Energy Policy 46 (2012) 1–3
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Energy efficiency: Lessons from transport Patrick Moriarty a,n, Damon Honnery b a b
Department of Design, Monash University, Caulfield Campus, PO Box 197, Caulfield East, Victoria 3145, Australia Department of Mechanical and Aerospace Engineering, Monash University, Clayton Campus, PO Box 31, Victoria 3800, Australia
a r t i c l e i n f o
abstract
Article history: Received 29 March 2012 Accepted 25 April 2012 Available online 8 May 2012
Many researchers have stressed the apparently great potential for improvements in energy efficiency to dramatically decrease total energy use, but despite steady progress in the technical efficiency gains, global primary energy use continues to rise. For transport, we show how the concept of energy efficiency has been progressively expanded over time, as our ideas on what constitutes transport output useful to individuals has evolved. Even the energy inputs regarded as necessary for transport have undergone revision, because of the need to compare different modes. Finally we discuss the relevance of the changes in our notions of transport efficiency for energy efficiency in general. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Energy efficiency Transport energy efficiency Transport outputs
1. Introduction According to noted energy researcher Amory Lovins (2004), energy efficiency can be defined as follows: ‘Broadly, any ratio of function, service, or value provided to the energy converted to provide it.’ Why improve energy efficiency? According to Cullen et al. (2011), the reasons include relieving energy resource depletion, saving energy costs, and reducing CO2 emissions. Many researchers have stressed the apparently great potential for improvements in energy efficiency to dramatically decrease total energy use (see, e.g., Lovins, 2004; Socolow and Pacala, 2006, Barker et al., 2007, Cullen et al., 2011). Further, many energy efficiency improvements can be made at low or even negative monetary cost. And as Wilhite (2008) has pointed out, the aim of energy policy appears now to rest on endeavours based on narrow definitions of technical energy efficiency rather than the broader concept of energy reduction, possibly because energy efficiency alone is seen as potentially making a major impact on energy use and carbon emissions. Despite steady progress in the efficiency of energy conversion devices (power station turbines, car engines, jet engines, electric lighting, etc.), global primary energy use has continued to rise over time, in a roughly linear manner over the past half-century (BP, 2011). Energy-related CO2 emissions have grown in step with energy use. Most of this rise is due to greatly increased numbers of energy-using devices, a result of continuing global economic growth. For example, the global car fleet has expanded from about 51 million in 1950 to over 800 million in 2007 (Moriarty and Honnery, 2011a). In a ‘business-as-usual world’ with
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continued economic growth, official energy forecasts foresee continued global primary energy consumption (International Energy Agency (IEA) 2011; Energy Information Administration (EIA), 2011). It therefore seems unlikely that technical efficiency improvements to devices alone can do more than marginally reduce energy use or greenhouse gas emissions, thus raising the question of the need for energy conservation. Many researchers distinguish energy efficiency from energy conservation. Thus Oikonomou et al. (2009) write: ‘A clear distinction between energy efficiency and energy conservation is that the former refers to adoption of a specific technology that reduces overall energy consumption without changing the relevant behaviour, while the latter implies merely a change in consumers’ behaviour’. This position is, however, in direct contrast to that of Lovins who, by extending the concept outside the bounds set by purely technical definitions (based on, for example, the laws of thermodynamics), opened up the possibility of human behaviour being linked to energy efficiency. Consider the case of electric power plant efficiency, where input and output are both energy terms. The net power output from a given fossil fuel power plant, and so its energy efficiency, depends to some extent on the level of emissions control for particulates, SOx and NOx. Today we increasingly accept that these emissions must be stringently controlled, but such was not always the case. The change came about because of changing levels of tolerance for air pollution (Moriarty and Honnery, 2011b). It might be argued that these emission controls had little effect on power plant efficiency, but what if CO2 emissions become unacceptable? In that case the drop in overall power plant efficiency from the installation of carbon capture technology would be very significant. Similar considerations apply to vehicular emissions and noise levels from road vehicles and aircraft. Along with speed limits, and compulsory vehicular safety
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equipment, these system-wide policies affect individual vehicle energy efficiency. In this paper we focus on transport energy efficiency. In particular, we look in Section 2 at how the concept of energy efficiency in transport has necessarily been broadened over time from simple transport equipment efficiency. In Section 3, we discuss the relevance of these changes in our notions of transport efficiency for energy efficiency in general.
2. Evolution of the transport energy efficiency concept Transport energy efficiency has been at the forefront in the expanded notion of energy efficiency, partly because, historically, different modes with very different characteristics have competed to provide passenger and freight services. Here, passenger transport is used to explore the complexity of defining efficiency for energy services. As a purely thermodynamic device, the efficiency of the passenger car engine can be easily defined by its principles of operation, and measured. However human interaction with passenger vehicles gives rise to the concept of travel, so rather than output power, the distance travelled becomes the parameter to be maximised for a given fuel or energy input. Vehicle efficiency was thus initially simply thought of as distance travelled per unit of fuel consumed, or ‘miles per gallon’ (‘mpg’). Once defined, this human-derived measure of efficiency, or task efficiency, enabled comparison of one car model with another. With public transport vehicles, such a comparison is not very meaningful, given their larger carrying capacity, although they can be compared on a seat-km basis. But for well over a century now (see e.g. Swain (1898)), railways have had to define their task in terms of passenger-km (and tonne-km for freight), simply because they charged fares and freight rates largely on this basis. Given that cars, buses and trains have long been considered alternative modes of passenger transport, their actual or potential efficiency could now be compared on a passenger-km/litre of fuel as well as a seat-km/litre basis. Such comparisons became increasingly common after the 1970s oil crises. Even defining the transport task as passenger-km has its difficulties. For many decades now (see e.g. Ashton (1947)), transport researchers have considered that transport, whether passenger or freight, is (mainly) a derived demand, that the value to us of passenger-km and tonne-km is that they satisfy some human need. But as Steg (2005) and Cao et al. (2009) have pointed out, much travel is not done to reach a destination but for the pleasure that car travel (and to some extent, other forms of travel) afford. Cao et al. also discuss other forms of travel for its own sake, including: ‘‘‘unnecessary’’ trips to destinations, destinations that are farther away than ‘‘necessary,’’ and routes to a given destination that are longer than ‘‘necessary’’’ (p. 254). Motorists, for example, often choose a route which will minimise trip time, rather than trip length. In such cases it is problematic whether the extra passenger-km generated by such trips should be counted in the transport task. Presumably, some human need is satisfied, but it is not a transport need. Similar considerations would apply to driver travel in ‘servepassenger’ trips, which form an important share of total travel (Sharpe and Tranter, 2010). For the case of a parent driving one child to school, then returning home, total passenger-km would need to be reduced by two-thirds to more accurately reflect the attainment of desired access. In contrast, the travel of drivers of public transport vehicles and taxis are not included in passengerkm statistics. For public transport vehicles that use electric power rather than diesel fuel, a further refinement was necessary for meaningful comparison: transport modes must be compared on a
passenger-km/MJ of primary energy basis. If this was not done, the high conversion efficiency of electricity to mechanical energy would bias the results toward electric traction. The comparison has already moved a long way from the simple mpg comparisons, in several ways. First, the importance of actual uptake of the potential energy service on offer is stressed; passenger-km is considered at least as important as potential uptake (seat-km). Policy measures that could increase the occupancy rate for both cars and public transport (such as high-occupancy vehicle lanes on arterial roads) are accordingly considered to be transport energy efficiency measures. With typical occupancy rates of 1.5 persons per car, (or 30% seat occupancy for a five-seat car), the potential for improvement is evident (Moriarty and Honnery, 2008a,b). If only seat-km per MJ is stressed, the potential for seat occupancy increases is likely to be overlooked. Second, the entire transport fuel system supply chain is now considered (‘well-to wheels’ efficiency), not just the ‘tank to wheels’ efficiency implicit in mpg analyses. This is crucial, because as non-conventional fossil fuel sources such as Canadian oil sands are progressively tapped, the energy costs of extraction will rise (Moriarty and Honnery, 2011b), partly offsetting any further gains in vehicle engine efficiency. This will be further complicated by the use of plug-in hybrid vehicles, which have two sources of fuel input. The availability and energy costs of the transport fuel used thus become a further factor to consider in this expanded notion of energy efficiency for transport. In future, it is even possible for tank-to-wheels efficiency gains to be made while the overall well-to-wheels efficiency is falling. Third, alternatives to the dominant technology are considered, even though many would argue that private and public passenger travel—let alone non-motorised travel—cannot be readily compared. They could argue that on a door-to-door basis these alternative modes are far slower than private car travel, and further, that private travel offers privacy, superior transport capacity for luggage, ability to travel without reliance on timetables, and so on. All these advantages are real, but supporters of alternative modes can point to different advantages for these modes. Non-motorised modes—and the walking inevitably associated with accessing public transport—provide exercise for the traveller. In this special case the energy expenditure may itself be regarded as a benefit rather than a cost, an output rather than an input, and the overall energy efficiency of non-motorised travel is accordingly even higher than usually calculated. Public transport riders can and do read or even work while they travel. This use of travel time for other activities (including physical exercise) makes the notion of one mode being faster than another, problematic (Lyons and Urry, 2005; Moriarty, 2002). Further, as Ivan Illich (1973) stressed several decades ago, the notion of time spent on travel, and thus travel speed, should be modified to include time spent working to pay for a car, for example (and, presumably, also fares in the case of public transport). Although some authorities assume that non-motorised travel is only for those without other options, its popularity in the highincome Netherlands, where some 46% of all trips are nonmotorised, argues against this assumption (Moriarty and Honnery, 2012). Shifting modes is now regarded as an important means of improving overall transport energy efficiency, as well as achieving other aims. Fourth, at least some behavioural change is assumed to be needed, as in the case of mode shift. Also, driver behaviour itself can significantly influence energy efficiency, as is recognised in the idea of ‘eco-driving’. According to a recent IEA report, fuel consumption for a given level of travel can be reduced by perhaps as much as 20% for some drivers and an average of 5%–10% long-
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term reduction in fuel use for all drivers (including truck and bus drivers) can be achieved (Kojima and Ryan 2010). Measures considered in eco-driving include minimising engine idling, and driving at ‘energy efficient’ speeds (usually in the range 60– 90 km/h). These recommendations, from a report entitled ‘Transport Energy Efficiency’ (Kojima and Ryan, 2010) show how far even official organisations are prepared to extend the concept in the direction of behavioural change.
3. Discussion: Extending the concept of energy efficiency In this section we outline how energy efficiency analyses in general might benefit from our discussion on transport efficiency. For the concept of energy efficiency to have meaning within systems designed to meet human needs, it must be defined as a ratio of an output useful in some way to humans, to the input energy. This is not usually done in cases such as lighting or building air-conditioning; lighting efficiency is commonly measured as lumen per watt—whether anyone is getting benefit from the lighting, was, at least until recently, not considered relevant. As with transport, we should consider alternatives to the dominant technology for meeting the relevant human need. Building temperature control can be achieved not only by airconditioning but also by passive solar energy or geothermal heat pumps. The latter shows how difficult defining energy efficiency can be: Are such heat pumps an alternative energy source (geothermal energy) or a means of improving the energy efficiency of conventional equipment? And how can we measure the efficiency of natural lighting, since lumen/watt is not relevant? Energy efficiency is also not easily disentangled from behavioural change, as evidenced by the example of ‘eco-driving’. Kunz et al. (2009) discuss cases where designers of energyefficient buildings greatly under-estimated actual energy use. Occupant behaviour, as well as equipment performance, proved crucial for energy consumption. For example, the need for human thermal comfort can to some extent be met by appropriate clothing—and even by acclimatisation (Auliciems, 2009). What we learn from transport is that the definition of energy efficiency is dynamic and should evolve as circumstances change. Hence, rather than focussing on improving technical energy efficiency, policies intended to reduce energy use overall should give far greater emphasis to how that energy is used to meet human needs.
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