Posted in GreenBiz
July 12, 2022

A 9,000-pound electric Hummer shows we can’t ignore efficiency of EVs


Electric vehicles have zero tailpipe emissions, unlike their gasoline-combusting counterparts, but they are still responsible for greenhouse gas emissions. As EV sales surge, policymakers and advocates should explore ways to increase their efficiency and reduce the cars’ environmental impact.

Fully electric vehicles with no gasoline engine (which we will refer to as EVs) get their power from the electric grid. And in the United States, about 60 percent of electricity is generated by burning fossil fuels. Until the grid is completely carbon-free, there will be emissions from generating the electricity to run EVs, known as upstream emissions.

Emissions per mile driven are lower for EVs than for similarly sized gasoline-powered cars, but they are not zero. The Chevy Bolt EV is responsible for about 92 grams of carbon dioxide (CO2) per mile when accounting for emissions from the electric grid. (The CO2 calculations are based on the national average, but electric grid emissions vary considerably across the country.) The gasoline-powered Chevy Malibu causes over 320 grams per mile. Comparing larger vehicles, the original Hummer H1 emits 889 grams of CO2 per mile and the new Hummer EV causes 341 grams, demonstrating that behemoth EVs can still be worse for the environment than smaller, conventional vehicles.

The environmental impact of EVs isn’t just about the electricity generated to power each mile. The manufacturing process also causes the release of greenhouse gases at several stages, known as the embodied emissions of the vehicle. EVs in particular—with heavy battery packs—use minerals that need to be mined, processed and turned into batteries. The pursuit of greater driving range and larger vehicles require increasing battery size, also increasing embodied emissions.

Mining the minerals used for batteries has a significant impact on the environment and can have negative social impacts, including the well-documented human rights abuses surrounding the mining of cobalt, an important mineral for many EV batteries. More-efficient EVs need less battery to have the same range, which means fewer emissions and fewer problems associated with mining the minerals.

Regulators must address EV efficiency

Most drivers have a good sense of how fuel efficient their gasoline-powered vehicle is, and policymakers have recently required greater efficiency in new vehicles. But the efficiency of EVs is often forgotten. As EVs proliferate, their efficiency should be a priority for policymakers. Just as efficiency of gasoline-powered vehicles has numerous benefits for the environment and consumers, greater EV efficiency does too. The less electricity needed to drive a mile, the fewer the emissions from electricity generation, and the more money saved by drivers. Greater efficiency can also mean that automakers could reduce battery size to achieve the same range, leading to less mining and fewer embodied emissions.  

The Environmental Protection Agency should explore ways to factor EV efficiency into fuel-efficiency and greenhouse gas standards, starting with accounting for EVs’ upstream emissions. At the moment, regulators calculate the emissions from gasoline vehicles and set requirements for automakers, but EVs are counted as causing no CO2 emissions. This means the sale of an EV Hummer can offset the sale of a highly polluting gasoline vehicle and increase emissions overall.

Accounting for upstream emissions would mean that the sale of a more efficient EV would be more advantageous for automakers to meet their regulatory requirements. All EVs do not have the same impact on the environment, and our vehicle regulations should reflect that.

What drives EV efficiency?

EV efficiency, much like the efficiency of gasoline-powered vehicles, is largely affected by the efficiency of the motor and drivetrain as well as the weight and aerodynamics of the vehicle. Energy is lost when going from the battery to the motor to the wheels. The amount lost can vary by vehicle and contributes to a variation in overall efficiency. Efficiency can also vary considerably by the type of vehicle (sedan, crossover, pickup) and its weight. Smaller vehicles tend to be more efficient, so reducing size and weight (as well as improving aerodynamics) can increase efficiency.

Efficiency, often measured in kilowatt-hours (kWh) per 100 miles of driving, can be improved either through engineering advancements or through reducing vehicle weight and size. Improvements in technology can reduce the amount of energy lost between the battery and the wheels. Decreasing EV weight, including from the battery, can reduce the electricity needed. EVs benefit from regenerative braking, when energy is captured from braking and returned to the battery, greatly increasing efficiency. It’s one reason electric drive systems are about twice as efficient as internal combustion engine systems.

More efficient EV models exist today

The current EV market is diverse, with vehicles of various sizes, weights, driving ranges and efficiencies. We used ACEEE’s GreenerCars database to analyze available vehicles and show the variety of options, including levels of efficiency. With better technology and lighter vehicles, automakers can improve efficiency. Figure 1 shows how even EVs of the same weight vary widely in efficiency.

Figure 1. EV efficiency versus weight

We found that lighter vehicles are more efficient in general, but even with roughly the same weight, more-efficient vehicles exist. Among the common weights of 5,000 to 5,500 pounds, there are vehicles with efficiencies ranging from almost 25 kWh/100 miles, the best in the market, to almost 48 kWh/100 miles, amongst the worst. The vehicles with superior efficiency could have more-efficient engines, better aerodynamics or better regenerative braking systems. In general, though, higher weights are associated with lower efficiency because it takes more energy to move a heavier car.

Battery packs can be a significant portion of an EV’s weight, but for a given battery chemistry a larger battery means more range, a desirable trait for many consumers. Automakers may wish to reduce only the non-battery weight of the vehicle to maintain a high range. We therefore also examined efficiency compared to vehicle weight excluding the battery pack, shown in figure 2.

Figure 2. EV efficiency versus non-battery weight

Even when examining non-battery weight, there is a wide variation in efficiencies, including among the most common non-battery EV weights of between 3,000 and 4,000 pounds. Vehicles in this weight range have efficiencies ranging from 25 to over 45 kWh/100 miles. Decreasing non-battery weight, often by reducing overall size, can considerably increase efficiency. Improving efficiency by 5 kWh/100 miles while keeping weight the same would reduce per mile emissions by 16 grams of CO2 — a 14 percent reduction for a vehicle with an efficiency of 35 kWh/100 miles.

All EVs are not created equal, so let’s not treat them like they are

Policymakers and automakers should put a greater focus on EV efficiency and emphasize its importance for buyers. Greater EV efficiency can reduce emissions from driving and manufacturing the vehicles and increase range and reduce costs. Reducing weight, enhancing aerodynamics, improving electric motors and reducing battery size will each increase EV efficiency.

Current greenhouse gas standards for vehicles do not include the upstream emissions from EVs, missing an opportunity to incentivize greater efficiency, save money and reduce greenhouse gas emissions.

July 12, 2022 at 01:12PM

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