Energy challenge will drive traction policy
The rail industry must reduce its energy consumption, for both environmental reasons and to contain the increasing cost of energy. Alternative fuels offer few advantages, and the best option may be to capitalise on strategies being adopted by the electricity generation industry to reduce carbon emissions, suggests Professor Roger Kemp
Professor Roger Kemp FREng is Professorial Fellow in the Engineering Department at Lancaster University, after a long career in the traction industry, where he was Engineering Director of GEC Transportation Projects Ltd
THE NEXT FEW years will be a challenging time for traction engineers. Energy and emissions will be the major driving forces in the evolution of rail traction technology, as the industry looks to maintain its environmental advantage over other modes and to control the inflationary effect of recent increases in energy costs.
Oil prices increased from US$10/barrel in 1999 to US$100/barrel at the end of 2007, and there are no indications that price rises will stop in the near future. There may be further problems for rail operators which have been paying little or no tax on their fuel. They may now find themselves paying carbon taxes like any other energy user.
While other commercial and domestic users can reduce their energy consumption in a few days by turning down thermostats, driving road vehicles more slowly or switching off lights, rail operators are often faced with a seemingly unalterable fuel bill. Commitments to governments or regulators require adherence to timetables or service levels, and changes to the physical infrastructure or rolling stock fleets can take decades.
In November there was a debate in the UK, between the Department for Transport and the rail industry, over the need for further electrification. But even if agreement is reached, significant work on the ground is unlikely to start for another five years and the effect on energy bills would not be felt for more than a decade.
A study published last July by the UK's Rail Safety & Standards Board1 identified several areas where 'quick wins' could be made in energy use. These include reducing the stabling load of electric trains, better matching of train length to passenger loadings, better train regulation and driving techniques and reduced diesel engine idling. In total, these were estimated to account for more than a quarter of total energy consumption. But whilst optimisation is always desirable, actual savings are unlikely to match the theoretical value.
The politics of energy
Apart from the direct cost of energy, there are important political considerations in keeping down energy use. Most rail operations rely on public subsidy to some extent and, increasingly, the rationale for this is that rail is seen as 'a good thing' environmentally.
The United Nations is arguing for an 80% reduction in energy use by developed countries, and the European Union is discussing road vehicle emission targets of 100 to 120 g/km. So the justification for transferring passengers from road to rail will depend, at least in part, on the industry reducing its energy use and CO2 emissions to maintain a clear environmental benefit. This is a challenging target as train speeds increase, passengers demand better facilities and safety requirements increase train weight.
Following the privatisation of the UK rail industry in the 1990s, several operators replaced 200 km/h diesel HSTs with shorter, high -performance DMUs. Environmentally these compare reasonably well with the current generation of road vehicles, but they will still be in service in 2020, by which time private cars will probably have reached CO2 emission levels of less than 120 g/km. This will have eroded any environmental benefit, and raises the question of how the rail industry will justify support from the public purse.
Electric traction evolves
The last 30 years of the 20th century was an interesting time to be a power equipment engineer. At the end of the 1960s there were still locomotives and EMUs in service with mercury-arc rectifiers2 and almost all DC units used resistor control. Over the following years traction technology moved rapidly through diode rectifiers, thyristor choppers, phase-angle controlled converters, voltage and current-fed inverters, synchronous motors, switched variable reluctance motors, induction motors, bipolar transistors, GTO choppers and inverters and, most recently, IGBT inverters and permanent-magnet motors.
For traction engineers, efficiency has always been important. In the 1980s SNCF undertook a major study3 into the efficiencies of three different types of drive on a locomotive producing 3 MW at 180 km/h. The DC drive beat the asynchronous drive by 3%, but modern semi-conductors have since brought the efficiency of the AC drive up to that of DC. The induction motor fed by an IGBT inverter is now the drive package of choice for almost all applications.
Regenerative braking has also produced significant improvements in energy efficiency. Hong Kong's MTR Corp reported a 46% improvement when its EMUs were changed from camshaft control to GTO choppers4. The switch from phase-angle controlled thyristor converters to regenerative force-commutated input converters on 25 kV networks has allowed regenerative braking which operates at a near-unity power factor, reducing both line currents and losses in the catenary. Measurements on Alstom's Class 390 Pendolino trains for Virgin West Coast show savings of between 16% and 18% following the introduction of regenerative braking.
But the big energy savings have now been made. Further developments will make small improvements - 1% here, 0·5% there - but major savings have to come from new approaches.
Many operators have been investigating alternative energy supplies to boost their environmental credentials, but this raises the fundamental question whether there is such a thing as 'green electricity'.
SNCF's TGV fleet draws power from the national grid, and as 80% of French generation capacity is nuclear, it can be argued that the carbon footprint is very low. So TGVs are environmentally friendlier than road transport, even if they use more energy per passenger-km.
Following the same line of argument, it is reasonable to assume that a high speed line in Norway would be environmentally desirable, as much of the electricity would come from hydro-electric sources. However, Are Wormnes of the Norwegian Centre for Transport Research argues that the country's electricity cannot be deemed carbon-free. There is only a certain amount of hydro-power and, if it were not used for a high speed line, it could be exported to Germany to replace the burning of lignite in conventional power stations, for example.
Similar arguments can be made about the choice of electricity supplier elsewhere. Generation in the UK uses a variety of fuels, predominantly gas (40%), coal (33%) and nuclear (20%). It can be argued that if the railway contracts with a nuclear generator the electricity is 'carbon-free', but if it buys from an operator of coal-fired power stations trains are responsible for a much higher carbon footprint. But is this valid?
The UK electricity market is subject to a regular auction process, in which generators bid to supply the available load and all operators are paid at the highest rate accepted. Operators of wind farms and nuclear power stations usually bid low, as this reflects their marginal cost of production and guarantees that their output will be accepted. The price they receive is related to the highest bid, which is likely to be from a coal-fired or open-cycle gas station where fuel represents a large fraction of the marginal cost. If a renewable energy or nuclear operator sells electricity directly to a large user, like a railway, there is less 'green' electricity going into the pool for other users. Thus the rail operator's choice makes absolutely no difference to the country's overall CO2 emissions.
Luckily, the production of electricity is being de-carbonised. The EU has agreed a binding target that 20% of energy consumption should be met from renewable sources by 2020, which effectively means that 40% of electricity will have to be generated by renewables. Add to this the likely increase in nuclear power and electric traction - at least in Europe - will have a progressively smaller carbon footprint. But this is still not enough to meet the long-term objective.
Can biofuel replace diesel?
A big question mark hangs over the future of diesel traction, particularly on the large networks in North America.
On both sides of the Atlantic there is political enthusiasm for producing fuel from biomass, but the rationale is sometimes not obvious. Politicians may claim that it is to reduce the carbon footprint of transport, but frequently the motivation appears to be to reduce the negative effect of rising oil prices on the balance of payments, to subsidise a key agricultural constituency or to insulate critical infrastructure from political tensions in the Middle East.
If a rail operator converts its entire fleet to run on biofuel, is it reasonable to claim this is low-carbon transport? Unfortunately the answer is probably no.
By the time transport, fertiliser production and the drying out of soil are taken into account, relative to the fossil fuels they replace, greenhouse gas emissions are reduced by only 12% by the production and combustion of maize-based ethanol, or by 41% using soya bean biodiesel5. In the worst cases, the biofuels are actually responsible for more greenhouse gases than the oil-based fuels they replace.
And some biofuel production is responsible for loss of rain forests and thus indirectly for an increase in net carbon emissions.
'Environmentally-responsible biofuel production' as a concept is similar to 'green electricity' - it may make the user feel better but has little basis in fact. If an environmentally-aware industrial consumer buys palm oil from a sustainable plantation, other organisations buying from that plantation are squeezed out. At the end of the chain, a less environmentally-responsible company clears virgin forest to produce the oil it needs.
If we assume that by 2020 all modes of liquid-fuelled transport will have achieved the very optimistic target of biofuels making up 20% of total fuel use, and that the total greenhouse gas contribution of biofuels, in terms of CO2 equivalent, is 50% of that of conventional diesel (which is current good practice), all modes of transport would see a 10% reduction in emissions. This would have almost no effect on the relative environmental impact of different modes and, taking into account predicted travel growth, would be far short of the target of a 30% cut by 2020 and 80% by 2050 from developed countries proposed by the UN.
Large sums are being poured into the development of hydrogen fuel cells and one might expect rapid progress. However, we have to ask whether the fuel cell is appropriate for the rail sector. Different countries have different priorities. The emphasis in the USA, at least as far as transport is concerned, is to decouple the personal mobility of the automobile from the vagaries of long-term oil supply. This does not apply to the rail industry, as electrification is a well-proven technical solution to supplying energy from non-oil sources.
Two years ago, a study suggested that adopting fuel cells rather than overhead electrification for inter-city train design was likely to reduce the overall space available for passengers by about 10%6. This increased the energy use per passenger, and the overall efficiency from 'well to wheel' would be less than that for an electric train. From the environmental point of view, using fuel cells instead of electrification for inter-city traction would greatly increase primary energy consumption and hence CO2 production.
Electrification is the answer
There is an alternative to biofuels or fuel cells, which is electrification.
On October 23 Network Rail Chief Executive Iain Coucher and Adrian Shooter, Chairman of the Association of Train Operating Companies, wrote to the UK Department for Transport, describing the use of fossil fuels to power trains when other methods are available as 'very short-sighted'.
Putting the case for a wider electrification programme that would place decisions on changing fuels 'elsewhere', Coucher and Shooter argued that it would be 'extraordinarily incautious' to equip the railway to run on one type of fossil fuel, only to find that the industry had “bet on the wrong fuel type”.'
The UK argument seems to be mainly about the capital cost of electrification, with the government reluctant to spend money and clutching at intellectual straws - such as the possibility of a low-carbon alternative to diesel being developed - to justify its position.
The position is rather different for vertically-integrated heavy freight railways. Only in the Americas have we seen the dismantling of main line electrification in favour of diesel haulage. But the continuing widespread use of diesel, particularly in countries that have adopted US standards, is a hangover from the days when oil was cheap and electricity supplies in remote areas were sparse and unreliable. However, there are several good examples elsewhere of how electrification can be effective for long-haul freight.
One is the 860 km Sishen - Saldanha heavy haul ore line in South Africa, where 20 000 tonne trains are hauled by 50 kV locomotives7. If the project were repeated, it is likely that the line would be electrified at the international standard of 25-0-25 kV with auto-transformers, rather than using 50 kV at the pantograph, but there is no doubt that electrification over long distances works.
A second example comes from China, where completion of the 25 kV electrification on the 1 500 km Beijing - Shanghai line was celebrated in July 2006. The Ministry of Railways believes that main-line electrification makes sense and over the past 40 years has established the world's third-largest electrified network. This stands at more than 20 000 route-km, and CR expects to electrify a further 6 000 route-km in 2006-10. And the dominant traffic on most routes is freight, rather than passengers.
Other major operators of electrified freight railways are Russia and India, with 42 000 and 18 000 route-km respectively. RZD completed the electrification of the Trans-Siberian corridor in December 2002, and frequent electrically-hauled freight trains cover the 9 880 km from Nakhodka to Moscow in less than 10 days (RG 3.04 p148). In terms of track-km, India has around 40 000 km wired, which is in the same order of magnitude as the total main-line trackage of Union Pacific, for example. Large-scale and long-distance electrification is clearly possible.
Saving energy and CO2
The pressure is on all transport operators to reduce energy use and CO2 emissions, and rail will not escape. Creative accounting by buying from 'green' suppliers or using a greater proportion of biofuels than other transport users has no net effect on a country's CO2 output, and cannot really be described as saving energy or reducing emissions. Further reduction in energy use or emissions will therefore require real improvements in efficiency.
Luckily, there are several examples of where this has been done. The double-deck TGV Duplex can be seen as a benchmark, increasing seating capacity by 45% compared to a single-deck TGV Réseau set of the same length. SNCF claims that this comes at virtually no increase in energy demand, suggesting that consumption per seat has been reduced by more than 30%.
Japanese high speed trains are well-known for their energy-efficient design. A recent study8 gives an energy consumption of 0·029 kWh/seat-km for a Series 700 trainset running at 300 km/h, which is almost exactly the same as the 200 km/h electric IC225s in the UK.
How do Shinkansen trains use so much less energy, despite travelling faster? Part of the reason is the 3·4 m car width, as opposed to 2·8 m in the UK, which permits 3+3 seating in standard class against 2+2. The trains are also longer. A 400 m long 16-car trainset holds 1 323 passengers, compared with 524 in an IC225 of barely half the length. Capacity is improved as there is proportionately less space from which passengers are excluded for safety reasons.
The Series 700 has been designed to minimise drag, with a long nose, pantograph fairing and attention to the underfloor area. Much of the impetus for improving aerodynamics came from the need to reduce trackside noise and pressure pulses on entering tunnels, but reducing drag has brought significant energy-saving benefits. On the Tokaido Shinkansen, attention to the design reduced the traction energy from 42·0 to 33·3 and 29·8 kWh/km for Series 0, 100 and 300 respectively9.
Higher, wider, slower?
It is clear that the rail industry has to reduce energy consumption, both to retain its environmental advantages over other modes and to control the increasing cost of energy. For non-electrified lines, the obvious solution is to electrify. Preliminary calculations suggest that, for the energy mix likely to prevail in the 2020s, CO2 emissions associated with electric trains in the UK will be only a third of those of diesel trains. And electrification helps to stabilise fuel costs because it enables a diversity of energy sources.
For networks that are already electrified, there is no magic solution to efficiency improvement. Operators will have to wage a war of attrition against energy losses. Enlarging the loading gauge to accommodate double-deck passenger trains or double-stacked containers and five or six-across seating is one approach. If government transport departments argued that road vehicle cross-sections had to be limited to those operating in the 19th century, the road haulage industry would be outraged. Why is the rail industry so very different?
Further improvements can be achieved by improving aerodynamics to reduce pressure loss at head and tail as well as skin friction, optimising internal design to maximise passenger capacity and reduce train weight. The odd percentage point can be gained by changing the material of motor laminations, the oil in the gearbox or the modulation pattern in the inverters. Add to these the loss reductions by improved train regulation, higher passenger loadings and better train management and the savings will be significant.
However, a combination of all these progressive changes will not result in the 80% cut in emissions that climate scientists say is needed and to which (at least some) politicians aspire. This will require a more revolutionary approach, which will probably require a reduction in train speeds as well as revisiting the balance between safety, accessibility and environmental impact that has evolved over the past decades.
CAPTION: The rapid expansion of biofuel production in the USA has brought extra traffic to the railways, typified by this BNSF ethanol train at Summit, California. Big questions remain over the long-term replacement of diesel traction on the continent's major freight arteries
- CAPTIONS: The rapid expansion of biofuel production in the USA has brought extra traffic to the railways, typified by this BNSF ethanol train at Summit, California. Big questions remain over the long-term replacement of diesel traction on the continent's major freight arteries
- SNCF is heavily promoting the environmental credentials of its TGV fleet compared to making equivalent journeys by road or air. France's extensive reliance on nuclear generation has helped to reduce the carbon footprint of rail travel
- Post-privatisation rolling stock designs in the UK are generally heavier and less efficient than older trains in terms of power per seat. Energy and weight saving are emerging as key issues driving future traction policy
- Close attention to aerodynamic design and weight saving have enabled the Japanese railways to reduce the energy consumption of successive Shinkansen trainsets despite their higher performance
- The completion of electrification on the Trans-Siberian main line in 2002 has enabled RZD to operate growing numbers of electrically-hauled freight trains between the Far East and Europe over distances of more than 10?000 km
- Double-stack freight trains and double-deck passenger stock have already helped to boost capacity and cut operating costs. Other railways may be able to reap the benefits of greater energy efficiency, despite the high capital cost of loading gauge enlargement
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