Current and Future Greenhouse Gas Emissions Associated with

May 22, 2014 - China's oil imports and greenhouse gas (GHG) emissions have grown rapidly over the past decade. Addressing energy security and GHG emis...
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Current and Future Greenhouse Gas Emissions Associated with Electricity Generation in China: Implications for Electric Vehicles Wei Shen,*,† Weijian Han,‡ and Timothy J. Wallington‡ †

Asia Pacific Research, Ford Motor Company, Unit 4901, Tower C, Beijing Yintai Center, No. 2 Jianguomenwai Street, Beijing 100022, China ‡ Research and Advanced Engineering, Ford Motor Company, Village Road, Dearborn, Michigan 48121, United States S Supporting Information *

ABSTRACT: China’s oil imports and greenhouse gas (GHG) emissions have grown rapidly over the past decade. Addressing energy security and GHG emissions is a national priority. Replacing conventional vehicles with electric vehicles (EVs) offers a potential solution to both issues. While the reduction in petroleum use and hence the energy security benefits of switching to EVs are obvious, the GHG benefits are less obvious. We examine the current Chinese electric grid and its evolution and discuss the implications for EVs. China’s electric grid will be dominated by coal for the next few decades. In 2015 in Beijing, Shanghai, and Guangzhou, EVs will need to use less than 14, 19, and 23 kWh/100 km, respectively, to match the 183 gCO2/km WTW emissions for energy saving vehicles. In 2020, in Beijing, Shanghai, and Guangzhou EVs will need to use less than 13, 18, and 20 kWh/100 km, respectively, to match the 137 gCO2/km WTW emissions for energy saving vehicles. EVs currently demonstrated in China use 24−32 kWh/ 100 km. Electrification will reduce petroleum imports; however, it will be very challenging for EVs to contribute to government targets for GHGs emissions reduction.

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INTRODUCTION Vehicle sales in China set a new record of 19.3 million units in 2012. China has been the world’s largest auto market for the past four years. China’s on-road vehicle fleet reached 109 million1 and consumed more than 150 million tonnes of gasoline and diesel in 2012.2 A total of 476 million tonnes of crude oil were used in China in 2012 and 57% of this was imported.1 It is projected that China’s vehicle population will be 530−623 million in 2050.3 To fuel such a large number of vehicles, China faces significant challenges in energy security. At the same time, China is the largest carbon dioxide (CO2) emitter in the world and contributed 26% of the world’s total CO2 emissions from fuel combustion in 2011.4 At the United Nations Climate Change Summit in 2009 the Chinese government comitted to reducing the carbon intensity per GDP in 2020 by 40%−45% from 2005 levels. Vehicle electrification is viewed by the Chinese government as an effective option to address both energy security and GHG reduction goals. In 2009 the government launched a “newenergy vehicle” (NEV) program where the viability of plug-in hybrid vehicles (PHEVs), battery electric vehicles (BEVs) and fuel cell vehicles (FCVs) could be demonstrated. The program extended to 25 cities with 27 000 NEVs, including 4400 private vehicles, by the end of 2012.5 In June 2012, the State Council approved the “Energy Saving and New Energy Vehicle Industry Development Plan (2012−2020)”. According to the plan, sales © 2014 American Chemical Society

of PHEVs and BEVs will reach a half million units by 2015 and 5 million units by 2020. The fuel consumption target of “Energy Saving Cars” and the average of new passenger cars included in the plan are shown in Table 1. From the fuel consumption target we calculated the WTW GHG emissions for a gasoline energy saving car. We note that irrespective of their WTW emissions, BEVs are not powered by petroleum and hence qualify as new energy vehicles under the regulations. Table 1. Government’s Fuel Consumption Target and Related WTW CO2 Emission of Passenger Cars fuel consumption (liter/100km)

WTW CO2 emission of cars powered by gasoline (g/km)

5.9

183

4.5

137

5.0

156

energy saving car, model year (MY) 2015 energy saving car, MY2020 average of new car fleet in 2020

Received: Revised: Accepted: Published: 7069

May May May May

23, 19, 22, 22,

2013 2014 2014 2014

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Table 2. Energy Consumption of Coal-Fired Power Generation Technologies (MJ/kWh) average best case in the energy use survey worst case in the energy use survey sample size in the survey (units) share of chinese total coal-fired power capacity

HP

VHP 135−150MW

VHP 200MW

SubC 300MW

SubC 600MW

SC

USC

12.2 11.9 12.9 39 10%

10.9 9.8 11.6 27 8%

10.7 9.6 11.3 61 7%

9.8 8.9 10.7 400 36%

9.4 8.9 10.2 113 13%

9.1 8.7 9.4 143 20%

8.5 8.2 9.2 52 6%

ultrasuper critical (USC) based on parameters of boilers and turbines. The temperature, pressure and introduction year for these technologies are listed in SI Table S1. We collected operating data for 835 coal-fired units. The average efficiencies of different technologies are shown in Table 2.14,16,17 The capacity factor (CF), which cannot be controlled by the power plant operators, has a substantial influence on the efficiency. Studies have shown that the coal consumption rate is higher than the design value when the capacity factor is less than 75% reflecting higher turbine heat loss and service power rate and lower boiler efficiency.18−20 The average CF of Chinese coalfired units was 55% in 2012, a little lower than that of 2011.14 To reduce air pollution in large cities, new coal-fired power plants are built in remote locations. Electricity is transmitted long distances to urban customers. Data released by the China Electricity Council (CEC) show that in 2012 there was a 6.6% loss of electricity during long distance transmission; comparable to US rates for 2007.14 Coal Mining, Processing and Transportation. Subsurface coal mining dominates the industry, accounting for 95% of coal extraction. Mining one tonne of coal consumes 34 kWh electricity and 27 kg raw coal.21 About 21% of the coal produced in China was cleaned and sorted in 2011.15 Electricity consumed was 3 kWh per tonne of coal cleaned and sorted. There is about 10% of gangue eliminated during the process and the total energy efficiency is approximately 95%.21 Key parameters and additional description of long-distance transportation are given in SI Table S2. Natural Gas (NG) and Oil Fired Power Generation. China is planning to increase annual NG consumption in the next five years to 250 billion cubic meters, more than double the current level. In 2011 NG used for power generation accounted for 17% of overall NG consumption.15 Increased use of NG for electricity generation in large cities is part of an ambitious plan to improve air quality in North and East China.22 The total capacity of NG-fired power generation in China was 38 GW in 2012.14 Among 119 NG-fired power plants we surveyed nationwide, 46 units were 180 MW natural gas combined cycle (NGCC) and 64 units were 390 MW NGCC, accounting for 98% of gas-fired capacity in China. The efficiencies of 180 MW and 390 MW NGCC plant could reach 50% and 55%, respectively. Statistical data show that the CF for most Chinese gas-fired units was only in the range 30−50% in recent years.23 The average CF of gas-fired units nationwide was only 36% in 2012.14 It has been reported that the power supply efficiency is reduced from 51% to 42% when CF declines from 100% to 45% and efficiency falls to 40% when CF drops to 30%.24,25 Oil-fired power has decreased greatly over the past two decades from 7.0% in the 1990s to less than 0.5% in 2012.14 Increased oil price and government policy to shut down small generation units have resulted in the existing oil-fired units now being generally used as backup power source for large enterprises and most do not connect to the grid.26

For the Chinese government, one of the key reasons for BEV promotion is GHG reduction.6,7 Although BEVs do not use gasoline or diesel and have zero emission of GHG in operation, the electricity they consume is primarily generated from coalfired power plants with high GHG emissions. It is essential to consider the GHG emissions associated with BEVs using a life cycle perspective. Recent studies have shown that GHG emissions of BEVs are related to regional electricity mix coming from different power sources.8−10 There are a variety of power generation technologies used in China which are not fully discussed in previous studies. The mixes of generation technologies vary significantly in the different regions and as a result there are large differences in the well-to-wheels (WTW) GHG emissions of BEVs in the different regions. The objective of this study is to provide an up-to-date (2012) assessment of the GHG emissions associated with electricity generation in different regions in China, project the future emissions for selected regions, and assess the implications for the future use of electric vehicles. A key contribution of the present work is a careful and detailed accounting of the different technologies in each grid which is not well documented in the literature. WTW analyses of BEVs, internal combustion engine vehicles (ICEV), and hybrid electric vehicles (HEV) were conducted using a version of the GREET (greenhouse gases, regulated emissions, and energy use in transportation) model11 which has been modified for use in China.12 The scope of the present analysis is energy consumption and GHG emissions in the fuel cycle, including feedstock recovery, processing, transportation and storage, fuel production, transportation, storage and distribution, and vehicle operation. Vehicle manufacturing and infrastructure construction are not covered within the scope of a WTW study. GHG emissions are expressed in terms of grams CO2-equivalent (gCO2e). The “equivalence” is based on global warming potentials of 25 for methane (CH4) and 298 for nitrous oxide (N2O) provided by the Intergovernmental Panel on Climate Change.13 The present work is the first to take the practical step of translating the future WTW gCO2 e /km “energy saving car” targets into kWh/100 km BEV energy efficiency targets for different regions in China.

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GHG BURDEN OF ELECTRICITY GENERATION

Coal-Fired Power Generation. As part of its strategy of “energy saving and emission reduction”, the Chinese government began to promote “green electricity” in its 11th five-year plan (2006−2010). The proportion of electricity generated from fossil fuels has declined modestly over the past 6 years, as shown in Supporting Information (SI) Figure S1. Half of China’s coal consumption was used to generate 76% of the nation’s electricity in 2012.14,15 Coal-fired power in China comes primarily from conventional pulverized coal-fired power plants. These pulverized coalfired units can be classified as high pressure (HP), very high pressure (VHP), subcritical (SubC), supercritical (SC), and 7070

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Figure 1. Electricity consumption mix in 2012 in different grids. The size of the pies is proportional to the absolute electricity consumption. The gray shading shows coal-fired plants which are broken down by technology type in the stack bars.

Petroleum and NG Recovery, Processing, and Transportation. Our previous study examined a large amount of data of more than 50 process technologies used in excavation and pretreatment processes of petroleum and gas from 14 major oil fields in China. The results show that the average energy efficiency of Chinese NG recovery and processing is similar to the latest European (EU) estimate and the energy use of domestic oil extraction is double or even triple that for the EU.12,27 According to our survey in four Chinese oil refineries with 10 million tonnes capacity each, the energy efficiencies of gasoline and diesel refining are 87% and 89%, respectively,12 a little lower than those reported in U.S. and EU.27,28 The majority of NG-fired power plants are located in southeast coastal areas to which NG is delivered either by long distance pipeline from west China, or by LNG ocean tanker. Energy efficiency for NG liquefaction is generally 85−93%.29−31 NG, crude oil and fuel transportation and distribution parameters are shown in SI Table S3 and S4. Renewable and Nuclear Power Generation. Hydropower is the second largest source of China’s electricity after coal. The construction of dams (including the production of building materials, such as steel and cement) leads to emission of CO2. As mentioned above, the fuel-cycle does not cover infrastructure development and related process and the associated GHG emissions are not included in WTW analyses. However, the CH4 and CO2 emission from the reservoir during the operation of hydropower station should be included. Following flooding of landscapes to create reservoirs, terrestrial plants die under the water surface. With the action of anaerobic bacteria, the organic carbon that was stored in plants and soils

is converted to CO2 and CH4, which are then released to the atmosphere. Organic material transported from upstream and into the reservoir, accounted for a significant part of the gases formed in the reservoir.32,33 The dam construction converts flowing, turbulent water to still water, which provides a suitable environment for methanogenesis. A review of 167 hydropower stations around the world found that GHG emissions differ greatly from site to site. The average GHG emission was 42 gCO2e/kWh; there were 14 reservoirs with emissions higher than 100 gCO2e/kWh and 1 reservoir with an emission higher than 1000 gCO2e/kWh.34 Direct GHG emissions of 12−2077 gCO2e/kWh have been reported for reservoirs in South America.35 Using static floating chamber technology, researchers measured fluxes of CH4 and CO2 from reservoirs in Southern China and evaluated GHG emissions of 73 large/ medium (capacity ≥25MW) and five small hydropower stations. The average GHG emissions of large/medium and small hydropower stations are 7.6 gCO2e/kWh and 180.3 gCO2e/kWh, respectively.36 According to Ministry of Water Resource, China’s small hydropower capacity was 28% of total hydropower capacity through the end of 2009.37 Electricity generated from biomass (agricultural residue, municipal waste, woody biomass, etc.) is regarded as “green electricity” in China but its development is not a priority. Feedstock collection is a large and expensive challenge for biopower plants as most of Chinese agriculture are small holdings. Because of heavy financial losses, a 5.5MW biomass IGCC (B/IGCC) demo plant was closed in 2007.38 B/IGCC will probably not play an important role in China because of unfavorable economics. Existing biopower plants in China use 7071

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Figure 2. Current (2012) and future (2020) electricity mix for three selected regions. The size of the pies is proportional to the absolute electricity consumption. The gray shading shows coal-fired plants which are broken down by technology type in the stack bars.

Northwest grids. The share of hydropower consumption is 23−36% in these three grids. Most of China’s windpower is generated and used in the northern regions. The South and East grids have roughly 4% nuclear power and 4−6% NG-fired power. Electricity Mix in 2020. Considering the limited data availability of power development plans, we choose three most important cities (and city groups) to illustrate the development of clean electricity in different regions: Beijing, Shanghai and the group of cities in the Pearl River Delta (Guangzhou, Shenzhen, Zhuhai, Foshan, Zhongshan, Dongguan, Jiangmen, Huizhou, and Zhaoqing). Guangzhou and Shenzhen are NEV demonstration cities, for convenience we will use Guangzhou as the example of a Pearl River Delta city. We chose these three regions because they are very important to the economy, have high population and vehicle densities, and contain several NEV demonstration cities. Figure 2 shows the current (2012) and projected future (2020) mixes in the three regions. Details of the GHG burdens for the different grids are given in the SI. For Beijing, in 2012 coal-fired power dominated the mix with roughly 55% of electricity transmitted from coal-fired power plants in west Inner Mongolia and Shanxi provinces (inside North grid). Another 15% was supplied by the Northeast grid. Only approximately one-third of electricity consumed in Beijing came from local power plants. To reduce air pollution, particularly PM2.5, all of the coal-fired power plants in Beijing will be replaced by NG-fired before 2018.22 The NG-fired electricity will reach one-third of the mix by 2020. Based on information from CEC, more than 40 USC and SC plants will be built in Inner Mongolia and Shanxi provinces by 2020 and in addition two nuclear power plants with a combined capacity of 6 GW are under construction in the Northeast grid. For Shanghai, hydropower (13% and 21% of the mix in 2012 and 2020) mainly comes from the upstream Yangtze River in the Central grid. Meanwhile, Shanghai imports nuclear power from Zhejiang province and coal-fired power from Anhui province (through a dedicated ultrahigh voltage line). There will be four new nuclear power units in Zhejiang and more than 20 new SC/USC coal-fired units in Anhui by 2020. NG-fired

either direct biomass combustion or cofiring (with coal) technologies, these will be the mainstream technologies for biopower in China through at least 2020. The power supply efficiencies (defined as electricity leaving the plant divided by primary energy used) of power plants with direct combustion technology was about 16−20%. This low efficiency reflects the small scale and relatively inefficient boilers used and the need for biomass collection over a collection radius of 100−200 km by diesel trucks.38,39 Pretreatment of the biomass is needed before combustion in boilers and the energy used for pretreatment is about 40 kWh per tonne.40 There are 16 nuclear power plants, with 40 GW capacity, under construction. Some of the Chinese nuclear power plants use imported uranium fuel from Australia. Considering the limited data accessible, we have assumed values for the energy intensity data of uranium mining, milling, conversion, enrichment, and fuel fabrication and transportation based on a published case study for Australia,41 as showed in SI Table S5. During operation and maintenance, Chinese nuclear power plants need, on average, 2.3 kWh coal-fired electricity input per MWh nuclear power output.36 Windpower stations and solar power stations neither consume fossil energy nor emit GHGs during operation. Electricity Mix in 2012. China has six regional power grids. Each grid includes several provinces and is named for the region it serves: Northeast, North, Central, East, Northwest, and South. Although most of the electricity used in each region comes from power plants within the region, electricity is transmitted between regions as well. With data from CEC,14 we calculate the generation mix for the electricity consumed in each of the six grids in 2012, as shown in Figure 1. Details of the GHG burdens for the different grids are given in the SI Table S6 and S7. Coal-based power is roughly 90− 95% in the Northeast and North generation mixes, about onethird coming from old HP and VHP units. In marked contrast, coal-fired power accounts for 79% in East grid, and approximately 85% of the units are new SubC, SC, and USC. There is more than 30 GW of USC capacity in East China. Most of hydropower plants are located in the western regions, including several provinces in the Central, South, and 7072

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Figure 3. WTW GHG emissions BEV in different regions and selected cities.

vehicle pathways. WTW GHG emissions of BEVs using electricity from different power generation technologies are summarized in Figure S2 of SI.

units accounted for about 25% of Shanghai’s local capacity in 2012 and this will nearly double by 2020.42 For the Pearl River Delta, clean electricity makes a larger contribution than for any other city group in China. The cities in the Pearl River Delta (e.g., Guangzhou) receive hydropower from the South grid and the Central grid. The hydropower supplied to this region is expected to increase 80% by 2020. Two of China’s largest nuclear power plants with a combined capacity of 6 GW are located in this region. Two others are under construction around the delta and the nuclear capacity will be doubled by 2020.43

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DISCUSSION Figure 3 shows the WTW GHG emissions of BEVs powered by electricity in the six regional grids, Beijing, Shanghai, and the Pearl River Delta cities (e.g., Guangzhou) in 2012 and in 2020. In the Central and South grids, where renewable and nuclear power account for 36−38% of the mix, BEVs with a fuel efficiency of 16 kWh/100 km would already meet the government’s MY2020 NEV target. In the Northwest and East grids, BEVs have lower emissions than conventional gasoline and diesel vehicles but they do not meet the government’s MY2015 NEV target. With very high coal-fired electricity proportions (94% and 90%), BEVs driven in north and northeast China have WTW GHG emissions which are 34% and 28% greater than those from hybrid vehicles. As seen in Figure 3, the GHG performance of BEVs in Beijing, Shanghai, and Guangzhou are very different. Even high efficiency (16 kWh/100 km) BEVs considered in our analysis when operated currently in Beijing would not achieve the GHG emission target of MY2015 NEV. Actually, their GHG emission level is very similar to that of a direct-injection spark-ignition (DISI) gasoline vehicle today. New NG-fired power plants will supply one-third electricity consumed in Beijing and as more new SC/USC plants are introduced in Shanxi and Inner Mongolia, GHG emissions of an EV will decrease 20% in Beijing by 2020. However, the emission level in 2020 will still be 7% higher than that of today’s hybrid cars and will not meet the MY2020 NEV target. The current GHG emissions of BEVs are 156 and 129 gCO 2e /km in Shanghai and Pearl River Delta cities, respectively. With the growing proportion of hydropower and nuclear power, GHG emissions of BEVs will be reduced 21% and 16% in Shanghai and Pearl River Delta cities (e.g., Guangzhou) by 2020, respectively. The WTW GHG emissions of BEVs in the Pearl River Delta cities will be about 30% lower than from hybrid cars. China is the world’s largest auto market and its vehicle population is expected to increase substantially in next 20−30 years. China is the world’s largest emitter of GHGs and its

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GHG EMISSIONS FROM TRADITIONAL AND ELECTRIC VEHICLES We compared BEVs with conventional gasoline, diesel, and hybrid electric cars in terms of WTW GHG emissions. Our baseline is a MY2011 midsize gasoline car with a gross vehicle weight (GVW) of 1280−1350 kg, 1.6 L engine with portinjection spark-ignition (PISI), and five-speed automatic transmission. The baseline car uses RON 93 gasoline and meets China Stage IV emission standards. The baseline car has a fuel consumption of 7.4 L per 100 km (l/100 km) under New European Drive Cycle (NEDC). Surveys indicate that on-road average fuel consumption of passenger cars in 22 Chinese cities (including Beijing and Shanghai) deviate by −8% to 34% from that in NEDC.44 We used the NEDC values to facilitate comparison of the different vehicle-fuel pathways considered in the present work and in previous studies. A diesel car with direct-injection compression-ignition (DICI) would have approximately 20% lower energy demand than the baseline vehicle (about 30% lower in terms of fuel volume). If directinjection is applied to a gasoline car, with turbocharging, fuel consumption could be reduced 10−15%; whereas a full HEV could deliver approximately 30% fuel consumption savings. Although many of the demo NEVs produced by the Chinese domestic OEMs consume more than 24 kWh/100 km,45 we assume that NEDC fuel consumption rate of a BEV, with stateof-the-art technologies, is 16 kWh/100km (the 33% improvement from 24 to 16 kWh/100 km is similar to that projected for BEVs in the U.S.27). The charging efficiency of BEVs is estimated to be in the range of 86−90%. We conducted WTW analyses for 24 fuel/vehicle systems, including 20 electric 7073

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emissions are increasing. Considering its resource endowment, it is rational for Chinese policy makers to search for solutions to reduce dependence on imported oil. It is also understandable that reduction in GHG emissions is a national priority. However, there is no “silver bullet”. With a high proportion of coal-fired electricity today, it is clear from the current and previous work8,10,46,47 that BEVs are not a favorable option to meet GHG reduction commitment in north and east China. The government should consider promoting BEV introduction in selected regions in the near-term, based on the carbon burden of electricity. The results presented here and in previous studies46,47 show that hybridization is an attractive option to reduce GHG emissions from the vehicle fleet in some regions, especially in northern China. Meanwhile, continued progress in providing cleaner energy is a key factor for the long-term success of NEV development and GHG reduction. Our study shows that, to have GHG emissions equivalent to the fuel consumption targets for energy saving cars in 2015 and 2020, BEVs in Beijing would need an energy consumption of less than 14 and 13 kWh/100km. In Shanghai and Guangzhou, BEVs would need to consume less than 19 and 23 kWh/100km to have equivalent GHG emissions as energy saving cars in 2015. The energy consumption rate would need to be reduced to 18 and 20 kWh/100km, in Shanghai and Guangzhou, respectively, to reach the new GHG target for 2020. As we mentioned above, EVs currently demonstrated in China generally use 24 kWh (or even 30 kWh) per 100km. While electrification of China’s vehicle fleet will reduce petroleum imports, it will be very challenging for EVs to meet the government targets for energy conservation and GHG reduction in 2015 and 2020.

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ASSOCIATED CONTENT

S Supporting Information *

Eleven pages, including Figures S1−S2 and Tables S1−S7. This material is available free of charge via the Internet at http:// pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 0086-10-85070828; fax: 0086-10-85070888; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Michael Tamor, John Ginder, Wulf-Peter Schmidt, and Hong Huo for helpful discussions. While this article is believed to contain correct information, Ford Motor Company (Ford) does not expressly or impliedly warrant, nor assume any responsibility, for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe the rights of third parties. Reference to any commercial product or process does not constitute its endorsement. This article does not provide financial, safety, medical, consumer product, or public policy advice or recommendation. Readers should independently replicate all experiments, calculations, and results. The views and opinions expressed are of the authors and do not necessarily reflect those of Ford. This disclaimer may not be removed, altered, superseded or modified without prior Ford permission. 7074

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dx.doi.org/10.1021/es500524e | Environ. Sci. Technol. 2014, 48, 7069−7075