Transport fuels
Although oil is an energy and chemical source in itself, when it comes to transport fuel it is energy storage per unit of volume and weight that is its main advantage over, say, electricity.
Electricity is already a viable transport energy alternative to oil in the urban areas where vehicles can be connected to the grid. But it is debateable if this is friendlier to the environment than petroleum. While electric motors are very efficient there are significant losses in the transmission of electricity over the grid, particularly to light rail (trams) where voltages must be kept low, and the electricity has to be generated by some means. In Australia this means burning coal or natural gas to make steam to drive turbo-alternators. Thus busses that use natural gas directly are likely to be more environmentally friendly than say, light rail, although this is very dependent on operational circumstances. Until we use nuclear or solar power to generate electricity, electric vehicles will remain just as polluting and resource consumptive as efficient petroleum or gas fuelled vehicles.
Electricity is not suitable for long distance road or air transport. In these areas the energy density (both by volume and weight) of the fuel used is a critical factor, influencing both the efficiency of transportation and its economic and technical realisation.
Hydrogen
The energy density of petroleum, in the form of petrol and aviation fuel is 46.9 and 42.8 MJ/kg, respectively. By volume to they yield 34.6 and 33 MJ/L. This compares with liquid hydrogen that yields only a third as much energy per litre but three and a third times more energy per kg.
Hydrogen is the most common element in the universe. On Earth almost all hydrogen occurs in its oxidised state, water. Because its reduction is expensive the main sources at present are biological in origin (fossil) about half comes from natural gas deposits and most of the remainder from oil and oil refining and from coal (see above). Although it comes from similar sources, hydrogen is presently more expensive, as a source of energy, than petroleum due to difficulties in handling and storage.
Fossil hydrogen obviously suffers the same resource limitations as petroleum. But effectively unlimited amounts of hydrogen can be made by the electrolysis of water. This is relatively expensive as it consumes electricity that, in turn, needs to be generated somehow (with consequent energy losses and capital investment). Thus hydrogen is a possible means of storing and transporting cheaply generated electricity. Only the lighter hydrogen component need be transported as the oxygen component is released to and recovered from the atmosphere at source, regenerating the water. This is the basis of the proposed ‘Hydrogen Economy’, cheap electricity would be generated using solar, geothermal or tidal power in remote locations and used to produce hydrogen which would then be compressed or liquefied and transported (or piped) to where the energy was required, where it would be converted back to electricity in a fuel cell or burnt (re-oxidised) to generate heat.
Some new technologies are under development in support of a Hydrogen Economy. High temperature electrolysis of water (HTE) requires considerably less electrical energy than conventional electrolysis. At even higher temperatures, hydrogen can be directly separated from water using the sulphur-iodine cycle. This promises very high efficiencies. This cycle has been demonstrated experimentally in several nuclear reactors worldwide but there are significant materials and design issues to be resolved. Nuclear plants are currently in the design phase that will produce both electricity and hydrogen by one method or the other. The overall efficiency of such a plant could be very much higher than existing nuclear plants, particularly as this would (if used in conjunction with fuel cells and local hydrogen storage) provide a means of optimising (peak v base) energy loads. It is possible that a future high temperature solar plant might employ the same technologies if the technical difficulties can be resolved.
In any electrolysis solution very significant quantities of water are implicitly transported concurrently from the generator to the consumer. This precludes low cost energy sources in deserts from participating in an electrolysis/hydrogen based solution.
Liquid hydrogen is the principal fuel of the space shuttle. It is very much more expensive to produce than gaseous hydrogen as it must be liquefied in very capital intensive equipment, using a great deal of energy (compression and latent heat, released as heat in the process), and then stored at minus 253° C. It is stored uncompressed, in cryogenic containers, and in order to retain its low temperature is constantly gently boiling and thus giving off hydrogen gas. This is both flammable and highly explosive if allowed to accumulate, for example in a vehicle cabin or a garage. In an accident if it splashes it may cause serious freezing injuries and, if ignited it burns rapidly, consuming all the available oxygen. In a large (eg tanker) fire it may asphyxiate victims in the accident area. But it is also quick to disperse and leaves no on-going risk to rescuers. A number of references suggest that on balance it is safer than petrol. Due to its high energy density per kilogram liquid hydrogen is a technically viable alternative fuel for air travel, where it would have significant environmental and efficiency advantages and accidents are usually remote from other infrastructure and rare. It will be very much more expensive than the kerosene presently used to fuel Aircraft. It is unlikely that liquid hydrogen could ever be made safe or cheap enough to use in cars, busses or trucks travelling in urban areas.
Compressed gaseous hydrogen is equally problematic. The energy density per litre is much lower and even when the tank is fully compressed it is less than one 7th that of petrol. A 700Bar tank, needed to get anywhere near this energy density, is very heavy and may explode in an accident. But the fire danger is said to be lower than that of petrol. Nevertheless as the survivors of the Hindenburg and those of us who have filled large plastic bags with hydrogen gas, and set them floating skyward with a burning paper tail know, hydrogen makes a very nice woomp, and spectacular flame when ignited.
Unlike liquid gases, the energy density of compressed gas declines as the tank empties and the pressure falls. From an energy density point of view even coal is a denser transport fuel than compressed hydrogen gas (recall the steamroller, steam trains and wagons of the past). But using fuel cell technology, far more of the stored energy in hydrogen can be converted to electricity and then to mechanical energy and transmitted to the wheels. A number of demonstration vehicles have been built using hydrogen as fuel. Most of these store the hydrogen in the form of metal hydrides rather than as a compressed gas. This technology is much safer, and is effectively emissions free, but adds significantly to the weight (about four times that of an equivalent full petrol tank), volume (about three times), initial cost (hundreds times more expensive) and complexity overall. It also has potential environmental costs and consumes scarce resources.
In the laboratory (and by children inflating balloons) hydrogen is commonly generated via a replacement reaction employing aluminium and caustic soda and this has sometimes been proposed as a method of fuelling a vehicle. But this is highly energy inefficient as the energy cost of creating both aluminium and caustic soda is very high and the energy efficiency at each step is low.
Hydrogen gas may already have been overtaken in energy density (by weight), safety and convenience by electricity storage in new high efficiency (eg lithium ion) batteries and possibly by other chemical energy storage options.
Electricity
Electricity is the ideal pollution free energy source. Electric motors are smaller and much more efficient than internal combustion engines; they are quieter, cooler and create zero emissions. In cars each wheel can have its own motor, obviating the need for gearboxes and differentials.
If electricity is stored in batteries, vehicles can use regenerative braking to recharge the batteries going down hills or when stopping. This is not available to hydrogen or petroleum fuelled vehicles.
Hybrid cars are already available that use a combination of battery and petrol power and it is possible that new battery technology might allow vehicles to ‘park and plug’ to eliminate the petrol motor component completely.
Because it is possible to control the times when batteries are recharged (eg through smart metering) irregularities in grid utilisation can be smoothed and as electric vehicle utilisation increases. And this might be done on a vey local basis. This could be used to offset the fluctuating electrical inputs from wind turbines and solar power generation.
Electric vehicles are familiar and very mature technology. The technology is used for trams, trolley buses, for milk delivery (particularly in Europe) and wheelchairs for the disabled and elderly. Electric motors produce no exhaust and are relatively quiet and maintenance free. These vehicles have previously needed to be connected to wires to the electricity supply or were very constrained in range, acceleration, carrying capacity and ability to repeatedly handle steep gradients.
Battery technology is now approaching a point at which it becomes possible to build a practical private motorcar that provides similar utility to one with a standard internal combustion engine.
Electric Cars
By using electricity generated outside of cities they effectively transfer the exhaust gas (and any pollution) to the electricity generation plant. If this electricity is produced from a non-combustion source such as wind, nuclear or solar there is no carbon pollution except that generated in the initial manufacture transportation and maintenance of the equipment involved in the various processes involved. According to a British parliamentary report, nuclear power has the lowest whole of life carbon footprint, followed by wind then solar.
But as over 80% of electricity in NSW now and for the foreseeable future is generated by burning coal and gas this benefit is limited to the transfer of the pollution and primarily focused on Sydney; which has the most serious ventilation and vehicle exhaust pollution issues.
Hybrid vehicles such as the Toyota Prius are already successfully competing with conventional internal combustion powered vehicles. These use the facility of electrically powered vehicles to regenerate electricity when running downhill or when braking. This energy is returned to the vehicle battery. The electricity to charge the battery for normal running is generated by a smaller conventional internal combustion engine that would normally power a car of that size and this combined with a more even power demand on the engine delivers greatly improved fuel efficiency.
Fully electric vehicles achieve similar energy efficiency but all the power required is provided by the remote engine (the electricity generating power station) and is stored in the vehicle battery.
Large stationary engines (steam turbines) are more efficient than small internal combustion engines but the electricity transmission grid consumes a proportion of the electricity generated offsetting this advantage. Further, existing petrochemical fuels have a lower carbon footprint than coal as they contain more hydrogen (that burns to water).
These factors mean that in NSW and Australia a fully electric car will have a larger carbon footprint than an equivalent hybrid for the foreseeable future.
An important disadvantage to electric vehicles is the present very high capital cost per vehicle. This is due first to the cost of lightweight batteries and second to the relatively low production runs of the vehicles and their components.
The original electric cars used the common lead acid battery technology still commonly used in cars and trucks. This has a very low energy density compared with liquid petroleum or even liquid petroleum gas and hence a very short range and or much higher weight and volume.
Modern battery technology (for example that used in mobile phones) has a very much higher energy density; approaching that of various hydrogen fuel alternatives; but still some way below that of petroleum. The leading current technology for electric vehicles is lithium-ion (Li-Ion) and its variations. This is used by all 'new generation' electric vehicles except one (that uses sodium metal chloride).
At the present time these batteries are still extremely expensive.
Notwithstanding much higher energy densities advanced batteries are still well short of the energy density provided by petroleum. Adding extra batteries adds volume weight that compromise performance and cost. Achieving a practical balance between these factors gives most present and proposed electric vehicles a range of around 100Km at which point they must be recharged. Thus there needs to be a recharging facility at the destination.
A shorter range would make the vehicle less expensive, improve its performance and reduce recharging time. So once these vehicles are commonplace and recharging stations can be found anywhere the technology will become more practical.
Until an electric vehicle user can be confident that the vehicle can be recharged anywhere they go it will be difficult to go far afield or to take unplanned side trips or excursions.
Further, there is not yet a single standard for recharging these vehicles with a common plug, voltage, frequency (if AC) or charging rate. There is not yet a suitable cost regime for such services. And there are several competing recharging and/or battery ownership models; including one in which batteries are exchanged rather than recharged by the vehicle owner. There will need to be a considerable 'shake-out' of these alternative models as the technology matures.
The battery technologies on which these vehicles depend are still very new, less than five years old. There are several competing battery technologies and although none presently matches the energy density of the Li-Ion family of batteries, some of these may be more appropriate to electric vehicle use and may be safer. The Toyota Prius uses more mature and less energy dense NiMH technology for this reason.
Lithium-ion battery technology has undergone rapid development but has had a number of hurdles to overcome. Early versions had relatively poor recharge cycle performance and the recharge and discharge rates both need close management to avoid shortening the overall life. The technology did not work well at temperatures below freezing or over 40 degrees Celsius. Batteries need to be cooled when in operation and there are still issues at the very low, or very high, temperatures experienced in extreme conditions (eg in a desert or the mountains).
Similar technology used in Laptop computers has resulted in explosions and fires. Batteries used in cars are very much larger than those used in a laptop and are, when charged, concentrated packages of many hundreds even or thousands of kilowatt hours of energy.
Unlike petrol, that is relatively safe as it consumes limited available oxygen to release its energy, battery energy may be immediately released in the event of an accident or electrical breakdown. Carrying a battery storing about the same energy as just 13 litres of petrol is roughly equivalent to carrying the explosive in a US 500 Pound Bomb [13 litres of Petrol = 116kWh = 418.4 MJ = 100kg TNT]; capable of destroying a substantial building. Because of this danger the batteries need elaborate built in electronics and must be compartmentalised with intermediate current limiting devices to ensure that any failure is contained to one section.
While every effort is made to avoid safety issues the technology is as yet unproven and could have a serious set-back should there be 'an incident'. Anyone who has seen what happens when a standard car battery explodes will take pause.
Electric Trains
Largely because of electricity’s convenience and low emissions, electric trains, trams and trolley buses are already widely used in urban areas. And because electricity is difficult , and potentially dangerous, to store the great majority of urban and long distance electric vehicles are connected to the electricity grid using electrified rails or overhead conductors.
In order to reduce resistive heating losses in these conductors, electric vehicles need to run at the highest voltage that is consistent with community safety. When wires run in public streets the light rail supply is limited (to 600V DC on Melbourne trams and to 700V DC on the more modern Sydney light rail). Heavy rail uses a more efficient higher voltage overhead supply (1500 volts DC in both New South Wales and Victoria – systems dating back to 1925). DC was used because practical AC traction motors awaited the development of high voltage high current silicon thyristors in the 1960s’.
If electric transport is to be expanded it would be very desirable that present system losses were minimised by the use of up-to-date technology.
To achieve this and to increase energy efficiency it would be desirable that the supply voltage was raised and that AC was used. But this would require a complete upgrade and replacement of all locomotives and commuter rolling stock in NSW (and Victoria). Several other Australian States already use more recent technology. Modern high-speed electric trains and heavy goods locomotives typically use 25,000V, 50Hz AC, for their overhead conductors. This is an argument for a separate ‘very fast train’ passenger, and separate high voltage freight network (Brisbane to Melbourne via Sydney). And rather than invest in more outmoded heavy rail suburban transport it would be a good idea to install modern metros in Sydney, Newcastle and possibly Wollongong.
A suburban Metro in Newcastle could preserve the controversial existing rail easement to Newcastle Station while allowing its paving as a pedestrian mall, across which people and cars could amble, as they do across tramways in Melbourne. The Newcastle Metro might eventually be connected to Sydney via a very fast passenger line, taking a coastal route with appropriate tunnels and viaducts. It might run east of Gosford and cross the Hawkesbury from Pearl Beach to West Head and then East to join a new northern beaches Metro line before passing through Ryde (the main Sydney Hub) and on to Melbourne. It could connect to this Metro line at say Ingleside or Terry Hills.
For Example:
The northern beaches Metro is needed now and would run through: Narrabeen; Brookvale; North Manly; Seaforth; and Cremorne; to North Sydney. This is similar the the route that Sydney's trams once ran.
Liquid Petroleum Gas
As an alternative to diesel and petrol, liquid petroleum gas (LPG) is already widely used for transportation. Australia’s reserves of LPG are far greater than those of petroleum oil but these are largely exported and could be depleted at about the same time as oil runs out. LPG is a mixture of propane and butane. It is possible to produce these gases by coal gasification but because not all the gases produced from coal, including hydrogen, are easily compressed the best method of achieving this would be a co-generation plant to produce electricity and transport gasses.
Many of these technologies will become economic as the price of petroleum rises after ‘peak oil’. Coal substitution technologies will soften the impact of peak oil. But because of relatively easy substitution, the coal price is linked to the price of petroleum. It is certain that as the cost of petroleum increases, so will the price of coal. As a result the cost of coal fired electricity is likely to rise substantially in the next two decades.
Coming on top of this are present concerns about carbon dioxide and the greenhouse effect. These will certainly lead to a carbon tax in the near future resulting in additional cost pressures on fossil energy sources. But although carbon taxes will bring on alternative energy sources more quickly and slow the rate of carbon dioxide release, the use of taxes to prevent exploitation (rather than simply making it more expensive) is probably politically untenable and impossible to enforce worldwide. Thus unless a lower cost alternative is developed, making the remaining reserves uneconomic to extract, coal and oil reserves will still be fully exploited, releasing the same amount of carbon dioxide as before (albeit at a higher price and over a slightly longer time frame).