Article pubs.acs.org/est
Climate and Environmental Effects of Electric Vehicles versus Compressed Natural Gas Vehicles in China: A Life-Cycle Analysis at Provincial Level Hong Huo,*,† Qiang Zhang,‡ Fei Liu,§ and Kebin He*,§ †
Institute of Energy, Environment and Economy, Tsinghua University, Beijing 100084, People’s Republic of China Center for Earth System Science, Tsinghua University, Beijing 100084, People’s Republic of China § State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, People’s Republic of China ‡
S Supporting Information *
ABSTRACT: Electric vehicles (EVs) and compressed natural gas vehicles (CNGVs), which are mainly coal-based and natural gas-based, are the two most widely proposed replacements of gasoline internal combustion engine vehicles (ICEVs) in P.R. China. We examine fuel-cycle emissions of greenhouse gases (GHGs), PM2.5, PM10, NOx, and SO2 of CNGVs and EVs relative to gasoline ICEVs and hybrids, by Chinese province. CNGVs can currently reduce emissions of GHGs, PM10, PM2,5, NOx, and SO2 by approximately 6%, 7%, 20%, 18% and 22%, respectively. EVs can reduce GHG emissions by 20%, but increase PM10, PM2.5, NOx, and SO2 emissions by approximately 360%, 250%, 120%, and 370%, respectively. Nevertheless, results vary significantly by province. Regarding their contribution to national emissions, PM increases from EVs are unimportant, because light-duty passenger vehicles contribute very little to overall PM emissions nationwide (≤0.05%); however, their NOx and SO2 increases are important. Since China is striving to reduce power plant emissions, EVs are expected to have equivalent or even lower SO2 and NOx emissions relative to ICEVs in the future (2030). Before then, however, EVs should be developed according to the cleanness of regional power mixes. This would lower their SO2 and NOx emissions and earn more GHG reduction credits.
1. BATTLE BETWEEN COAL AND NATURAL GAS Under the strong influence of continual “hazy days” in many regions since autumn 2011 (covering Beijing, Shanghai, Nanjing, Wuhan, and others), China has made a firm commitment to improve its air quality. In February 2012, the China State Council approved its first national ambient air quality standard for PM2.5, which will come into effect by the end of 2015.1 Since substantial coal use (equivalent to 50% of global coal consumption) is the primary reason for the poor air quality, China is considering setting a cap on its use.2 According to the 12th Five-Year Plan of the China Coal Industry (2011− 2015) formulated by the National Development and Reform Commission of China (NDRC), coal consumption will be limited to 3900 million metric tons (MMT) by 2015, which will present a challenge given the tremendous increase in coal use within the last 5 years (2300 MMT in 2006 and 3200 MMT in 2010).3,4 Setting a cap on coal use while maintaining economic growth at a high level means that China must resort to other energy sources, such as natural gas (NG) and renewable fuels, to fill the energy supply gap. Since coal-use control is a near-term goal, NG appears more adequate than other energies to replace © 2012 American Chemical Society
coal in the short term, because of its greater availability and technological maturity. Under such circumstances, there will be a battle between coal and NG in many sectors, particularly the on-road transport sector, which is exclusively petroleumdependent but currently facing a worldwide oil shortage. The enormous growth in vehicle population in China (from 5 million in 1990 to 100 million in 2011) has raised serious concerns about energy supply security.5 During the past decade, the ratio of imported oil within national oil consumption increased rapidly, from 31% in 2000 to 57% in 2011.4 According to various projection studies, the energy demand of vehicles will continue to grow rapidly because vehicle ownership (vehicles/1000 people) is still relatively low in the country (75 vehicles/1000 people in 2011 versus 500−600 vehicles/1000 people in Europe and 800 vehicles/1000 people in the U.S.).6−8 Received: Revised: Accepted: Published: 1711
August 20, 2012 December 28, 2012 December 31, 2012 December 31, 2012 dx.doi.org/10.1021/es303352x | Environ. Sci. Technol. 2013, 47, 1711−1718
Environmental Science & Technology
Article
Figure 1. Consumption-based power mixes and NG transmission distances by Chinese province in 2010. Consumption-based power mixes estimated based on provincial data provided by China Energy Statistical Yearbook 20114 (data include amount of electricity produced from coal, NG, hydro and others, and amount of electricity imported from and exported to other provinces), under the following assumptions: (1) Electricityimported provinces first import electricity from other provinces under the same interprovincial power grid, then from neighboring grids (China has six interprovincial power grids serving six regions, respectively; for details refer to our previous study13); (2) the mix of exported electricity is 100% coal considering the marginal effect, except for provinces (e.g., Hubei and Sichuan) where huge hydropower projects (e.g., the Three Gorges project) are built with intent to export hydropower outside the province. NG transmission distances are estimated based on NG source information (e.g., source locations and amount of NG from each source) from local official documents regarding energy or NG development.
the share of taxis and buses fueled with CNG was more than 95%.12 The tremendous vehicle growth and the oil shortage portend competition between coal and NG for vehicle fuel. The preferred fuel path(s) will depend to a great extent on their climate and environmental performance, which is of national concern. The fuel paths may perform differently by region because energy-use characteristics differ significantly by region. This work examines the following on a provincial basis: fuelcycle (well-to-wheels, WTW) emissions of greenhouse gases (GHGs, including CO2, CH4, and N2O) and criteria pollutants (PM10, PM2.5, SO2, and NOx; the latter two are also known as precursors of PM2.5) of conventional gasoline internal combustion engine vehicles (ICEVs), gasoline hybrid vehicles (HEVs), EVs, and CNGVs in present-day China (2010) and in the future (2030). We also discern strengths and weaknesses of EVs and CNGVs from a perspective of climate change and environmental impact.
Many fuel-substitute measures have been taken, both coalbased and NG-based, with electric vehicles (EVs) and compressed natural gas vehicles (CNGVs) as their representatives. China recently launched several EV demonstration programs (e.g., the Ten Cities, Thousand Vehicles Program) and issued numerous economic policies favoring the purchase of EVs.9 In April 2012, the State Council approved the “Development Plan of Energy-Efficient and New-Energy Vehicles (2012−2020),” which plans to achieve accumulated sales of 500 000 new-energy vehicles (including hybrids and EVs) by 2015, and 5 million by 2020.10 Since EVs use electricity as fuel and Chinese electricity is primarily generated from coal-fired power plants (national average about 77% in 2010), EVs can be regarded as a coal-based option. Compared to EVs, CNGVs have a longer history in China, which initiated programs for CNGVs in the late 1990s. By 2010, the country had about 1300 natural gas stations.5 According to the International Association for Natural Gas Vehicles, by May 2012, there were 1.1 million natural gas vehicles (NGV) nationwide, with 98.9% of those operating on compressed natural gas (CNG).11 In Chongqing and Sichuan, 1712
dx.doi.org/10.1021/es303352x | Environ. Sci. Technol. 2013, 47, 1711−1718
Environmental Science & Technology
Article
Table 1. Comparison of Key Life-Cycle Energy and Emission Data between U.S. and China in 2010a parameters (“*” indicates provincial data available in analysis)
U.S. (GREET default unless noted otherwise)
*national average generation mix (%) fossil (Coal, NG, petroleum) nonfossil (Hydro, nuclear, others) energy efficiencies of coal mining crude recovery *coal-fired power generation distances of feed/fuel transport and distribution (km) *coal: rail, road, water *NG to refilling stations: pipeline energy intensity of transport tools (MJ/tonne-km) train, heavy truck, barge pipeline: Oil, NG fuel economy of 2010 model-year (MY) vehicles ICEVs, HEVs, EVs, CNGVs (mi/gasoline-eq gal) *emission factors of coal-fired stationary sources *power plants average: PM10, PM2.5, NOx, SO2 (mg/kWh) 2012 new power plants: PM10, PM2.5, NOx, SO2 (mg/kWh) *boilers: PM10, PM2.5, NOx, SO2 (mg/MJ fuel) NOx emission factors of 2010 MY vehicles (mg/km) Euro IV ICEVs, HEVs, EVs, CNGVs, heavy trucks *share of surface coal mining a
70.1 (45.1, 24.1, 0.9) 16 29.9 (6.2, 19.7, 4.0) 16
China (national average) 79.9 (77.4, 2.0, 0.5) 20.1 (17.3, 1.8, 1.0)
99.3% 98.0% 34.5%
97.8% 4 95.0%4 35.1%4
530, 80, 700 1200
630, 290, 15004,17 1100
0.269, 0.747, 0.258 0.183, 0.294
0.280, 4.392, 1.100 0.146,18 0.234
4 4
4
24.8, 34.7, 84.4, 22.9
29.5,19 41.3, 100, 27.3
150, 118, 1384, 3938 94.8, 47.4, 147, 190
447, 287, 2908, 257620,21 80, 50, 263, 525 22 123, 86.3, 211, 730
43, 36, 0, 43, 1570 69%
50,23 42, 0, 50, 806024 10% (2009 data)25
Table S1 of the SI provides more data details.
west to fulfill their needs (as part of the “Project of Power Transmission from West China to East”). Therefore, the consumption-based power mix of such eastern provinces may be very different than their own generation mix. For example, Beijing generated 27 billion kWh of power (93% coal-based electricity) and bought 56 billion kWh from Inner Mongolia and Shanxi (100% coal-based electricity) in 2010,4 which increased the share of coal-based electricity in Beijing’s consumptionbased power mix to 98%. (2) CH4 leakage during NG transmission, which is a major source of fuel-cycle GHG emissions of CNGVs, is a function of pipeline distances, and distances to access NG vary in each province. According to the U.S. Environmental Protection Agency, NG transmission, storage and distribution contributed approximately 33% to total CH4 emissions from natural gas systems in the U.S.14 Burnham et al. estimated that CH4 leakage during NG transmission and distribution represented 7% of fuelcycle GHG emissions of U.S. CNGVs.15 NG resources in China are concentrated in a few western provinces (Xinjiang, Shaanxi, Qinghai, Sichuan, and others), and NG is transmitted from western to eastern regions via pipelines (e.g., the West-East Gas Transmission Project and Sichuan-East Gas Transmission Project). For instance, Shanghai gets half its NG supply from Xinjiang and Sichuan, which are 4500 km and 1800 km away, respectively. NG transmission distances of provinces range from 200 km to 4500 km (Figure 1). Although some factors are regionally different, they are less important because they change the life-cycle results very little. Taking coal transportation as an example, coal reserves are mainly in Shanxi, Inner Mongolia, and Shaanxi. Coal from these provinces is transported to northern regions (e.g., Beijing and Tianjin) by train or truck (350−500 km). However, for transport to eastern regions (e.g., Shanghai and Zhejiang), it is
2. WHY AT A PROVINCIAL LEVEL? 2.1. Improving the Accuracy of Life-Cycle Analysis. Previous life-cycle studies in China have tended to estimate the life-cycle energy use and emissions using national average data, which is acceptable for technologies that are evenly distributed across the country (e.g., conventional gasoline vehicles). However, for technologies that primarily operate in designated cities, which is the case for EVs and CNGVs in China, using national averages may severely underestimate or overestimate results, and thereby convey inaccurate and incomplete messages to society and decision makers. This is because energy-use characteristics differ significantly by region. Fuel-cycle emissions of EVs are generated mainly from power generation processes. These emissions of CNGVs are from NG recovery and processing, NG transportation (via pipelines), NG compression (using electricity), and vehicle operation (NG combusted in engines). Fuel-cycle emissions of both EVs and CNGVs in China are highly subject to a variety of regional factors, for the following reasons: (1) Consumption-based power mixes differ significantly across provinces, as shown in Figure 1.4,13 For instance, Beijing has 98% coal-fired power in the mix, whereas Hubei has 31% coal-fired power and 67% hydropower. Because power generation processes account for a very large percentage of EV fuel-cycle emissions, differences in provincial power mixes can significantly affect the EV results. These differences can also affect CNGVs, since the NG compression process consumes only electricity and this process usually comprises 6−10% of fuel-cycle energy use. Note that we use consumption-based power mixes instead of generation mixes, because the former can better reflect emissions from EV use. Given regional disequilibrium in resource distribution and economic development in the country, many eastern provinces have to purchase vast amounts of electricity from the 1713
dx.doi.org/10.1021/es303352x | Environ. Sci. Technol. 2013, 47, 1711−1718
Environmental Science & Technology
Article
Figure 2. Fuel-cycle GHG emissions of EVs, CNGVs, gasoline ICEVs and HEVs.
first carried by train to the ports of Hebei or Tianjin (700 km− 1000 km) and then conveyed to the destination by barge (900 km−1200 km). These two paths only contribute a difference of
