Interference with the Earth’s climate system by mankind is widely accepted as something that will impact heavily on the future of the planet. The increase in the global average surface temperature since the industrial revolution is thought to be linked to the concentration levels of various so-called ‘greenhouse gases’, which have risen from an equivalent of 280ppm carbon dioxide (CO2) to around 430ppm today. CO2 has been identified as the most important greenhouse gas, contributing 60 percent of the increased global warming effect. The associated temperature rise is projected to accelerate during this century and global warming is predicted to cause increase in sea levels and precipitation leading to higher risks of flooding of low-lying countries.

 

Compared to liquid fuels, molecular hydrogen has significant disadvantages as a fuel, nearly all of which are concerned with its distribution and storage. Since it is a low-density energy storage medium, only about 20 percent of the energy which can be stored in a tank of gasoline can be stored in a hydrogen tank. This means that frequent refuelling will be necessary. Furthermore, by necessity, there will be a period requiring vehicles to be of dual-fuel nature in the transition to any alternative fuel economy, i.e. vehicles will have to carry two independent fuel systems. BMW and Mazda now offer dual-fuel hydrogen/gasoline vehicles for fleet trials. These share three characteristics: reduced power and range on hydrogen, the need for two separate fuel systems, and the complexity, mass and expense of the hydrogen tank. It should be noted that even at production levels of 100,000 per annum, estimates of US$ 14,250 have been made for the cost of such systems. These vehicles also highlight the fact that a dual distribution infrastructure will be necessary in any transition to a molecular hydrogen economy: this has huge cost implications for the fuel distributors and retailers.

 

 

Production of ethanol makes it possible to reduce fossil-based CO2 release by using biomass as the main feedstock in its production, leading to a partially-closed CO2 production-and-use ‘cycle’. With current levels of technology using sugars as the feedstock, up to 90 percent of the CO2 can be kept in this cycle, though the savings are very process-dependent. However, it would not be possible to provide much more than 10 percent of the primary energy required for road transport from ethanol, and there are concerns about using food crops as the primary feedstock, which is ethically unacceptable and (in many cases) geopolitically impractical. These concerns have spurred the development of new production processes which break down the lignin and hemicellulose in biomass or waste to manufacture ethanol; such processes promise to further increase the proportion of CO2 capture and simultaneously to massively increase the proportion of renewable energy available to transportation without affecting food production.