13.4: Merging of Transportation

The next generation of vehicles is emerging in response to environmental pressures and a goal of fuel independence. The environmental pressures, which include the mitigation of climate change and air quality degradation, require a dramatic reduction in the emission of GHGs and air pollutants from the transportation sector as well as the electric sector. Fuel independence requires removing reliance on the international sourcing of carbon-rich fossil fuels and the associated geopolitics. In response, vehicles of all sizes are transitioning from combustion engines and mechanical drive-trains to alternative vehicles with battery and fuel cell engines and electric drive-trains. The transition began with light-duty vehicles, expanded into medium-duty vehicles, and is now emerging with heavy-duty vehicles including buses. This transition involves a merging of the transportation system with the electricity generation system.

Alternative vehicles encompass fuel cell electric vehicles (FCEVs) and plug-in electric vehicles (PEVs). Examples of PEVs are battery electric vehicles (BEVs) and plug-in fuel cell electric vehicles (PFCEVs). All of these vehicles have a few key characteristics in common. First, alternative vehicles are designed to operate on fuels that portend (1) a potential of zero emission of both GHG and criteria pollutants and (2) an opportunity to be generated locally and thereby achieve the goal of fuel independence. Second, alternative vehicles have no tailpipe emissions of carbon or criteria pollutants. The GHG and criteria pollutant emissions, if any, come solely from the fuel supply chain, such as the generation of electricity or production of hydrogen. Electricity and hydrogen are the two fuels emerging to power alternative vehicles.

Electricity as a fuel

Figure 13.4.1 Merging of transportation and the electric grid.

For PEVs, the electric grid becomes the source of the fuel. As shown in Figure 13.4.1, PEVs garner electricity from the home, from the place of work, and in the conduct of business at commercial centers such as big-box stores, shopping centers, and hotels. Referred to as G2V (grid-to-vehicle), extracting energy from the grid adds a new load to the grid. Conversely, PEVs have the potential to provide beneficial attributes to the grid. With what is called V2G (vehicle-to-grid), energy can be extracted from qualified vehicles to serve loads when generating assets are strained.

The existing grid is able to accommodate modest charging events, but as the number of charging events increases (for example, at homes), local transformers may overload and fail. As a result, either upgrades to transformers or controlled charging (that is, smart charging), or both, will be required.

In Figure 13.4.1, while the emissions of pollutants from the tailpipes and electric grid are virtually zero and the emission of carbon from the vehicles is zero, the carbon emissions from the electric grid will not be zero with stationary fuel cells (as mentioned above) operating on fossil fuels (for example, natural gas) and biogas. What is required is a zero-carbon fuel.

Hydrogen as a zero-carbon fuel

For FCEVs, hydrogen is the fuel. For PFCEVs, hydrogen is the “longrange” fuel (300 to 400 miles) while electricity is the “short-range” fuel (50 to 150 miles). While the vehicles themselves emit zero carbon, the supply chain of electricity (as noted above) and hydrogen can be major sources of atmospheric carbon if not carefully planned. For example, hydrogen has been traditionally generated in large plants by the steam reformation of natural gas at elevated temperatures. The principal component of natural gas is methane (CH₄), with concentrations varying around the world from 70% to over 90%. Other components can be other hydrocarbons (for example, propane and ethane) and inert chemicals such as carbon dioxide and nitrogen.

Today, over 50 million metric tons of hydrogen from steam methane reformation (SMR; see Section 13.2) are produced annually worldwide, and 11 million metric tons are produced in the United States to support manufacturing (for example, of chemicals, foods, and electronics) and the refining of petroleum to generate gasoline. Notably, the amount of hydrogen needed to fuel 20 million FCEVs in California (today’s population of all vehicles in California) is just 20% more than the hydrogen generated today for the production of gasoline in California. If all the vehicles were PFCEVs, less than 80% would be required. However, SMR hydrogen has an associated emission of CO₂. What is required is the generation of renewable hydrogen without the emission of carbon.

A representative zero-carbon cycle is shown in Figure 13.4.2 for the future generation, distribution, and utilization of renewable hydrogen for the transportation sector as well as the electricity sector. As described in Figure 13.3.1b, an initial step in the production of renewable hydrogen is the generation of carbon-neutral biohydrogen using tri-generation (Figure 13.4.2 ⓵) for fueling FCEVs and PFCEVs as well as stationary fuel cells. As noted previously, the vast majority of renewable hydrogen is expected to be sourced from the generation of electrolytic zero-carbon hydrogen from otherwise curtailed solar and wind. Not only can electrolytic zero-carbon hydrogen be stored over long periods of time and used in stationary fuel cells as diurnal or seasonal demand requires (Figure 13.3.1b), it can also be used to fuel FCEVs and PFCEVs (Figure 13.4.2 ⓶).

Figure 13.4.2 100% renewable grid and transportation.

To use the California example again, systems analyses show that the amount of renewable zero-carbon hydrogen generated by otherwise curtailed renewable resources will be more than ample to fuel FCEVs. While water is also required, fueling all the state’s 20 million vehicles with electrolytic zero-carbon hydrogen would need less than 1% of the daily water flow in the California Aqueduct. If all vehicles were PFCEVs, less than 0.2% would be required.

For dispensing hydrogen to FCEVs, fueling stations are today being deployed at existing gasoline stations (Figure 13.4.2 ⓶). The locations are already zoned for fueling, and the public is familiar with the location as a fueling site. Hydrogen dispensing can be added to an existing island (displacing a gasoline dispenser) or on a newly established fueling island. Over time, gasoline dispensers could be replaced one by one as hydrogen-fueled vehicles displace gasoline-fueled vehicles.

California, again, provides an illustration of the scale of fueling infrastructure that will be required. Approximately 9,800 gasoline stations serve the California population, with multiple stations often sharing the same intersection. However, hydrogen dispensing will not be required at all of the existing gasoline stations. The reasons include the high efficiency of hydrogen vehicles, meaning they can drive farther before refueling than gasoline-powered cars can, and the replacement of competition from the fuel pricing at intersections (often leading to four gasoline stations at an intersection) to the smart phone. For example, it is estimated that a minimum of 1,600 hydrogen stations are needed to fuel a full build-out of FCEVs in 2050. While this number of stations gives drivers a maximum 6-minute access to a hydrogen dispenser, the actual number will likely be larger in order to not overcrowd any one station. If PFCEVs alone were deployed (that is, no FCEVs), the minimum number of stations required statewide would be 93. The larger the percentage of PFCEVs in 2050, the fewer the number of stations over and above 1,600.

Figure 13.4.3 Hydrogen fueling stations in California in 2019. Green, in operation; yellow, in development; gray, not operational. Reproduced from California Fuel Cell Partnership.

In 2019, the number of hydrogen stations in California is approximately 50 (Figure 13.4.3). They are concentrated at population centers targeted for the introduction of FCEVs by the automobile manufacturers, along with key connector stations (for example, between northern and southern California) and destination stations popular with tourists (for example, Santa Barbara, Lake Tahoe, and Napa Valley).