Is an Electric Car Better for the Planet?電動汽車對地球更好嗎？

本杰明·普萊克特 譯/袁欣 審訂/李瑞林

It depends on how we make electricity that power these cars.

這要看汽車電能的生產方式。

Which is better for Earth： an electric or gas-powered vehicle？ The answer to this question might seem blindingly1 obvious： Of course electric cars must be better for the environment， because they don’t have exhausts2 and so don’t emit greenhouse gases as they drive. However， electric vehicles （EVs） aren’t perfect， and they come with their own set of polluting problems. Notably， their batteries contain components， such as lithium， that require a significant amount of energy to source3 and extract.

But battery production is just one part of an electric car’s life span. A 2014 study published in the journal Proceedings of the National Academy of Sciences looked at the entire life cycle of an EV’s emissions， from mining the metals required for the batteries to producing the electricity needed to power them， and then compared this with the average emissions of a gas-powered vehicle. The team found that when electric vehicles are charged with coal-powered electricity， they’re actually worse for the envir-onment than conventional gasoline cars.

In much of the world， however， national grids are now clean enough for EVs to beat their gasoline-powered counterparts when it comes to pollution and greenhouse-gas emissions during their lifetimes.

“Only when connected to the dirtiest， coal-heavy electric grids do gasoline internal combustion engines become comparable to EVs on a greenhouse gas basis，” said Colin Sheppard， a researcher with expertise in energy and transportation systems engineering at the Lawrence Berkeley National Laboratory in California.

China’s grid is improving with more investments in renewables， and it builds more solar panels per year than any other countries， according to Nature magazine.

“This pattern of improvement—more renewable energies and fewer fossil fuels—is a global one and it helps to boost the environmental credentials4 of electric vehicles，” said Gordon Bauer， an electric vehicle researcher at the International Council on Clean Transportation in San Francisco. “As grids become greener during the lifetime of an electric vehicle， it’s only going to get better.”

In a study published in the journal Environmental Science and Technology， Sheppard modeled a hypothetical future scenario in which all cars were electric. “We wanted to understand what the energy， infrastructure and emissions implications might be if all passenger vehicles are electrified，” Sheppard told Live Science. Bauer also collaborated with Sheppard on the project. Their findings come out strongly in favor of an electric vehicle future.

For example， Sheppard calculated that if all privately owned vehicles in the U.S. were electric， it would reduce greenhouse-gas emissions in the country by 46% annually （0.5 gigatons5 of carbon dioxide） compared with conventionally gas-powered cars. This reduction could be increased even further if those vehicles were subject to so-called “controlled charging，” a technique also known as “smart charging，” in which vehicles are recharged at strategically chosen times to minimize the financial cost of generating electricity. （For instance， charging at night is often less pricey than during the day; this strategy also favors more efficient energy-producing plants that produce cheaper electricity.） If all privately owned electric cars were charged in such a way， the emissions savings could rise to 49% annually.

These estimates are based on what Sheppard admits is an “ambitious” imagining of the U.S.’s future energy portfolio. This future envisions a country with a lot more renewable energy， but which still hasn’t reached the goal of zero carbon， or having a national grid that doesn’t contribute to climate change， he said. There is a considerable amount of political will and practical change that needs to happen to make this scenario possible， but it’s still helpful to map out the full theoretical potential of electric vehicles under these circumstances.

In short， it’s far easier to argue in favor of buying an EV than a gas- or diesel-powered vehicle from an envir-onmental perspective. But what about cost？ Aren’t electric vehicles too expensive for most people to afford？

A 2020 report from the consumer rights group， Consumer Reports， suggests this is also changing. The paper estimated that the per-mile repair and maintenance costs over the lifetime of an EV is a little less than half that of traditional vehicles with internal combustion engines. This is largely because electric motors have just one moving part， compared to traditional engines which often have dozens. This means fewer components need to be replaced in an EV， resulting in significant savings albeit6 not at the point of sale.

“It may sound radical right now， but by the time 2030 rolls around7， I think the problem will be about how quickly manufacturers can make them，” Bauer said.

In a recent U.S.-wide analysis carried out by Bauer， he concluded that the high rate of depreciation8 for new electric vehicles will lead to larger benefits for lower-income households that are more likely to buy used cars. This， along with other factors driving price reductions， such as technological innovations and increased supplier competition， will mean that an EV should cost the same as a conventional gasoline-powered car for almost all income levels by approximately 2029， Bauer found. Furthermore， Bauer calculated that by 2030， low-income households in the U.S. stand to9 save $1，000 per year from fuel savings if they were to switch to an EV.

電動汽車和汽油汽車，哪種對地球更好呢？問題的答案似乎非常明顯：當然，電動汽車一定更環保，因為它們沒有排氣管，行駛時不排放溫室氣體。不過，電動汽車并非完美無缺，也存在它們特有的污染問題。尤其要注意的是，電動汽車的電池含有鋰等成分，探尋和提純其原料需要消耗大量能源。

可是，電池生產只是電動汽車生命周期的一個環節。美國《國家科學院學報》2014年發表的一項研究考察了電動汽車氣體排放的全生命周期——從開采金屬來生產電池到發電來驅動汽車，然后和汽油汽車的平均排放量進行了比較。該研究團隊發現，電動汽車如果充的是煤電，對環境的危害實際上比傳統汽油汽車更嚴重。

盡管如此，說到生命周期內造成的污染和溫室氣體排放量，世界上大部分地區的國家電網目前已非常清潔了，足以讓電動汽車勝過汽油汽車。

加州勞倫斯伯克利國家實驗室能源與運輸系統工程專業研究員科林·謝潑德講道：“電動汽車只有在和清潔度最低、嚴重依賴燃煤的電網相連的情況下，其溫室氣體排放量才跟汽油汽車內燃機不相上下。”

根據《自然》雜志所述，中國電網加大可再生能源的投資，清潔度隨之提高。每年新建太陽能面板超過其他任何國家。

“多用可再生能源，少用化石燃料，這一改良模式是全球性的，有助于提升電動汽車的環保資質。”舊金山國際清潔交通委員會電動汽車研究員戈登·鮑爾如是說，“在電動汽車生命周期之內，隨著電網越來越綠色，情況只會越來越好。”

美國《環境科學與技術》雜志發布的一項研究顯示，謝潑德對所有汽車皆電動這一假設性的未來場景進行了建模。他對趣味科學網說：“我們想搞清楚，如果所有乘用車都是電動，可能會對能源、基礎設施和排放量產生什么影響？”與謝潑德合作開展此項研究的還有鮑爾。他們的研究成果表明電動汽車未來發展前景光明。

例如，根據謝潑德的計算，如果美國所有私家車都是電動的，那么和傳統汽油汽車相比，美國每年可減排溫室氣體46%（5億噸二氧化碳）。如果采用所謂的“受控充電”（亦稱“智能充電”）技術，減排量還可進一步提高。“受控充電”是指策略性地選擇充電時間，以最大限度降低發電成本。（例如，晚間充電通常比白天便宜。這一策略也有利于發電效率較高、電價較低的能源生產企業。）如果所有私家電動車都采取這一充電技術，每年的減排量則會提高到49%。

謝潑德承認，上述估算是基于對美國未來能源組合的“大膽”想象做出的。他表示，在這一設想下，未來的美國將擁有更多可再生能源，但仍無法達成零碳目標，或擁有對氣候變化不會產生負面影響的國家電網。要讓這樣的場景成為現實，需要十分強大的政治意志和切實可行的變革。不過，在這些條件下從理論上對電動汽車的一切可能性進行規劃也是有裨益的。

簡而言之，從環境角度看，相對于汽油車或柴油車來說，提倡人們購買電動汽車就容易多了。但是，從價格上看又會如何？電動汽車是不是貴得讓多數人買不起？

消費者權益組織《消費者報告》雜志2020年發布的報告表明，上述情況也正在改變。據該報告估算，電動汽車生命周期內每英里的維修保養費用還不到傳統燃油汽車的一半。這主要是因為傳統引擎通常有數十個部件，而電動機只有一個活動部件。也就是說，電動汽車需要更換的部件更少一些，即便賣得不便宜，維護也能節省不少費用。

鮑爾表示：“眼下聽起來可能很激進，但我認為，到了2030年，就怕制造商的產出速度跟不上了。”

新近，鮑爾對全美的情況進行了一次分析。他的結論是，新款電動汽車折舊率高，這將會給更可能買二手車的低收入家庭帶來更多好處。據他發現，伴隨技術創新、供應商競爭加劇等其他降價因素，折舊率高則意味著到2029年前后，對差不多所有收入階層來說，電動汽車的價格會和傳統汽油汽車持平。還有，據鮑爾估算，到2030年，美國低收入家庭假如都改用電動汽車，每年便可節省加油費1000美元。