When comparing the environmental footprints of alternative energy technologies, it is important that the power generation or combustion stage of the technology not be isolated from other stages of the “cycle.” To accomplish this, the concept of life cycle analysis has been developed. Life cycle analysis (LCA) is based upon a comprehensive accounting from “cradle to grave” of all energy and material flows associated with a system or process. The approach has typically been used to compare the environmental impacts associated with different products that perform similar functions, such as plastic and glass bottles. In the context of an energy product, process, or service, an LCA would analyze the site-specific environmental impact of fuel extraction, transportation, and preparation of fuels and other inputs, as well as plant construction, plant operation/fuel combustion, waste disposal, and plant decommissioning. Thus, it encompasses all segments of the process, both upstream and downstream, and consequently permits an overall comparison (in a cost-benefit analysis framework) of short- and long-term environmental implications of alternative energy technologies. Central to this assessment is the valuation of environmental externalities of current and prospective fuel and energy technology cycles. It should be noted, however, that only material and energy flows are assessed in an LCA, thus ignoring some externalities, such as supply security as well as technology, reliability, and flexibility.

Life-cycle analysis is a scientific process involving the following methodological steps: the definition of the product cycle’s geographical, temporal, and technical boundaries, the identification of the environmental emissions and their physical impacts on receptor areas, and the quantification of these physical effects in monetary terms.

Quantifying the physical impacts of emissions of pollutants requires an environmental assessment that ranges over a vast area—the entire planet in the case of carbon dioxide emissions. Thus the dispersion of pollutants emitted from fuel chains must be modelled and their resulting impact on the environment measured by means of a dose-response function. Generally, for damages to humans, such functions are derived from studies that are epidemiological—assessing the effects of exposure to pollutants in real life situations.

In other cases, the link between the environmental burden, physical impact, and monetary cost is far more complex. In reality, much of the required data is either incomplete or simply does not exist. A number of policy objectives that are more difficult to quantify are also of significance in the planning of future technology options. Currently, the most important of these would appear to be the security of the supply of energy resources and their associated transmission and distribution systems.

To effectively address these environmental matters and energy supply security concerns, radical changes in power generation, automotive engines, and fuel technologies will probably be required. Such changes must offer the potential for achieving negligible emissions of air pollutants and GHGs and must diversify the energy sector away from its present heavy reliance on fossil fuels, particularly gasoline in the transportation sector. A number of technologies, including those that are solar- or hydrogen-based, offer long term potential for an energy system that meets these criteria.

Transportation Sector

Concerns over the health impacts of small particle air pollution, climate change, and oil supply security have combined to encourage radical changes in automotive engine and fuel technologies that offer the potential for achieving near-zero emissions of air pollutants and GHG emissions as well as the diversification of the transport sector away from its present heavy reliance on gasoline. The hydrogen fuel cell vehicle is one technology that offers the potential to achieve all of these goals, provided that the hydrogen is derived from a renewable energy source.

Fuel cells are not, per se, a new energy source, but are a new form of primary energy conversion devices. Fuel cells convert hydrogen and oxygen directly into electricity. They have three major advantages over current internal combustion engine technology in the transport sector. The first advantage is the gain in energy efficiency. “Well to wheels” efficiency for gasoline engines averages around 14 percent, for diesel engines 18 percent, for near-term hybrid engines 26 percent, for fuel cell vehicles 29 percent, and for the fuel cell hybrid vehicle 42 percent. Thus, up to a three-fold increase in efficiency is available relative to current vehicles. The second advantage of fuel cells is their very low emission of air pollutants. Regardless of the type of fuel used, fuel cells largely eliminate sulphur and nitrogen oxides and particulates that are associated with conventional engines. The third advantage is the negligible emissions of GHGs.

Prototype fuel cell buses powered by liquid or compressed hydrogen are currently undergoing field trials in North America, while the European Union is supporting the demonstration of 30 fuel cell buses in 10 cities over a two-year period, which commenced in 2003. In addition, the United Nations Development Program Global Environmental Facility is supporting a project to demonstrate the technology using 46 buses powered by fuel cells in the heavily polluted cities of Beijing, Cairo, Mexico City, New Delhi, Sao Paulo, and Shanghai.

There are a number of reasons why hydrogen in compressed form seems to be a likely option for large vehicles, such as buses. Large vehicles return regularly to a depot, thus minimizing fuel infrastructure requirements, their large size minimizes the need for compactness of the technology, and they operate in urban areas, so low or zero emissions vehicle pollution regulations will assist their competitiveness as compared with diesel-powered buses. Additionally, subsidies may be available from urban authorities in order to demonstrate urban pollution reduction commitments. Hydrogen buses also avoid pollution problems related to diesel buses and operate almost continually over long periods, making them attractive fuel-efficient technology.

Fuel cell cars are currently being developed by all of the world’s major automobile companies, but there are significant obstacles to their widespread adoption within the foreseeable future. Briefly, these include the relatively high cost of fuel cells in the absence of economies of scale in production, on-board storage space of hydrogen, the lack of a hydrogen-refueling infrastructure, and public perceptions with regard to the safe use of hydrogen. Nevertheless, concerns relating to the security of oil supplies have encouraged the governments of many developed nations to invest significant resources into hydrogen research to overcome these shortcomings as soon as practicable.