MIT Energy Initiative, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Environ Sci Technol. 2020 Dec 15;54(24):16071-16085. doi: 10.1021/acs.est.0c02312. Epub 2020 Nov 26.
Light-duty vehicles emit ∼20% of net US greenhouse gases. Deployment of electric vehicles (EVs) can reduce these emissions. The magnitude of the reduction depends significantly on EV charging patterns and hourly power grid variations. Previous US EV studies either do not use hourly grid data, or use data from 2012 or earlier. Since 2012, US grids have undergone major emission-relevant changes, including growth of solar from ∼1 to ∼20% of generation in California, and >30% reduction of coal power countrywide. This study uses hourly grid data from 2018 and 2019 (alongside hourly charging, driving, and temperature data) to estimate EV use emissions in 60 cases spanning the US. The emission impact of charging pattern varies by region. In California and New York, respectively, overnight EV charging produces ∼70% more and ∼20% fewer emissions than daytime charging. We quantify error from two common approximations in EV emission analysis, ignoring hourly variation in grid power and ignoring temperature-driven variation in fuel economy. The combined error exceeds 10% in 30% of cases, and reaches 50% in California, home to half of US EVs. A novel EV emission approximation is introduced, validated (<1% error), and used to estimate EV emissions in future scenarios.
轻型车辆排放了美国 20%的温室气体净排放量。电动汽车（EV）的部署可以减少这些排放。减排的幅度在很大程度上取决于电动汽车的充电模式和每小时电网的变化。以前的美国电动汽车研究要么没有使用每小时的电网数据，要么使用的是 2012 年或更早的数据。自 2012 年以来，美国电网发生了重大的与排放相关的变化，包括加利福尼亚州的太阳能发电从约 1%增长到约 20%，以及全国范围内煤炭发电量减少了 30%以上。本研究使用了 2018 年和 2019 年的每小时电网数据（以及每小时充电、驾驶和温度数据），来估算美国 60 种情况下的电动汽车使用排放。充电模式的排放影响因地区而异。在加利福尼亚州和纽约州，分别是夜间电动汽车充电比白天充电产生的排放多约 70%，少约 20%。我们量化了电动汽车排放分析中两个常见近似值的误差，忽略了电网功率的每小时变化和燃料经济性的温度驱动变化。在 30%的情况下，这种组合误差超过 10%，在拥有美国一半电动汽车的加利福尼亚州，误差达到 50%。引入了一种新的电动汽车排放近似值，对其进行了验证（误差小于 1%），并用于估计未来情景中的电动汽车排放。
