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Stabilizing atmospheric levels of carbon dioxide (CO2) will eventually require deep reductions in anthropogenic emissions from all sectors of the economy. Managing CO2 emissions from the transportation sector may be the hardest part of this challenge. In sectors such as power generation, several options are currently available including wind power, nuclear power and carbon capture and storage (CCS) technologies. Each can be implemented, in the near term, at a scale large

Geo-Engineering Climate Change: Environmental Necessity or Pandora's Box?, eds. Brian Launder and Michael Thompson. Published by Cambridge University Press. © Cambridge University Press 2010.

enough to enable deep reductions in CO2 emissions at costs of under $100 per tonne CO2 (tCO2) or an electrical premium of the order of $37(MWh)-1, based on representative CO2 emissions from a pulverized coal plant (IPCC 2005). It is recognized that in the last few years, the capital costs of constructing heavy equipment have escalated rapidly here and elsewhere; but we assume that recent capital cost increases are a transient phenomenon and use cost estimates prevailing in the 2000-2005 time window. Adding this premium to the lowest cost of electricity, subcritical coal at $48 (MW h)-1 (Breeze, Chapter 5), we establish a total electricity cost of $85 (MW h)-1. All of the options listed by Breeze are below this threshold with the exception of expensive wind power sites. The transportation sector does not have such low-cost solutions. While there is ample opportunity for near-term gains in overall vehicle efficiency, these improvements cannot deliver deep cuts in emissions in the face of increasing global transportation demand.

Beyond efficiency, deep reductions in emissions from the transportation sector will require a change in vehicle fuel. Changes in fuel are challenging owing to the tight coupling between vehicle fleet and refuelling infrastructure. Economic network effects and technological lock-in arise because users demand ubiquitous refuelling, yet investments in new fuel infrastructure are typically uneconomic without a large vehicle fleet. Moreover, each of the three leading alternative fuel options, hydrogen, ethanol and electricity, faces technical and economic hurdles precluding near-term, major reductions in transportation emissions using these technologies.

We consider a fourth alternative: carbon neutral hydrocarbons (CNHCs). Hydrocarbons can be carbon neutral if they are made from carbon recovered from biomass or captured from ambient air using industrial processes. The individual capture technologies required to achieve CNHCs have been considered elsewhere; our goal is to systematically consider CNHCs as an alternative and independent route to achieving carbon neutral transportation fuels. We compare various methodologies for producing CNHCs, in terms of dollars ($) per gigajoule (GJ) of delivered fuel, using hydrogen as a reference case. We argue for the development of CNHC technologies because they offer an alternative path to carbon neutral transportation with important technical and managerial advantages. We do not claim that CNHCs are ready for large-scale deployment or that they will necessarily prove superior to the three leading alternatives. We do argue that they are promising enough to warrant research and development support on a par with efforts aimed at advancing the alternatives.

CNHCs are effectively an alternative method for using carbon-free hydrogen, as shown in Figure 7.1. Converting CO2 into fuel by adding hydrogen can be viewed

Figure 7.1 Two pathways for using centrally produced hydrogen in the transportation sector.

as a form of hydrogen storage (Kato et al. 2005). Once the hydrogen is produced, a choice exists between distribution and incorporation into a hydrocarbon fuel. The latter is potentially attractive because the energy cost of centrally produced hydrogen is inexpensive compared with crude oil or gasoline at the pump. Even with CCS, hydrogen can be produced from coal or natural gas at costs in the range $7.5-13.3 GJ-1 (IPCC 2005), whereas the current cost of crude is $17 GJ-1 (at $100 per barrel) and the cost of gasoline exceeds $20 GJ-1 (neglecting taxes). The barrier to the use of hydrogen in transportation systems is distribution and vehicle design rather than the cost of central hydrogen. When CNHCs are considered, the competition is between developing a new distribution and use infrastructure or capturing CO2 and synthesizing a hydrocarbon.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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