Hydrogen (H2) is the most abundant of element on earth. It is a secondary source of energy. That means it stores and transports energy produced from other resources (fossil fuels, water, and biomass). Hydrogen does not exist by itself; it has to be separated from the other elements with which it commonly combines. Hydrogen can also be produced by passing electricity through water, breaking the water into its constituent components of hydrogen and oxygen.
Hydrogen has a variety of industrial uses and is a key part of the fossil-fuel refining process. It has been used as a fuel in NASA spacecraft for more than 70 years. It also has a long history of being used as a fuel for land-based vehicles. That has intensified over the past few decades. Hydrogen has enough energy density to function as a transportation fuel, but it needs to be compressed or cryogenically cooled. H2 is considered a zero-emission fuel since, when used in a fuel-cell vehicle, its only tailpipe emission is water vapor. It is viewed as a viable transportation fuel since it has the potential to provide relatively long driving ranges, as well as refueling times, comparable to conventional fuels like gasoline and diesel.
According to the National Renewable Energy Lab (NREL), most hydrogen production occurs by steam reforming natural gas. This process releases some carbon dioxide in the process that adds to the greenhouse effect. Hydrogen has a relatively high energy for its weight, but very low energy for its volume, so new technology is needed to store and transport it. And fuel cell technology is still in early development, so improvements in efficiency and durability are needed.
One of the key elements for the environmental evaluation of hydrogen is based on its production process. This has led to an unofficial, though widely used, system of classifying hydrogen by color signifying its origin and relative positive environmental impact. The system as it is generally recognized has four main “colors” of hydrogen:
There are about 48 hydrogen vehicle fueling stations in the US, nearly all in California according to the Energy Information Administration.
Hydrogen in Transportation Applications
There is a general consensus that hydrogen-fueled vehicles are a viable strategy for decarbonization of the transportation sector. Engine and vehicle manufacturers are exploring two strategies for using hydrogen to power their engines and vehicles: fuel cells or internal combustion engines.
Fuel cells have long been the primary focus of hydrogen development, where a process known as electrolysis creates electricity that then drives electric motors. Further refinements are needed to meet the power and other demands in vehicle applications.
Use of hydrogen in an internal combustion engine is gaining new ground. The approach does produce a small amount of emissions including NOx, particulate matter (PM), and more because of the lubricating oils used in the engine.
While hydrogen used in vehicles has clear environmental benefits over fossil fuels, as with all alternative fuels, lifecycle carbon consideration must be evaluated, including fuel production and transportation, as well as vehicle tailpipe emissions.
Current policies in the three major vehicle markets – China, the United States, and the European Union – all support hydrogen as a transportation carbon reduction tool and have financed demonstration projects to illustrate the potential of the technology.
For much of the past 20 years, the development of hydrogen-fueled vehicles has focused on passenger vehicles. Nearly all the major automakers participated in projects such as the California Fuel Cell Partnership to pursue policy support and share early-stage technology development.
Use of fuel cells in transit buses is growing, with several options available that compete with diesel, natural gas, and battery electric buses. Cost of fuel cell technology and access to refueling are barriers to wider spread adoption.
Manufacturers are now focused on the heavy-duty sector as hydrogen-power is increasingly seen as a path toward a zero-emission truck capable of being a one-to-one replacement for a long-haul diesel truck. With longer ranges and faster fueling than battery-electric trucks, this appears to be a segment suited for hydrogen-fueled trucks. The fast-fueling capability also could be an advantage over battery-electric trucks in other sectors as well.
Hydrogen-powered demonstration vehicles are being launched in off-road sectors such as construction equipment, marine and rail. The advantage in these sectors is similar to on-road vehicles that have the power and functionality of diesel, but with zero emissions.
While some of the heavy-duty on-road demonstration programs have shown the capability of hydrogen-powered vehicles to perform in the real world, they’ve also demonstrated the need for new fueling infrastructure. Off-road pilot projects are in still the early stages.
The attraction of zero emission vehicles delivering as good, or even better, performance than the diesel or gasoline powertrains they’re replacing is real. On-road H2-powered fuel cell, or internal combustion engine, models are demonstrating the viability of the technology.
Its challenges remain high. While a nascent light-duty fueling infrastructure remains under development in California, little exists elsewhere in the US, so any hydrogen vehicles are limited to in-state use. While that infrastructure has become more robust during recent years, it still faces serious issues of reliability and supply challenges. Vehicle production remains limited to low-volume operations. While concept models of future fuel cell cars have been shown, none are for sale yet.
The challenges are even greater for the on-road and off-road heavy-duty sector. The vehicles being developed are significantly more expensive than the typical diesel they aim to replace, the fueling infrastructure is basically non-existent and expensive to create, and longer-term issues such as durability and reliability have yet to be established.
Government regulations are encouraging and supporting technologies such as hydrogen-fueled vehicles, mandating a switch to zero emission technology. Incentives to cover some of the incremental costs of the advanced technology are available, as are other grants for infrastructure development. Fuel cell technology is not commercialized as of yet, but industry representatives have said publicly that they expect to have vehicles for sale by the end of the decade (2030).