CO₂ emissions from Iran's power sector and analysis of the influencing factors using the stochastic impacts by regression on population, affluence and technology (STIRPAT) model

ABSTRACT

The current status of CO₂ emissions from Iran's power sector and the socio-economic factors that influence these emissions are fully covered in this paper. To begin, the amount of CO₂ emissions is calculated based on the IPCC guidelines for national GHG inventories. The analysis of socio-economic influencing parameters is performed by the stochastic impacts by regression on population, affluence and technology (STIRPAT) model using population size, gross domestic product (GDP) per capita, electricity intensity and consumption of energy resources for electricity generation. Then CO₂ emissions related to the electricity consumption in six sectors (residential, industrial, public, agriculture, trade and lighting) as well as grid losses and internal electricity consumption of power plants are estimated. Finally, CO₂ emissions from Iran's power sector are compared with their alternatives in Turkey and China. The results indicate that CO₂ emissions increased from 78.778 Tg in 2003 to 149.691 Tg in 2013, and the average CO₂ specific emission factor is 571.29 g/kWh. The outputs of the STIRPAT model illustrate that population size, GDP per capita, electricity intensity and the consumption of fossil fuels for electricity generation positively influence CO₂ emissions, while electricity generation by hydropower, renewable energies and nuclear energy negatively do.

KEYWORDS:

• CO₂ emissions
• electricity generation
• socio-economic parameters
• STIRPAT model

Introduction

Carbon dioxide as the main greenhouse gas is emitted from anthropogenic sources. The main anthropogenic sources which emit CO₂ are thermal power plants consuming fossil fuels (such as coal, natural gas and oil fuel) for electricity generation. Electricity is the most important source of energy in the world and it is used to power homes, businesses and industries [101]. On the other hand, CO₂ emissions from anthropogenic sources (especially fossil-fueled power plants) have led to the global warming phenomenon which has serious effects on people's living environment, and human societies [1]. CO₂ emissions to the atmosphere are responsible for approximately 60% of global warming effects, and thermal power plants emit 29% of the total CO₂ emissions [2].

The CO₂ concentration in the atmosphere has increased from 280 ppm (before the Industrial Revolution) to approximately 400 ppm, and has caused about 75% of the expected 1°C warming [2,3,102]. It is anticipated that by the year 2100, the CO₂ concentration in the atmosphere may reach 570 ppm, causing a rise in global temperature of around 2°C [2,4]. Even a much higher temperature increase of approximately 1.4 to 5.8°C is anticipated [2,5,6,103,104].

In 2012, Iran was introduced by the US Energy Information Administration (EIA) as the eighth country in the world to emit 603.586 Tg CO₂ from anthropogenic sources to the atmosphere [105]. The use of fossil fuels as the main source of electricity generation, the low price of energy and depletion of it as heat, the low thermal energy conversion efficiency to electricity, the electricity losses in the transmission and distribution grids, and the inappropriate usage of renewable energy resources in Iran have led to an increase of CO₂ emissions from Iran's power sector [106,107].

Electricity generation in Iran (between 2003 and 2013) has increased by 74%, from 146.988 to 255.571 TWh [107]. Therefore, the trend of CO₂ emissions from Iran's power sector as a result of increasing consumption of fossil fuels such as natural gas, heavy oil and gas oil for electricity generation is ascending. On the other hand, in 2009 Iran's government established and approved national regulations for the implementation of UNFCCC and the Kyoto protocol. Thus, the control of CO₂ emissions from Iran's power sector as the main responsibility of Iran's governors is an indisputable fact [106]. In this regard, the main objectives of this study are illustrated as follows:

• Estimating the CO₂ emissions from Iran's electricity generation sector between 2003 and 2013 and comparing these results with their alternatives in Turkey as Iran's neighboring country, and China as the largest CO₂ emitter in the world, to learn how these countries have decreased CO₂ emissions from their power plants;

• Studying and analyzing the influence of socio-economic parameters and electricity generation-related factors on CO₂ emissions from Iran's power sectors using the stochastic impacts by regression on population, affluence and technology (STIRPAT) model.

The results of this study have implications of the utmost importance for Iran's decision makers and governors to select the best policies and strategies and establish a roadmap for reducing CO₂ emissions from Iran's electricity generation sector.

Literature review

In recent years, the influence of population, affluence and technology on CO₂ emissions in the different sectors of some countries such as OECD countries and China have been studied in several literatures by scholars using the STIRPAT model. Lin, Zhao, and Marinova [7] studied the effect of population, urbanization level, gross domestic product (GDP) per capita, industrialization level and energy intensity on the country's environment impact with data from 1978 to 2006. Li et al. [8] analyzed the driving forces (including GDP per capita, industrial structure, population, urbanization level and technology level) influencing China's CO₂ emissions. Wei [9] studied the application of STIRPAT to environmental impacts of population and affluence. Martínez-Zarzoso and Maruotti [10] analyzed the impact of urbanization on CO₂ emissions in developing countries from 1975 to 2003. Zhu and Peng [11] investigated the impacts of population size, population structure and consumption level on CO₂ emissions in China from 1978 to 2008. Li et al. [1] divided China's 30 provincial-level administrative units into five emission regions according to the annual average value of provincial CO₂ emissions per capita during 1990 and 2010, and they studied the regional differences in impact factors on CO₂ emissions. Wang et al. [12] studied the influences of urbanization level, economic level, industry proportion, tertiary industry proportion, energy intensity and R&D output on CO₂ emissions in Beijing. Wang et al. [13] examined the impact factors of population, economic level, technology level, urbanization level, industrialization level, service level, energy consumption structure and foreign trade degree on the energy-related CO₂ emissions in Guangdong Province from 1980 to 2010. Shafiei and Salim [14] explored the determinants of CO₂ emissions from OECD countries from 1980 to 2011. Wang and Yang [15] used an improved STIRPAT model to empirically study the influences of urbanization level, economic level, Engel coefficient, energy intensity and industry structure on indirect carbon emissions. León, Arana, and Alemán [16] investigated the relationships between CO₂ emissions and tourism in the context of both developed and less developed countries for the period from 1998 to 2006. Huo et al. [17] conducted an empirical analysis of the impact of social and economic development on CO₂ emissions in Xinjiang province of China from 1958 to 2010. Li, Liu and Li [18] investigated the determinant factors driving CO₂ emissions in Tianjin during the period 1996–2012.

There are few studies that represent the relationship between electricity generation and the associated CO₂ emissions in Iran. Carbon dioxide emissions from different types of Iran's thermal power plants in 2006 were reported in Iran's second National Communication to the UNFCCC. According to this report, total CO₂ emissions from Iran's thermal power plants in 2006 were estimated at 110.21 Tg. Additionally, CO₂ emissions (in 2006) from steam, gas turbine, combined cycle and diesel power plants were reported at 58.11, 32.25, 19.68 and 0.17 Tg, respectively [106].

Nazari et al. [19] reported the emission factor of CO₂ emitted from Iran's thermal power plants over the period 2007 to 2008. This factor was experimentally calculated by considering the operational characteristics of thermal power plants including the electricity generation capacity and fuel types, and the amount and corresponding alterations, stack specifications, analysis of flue gases and physical details of combustion gases. In this study, the CO₂ emission factor was calculated as 620 g/kWh and the total CO₂ emissions from Iran's power sector (in 2008) were found to be 125.34 Tg.

Abbaspour et al. [20] reported on the role of nuclear power in CO₂ emissions reduction from the electricity generation sector in Iran. According to this study, a comparison of different kinds of power plants indicates that nuclear power is not directly emitting greenhouse gases. So, nuclear power plants could be a suitable replacement for the thermal power plants in Iran.

Mazandarani et al. [21] reported CO₂ emissions from Iran's power plants in 2009, and predicted CO₂ emissions until 2025. According to this study, CO₂ emissions were calculated as 118.21 Tg and 252.11 Tg in 2009 and 2025 respectively. Also, CO₂ emissions based on three scenarios (including new composition of power plants, old composition of power plants and fuel switching policy) were estimated at 187.34, 252.11 and 175.21 Tg, respectively.

According to the literature review, there is a literature gap in determining the share and effect of influencing factors such as population size, economic factors, electricity intensity and electricity generation by different resources on CO₂ emissions from Iran's power sector. Also, for the first time, the CO₂ emissions and CO₂ emission factor of Iran's power sector between 2003 and 2013 are reported in this study.

The structure of Iran's power sector

Electricity energy generation

The trend of electricity generation in Iran is ascending. It increased from 146.988 TWh in 2003 to 255.571 TWh in 2013. Combustion of fossil fuels is the main method used for electricity generation (almost 95% of the total electricity generation) in Iran. Natural gas is the largest source of fuel used for electricity generation in Iran. The trend of natural gas consumption for electricity generation in Iran between 2003 and 2013 was descending and it decreased from 75.9% in 2003 to 51.7% in 2013, although it increased to 73.9% in 2008 [107].

The general trend of heavy oil and gas oil consumption for electricity generation in Iran between 2003 and 2013 was ascending, and it increased from 13.2 and 3% in 2003 to 23.3 and 17.5% in 2013, respectively [107]. On the other hand, the trend of hydroelectric power plants to generate electricity in Iran is divided into two periods. First, it increased from 7.9% in 2003 to 9.7% in 2006, after which it decreased (as a result of widespread drought in Iran) from 9% in 2007 to 5.7% in 2013 [107].

The growth rate of renewable energies to generate electricity in Iran between 2003 and 2013 was very slow, reaching from 0.02% in 2003 to 0.08% in 2013, although it had a maximum value in 2009 (0.11%) [107].

The first nuclear power plant, which came online in 2011, generated 0.36 TWh of electricity (0.2% of total electricity generation), 1.86 TWh of electricity (0.8% of total electricity generation) and 4.6 TWh of electricity (1.8% of total electricity generation) in 2011, 2012 and 2013 respectively [105,107].

The total electricity generation and the share of each energy source to generate electric power in Iran between 2003 and 2013 are illustrated in Figure 1 [107].

Figure 1. Electricity generation in Iran's power sector by different sources (between 2003 and 2013) [107].

According to Iran's electricity energy generation perspective in 2025 (named Iran's 20-year perspective), the total capacity of Iran's power plants (including thermal power plants, hydroelectric, renewable energies and nuclear energy) will reach 136.32 GW by 2025, and Iran's power sector will generate up to 713 TWh of electricity in that year [19]. The share of fossil fuels such as natural gas, fuel oil (including heavy oil and gas oil) and coal used for electricity generation will reach 79.4, 6.6 and 2.6%, respectively, by 2025. On the other hand, the share of renewable energies including hydropower and nuclear energy in Iran's electricity generation will reach 6.2 and 5.2%, respectively, by 2025 [19].

Electricity energy consumption

The electric energy generated by Iran's power plants is consumed in six sectors including residential, industrial, agriculture, trade, public and lighting. The trend of the electricity consumption in the four sectors residential, industrial, agriculture and trade is ascending (Figures 2 and 3). The electricity consumption in the residential, industrial, agriculture and trade sectors has increased from 37.91, 36.88, 13.86 and 7.44 TWh (in 2003) to 66.77, 73.3, 35.17 and 13.69 TWh (in 2013), respectively. The growth rate of electricity consumption in the agriculture sector (especially after 2010) is higher than in the other sectors. On the other hand, the trend of electricity consumption in the lighting sector is descending (Figure 3). Electricity consumption in this sector has decreased from 4.7 TWh (in 2003) to 3.79 TWh (in 2013). In the public sector, the trend of electricity consumption is divided into two periods (Figure 3). The first period (from 2003 to 2009) was ascending, and the electricity consumption of this sector increased from 12 TWh to 13 TWh. The second period (from 2009 to 2013) was descending, and the electricity consumption of this sector decreased from 13 TWh to 8.5 TWh. The electricity energy-saving policy in the public sector (from 2009 to 2013) and the lighting sector has the most important implications for reducing electricity consumption in these sectors [107].

Figure 2. Trend of electricity consumption in residential, industrial and agriculture sectors (this study; [107]).

Figure 3. Trend of electricity consumption in public, trade and lighting sectors (this study; [107]).

The trend of grid losses in Iran's power sector is divided into three periods (Figure 4). In the first period, this trend is ascending (from 2003 to 2007) and electricity losses increased from 25.83 to 38.01 TWh. In the second period (from 2007 to 2011), the trend decreased from 38.01 to 33.25 TWh, and in the third period (from 2011 to 2013) electricity consumption increased from 33.25 to 36.53 TWh [107].

Figure 4. Trend of grid losses and internal electricity consumption of power plants (this study; [107]).

The trend of the internal electricity consumption of power plants in Iran's power sector is divided into four periods (Figure 4). In the first period (from 2003 to 2007), the internal electricity consumption of power plants increased from 6.63 to 8.49 TWh. In the second period (from 2007 to 2008), the trend decreased from 8.49 to 7.57 TWh. In the third period (from 2008 to 2010), the electricity consumption rate was approximately constant, and in the fourth period (from 2010 to 2013), electricity consumption increased from 7.74 to 8.42 TWh [107].

Methodology

Carbon dioxide emissions estimation method

In this section, a procedure including four steps to estimate CO₂ emissions from Iran's electricity generation sector and an approach used to determine the carbon dioxide-specific emission factor are illustrated (Figure 5; [22,108]. The methodology used for estimating the quantity of CO₂ emissions from Iran's thermal power plants (based on the IPCC approach) is illustrated by Equation (1)(1) [22,108]: (1)

Figure 5. Computation stages of CO₂ emissions estimation (based on IPCC methodology [108]).

where E is the CO₂ emissions (kg), FC is the fuel consumption (TJ) and EF is the emission factor for each fuel (kg of CO₂/TJ) which are presented in the IPCC guidelines. In this study, the default emission factors for natural gas (56100 kg of CO₂/TJ), heavy oil (77400 kg of CO₂/TJ) and gas oil (74100 kg of CO₂/TJ) are taken [22].

Providing the main data including fuel types (natural gas, heavy oil and gas oil) and the quantities of them for each year (between 2003 and 2013) obtained from Iran's power industry statistics is necessary to estimate CO₂ emissions from Iran's electric power sector. In the first step of the methodology for estimating CO₂ emissions from Iran's power sector, the amount of energy released from the combustion of fuels based on Lower Heating Value (LHV) is calculated using Equation (2)(2) [22]: (2)

where LHV is the fuel low heating value (kJ/kg for liquid fuels and kJ/m for natural gas) and FA is the fuel amount (kg for liquid fuels and m³ for natural gas) [22].

In the second step of CO₂ emissions estimation from Iran's power sector, the emission factors of each fuel type are obtained from the IPCC guidelines for stationary combustion in the energy industry. In these guidelines, the upper, lower and average default emission factors for various types of fuels used in the energy industry are illustrated [22]. In this study, the average amounts of the IPCC emission factors are used for estimating CO₂ emissions from Iran's electricity generation sector.

In the third step of the methodology for estimating CO₂ emissions from Iran's power sector, the fuel consumption is multiplied by the related emission factors (based on the IPCC guidelines) of each fuel type, and the total CO₂ emissions from Iran's electricity generation sector for each year (between 2003 and 2013) are calculated using Equation (3)(3) [22]:(3)

where E_T, i and n are the total CO₂ emissions (kg), the fuel type and the number of fuel types, respectively.

In the fourth step of the methodology, the amount of specific CO₂ emission factors (SEF) of Iran's power sector for each year (between 2003 and 2013) is calculated using Equation (4)(4) . The carbon content of the fuels used for the electricity generation, the efficiency of thermal energy conversion to electricity generation and the share of electricity generation methods such as fossil fuels, renewable energies (including hydropower, wind and solar energy) and nuclear energy have the most important implications for this factor. The SEF is calculated by dividing the amount of associated CO₂ emissions for each year by the amount of the total electricity generation for each year (between 2003 and 2013) [22–24].(4)

where SEF and EG are the specific emission factor (g kWh^–1) and the total electricity generation (kWh), respectively, and j is the year for which CO₂ emissions have been estimated [22].

The average SEF over several years (in this study, between 2003 and 2013) is calculated using Equation (5)(5) [[19]: (5)

The share of CO₂ emissions from Iran's power sector in comparison with Iran's total CO₂ emissions (based on the data obtained from EIA) is calculated by dividing the amount of CO₂ emissions from Iran's electricity generation sector (Iran's thermal power plants) by the amount of Iran's total CO₂ emissions for each year (between 2003 and 2013) [109]. The cumulative CO₂ emissions with respect to fossil fuel consumption for electricity generation and the cumulative CO₂ emissions related to each electricity consumption sector, the grid electricity losses and the power plant's internal electricity consumption are calculated by considering the total CO₂ emissions between 2003 and 2013, total consumption of each fuel type for electricity generation, total electric energy consumption in each sector between 2003 and 2013 and total electricity generation in these years. The share of CO₂ emissions for each year with respect to the consumption of each fuel type and the consumption of electric energy in each sector are estimated by the ratio of CO₂ emissions for each fuel type to total CO₂ emissions, and the ratio of the electric energy consumption for each sector to the total electricity generation [110].

STIRPAT model description

In the early 1970s, Ehrlich and Holdren proposed the model named I = P × A × T (IPAT) for analyzing the proportional impact of human activities on the environment [25; see also 1]. This model has a multiplicative structure and describes the environmental impact (I) of three main elements including population (P), affluence (A) and technology (T). However, this model only estimates the proportionate impact of environmental change by changing one parameter and simultaneously holding the other parameters constant. Therefore, to overcome this limitation, the IPAT model was reformulated into a stochastic model by Dietz and Rosa, and the new model, named stochastic impacts by regression on population, affluence and technology (STIRPAT), can consider the non-proportional impacts of variables on the environment [26]. The STIRPAT model is formulated by Equation (6)(6) [1,7,9–18,26]:(6)

where a is the constant, b, c and d are the coefficients of P, A and T, respectively, and e represents the error term. For the quantitative analysis of sequence data, the logarithmic form of the model is used. This form of the model is illustrated by Equation (7)(7) [1,7,9–18]:(7)

For the comprehensive analysis of the impact of economic and social change on CO₂ emissions from Iran's power sector, the energy resource structure (including natural gas, heavy oil, gas oil and summation of hydropower, renewable energies and nuclear energy) was introduced into the model. Therefore, Equation (7)(7) is reformulated into Equation (8)(8) :(8)

In this study, the variables in Equation (8)(8) are defined as follows: I represents the environmental impact indicated by the total CO₂ emissions (Tg), P represents the population size (million people), A represents GDP per capita (US $), T represents electricity energy intensity indicated by the electricity energy generation per economic output (kWh/$ 2005). NG, HO, GO and SUM represent the electricity generation (TWh) from natural gas, heavy oil, gas oil and the summation of hydropower, renewable energies and nuclear energy, respectively. The terms f, g, h and j are the coefficients of parameters NG (the electricity generation related to natural gas consumption), HO (the electricity generation related to heavy oil consumption), GO (the electricity generation related to gas oil consumption) and SUM (summation of the electricity generation by hydropower, renewable energies and nuclear energy), respectively. After building the STIRPAT model, partial least squares (PLS) regression is used to fit the model. This type of regression has much better outputs than the classical regression type, especially when the number of variables is higher and multiple correlation exists among variables while the number of monitoring data is lower [8,15].

Data source

Data used in this study are given from international and national references such as the US EIA, IPCC, World Bank, Tavanir holding company and Statistical Center of Iran. EIA has represented Iran's total CO₂ emissions [105]. CO₂ emission factors based on kg of CO₂ gas per thermal energy input of power plants (for calculation of CO₂ emissions estimation from Iran's power sector) are obtained by the IPCC guidelines [108]. Iran's annual GDP and Iran's population size are obtained by World Bank data and the Statistical Center of Iran respectively [111,112]. The electricity generation (including fossil-fueled electricity generation, hydropower, renewable energies and nuclear energy), power plants' internal electricity consumption, grid losses, electricity consumption (in the six sectors including residential, industrial, public, agriculture, trade and lighting) and consumption of each fuel type are obtained by Iran's statistical reports on the electric power industry [107].

Results

Carbon dioxide emissions from Iran's power sector

The CO₂ emissions from Iran's electricity generation sector have been calculated according to the IPCC methodology. The trend of CO₂ emissions from Iran's power sector (between 2003 and 2013) is ascending, and it increased from 78.778 Tg in 2003 to 149.691 Tg in 2013. The growth rate of CO₂ emissions from Iran's power sector is constant (approximately 7.095 Tg/year). The other amounts of CO₂ emissions from Iran's power sector in comparison with Iran's total CO₂ emissions have been illustrated in Figure 6.

Figure 6. CO₂ emissions from Iran's power sector in comparison with Iran's total emissions (this study; [105]). EIA: US Energy Information Administration.

The share of CO₂ emissions from Iran's total CO₂ emissions (based on the EIA database) has two maximums, in 2008 as a result of decreasing the electricity generation by hydroelectric power plants and in 2013 as a result of increasing the electricity generation by fuel oil (including heavy oil and gas oil). Therefore, the trend of this share is divided into two periods. In the first period (from 2003 to 2007) it increased from 20.33 to 22.34%, and in the second period (from 2009 to 2012) it increased from 22.33 to 23.55%. The average share of CO₂ emissions from Iran's total CO₂ emissions (between 2003 and 2013) is estimated at 22.47%.

According to Figure 7, the trend of SEF is divided into two periods. In the first period (from 2003 to 2007), the average SEF is calculated at 546.37 g/kWh and in the second period (from 2008 to 2013), this factor is estimated at 586.87 g/kWh. In the first period (from 2003 to 2007), the average shares of heavy oil, gas oil, natural gas, hydropower and renewable energies used for the electricity generation were 14.97, 5.49, 70.99, 8.51 and 0.04%, respectively. In this period, the share of nuclear energy for electricity generation was zero. On the other hand, in the second period (from 2008 to 2013), the average shares of heavy oil, gas oil, natural gas, hydropower, renewable energies and nuclear energy used for electricity generation were 19.25, 11.35, 64.54, 4.32, 0.09 and 0.45%, respectively [107]. In the first period (from 2003 to 2007), the average efficiency of converting the thermal energy to the electric energy is equal to 36.34%, and in the second period (from 2007 to 2013), it is equal to 36.62% [107]. The difference between the electrical efficiency of the two periods is negligible. In the second period, the increase in consumption of heavy oil and gas oil, which have high carbon content, and the decrease in consumption of natural gas, which has low carbon content in comparison with fuel oil, as well as the decrease in electricity generation by hydropower power plants led to increasing the SEF.

Figure 7. Specific CO₂ emission factor in Iran's power sector (this study).

According to Figure 8, the cumulative CO₂ emissions (between 2003 and 2013) are calculated as 1281.76 Tg, and the amounts of CO₂ emissions related to natural gas, heavy oil and gas oil are estimated as 908.772, 244.205 and 128.783 Tg, respectively. The high share of natural gas between these years (approximately 67.47%) led to increasing CO₂ emissions from this source in Iran's power sector. The share of CO₂ emissions with respect to the consumption of fossil fuels in Iran's power sector between 2003 and 2013 is illustrated in Figure 9. According to this figure, the share of natural gas from CO₂ emissions in Iran's power sector has decreased (as a result of decreasing natural gas consumption in Iran's thermal power plants) from 82.46% in 2003 to 55.87% in 2013. On the other hand, the share of heavy oil and gas oil from CO₂ emissions in Iran's power sector have increased (as a result of increasing heavy oil and gas oil consumption in Iran's thermal power plants) from 14.31 and 3.23% in 2003 to 25.22 and 18.91% in 2013, respectively.

Figure 8. Cumulative CO₂ emissions with respect to fossil fuels consumption for electricity generation in Iran (this study).

Figure 9. Share of CO₂ emissions with respect to fossil fuels consumption for electricity generation in Iran (this study).

The cumulative CO₂ emissions (between 2003 and 2013) with respect to the electricity consumption in the six sectors residential, industrial, public, agriculture, trade and lighting, as well as the electricity losses in the transmission and distribution grid and the internal electricity consumption of power plants, are illustrated in Figure 10. Residential and industrial sectors with high electricity consumption (65.69%) account for the highest amounts of CO₂ emissions. On the other hand, the lighting sector and the internal electricity consumption of power plants account for the lowest amounts of CO₂ emissions. Carbon dioxide emissions related to residential, industrial, public, agriculture, trade and lighting, as well as electricity losses in the transmission and distribution grids and the internal electricity consumption of power plants, are calculated at 332.207, 339.734, 114.627, 141.844, 67.293, 26.074, 211.781 and 48.202 Tg, respectively. The share of CO₂ emissions with respect to the electric energy consumption (between 2003 and 2013) in the six sectors, electricity losses in the grids and the internal electricity consumption of power plants are illustrated in Figure 11. According to this figure, the average share of CO₂ emissions with respect to the electricity consumption in the six sectors residential, industrial, public, agriculture, trade and lighting, as well as electricity losses in the transmission and distribution grid and the internal electricity consumption of power plants (between 2003 and 2013), is estimated at 25.88, 26.26, 9.07, 10.79, 5.21, 2.15, 16.08 and 3.84%, respectively. The trend of the electricity consumption or losses has the most important implications for the share of CO₂ emissions in these sectors. The general trend of the lighting sector, public sector, grid losses and power plants' internal consumption with respect to CO₂ emissions as a result of the electric energy saving policy in these sectors is descending. On the other hand, the general trend of the agriculture and industrial sectors with respect to CO₂ emissions is ascending. The general tend of the trade and residential sectors with respect to CO₂ emissions is approximately constant.

Figure 10. Cumulative CO₂ emissions with respect to the electric energy consumption in Iran (this study).

Figure 11. Share of CO₂ emissions with respect to the electric energy consumption in Iran (this study).

Results of the STIRPAT model

The coefficients of the STIRPAT model illustrated by Equation (8)(8) are calculated using PLS regression. These coefficients are illustrated in Table 1. The results indicate that population size, GDP per capita, electricity intensity and the electricity generation by fossil fuels including natural gas, heavy oil and gas oil have positive implications for CO₂ emissions from Iran's power sectors. On the other hand, the electricity generation by hydroelectric, renewable energies and nuclear energy has a negative implication for CO₂ emissions from Iran's electricity generation sectors. Population size has a distinctive influence on CO₂ emissions from Iran's power sector. Every 1% increase in population scale led to a 1.834% increase in CO₂ emissions. Increasing the number of households and urbanization as a result of increasing population size in Iran has led to increasing the electric energy demand and subsequently to increasing CO₂ emissions from Iran's power sector [13]. The trend of the number of households in Iran between 2006 and 2013 is ascending, from 17.502 million households (including 12.406 million households in urban areas) in 2006 to 22.898 million households (including 16.841 million households in urban areas) in 2013 [112]. The average urbanization in Iran between 2003 and 2013 was 69.58% and the trend of it is ascending, from 66.6% in 2003 to 72% in 2013 [112].

Table 1. Coefficients of STIRPAT model calculated using partial least squares regression (this study).

Variables	Coefficients
Constant	−5.135
Population	1.834
Gross domestic product per capita	0.036
Electricity intensity	0.042
Electricity generation by natural gas	0.223
Electricity generation by heavy oil	0.158
Electricity generation by gas oil	0.074
Electricity generation by hydroelectric, renewable energies and nuclear energy	−0.041
R^2	0.999

The implications of GDP per capita and electricity intensity for CO₂ emissions from Iran's power sector are approximately equal. Every 1% increase in GDP per capita and electricity intensity has led to 0.0365% and 0.042% in CO₂ emissions from Iran's electricity generation sector, respectively. Iran's GDP per capita between 2003 and 2011 as a result of increasing Iran's oil price is ascending from $1976 to $7006, respectively. On the other hand, this parameter between 2011 and 2013, as a result of Iran sanctions related to the Iranian nuclear program, is descending, from $7006 to $3475, respectively [111,112]. Electricity intensity in Iran between 2003 and 2011 descended from 1.04 kWh/$ 2005 to 0.44 kWh/$ 2005, and this parameter ascended between 2011 and 2013 from 0.44 kWh/$ 2005 to 0.69 kWh/$ 2005.

In Figure 12, the trend of CO₂ emissions from Iran's power sector, population, GDP per capita and electricity intensity is illustrated. According to this figure, the upturn of GDP per capita in Iran between 2006 and 2011 as a result of increasing Iran's oil price, and the downturn of it after 2011 as a result of Iran sanctions, are depicted. The general trend of electricity intensity between 2006 and 2011 as a result of the upturn of GDP per capita is descending. On the other hand, this trend between 2011 and 2013 as result of the downturn of GDP per capita is ascending. These results indicate that electricity intensity in Iran between 2003 and 2013 is controlled by GDP per capita and the implication of the electric energy saving for it is very negligible. Therefore, the parameters related to affluence (GDP per capita) and technology (electricity intensity) in the STIRPAT model have counterbalanced each other's effect, and Iran sanctions do not have any implications for the CO₂ emissions trend in Iran's power sector.

Figure 12. Trend of CO₂ emissions in comparison with population size, gross domestic product per capita and electricity intensity (this study; [107,111,112]).

The electricity generation by fossil fuels including natural gas, heavy oil and gas oil has a positive influence on CO₂ emissions from Iran's power sector. On the other hand, the electricity generation by hydropower, renewable energies and nuclear energy has a negative implication for these emissions. Every 1% increase in electricity generation by natural gas, heavy oil, gas oil and the summation of hydropower, renewable energies and nuclear energy has led to 0.223, 0.158, 0.074 and –0.041% of CO₂ emissions from Iran's electricity generation sector, respectively.

In Figure 13, the trend of CO₂ emissions from Iran's power sector, the electricity generation by natural gas, heavy oil and gas oil and the summation of hydropower, renewable energies and nuclear energy are illustrated. According to this figure, the general trend of the electricity generation (between 2003 and 2013) by fuel oils including heavy oil and gas oil (except 2012), as a result of decreasing natural gas production in Iran and increasing natural gas consumption in the household sector, is ascending [105,107]. On the other hand, the general trend of electricity generation by natural gas between 2003 and 2010 is approximately constant, and this trend became a descending one between 2010 and 2013. The general trend of the electricity generation by hydroelectric, renewable energies and nuclear energy is divided into three periods. In the first period (from 2003 to 2007), this trend was ascending, as a result of the upturn of the electricity generation by hydroelectric power stations. In the second period (from 2007 to 2008) this trend, as result of the downturn of the electricity generation by hydropower power plants, was descending, and in the third period (from 2008 to 2013), this trend was ascending, as a result of the gradually increasing of the electricity generation by theses power plants [107].

Figure 13. Trend of CO₂ emissions in comparison with electricity generation by natural gas, heavy oil, gas oil and summation of hydropower, renewable energies and nuclear energy (this study; [107]).

Comparison of carbon dioxide emissions from Iran's power sector with their alternatives in Turkey and China

Turkey's net electricity generation was 228 TWh in 2012. Turkey's electricity demand grew approximately more than 90% from 2001 to 2011. Much of this growth occurred between 2002 and 2008 [113,114]. Fossil fuel and hydropower account for approximately all of Turkey's electricity. Fossil fuel sources have historically been the main and the largest power source in this country. Natural gas consumption for electricity generation increased significantly in the past decade, and it reached 43% of total electricity generation in 2012 [113,114]. Turkey's government plans to decrease the share of natural gas consumption for electricity generation, replacing it with other sources including nuclear energy and coal. Increasing the share of renewable energies to 30% of its electricity generation by 2023, installing 20 GW of wind turbines and installing 600 MW of geothermal power plants are the most important future programs of Turkey's government. Although Turkey does not have any nuclear power plants, the government has been planning to construct two nuclear power plants in order to generate at least 5% of its electricity generation by 2023 [113,114]. The shares of natural gas, fuel oils, lignite, coal, hydropower, wind and geothermal in 2011 for electricity generation in Turkey were 44.71, 1.67, 16.9, 10.99, 22.8, 2.64 and 0.29%, respectively [113,114]. The trend of CO₂ emissions from Turkey's power sector is divided into three periods. In the first period (from 2003 to 2008), this trend is ascending, from 63.411 to 101.382 Tg. In the second period (from 2008 to 2010), this trend, as a result of the economic slowdown, descended from 101.382 to 97.152 Tg, and in the third period (from 2010 to 2011), this trend is ascending, from 97.152 to 108.277 Tg. The average SEF and CO₂ intensity in Turkey have been reported as 469.08 g/kWh and 0.15 kg/US$, respectively (Table 2). These factors are approximately 100 g/kWh and 0.21 kg/US$ lower than those of Iran's power sector (571.29 g/kWh and 0.36 kg/US$) [114,115]. The use of technical efficiency improvements in procedures in the existing power plants, the development of clean coal technology such as circulating fluidized bed combustion (CFBC) for power generation, the construction of nuclear power plants, managing the demand side electricity consumption, expanding the use of cogeneration of heat and power in the industrial sector, constraining the gas supply combined with the use of new sub-critical and super-critical coal-fired power stations, expanding the use of renewable energies for electricity generation, and carbon tax are the most important Turkish government policies to reduce CO₂ emissions from its power sector. Using renewable energies and energy efficiency improvement projects have the most important implications for CO₂ emissions reduction in Turkey, by more than 3 million tons per annum [116,117].

Table 2. The average specific carbon dioxide emission factor and carbon dioxide intensity in Iran's power sector in comparison with their alternatives in Turkey and China (this study; [119]).

Country	Average electricity generation (TWh)	Average of specific emission factor (g/kWh)	CO2 intensity (kg/US$ 2005)
Iran (2003 to 2013)	203.97	571.29	0.36
Turkey (2003 to 2011)	183.89	469.08	0.15
China (2003 to 2011)	3213.42	811.34	0.67

According to an EIA report, China's net power generation was approximately 4476 TWh in 2011 [118]. Electricity generation in this country has increased by more than 89% since 2005, and the total net electricity generation will increase to 7295 TWh by 2020 and 11595 TWh by 2040 [118]. The Chinese government plans to generate more electricity based on nuclear energy, other renewable sources and natural gas. These programs will lead to reducing carbon emissions and air pollution in urban areas. Fossil fuels, primarily coal, generate approximately 80% of electricity [118]. Coal is expected to remain the main fuel in China's power sector in future years, while natural gas will be set to increase and replace some of the coal consumption for electricity generation in the southeastern and coastal regions where electricity demand is higher [118]. Oil consumption for electricity generation is expected to remain very low in the next two decades. In 2011, China's power sector generated approximately 3596 TWh from fossil fuel sources (approximately 17% higher than in 2010). China's nuclear power plants generated 83 TWh in 2011(2% of total net generation). Although nuclear generation represents a small portion of total power generation, China's government is actively expanding nuclear energy as a clean, efficient and certain source of power generation [118]. Hydropower power plants have become the dominant source of renewable energy for electricity generation in China (because of their reliable cost-effectiveness and sizeable resource potential). China, as the world's largest producer of hydroelectricity, generated 687 TWh in 2011 (15% of the country's total electricity generation). The severe drought (especially in the southwestern region) in 2010 led to a decrease in electricity generation from hydropower power stations [118]. In 2011, China, as the world's second largest wind producer, generated 73 TWh (approximately 64% higher than in 2010). China's installed wind turbine capacity was 61 GW in 2012 (and it has almost doubled each year since 2005) [118]. The shares of coal, fuel oils, natural gas, hydropower, renewable energies and nuclear energy in 2011 for electricity generation in China were reported as 78.95, 0.21, 1.78, 14.92, 2.21 and 1.83%, respectively [118]. The trend of CO₂ emissions from China's power sector is ascending, from 1639.402 Tg in 2003 to 3602.795 Tg in 2011 [119]. The average SEF and CO₂ intensity in China were reported as 811.34 g/kWh and 0.67 kg/US$, respectively (Table 2). These factors are approximately 240 g/kWh and 0.31 kg/US$ higher than those of Iran's power sector (571.29 g/kWh and 0.36 kg/US$) [111,119]. China's government has policies in place to reduce CO₂ intensity by 40 to 45% by 2020 from the 2005 levels. Furthermore, China's government has carried out a series of new actions to deal with climate change policy since 2012. These actions include the first national low-carbon day and a carbon exchange pilot project [120].

Policy options for reducing carbon dioxide emissions from Iran's power sector

According to the results of this study, the mixture of sources such as natural gas, heavy oil, gas oil, hydropower, renewable energies and nuclear energy used for electricity generation has the most important effects on the differences depicted between the share of CO₂ emissions from Iran's power sector between 2003 and 2013. Therefore, using low-carbon sources for electricity generation has led to reducing CO₂ emissions from Iran's power sector.

Three parameters, including the carbon content of the fuels consumed for the electricity generation, the mixture of sources such as fossil fuels, hydropower, renewable energies and nuclear energy used for electricity generation and the efficiency of converting thermal energy to electric energy have the most important implications for the SEF [19]. The results of this study verify those of previous study [19] and illustrate that the mixture of sources used for electricity generation has the most important implications for SEF in Iran's power sector.

After reviewing the CO₂ emissions reduction programs, plans and road maps in China, Turkey and other developed countries such as the USA [27,28,113,116–118,120] as well as the results of this study, using the following policies and strategies are indispensable for reducing CO₂ emissions from Iran's power sector:

• Retrofitting and increasing the efficiency in existing power plants as well as expanding the installation of cogeneration of heat and power (CHP) units near the power stations;

• Using renewable energies and hydroelectric potential for electricity generation;

• Establishing the mechanisms related to CO₂ emissions tax and trade;

• Decreasing electricity consumption, especially in residential, agriculture and industrial sectors, as well as reducing electricity losses in the grids;

• Investing in CO₂ emissions control technologies and promoting thermal power plants to install mature technologies for CO₂ capture and utilization.

Conclusion

In this paper, CO₂ emissions from Iran's power sector (between 2003 and 2013) have been estimated using the IPCC methodology. Additionally, the impact of population size, GDP per capita, electricity intensity and the consumption of energy resources (natural gas, heavy oil, gas oil, hydropower, renewable energies and nuclear energy) for electricity generation in Iran's power sector have been analyzed, using the STIRPAT model. The following conclusions are illustrated:

• The trend of CO₂ emissions from Iran's power sector is ascending, and the amount of these emissions over 10 years grew two times in comparison with the year 2003 (78.778 Tg);

• The average share of CO₂ emissions from Iran's total CO₂ emissions was estimated at 22.47%;

• The average specific CO₂ emission factor in the first period (between 2003 and 2007) was calculated at 546.37 g/kWh, and in the second period (between 2008 and 2013) it was assessed as 586.87 g/kWh;

• The amount of cumulative CO₂ emissions related to natural gas, heavy oil and gas oil were estimated at 908.772, 244.205 and 128.783 Tg, respectively;

• The amounts of cumulative CO₂ emissions related to residential, industrial, public, agriculture, trade and lighting, as well as electricity losses in the transmission and distribution grids and the internal electricity consumption of power plants, were assessed at 332.207, 339.734, 114.627, 41.844, 67.293, 26.074, 211.781 and 48.202 Tg, respectively;

• Population size has the most important positive effect on CO₂ emissions from Iran's power sector, and the summation of hydropower, renewable energies and nuclear energy has an inhibiting effect on CO₂ emissions;

• The effects of affluence and technology on CO₂ emissions are approximately equal, and these factors counterbalance each other. Therefore, Iran sanctions related to Iran's nuclear programs have no implications for the CO₂ emissions trend in Iran's power sector;

• Every 1% increase in population scale, GDP per capita, electricity intensity, electricity generation by natural gas, heavy oil, gas oil and the summation of hydropower, renewable energies and nuclear energy has led to 1.834, 0.0365, 0.042, 0.223, 0.158, 0.074 and –0.041% in CO₂ emissions, respectively.