Clean Transportation: An Introduction

Let’s change gears to transportation, which accounts for around 20% of global carbon dioxide emissions, mostly from road transportation. Nearly half of all transportation emissions come from cars. Transportation, of course, can be done much more efficiently than in private passenger vehicles. Studies have estimated that around 600-1600 people per hour can be transported within a typical car lane, but bicyclists in the same area can move at a rate of 7,500 people per hour. Walking is more efficient than both at 9,000 people per hour, because many more pedestrians can fit within the same space.

Cars use large amounts of materials and energy, waste our time, and are quite dangerous as well. In many locations around the world, cars are the most significant source of pollution. Many communities of color in the United States that are currently exposed to high road pollution burdens have suffered from an unjust transportation system in many ways, for instance, being split apart during the construction of highways. It’s always better to use less, but we can also reduce carbon emissions and air pollution at the same time by either electrifying everything, or using hydrogen fuel cells.

Freedom from fossil transport fuels would be nice. It would mean less chance of disasters from refineries and pipelines, as well as less air pollution in the form of heat-trapping gases, nitrogen oxides, and ozone. Many oil refineries still use hydrofluoric acid (HF), one of the most deadly industrial chemicals, in their refining process, even though it’s not necessary to use such a dangerous substance. The Philadelphia Energy Solutions refinery was one such facility. Community groups like Philly Thrive had fought vehemently for the plant to close down, highlighting concerns like particulate matter concentrations in the air and cancer-causing toxins like benzene. The plant exploded on June 21, 2019 in a giant conflagration. A 38,000 pound vat was lofted over 2100 feet away, all the way across the Schuylkill River. The explosion released over 3200 pounds of HF into the air. If this had been a little closer to the ignition, it is possible that more than one million people would have been exposed in Philadelphia, with many likely deaths or severe injuries. The PES plant is now closed but refineries around the country still use HF in their process, endangering workers and local residents alike. Now 48 out of 150 refineries in the US use HF, and disasters are frequent. Torrance, California had an incident in 2015. A plant in Wisconsin experienced large explosions in 2018 and the town was evacuated due to hydrofluoric acid release, among other chemicals. The refinery continues to use the deadly gas. The Marathon refinery in Texas had a hydrofluoric acid leak in May 2021 which required nearby residents to shelter in place.

Due to its many associated pollutants, it’s important to stop using gasoline and diesel as quickly as possible. From a justice perspective, can we prioritize electric vehicles for low-income communities and communities of color who have suffered the largest damages from pollution in the past? Otherwise the new technologies will continue to be adopted by the wealthy first. Can we reduce the usage of vehicles while still prioritizing justice? How can public transportation systems be upgraded, to ensure more equitable options for all?

Cars with less emissions come in many forms. Hybrid vehicles have two propulsion systems, an internal combustion engine and an electric engine. They can regenerate energy while braking. Plug-in hybrids can run all-electric for a certain range, and then switch over to gasoline to extend their range. Battery electric vehicles run on electricity only, and require no liquid fuel.

A major environmental concern with electric vehicles are the batteries, which require minerals like lithium and cobalt. Electric motors require minerals like neodymium for use as a permanent magnet. We’ll discuss the justice implications of mining of these and other minerals important for clean energy in the next chapter.

There have been massive increases in the usage of electric vehicles worldwide with exponential increases in sales, with market shares reaching nearly 9% in 2021. Roughly half of the sales were in China, a third in Europe and much of the rest in the US. Norway leads the world in terms of percentages, with 72% of new car sales being EVs. Sweden sells 45% EVs, and the Netherlands 30%. There have also been exponential increases in charger installations, which is an important part of increasing access.

Fuel economy

It’s worth a bit of a diversion into the fuel efficiency of cars, even when considering visions of an all-electric future. Americans may be used to the measure “miles per gallon” (mpg) for fuel economy. It turns out, though, that the reciprocal, gallons per mile, is much more useful. This is since typically drivers have a certain amount of distance they need to travel, and need to know how much fuel will get them there. In the metric system, liters per 100 km is a standard measure, and now gallons per 100 miles is listed on all new cars in the US. The difference between fuel per distance measures and distance per fuel measures is most apparent on the low end, when small difference in mpg among small mpg cars amounts to a large difference in gallons per 100 miles.

What is a fuel economy measure if there’s no liquid fuel, i.e., if the car runs on electricity only? There are measures like liters-equivalent per 100 km (Le/100 km), where the electricity equivalent of a liter of gasoline is calculated based on the heat content of gasoline, 9.5 kWh/L (33.7 kWh/gal). Typical electricity consumption values for battery electric vehicles are 1.5-2.5 Le/100 km (14.25-23.75 kWh/100 km). We described in earlier chapters that a large amount of heat is wasted within internal combustion engines, due to fundamental limitations of thermodynamics. This means that in fuel efficiency measures, EVs have much larger efficiency, when measured in Le/100 km or mpg-e.

While internal combustion cars have fuel efficiency that is largely proportional to weight (with heavier cars using much more gas or diesel), EVs have less dependence on weight. This is because EVs recover energy while braking, and a larger vehicle has more kinetic energy. Unfortunately, car sales are trending larger and larger. Sport utility vehicle sales now make up over 50% of vehicle sales in the US, and large cars are becoming more common in other countries around the world as well. This has largely offset the fuel efficiency gains that would have occurred due to technological innovation.

Hydrogen fuel cells

Hydrogen fuel cells act like a battery, with one terminal (the anode) the hydrogen fuel, and the other terminal (the cathode) oxygen from the air. The chemical reaction is simply hydrogen plus oxygen yields water and energy as electricity, a pretty clean set of products. The downside is that hydrogen has to be produced, which requires energy.

Hydrogen fuel cells can be used for electricity in EVs, which then drives an electric motor. They are less efficient in terms of electricity usage than battery electric vehicles, requiring 1.7-4 times more electricity as measured in Le/100 km. Hydrogen, however, can be more efficient for certain types of heavy or long-distance transportation. This includes options like heavy trucks, trains, ships and airplanes.

One way to produce hydrogen is electrolysis, which splits water with electricity, to release hydrogen and oxygen. This could be a particularly appealing way to use excessive renewable capacity on a sunny or windy afternoon. Unfortunately only 0.1% of hydrogen is currently produced in this manner.

Most hydrogen production is done with fossil gas, the source of 75% of production worldwide. Most of the rest is created from gasification of coal. Those pushing for increased hydrogen usage are often from the fossil fuel industry, so should be treated with skepticism. On the other hand, if the current hydrogen usage worldwide were switched to electrolysis, this could cause marked reductions in the emissions associated with processes like steelmaking and the chemical industry. Much of the rest of the hydrogen is used in oil refining, which should be eliminated as quickly as possible.

Hydrogen fuel cells have been used in California for a while, and are currently being rolled out rather quickly in China, Japan and Korea. Announced projects would triple the amount of clean hydrogen production within the next 3 years.