislx~oal]
inv2.1 inv6
Fig. 1. Energy flow diagram of the models.
RESULTS OF SIMULATION Scenario 1 Objective function is to minimize total primary energy required to fullfil energy demand and to construct capital plants as described above. Fig.2 (a-c) show the computed results of Scenario 1. Fig.2.a indicates a steep increase of solar energy in the total primary energy. Consequently solar energy substitute all fossil energy by 2070. O92 emission is very low because of large share of solar energy, and we do not need to recover and to dispose of CO 2 in Scenario 1. However Scenario I would not
802
MATSUHASHI et al.: SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
be accepted in the real world, because we focus our attention only on minimizing primary energy and neglect economic feasibility of energy technologies.
60O0O
Mtoe
50000
f
40000
J
30000 20000
•
Coal
•
Gas
J
J [ ] Oil Shale
0 1990
2065
I 2140 2215 Ye~
2290
[ ] Solar
Fig.2.a. Primary energies in Scenario 1.
- - Coal
10 8
ROll
6 4
" - Gas
2 l
.... Oil Shale
0 1990
2065
2140
2215
2290
~ Solar
Year Fig.2.b. Energy balances of resources. Mt-CO2 200000 150000 100000 50000
1990
2065
2140 2215 Year
•
Electricity
[]
Heat
•
Disposal
2290
Fig.2.c. CO z emissions in Scenario 1 Scenario 2 In reality, energy resource and plants are allocated not to minimize total primary energy, but to minimize
MATSUHASHI et
al.:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
803
capital and running costs. For examining the discrepancy between the above two criteria, we estimated the ratio of the construction cost of each energy plant to the cost of energy required to construct the plant. We call this index "Cost-energy ratio". The result is shown in Table 2. Table 2 indicates that Cost-energy ratio is very high around 200 concerning fossil fuel power stations. This is because many factors such as human costs other than energy costs influence the construction costs. Therefore in Scenario 2, we multiply the energy required to construct each energy plants by the Cost-energy ratio of the plant. Other parts of the objective function is the same as that of scenario 1. We call this type of simulation "costequivalent energy analysis". Table 2. The Cost-energy ratio of major energy plants.
Coal
Oil
Gas
Solar
Construction cost ( it:/kWh)
11.6
8.5
8.5
125.0
b. Energy cost ( :~/kWh) Cost-energy ratio (a/b)
0.055
0.043
0.043
10.3
a.
210
199
199
12
Simulated results of Scenario 2 are shown in fig.3 a-c. These figures indicate that we would continue relying on fossil fuels (especially coal) nearly 200 years if we optimize energy system by the economic criteria ( cost-equivalent energy). Furthermore, optimization of energy system becomes infeasible after 2185. This is because all fossil fuels are depleted and no substitutable energy is available in periods after 2185. In short, scenario 2 is not the scenario for sustainable development.
Mtoe •
60000
Coal
50000 40000 30000 1 Gas 20000 10000
•
Oil Shale
0 1990
2039
2 0 8 8 2136 Year
2185
[ ] Solar
Fig.3.a. Primary energies in Scenario 2. Fig.3.b shows energy balances (ratio of energy output to that foi" constructing capital plants) of resources. It indicates that energy balances of fossil fuels rapidly go down as they begin to be depleted. Photovoltaics is not introduced all through the planning periods for lack of economic feasibility. Therefore the energy balance of photovoltaics does not go up all through the planning periods.
804
MATSUHASHI et
aL:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
--Coal
--Oil
" - Gas
1
.~_ .
1990
.
.
2039
.
~.__~_
2088
2136
•"--" Oil Shale
2185
' - ' Solar
Year Fig.3.b. Energy balances of resources. Fig.3.c shows the quantity of CO 2 which is emitted in the air and is disposed of. O92 disposal is used as a powerful option to reduce CO 2 emission in the air. We continue to rely on fossil fuels and CO 2 disposal in Scenario 2. As a result, energy supply becomes infeasible after 2185.
MFC02 2OOO00 150000 • 100000
Electricity
[ ] Heat •
50000
Disposal
0 1990
2039
2088
2136
2185
Year
Fig.3.c. CO 2 emitted in the air and disposed of.
Scenario 3 In Scenario 1, in which we aimed at minimizing total primary energy, solar energy substituted other energy resources pretty soon ( in the midst of 21st century). This is one way of realizing sustainable use of energy resource. However, Scenario 1 is not realistic in the sense that economic feasibility of energy technologies is neglected. Probably such a steep increase of photovoltaics in Scenario ! would be a burden for the world economy. On the other hand, we investigated the results of "cost-equivalent energy analysis" in scenario 2. Scenario 2 is thought to be more realistic in the sense that we make much of economic feasibility of the technologies. However, solar energy is not introduced in the energy system during the whole periods and energy supply becomes infeasible after 2185. Thus Scenario 2 represents unsustainable way of energy use. In short, Scenario 1 is unrealistic, and Scenario 2 is unsustainable. Here we investigate the possibility of realistic and sustainable way of energy use in Scenario 3. For this purpose, we apply Herman Daly's principle (Meadows ct al., 1991), in which part of fossil fuels are systematically invested in constructing photovoltaics. Ma'~assumptions are as follows.
MATSUHASHI et
al.:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
805
Investment for constructing photovoltaics begins at 2000. And the rate of investment is assumed to increase linearly from 2000 so that it reaches 30% of fossil energy consumed in the end of the planning period. Fig.4.(a-c) show the computed results of Scenario 3. Fig.4 a indicates that share of solar energy steadily increases from midst of twenty first century. And it becomes dominant energy sources from midst of twenty third century when coal begins t.o be depleted. Thus the energy system based on fossil fuels shifts to the energy system based on the renewable resource in the far future. In this sense, Scenario 3 is a sustainable way of using energy resources.
Mtoe 60000 --.
•
Coal
50000
40000 "
Qou
Y
30000 •
Gas
20000 10000
~1 Oil Shale
1990
2065
2140 2215 Ye,T
2290
D Solar
Fig.4.a. Primary energies in Scenario 3. Fig.4.b shows CO 2 which is emitted in the air and is disposed of. 032 disposal is used as a powerful option to reduce CO 2 emission in the air. But it begins to decrease from the beginning of twenty third century, and disappears in the end of twenty third century. In short, CO 2 disposal plays an important, but a transitional role. We still have following two questions. 1. In Scenario 3, a huge quantity of CO 2 (12 trillion ton ) is disposed of. Is it possible and permitted from an environmental point of view? 2. In Scenario 3, a huge area of land (3 million km 2) is required for photovoltaics. This area corresponds to about 10% of whole desert area in the earth. Is it possible to obtain that huge area for photovoltaics? We discuss below on the above questions. Computed results of Scenario 3 is based on the demand assumed in the model. If energy demand does not increase as rapidly as in this model, we do not need to dispose of that quantity of CO 2. Furthermore, energy demand could be considerably reduced by energy conservation technologies, as many researchers have pointed out. We can reduce the quantity of CO 2 disposal and land requirement by the above possibilities. Therefore we need such efforts as promoting energy conservation, although we here deal with only one aspect of sustainable use of energy. 200000
Mt-CO2
150000 •
Electricity
[ ] Heat •
0ooo
o
"."~V"/..: 1990
2065
2140 2215 Ye~
2290
Fig.4.b. CO 2 emitted in the air and disposed of.
Disposal
806
MATSUHASHIet
aL:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
CONCLUSIONS We aim at drawing an energy supply scenario for sustainable development taking CO 2 constraints and resource depletion in consideration. Major f'mdings are summarized as follows. 1. If we focus our attention only on minimizing total primary energy with a given demand (Scenario 1), photovoltaics are attractive technology even in the present energy balance (ratio of energy output to that required to construct photovoltaic power plants). 2. If we optimize world energy system by minimizing the cost-equivalent index (Scenario 2), we continue to rely on fossil fuels even in the very long term. Consequently we have to recover and dispose of huge quantity of CO 2, and finally energy supply becomes infeasible. Thus energy resources can not be used sustainably in Scenario 2. 3. If we systematically invest part of fossil fuels consumed in renewable energy technologies such as photovoltaics (Scenario 3), energy resources can be used sustainably. CO 2 disposal plays an important but a transitional role in Scenario 3.
FUTURE WORK (1) As mentioned in chapter 2, nuclear energy is not considered in this model, since it has much uncertainty in social acceptance problem and it has also a serious problem of nuclear proliferation. However, various problems on nuclear energy could be improved. Therefore we should include nuclear fuels in future work. (2) As huge quantity of CO 2 have to be disposed of, only the ocean or aquifer might be the ultimate sinks of CO 2. We should further investigate the feasibility and the capacities of CO 2 disposal in the ocean, aquifer, depleted gas well and oil well. (3) We need other efforts such as promoting energy conservation so as to realize a sustainable use of energy resource. Next we would like to integrate energy conservation and the work done here. REFERENCES Donella H Meadows, Dennis L Meadows, Jorgen Randers (1991). Green Publishing Co., p46.
BEYOND THE LIMITS. Chelsea
0196-8904/93 $6.00+ 0.00 Copyright © 1993PergamonPress Ltd
Printed in Great Britain. All fights reserved
Scenario Analysis for Sustainable Development Considering CO2 Disposal Ryuji Matsuhashi, Fukashi Watanabe and Hisashi lshitani
Department of Mineral Development Engineering, Faculty of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
ABSTRACT Depletion of the fossil fuels and climate change caused by the greenhouse effect is threatening the sustainable development of mankind. Since the CO 2 produced by burning fossil fuels is the dominant source of anthropogenic greenhouse gas emissions, CO 2 disposal is expected to be an effective option for mitigating climate change. However, if we took the option of CO 2 disposal and continued relying on fossil fuels, it could not be the sustainable use of energy resources. Therefore we need some theoretical framework for realizing the sustainable development. In this paper, we have developed a model to demonstrate the way of sustainable use of energy resources under constraints on CO 2 emissions. Computed results have shown that present energy system based on fossil fuels shifts to the system based on renewable resources in the ultra-long term with appropriate incentives. 032 disposal plays an important but a transitional role in this analysis.
KEYWORDS Sustainable development; fossil fuels; CO 2 disposal; renewable resources; photovoltaics.
INTRODUCTION Climate change caused by the greenhouse effect could be a serious threat to mankind, although it is quite uncertain how climate change damages to the human society. Since the CO 2 produced by burning fossil fuels is the dominant source of anthropogenic greenhouse gas emissions, CO 2 disposal is expected to be an effective option for mitigating climate change. However, if we took the option of CO 2 disposal and continued relying on fossil fuels, it could not be the sustainable use of energy resources. Therefore we need some theoretical framework for realizing the sustainable development. Concerning this, Word Bank economist Herman Daly (Meadows et al., 1991) has proposed three principles, by which we could maintain the sustainable development in the"~--arth'ssystem as follows. 1. For a renewable resource -soil, water, forest, fish- the sustainable rate of use can be no greater than the rate of regeneration. For example, fish are harvested sustainably when they are caught at a rate that can be replaced by the remaining fish population. 2. For a non-renewable resource - fossil fuel, high-grade mineral ore - the sustainable rate of use can be no greater than the rate at which a renewable resource, used sustainably, can be substituted for it. For example, an oil deposit would be used sustainably if part of the profits from it were systematically invested in solar collectors or in tree planting, so that when the oil is gone, an equivalent stream of renewable energy is still available. 3. For a pollutant the sustainable rate of emission can be no greater than the rate at which that pollutant can be recycled, absorbed, or rendered harmless by the environment. For example, sewage can be put into a stream or lake sustainably at the rate at which the natural ecosystem in the water can absorb its nutrients. In particular, the principle 2 is remarkable for sustainable use of energy resource. T h e r e f o r e we have developed the model to demonstrate the energy scenario for sustainable development of mankind based on ~.-H
799
800
MATSUHASHIet
aL:
SUSTAINABLEDEVELOPMENT CONSIDERING CO2 DISPOSAL
the principle 2. We have demonstrated three types of energy scenarios under constraints on CO 2 emissions in the ultra-long t6rm in this paper. In Scenario 1, the model determines the share of each energy resource under given demands of the whole world to minimize total primary energy. In Scenario 2, the objective function is not a total primary energy, but a cost-equivalent index, which is thought to reflect the actual economic criteria of the world. We explain the cost-equivalent index in the chapter of RESULTS OF SIMULATION. in Scenario 3, objective function is the same as that of Scenario 2, but is different in the point that part of the fossil fuels consumed are systematically invested in renewable energy technologies such as photovoltaics according to the principle 2. In other words, we have demonstrated in the scenario 3 that conventional energy system based on fossil fuels shifts to the sustainable system based on renewable energy system with appropriate incentives. Scenario 3 has also indicated that CO 2 disposal could play a significant but a transitional role for reducing global CO2 emissions.
ULTRA-LONG TERM ENERGY MODELS Basic Framework As mentioned above, we have developed the models to represent three types of scenarios. Basic structures and assumptions of the models are described as follows. (1) The models have 60 time periods, and each time period has time length of 5 years. Thus the time horizon of these models are 300 years ahead from now. In each time period, the model determines shares of different energy resources and technologies to minimize the objective function in each scenario. We simulate energy system by minimizing the objective function in each time period repeatedly for 60 times. A linear programming method is used to optimize an energy system in each time period. (2) In Scenario 1, the model determines the share of each energy resource under given demands of the whole world to minimize total primary energy. We estimate the total primary energy including that required to construct capital plants. In Scenario 2, the objective function is not a total primary energy, but the cost-equivalent index, which is thought to reflect the actual economic criteria of the world. In Scenario 3, objective function is the same as that of Scenario 2, but is different in the point that part of the fossil fuels consumed are systematically invested in renewable energy technologies such as photovoltaics. Technical Assumptions Next we describe on technical assumptions of the models. (1) Four kinds of fossil fuels ( coal, oil, natural gas and oil shale ) are considered. Unconventional oil such as Orinoco-Tar is included in oil, and the energy required to extract Orinoco-Tar is assumed to be higher than conventional oil. (2) Photovoltaics is selected as a representative of renewable energy technologies, since it is most abundant and promising renewable energy technologies. Both fossil fuels and electricity is permitted to fabricate photovoltaics. (3) Nuclear energy is not considered in this model, since it has much uncertainty in social acceptance problem and it has also ,serious problem of nuclear proliferation. (4) It is almost impossible to incorporate all possible technologies in 300 years in these models. Therefore we drastically simplified the model and incorporated the necessary minimum number of technologies. Recovery and disposal of CO 2 is assumed to be available in power generation and in coal gasification. (5) We classify final energy demands into two types, i.e. heat sector and electricity sector. Each energy demand is assumed to increase linearly. Generated electricity is not only used in the electricity sector, but also in the heat demand sector. (6) Constraints on CO 2 emissions is assumed to be 50% higher than present global CO 2 emissions produced by burning fossil fuels. (7) As accumulated production of each fossil fuel increases and the fuel begins to be depleted, more energy is required to extract the fuel. This relationship is expressed in the following equation.
(i) a {1 + exp(b x stat / URES - c)} URES : Ultimate reserves of a resource; stat : Accumulated production of a resource; a,b,c : Constan~ ef£i =
On the other hand, the energy balance (ratio of output energy to the energy required to construct photovoltaics) increases, as annual production of solar cells expands. This relationship is expressed in
MATSUHASHI et
al.:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
801
the equation (2). eff.5 =
d
(2)
{1 + e x p ( - e x sout / f)} sout : Annual production of solar cell; d,e,f : Constants Initial energy balances of fossil fuels and of solar energy (photovoltaics) are shown in table. 1. Those values were estimated by bottom up method accounting all materials required in those technologies. Table 1. Energy balances of energy resources.
Heat Electricit)
Coal
Oil
Gas
Shale
19.5
23.7
6.8
7.5
6.5
8.0
2.2
2.7
Solar 1.3
(8) Energy flow diagrams of the models are depicted in fig. 1. inv3.i
I
I 0utll,i
inv2.i inv5,i
0utl.5 inv4.i 0ut21
0ut22 C02 dislx~oal]
inv2.1 inv6
Fig. 1. Energy flow diagram of the models.
RESULTS OF SIMULATION Scenario 1 Objective function is to minimize total primary energy required to fullfil energy demand and to construct capital plants as described above. Fig.2 (a-c) show the computed results of Scenario 1. Fig.2.a indicates a steep increase of solar energy in the total primary energy. Consequently solar energy substitute all fossil energy by 2070. O92 emission is very low because of large share of solar energy, and we do not need to recover and to dispose of CO 2 in Scenario 1. However Scenario I would not
802
MATSUHASHI et al.: SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
be accepted in the real world, because we focus our attention only on minimizing primary energy and neglect economic feasibility of energy technologies.
60O0O
Mtoe
50000
f
40000
J
30000 20000
•
Coal
•
Gas
J
J [ ] Oil Shale
0 1990
2065
I 2140 2215 Ye~
2290
[ ] Solar
Fig.2.a. Primary energies in Scenario 1.
- - Coal
10 8
ROll
6 4
" - Gas
2 l
.... Oil Shale
0 1990
2065
2140
2215
2290
~ Solar
Year Fig.2.b. Energy balances of resources. Mt-CO2 200000 150000 100000 50000
1990
2065
2140 2215 Year
•
Electricity
[]
Heat
•
Disposal
2290
Fig.2.c. CO z emissions in Scenario 1 Scenario 2 In reality, energy resource and plants are allocated not to minimize total primary energy, but to minimize
MATSUHASHI et
al.:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
803
capital and running costs. For examining the discrepancy between the above two criteria, we estimated the ratio of the construction cost of each energy plant to the cost of energy required to construct the plant. We call this index "Cost-energy ratio". The result is shown in Table 2. Table 2 indicates that Cost-energy ratio is very high around 200 concerning fossil fuel power stations. This is because many factors such as human costs other than energy costs influence the construction costs. Therefore in Scenario 2, we multiply the energy required to construct each energy plants by the Cost-energy ratio of the plant. Other parts of the objective function is the same as that of scenario 1. We call this type of simulation "costequivalent energy analysis". Table 2. The Cost-energy ratio of major energy plants.
Coal
Oil
Gas
Solar
Construction cost ( it:/kWh)
11.6
8.5
8.5
125.0
b. Energy cost ( :~/kWh) Cost-energy ratio (a/b)
0.055
0.043
0.043
10.3
a.
210
199
199
12
Simulated results of Scenario 2 are shown in fig.3 a-c. These figures indicate that we would continue relying on fossil fuels (especially coal) nearly 200 years if we optimize energy system by the economic criteria ( cost-equivalent energy). Furthermore, optimization of energy system becomes infeasible after 2185. This is because all fossil fuels are depleted and no substitutable energy is available in periods after 2185. In short, scenario 2 is not the scenario for sustainable development.
Mtoe •
60000
Coal
50000 40000 30000 1 Gas 20000 10000
•
Oil Shale
0 1990
2039
2 0 8 8 2136 Year
2185
[ ] Solar
Fig.3.a. Primary energies in Scenario 2. Fig.3.b shows energy balances (ratio of energy output to that foi" constructing capital plants) of resources. It indicates that energy balances of fossil fuels rapidly go down as they begin to be depleted. Photovoltaics is not introduced all through the planning periods for lack of economic feasibility. Therefore the energy balance of photovoltaics does not go up all through the planning periods.
804
MATSUHASHI et
aL:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
--Coal
--Oil
" - Gas
1
.~_ .
1990
.
.
2039
.
~.__~_
2088
2136
•"--" Oil Shale
2185
' - ' Solar
Year Fig.3.b. Energy balances of resources. Fig.3.c shows the quantity of CO 2 which is emitted in the air and is disposed of. O92 disposal is used as a powerful option to reduce CO 2 emission in the air. We continue to rely on fossil fuels and CO 2 disposal in Scenario 2. As a result, energy supply becomes infeasible after 2185.
MFC02 2OOO00 150000 • 100000
Electricity
[ ] Heat •
50000
Disposal
0 1990
2039
2088
2136
2185
Year
Fig.3.c. CO 2 emitted in the air and disposed of.
Scenario 3 In Scenario 1, in which we aimed at minimizing total primary energy, solar energy substituted other energy resources pretty soon ( in the midst of 21st century). This is one way of realizing sustainable use of energy resource. However, Scenario 1 is not realistic in the sense that economic feasibility of energy technologies is neglected. Probably such a steep increase of photovoltaics in Scenario ! would be a burden for the world economy. On the other hand, we investigated the results of "cost-equivalent energy analysis" in scenario 2. Scenario 2 is thought to be more realistic in the sense that we make much of economic feasibility of the technologies. However, solar energy is not introduced in the energy system during the whole periods and energy supply becomes infeasible after 2185. Thus Scenario 2 represents unsustainable way of energy use. In short, Scenario 1 is unrealistic, and Scenario 2 is unsustainable. Here we investigate the possibility of realistic and sustainable way of energy use in Scenario 3. For this purpose, we apply Herman Daly's principle (Meadows ct al., 1991), in which part of fossil fuels are systematically invested in constructing photovoltaics. Ma'~assumptions are as follows.
MATSUHASHI et
al.:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
805
Investment for constructing photovoltaics begins at 2000. And the rate of investment is assumed to increase linearly from 2000 so that it reaches 30% of fossil energy consumed in the end of the planning period. Fig.4.(a-c) show the computed results of Scenario 3. Fig.4 a indicates that share of solar energy steadily increases from midst of twenty first century. And it becomes dominant energy sources from midst of twenty third century when coal begins t.o be depleted. Thus the energy system based on fossil fuels shifts to the energy system based on the renewable resource in the far future. In this sense, Scenario 3 is a sustainable way of using energy resources.
Mtoe 60000 --.
•
Coal
50000
40000 "
Qou
Y
30000 •
Gas
20000 10000
~1 Oil Shale
1990
2065
2140 2215 Ye,T
2290
D Solar
Fig.4.a. Primary energies in Scenario 3. Fig.4.b shows CO 2 which is emitted in the air and is disposed of. 032 disposal is used as a powerful option to reduce CO 2 emission in the air. But it begins to decrease from the beginning of twenty third century, and disappears in the end of twenty third century. In short, CO 2 disposal plays an important, but a transitional role. We still have following two questions. 1. In Scenario 3, a huge quantity of CO 2 (12 trillion ton ) is disposed of. Is it possible and permitted from an environmental point of view? 2. In Scenario 3, a huge area of land (3 million km 2) is required for photovoltaics. This area corresponds to about 10% of whole desert area in the earth. Is it possible to obtain that huge area for photovoltaics? We discuss below on the above questions. Computed results of Scenario 3 is based on the demand assumed in the model. If energy demand does not increase as rapidly as in this model, we do not need to dispose of that quantity of CO 2. Furthermore, energy demand could be considerably reduced by energy conservation technologies, as many researchers have pointed out. We can reduce the quantity of CO 2 disposal and land requirement by the above possibilities. Therefore we need such efforts as promoting energy conservation, although we here deal with only one aspect of sustainable use of energy. 200000
Mt-CO2
150000 •
Electricity
[ ] Heat •
0ooo
o
"."~V"/..: 1990
2065
2140 2215 Ye~
2290
Fig.4.b. CO 2 emitted in the air and disposed of.
Disposal
806
MATSUHASHIet
aL:
SUSTAINABLE DEVELOPMENT CONSIDERING CO2 DISPOSAL
CONCLUSIONS We aim at drawing an energy supply scenario for sustainable development taking CO 2 constraints and resource depletion in consideration. Major f'mdings are summarized as follows. 1. If we focus our attention only on minimizing total primary energy with a given demand (Scenario 1), photovoltaics are attractive technology even in the present energy balance (ratio of energy output to that required to construct photovoltaic power plants). 2. If we optimize world energy system by minimizing the cost-equivalent index (Scenario 2), we continue to rely on fossil fuels even in the very long term. Consequently we have to recover and dispose of huge quantity of CO 2, and finally energy supply becomes infeasible. Thus energy resources can not be used sustainably in Scenario 2. 3. If we systematically invest part of fossil fuels consumed in renewable energy technologies such as photovoltaics (Scenario 3), energy resources can be used sustainably. CO 2 disposal plays an important but a transitional role in Scenario 3.
FUTURE WORK (1) As mentioned in chapter 2, nuclear energy is not considered in this model, since it has much uncertainty in social acceptance problem and it has also a serious problem of nuclear proliferation. However, various problems on nuclear energy could be improved. Therefore we should include nuclear fuels in future work. (2) As huge quantity of CO 2 have to be disposed of, only the ocean or aquifer might be the ultimate sinks of CO 2. We should further investigate the feasibility and the capacities of CO 2 disposal in the ocean, aquifer, depleted gas well and oil well. (3) We need other efforts such as promoting energy conservation so as to realize a sustainable use of energy resource. Next we would like to integrate energy conservation and the work done here. REFERENCES Donella H Meadows, Dennis L Meadows, Jorgen Randers (1991). Green Publishing Co., p46.
BEYOND THE LIMITS. Chelsea