Notes

1. Obviously, the service "commuting to work" also requires a road infrastructure. Such infrastructures, however, although representing embodied technology, know-how, materials, and energy services, are only indirectly considered part of the energy system.

2. Exergy defines the maximum amount of work theoretically obtainable from a system as it interacts to equilibrium with the environment. While the energy of 11 litres of water at 80°C and 1 kWh of electricity is approximately the same, it should be obvious that 1 kWh of electricity enables the production of more useful work than the 11 litres of hot water. Exergy, therefore, is a quality measure for different types and forms of energy. Moreover, unlike energy, exergy is not conserved and the initial exergy potential is destroyed by the irreversibility's present in any conversion process. Contrary to energy efficiencies, the use of exergy efficiency relates actual efficiencies to the ideal maximum. Although this maximum can never be reached, exergy efficiencies provide a means to identify those areas with the largest improvement potentials or applications where there is a mismatch between the energy service and the energy supplied to provide that service.

3. Useful exergy is defined as the exergy supplied by the service conversion technology (e.g. the mechanical energy at the wheel of an automobile engine, the heat supply to a room by a radiator, or the luminosity of a light bulb), while the corresponding services could be measured in person kilometres travelled, the desired temperature in a room, or adequate illumination for reading.

4. Generating efficiencies are based on the current OECD production mix, which is dominated by thermal power plants.

5. The overall efficiency from crude oil production to the supply of gasoline to an internal combustion engine of a vehicle is, on average, 80 per cent. The overall efficiency of hydrogen produced for the same vehicle, while depending on the primary energy source and subsequent conversion steps, is certainly lower. For example, one possible source-to-currency onboard pathway commences with nuclear-generated electricity, which is used to split water electrolytically into hydrogen and oxygen. The hydrogen then is liquefied (using nuclear electricity) and distributed to the filling station, stored, and dispensed to the cryogenic tank of the vehicle. Based on future technologies, the overall efficiency is expected to range between 20 and 25 per cent. If photovoltaic technology replaces nuclear electricity in this chain at an assumed conversion efficiency of 15 per cent, the overall efficiency of this pathway ranges between 6 and 9 per cent. If the solar radiation is considered free, then the pathway efficiency becomes some 50 per cent. Another pathway could utilize biomass for methanol production. Distribution and dispensing could use the present oil product infrastructures. Onboard the vehicle, the methanol would be re-formed on demand to generate hydrogen. The estimated efficiency is 45-55 per cent.

6. The technologies for effective leakage control exist but are often too capital intensive to be considered economical under present market conditions.

7. There are four routes for a substantial expansion of the role of natural gas in transportation. Two routes use natural gas directly as onboard fuels, i.e. CNG or LNG (liquefied natural gas). The other two routes, methanol and hydrogen, use natural gas indirectly. Although methanol has been promoted as a clean substitute for gasoline, it is unlikely that it will have a major impact on the transportation fuel market. Methanol appears attractive because, unlike the other natural gas options, it is a liquid at ambient conditions and thus can use the existing gasoline distribution and storage infrastructure. Still, the production and use of methanol generates considerable CO₂ emissions. Used in internal combustion engines, the greenhouse gas emissions from methanol are comparable to those from oil products, whereas a significant reduction could be achieved after re-formation and use in fuel cells. Large-scale use of fossil-derived methanol is neither compatible with nor in support of objectives such as eco-restructuring, de-materialization, or carbon free energy service production. Fossil-sourced methanol is, therefore, at best an incremental transition solution. However, the outlook for methanol would change markedly if it were biomass sourced.

8. Storage in depleted natural gas and oil fields is another option; the storage capacities, however, are considerably smaller than ocean disposal and are unlikely to offer permanent solutions to CO₂ emissions from the long-term use of fossil energy sources.

9. An alternative to growing forests for carbon fixation from fossil fuels, however, is to grow biomass sustainably as an energy substitute for fossil fuels.

10. The United Nations Framework Convention on Climate Change (UNFCCC) addresses the issue of technology and capital transfer from the North to the South under the label Activities Implemented Jointly (AIJ). At the First Conference of the Parties held in Berlin in the spring of 1995, it was decided that a pilot phase should be established for AIJ projects. However, no credits to ANNEX I will occur as a result of GHG emissions reduced or sequestered from activities implemented jointly (UNFCCC 1995).