Stand Tall and Speak Up

No “Free Lunches” in Energy

Eve S. Sprunt, 2006 SPE President, president@spe.org

A few months ago, I read an online report that said “Automakers are all investing heavily in what they think will be the next big breakthrough in cars, emission-free fuel cells. These fuel cells, which run on hydrogen and produce nothing but water vapor, are expected to power a new generation of cars that will free the world from reliance on oil.”*

Many of us have read similar news clips or seen equivalent television coverage. If only it were so easy. Remember, there’s no such thing as a free lunch. Everything has some kind of environmental impact. If a sunbeam is deflected from its previous path or if water is diverted, something changes. The issue is whether, in the grand scope of things, society finds the cost/benefit ratio of the change to be acceptable.

To compare different methods of powering transportation, the correct approach is to look at the full life cycle and to compare all the options on a common basis. Evaluation of everything involved in all the components that lead to the end product is a huge undertaking, so usually the comparison focuses on specific aspects—for example, the fuel supply chain. The differences in the emissions associated with manufacturing different components of the vehicle—for example, fuel cells or batteries as opposed to an internal combustion engine—are not included.

In the example quoted, the hydrogen fuel-cell vehicle is like an electric vehicle. It is not a zero-emission vehicle when evaluated on a full life-cycle basis, but rather a remote-emission vehicle. Just as the emissions associated with an electric vehicle depend on the source of the electricity, the emissions involved in use of hydrogen depend upon how the hydrogen is generated.

On earth, hydrogen is almost always found in combination with other elements, as for example in water. Therefore, it is more appropriate to view hydrogen not as an energy source, like hydrocarbons, but rather as an energy carrier, like electrons. Decarbonization of the energy supply may lead us not to a hydrogen economy, but to an electron economy.

With current technology, the most cost-effective method of producing hydrogen is from natural gas and water at high temperatures in catalytic reactors using a process called steam reforming. The hydrogen is subsequently further purified to minimize damage to fuel-cell membranes from contaminants. Worldwide, extensive research is underway to produce hydrogen from renewable sources on a cost-competitive basis, but additional technical breakthroughs are needed to achieve that goal.

On a weight basis, hydrogen has more than twice the energy content of gasoline. For transportation, the key property of the fuel is not energy per unit weight, but energy per unit volume. At room temperature and pressure, a kilo of gasoline is easily transported, but a kilo of hydrogen is not. Even when hydrogen is converted to a liquid at cryogenic temperatures below its boiling point of –252.8ºC at 1 atm of pressure, hydrogen has only about one-quarter the energy density of gasoline. The low energy density of hydrogen means that transportation of hydrogen, whether from the point of production to the point of fueling or onboard a vehicle, is a huge technical challenge.

Fig. 1 compares representative CO2 emissions associated with three different types of light vehicles, standard internal-combustion engines, hybrid vehicles with internal-combustion engines (such as the Toyota Prius or Honda Civic), and hydrogen fuel-cell vehicles. Hydrogen can be used as a fuel for internal-combustion vehicles, but replacement of gasoline with hydrogen generated from natural gas does not significantly reduce CO2 emissions. A larger emission reduction is obtained by switching from gasoline to diesel or compressed natural gas (CNG). However, a change from gasoline to diesel can result in increased NOx and particulate emissions—though this difference is decreasing rapidly with advanced emissions-control technology. The change to CNG requires significantly more storage volume (often with a sacrifice of trunk space) and some added weight for fuel storage to allow equivalent vehicle range per refueling.

Fig. 1—Light vehicle greenhouse gas emissions. (Courtesy H. Sigworth, Chevron Energy Technology Co.)

On a full-cycle basis, for a hydrogen fuel-cell vehicle to generate no CO2 emissions, it must be powered by hydrogen generated exclusively from emissions-free renewable energy. Many technical hurdles remain to generating sufficient hydrogen from renewable sources to replace gasoline and diesel as transportation fuels. Additional challenges remain to making renewable hydrogen and hydrogen fuel-cell vehicles affordable and reliable under a wide range of conditions.

To satisfy society’s growing appetite for energy, we are anticipating that a wide range of energy alternatives must be implemented. In weighing the alternatives, the full life cycle, rather than just a segment of the energy chain, must be considered. When someone tells you about a miracle new form of energy, engage them in a discussion. Help them understand what is needed to bring energy to the point of use.

It will be many years until oil is replaced as the predominant transportation fuel. Everyone in the oil industry should be proud of their role in providing the transportation fuel that enables modern society.

*Source: http://www.newstarget.com/007082.html