|Fuel-cycle SO2 emissions of EVs compared to those of gasoline ICEVs and HEVs in China, current (left) and future (right). Credit: ACS, Huo et al. Click to enlarge.|
A new study by researchers from Tsinghua University (China) and Argonne National Laboratory (US) concludes that the mass use of electric vehicles in China could result in multiple environmental issues, including higher emissions of CO2 and criteria pollutants than from conventional and hybrid gasoline vehicles, because electricity is generated primarily from coal in China. The study was published online 24 May in the ACS journal Environmental Science & Technology.
The study examined the fuel-cycle CO2, SO2, and NOx emissions of EVs in China in both current (2008) and future
(2030) periods and compared them with those of conventional
gasoline vehicles and gasoline hybrids. The researchers found that while EVs do offer a very promising solution to energy issues due to their replacement of petroleum fuels, for now “the high pollution levels of coal-fired power plants will trade off EVs’ potential energy benefits in China”.
The vehicle population in China was about 63 million by 2008, and it is projected to be 550-730 million by 2050, 38-83% higher than that of the US in
2050. One important question raised is how to accommodate this large number of vehicles in terms of energy sources. Today in China one frequently proposed answer is electric vehicles (EVs), which could alleviate dependence on
petroleum by using other energy sources such as coal and
hydro…Nowadays, China is considered to be a very promising market for EVs.
The power of EVs is electricity from the grid. While EVs can offer attractive benefits in petroleum reduction, they could result in more CO2 emissions than conventional vehicles because of the fact that the majority of electricity
is generated from coal in China. Another concern associated
with EVs is that they could increase emissions of criteria pollutants like SO2 and NOx because power plants are believed to be the largest contributor to China’s SO2
and NOx emissions.
|Generation mix of the six interprovincial power grids in 2008. Credit: ACS, Huo et al. Click to enlarge.|
China comprises six large interprovincial power grids: Northeast China, North China, Central China, East China, Northwest China, and South China. Coal and hydro are the two major energy sources of power generation in China, and the split between them varies by region. Coal-based power dominates in the Northeast and North generation mixes, with a proportion as high as 95-98%. The Northwest, Central, and South mixes consist of more than 22% hydro power, although coal is still the majority. The South and East grids also have 5% nuclear
Among the findings of the study:
CO2. EVs do not promise
much benefit in reducing CO2 emissions currently, but greater
CO2 reduction could be expected in future if coal combustion
technologies improve and the share of non-fossil electricity
The regions with smaller fractions of coal-based electricity should be the priority EV markets, such as the South, Central, and Northwest regions. As an example, the authors said, EVs are a good choice for Chongqing (Central) and Shenzhen (South), but HEVs would be a better choice than EVs for Beijing (North)
and Shanghai (East) in terms of CO2 emission reduction.
SO2. Powered by the current electricity mix, EVs could cause a significant increase in SO2 emissions by 3-6 times relative to ICEVs and 5-10 times relative to HEVs. Gasoline vehicle exhausts contribute very little to total national SO2 emission (0.2% in 2006) but if they are replaced by EVs, the contribution would rise to 2-4%.
EVs will pose a new challenge to China’s target of controlling the total amount of SO2 emissions. In the future, even with more advanced combustion technologies and 100% FGD penetration, the SO2 emissions of EVs would still be 1.3-5 times the emissions of ICEVs and 3-7 times the emissions of HEVs. Even with an additional 100% coal washing, which is infeasible in practice, it is not possible to bring the SO2 emissions of EVs down to
the level of ICEVs and HEVs for most regions in China.
—Huo et al.
NOx. China is currently implementing the Euro III vehicle emission standard nationwide (except for some large cities where Euro
IV is already in effect, such as Beijing). The Euro IV and
V standards are expected to be in place within 10 years. If charged by the current electricity mix, EVs would double the NOx emissions of Euro III gasoline vehicles. By 2030, the study found, EVs will still increase NOx emissions by 16-86% compared to Euro V gasoline vehicles if the penetration of SCR for NOx treatment at the coal plants is zero. If the application ratio of SCR reaches 20%, EVs charged by the generation grid with 50% coal-based electricity could have lower NOx emissions than gasoline vehicles.
EVs charged by higher coal-intensity generation grids would
require higher SCR penetration, e.g., electricity with 80% coal
will need at least 44% SCR penetration. The widespread
application of SCR will be the key for EVs to compete with
gasoline vehicles in terms of NOx emissions.
—Huo et al.
As analyzed in this work, it is the current high emissions of power plants that are going to make EVs a less favorable option than other alternatives in China, such as HEVs, which are more environmentally
friendly, more commercially mature, and less cost-intensive. Currently, in the Chinese vehicle market, taking products of the BYD Company as an example, HEVs (20,000-25,000 US dollars) are much more expensive than conventional ICEVs
(8000-10,000 US dollars) of equivalent size, but the price of EVs is even higher (>30,000 US dollars). The costs and benefits of different technological options need to be further explored.
—Huo et al.
The authors make several recommendations to make EVs a more attractive environmental option for China, including:
- Special strategies for emission control of coal-fired power plants as the development of EVs progresses;
- Designation of appropriate places with low carbon electricity for the introduction of EVs.
- Wide application, with financial support of the government, of advanced
coal combustion technologies, as well as technical measures
to remove pollutants (such as SCR and coal cleaning).
…because power plants have a longer
lifetime than vehicles, the technology shift in the power sector
could be slower than that of the transportation sector.
Therefore, coordinated policies between these two sectors
are needed to reinforce EVs’ progress toward a cleaner future.
—Huo et al.
The work was supported by the National Natural Science
Foundation of China.
Hong Huo, Qiang Zhang, Michael Q. Wang, David G. Streets and Kebin He (2010) Environmental Implication of Electric Vehicles in China.
Environ. Sci. Technol., Article ASAP doi: 10.1021/es100520c