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Moriarty, P.; Honnery, D. Potential and Barriers of Energy Efficiency Improvement. Encyclopedia. Available online: (accessed on 17 June 2024).
Moriarty P, Honnery D. Potential and Barriers of Energy Efficiency Improvement. Encyclopedia. Available at: Accessed June 17, 2024.
Moriarty, Patrick, Damon Honnery. "Potential and Barriers of Energy Efficiency Improvement" Encyclopedia, (accessed June 17, 2024).
Moriarty, P., & Honnery, D. (2023, July 20). Potential and Barriers of Energy Efficiency Improvement. In Encyclopedia.
Moriarty, Patrick and Damon Honnery. "Potential and Barriers of Energy Efficiency Improvement." Encyclopedia. Web. 20 July, 2023.
Potential and Barriers of Energy Efficiency Improvement

The published literature demonstrates the apparently great potential for improvement in the energy efficiency for all sectors of the economy, including passenger transport and household energy use. Some researchers have even claimed that many energy efficiency improvements will pay for themselves, i.e., have negative cost. 

climate change domestic energy energy efficiency

1. Introduction

Climate researchers sometimes conceptualise the global warming problem by means of the ‘carbon budget’ (or ‘carbon pie’). The carbon budget refers to the gigatonnes of carbon (GtC) in the form of carbon dioxide (CO2) that can be safely released into the atmosphere before seriously disruptive climate change occurs. In 2018, global carbon emissions from fossil fuel and industry alone were estimated at 10.1 gigatonnes of carbon (GtC) or 37.1 Gt CO2 [1]. In 2007, Broecker [2] wrote that for every 4 Gt of fossil carbon burnt, the CO2 atmospheric concentration rises by one part per million (ppm), resulting in the carbon budget size shrinking by 70–80 Gt per decade. Estimates for the current size of the budget vary, but according to a 2017 New Scientist article, ‘Climate scientists had estimated that this means we can emit no more than 70 (GtC) after 2015 [3]. At current emission rates, we will pass this threshold by 2022’. Other estimates put it as high as 200 Gt, but several researchers think it is smaller than usually modelled, because climate sensitivity is higher than usually calculated [4] and/or because the carbon budget for the 1.5 and 2 °C Paris targets will be ‘lowered by natural wetland and permafrost feedbacks’ [5].
The amount of fossil fuel carbon that can be burnt as fuel is also limited in another way: by limited reserves of fossil fuels (FFs). Although such reserves are usually regarded as several times the climate limit [1], such figures ignore the energy return on energy invested (EROI) which will progressively shrink as non-conventional FFs, such as oil sands, must be tapped and their environmental costs eventually factored in [6][7]. Even if such corrected reserves are still much larger than the climate change carbon budget, it is still the case that FFs are not a long-term solution for global energy supply.
The researchers and others have earlier shown [6][8][9][10][11][12][13][14] that the potential for environmentally sustainable renewable energy (RE) is also limited and may well be much lower than current global primary energy use. For RE to replace fossil fuels, there would need to be high technical potential, high energy return on energy invested [6][8], no shortage of available land [10][13], low energy losses for energy storage of intermittent RE, low costs and few environmental problems with very large-scale expansion [8]. These conditions are unlikely to be met [6][10][11][12][13][14]. Since the remaining possible energy source, nuclear power, is not expected to contribute more than a minor share of primary energy [8][15], it follows that not only must the use of fossil fuels be drastically cut, but the same is true for overall energy use. Present approaches for fossil fuel reductions are clearly not working: both primary energy and fossil fuel CO2 emissions are again growing strongly—FF-derived CO2 grew 2% over 2017 values in 2018 [1].
Energy use depends on the task and the efficiency with which it is undertaken. For example, in transport, the task could be described by the total number of passenger kilometers (p-km) travelled by private cars, and efficiency by the ratio of the task to the total energy (MJ) used by private cars (p-km/MJ). Therefore, cutting energy use can be achieved by either reducing the task through conservation measures or by reducing the energy consumed by the devices used to undertake a given task. Hence, energy can be cut by
  • Using devices less intensively, for example, by driving each car less each year
  • Reducing the number of energy using devices
  • Improving the efficiency of some or all of the energy using devices used to undertake the task
  • Using devices that have less energy embodied in them, for example a bicycle rather than a car.

2. Global Energy Use Patterns

Table 1 shows total final consumption (TFC) and total primary energy supply (TPES) for the world as a whole, as well as the OECD and non-OECD groupings of countries for both 1973 and 2016. Although growth in TFC has occurred in all energy sectors, it has been especially rapid in transport. The category ‘other TFC’ is predominantly for energy use in residences and commercial buildings. For both regions and the world, the return on TFC from TPES, expressed as TFC/TPES, has reduced since 1973, largely because of increased electrification of TFC.
Table 1. Energy statistics (in EJ) for 1973 and 2016, Organization for Economic Cooperation and Development (OECD), non-OECD, and the world.
* mostly buildings, but also includes agriculture and non-energy uses. Source: [16].
Worldwide, both the passenger transport energy used and the task have risen greatly over the period 1900–2016—by as much as a factor of 225. Estimates vary, but in 2016, global travel was probably around 45 trillion p-km [17]. Cars are now the dominant form of passenger transport worldwide, accounting for over 50% of all travel. In recent decades, ownership growth has been strongest outside the OECD [18], especially in China, which is now easily the world’s largest producer of private vehicles [19]. Commercial air travel has grown rapidly since the 1950s, and in 2016, it had a roughly 17% share of the global travel market. Air travel was expected to double over the years 2018–2037 [17][20].
Since 1900, growth in domestic energy use has been far slower than that for transport, partly because of the progressive replacement of wood, coal and town gas by natural gas and electricity in OECD countries. A full list of OECD countries is given in [16]; all other countries are non-OECD. Total domestic energy use per household fell in all regions from 2000 to 2017, and ExxonMobil [21] forecasted this global trend to continue until 2040. In Europe and North America, electricity consumption per household was flat or falling from 2000 to 2017, with further declines expected until 2040. In all other regions, however, household electricity use is growing rapidly, a trend that is also expected to continue. Globally, only electricity use per household was forecast to grow; the use of all other energy sources will fall [21].
In absolute terms, ‘other TFC’ energy use in primary energy terms has still grown rapidly, as shown in Table 1, largely driven by the rise in global household numbers. Fuel wood is still an important component of household energy TFC, accounting for 37 EJ in 2016 [21]. Even the poorest households use much of this low-efficiency fuel, so that household energy for cooking (and water heating) is comparable or even greater than that in OECD households. Absolute fuelwood use is expected to fall and be replaced by more efficient fuels, which will moderate growth in household energy use from rising appliance ownership, especially in Africa.

3. Energy Efficiency Improvement: Potential and Barriers

3.1. Transport Energy Efficiency Potential

Lovins [22] has claimed that with a shift to electric drive vehicles combined with reductions in road load (the sum of vehicle inertial, air and rolling resistances) an approximately five-fold efficiency improvement is possible compared with equivalent conventional vehicles. Creutzig et al. [23] argued that all vehicular travel energy (including air) could be halved by 2050, even with some global demand growth, but this level of reduction would require a carbon tax of some $US460 per tonne of CO2 by 2050.
Others e.g., [24][25] have stressed that in practical terms, the scope for improvement is far more limited, especially for conventional internal combustion engine vehicles (ICEVs). Although the fuel efficiency of petrol cars is improving, diesel cars are generally more fuel efficient. However, concerns about NOx and particulate emissions from diesel vehicles has led several global cities to plan banning them, beginning in 2025 [26]. Going further, many countries are looking to eliminate new sales of all ICEV cars (or even all ICEV vehicles) entirely by the year 2030 [26][27].
Electric vehicles (EVs) look like the obvious replacement for ICEVs, and worldwide sales are now increasing rapidly. Forecasts made in 2018 predict several hundred million EVs globally by 2040 [28][29]. For comparison, the global car fleet was over 1.1 billion in 2017, and OPEC [18] projected a total of almost two billion by 2040. EVs are more energy efficient than equivalent conventional ICEVs, partly because of regenerative braking and lower accessory power demand. However, this benefit is partly cancelled out by the high embodied energy costs for EVs compared with equivalent ICEVs—mainly because of battery energy costs [30]. If passenger car ICEVs are phased out over the next two decades, the prospects for all ICEV fuels, including bioliquids and natural gas, are poor. Improving ICEV engine efficiencies would then be a dead end, except possibly for heavy vehicles where progress to find a replacement power system is well behind that for passenger vehicles.
Some researchers see, e.g., [31][32] believe that fully automated vehicles (AVs) could markedly improve energy efficiency, for several reasons. First, cars could thus be driven in the most ‘eco-efficient manner’, saving fuel. Second, cars could thus travel much closer together on roads so that air resistance on following vehicles would be reduced. Third, improved safety resulting from elimination of driver error—a contributory factor in most traffic accidents—would allow redesign of vehicles with present safety and manual control features removed. The resulting lighter vehicles would be more fuel-efficient.
Others, however, have argued that car fuel use could rise overall. With no need for drivers, the pool of possible car owners would be enlarged. Travel costs comprise money and travel time costs. With AVs, travel time cost would fall, since drivers could use their time for other purposes. Furthermore, the present time-use advantage of public transport would be lost, initiating a possible shift back to less efficient car travel. In summary, future vehicles could well be EVs, which should improve fuel efficiency (in terms of vehicle-km per unit of primary MJ), but fully AVs are unlikely to lead to further energy reductions. Indeed, such vehicles are still decades away, and may never replace driver-controlled vehicles [33][34]. Finally, if only partly automated, the energy efficiency advantages would be largely lost.
One important barrier to the adoption of more fuel-efficient cars is the initial purchase cost. Lower-income households tend to own older, less fuel-efficient cars on average, so the reaction to a fuel price rise may be simply to drive less. Smaller, more fuel-efficient cars have been available for decades, but as shown below, the current trend in OECD countries is to purchase larger vehicles. An important reason is that vehicles are bought with maximum passenger loadings in mind, not the average load of typically 1.5 persons per car, and increased vehicle size can provide increased safety in mixed traffic. Another factor slowing fuel efficiency improvement is a trend toward more power-consuming auxiliaries, such as power steering, air conditioning and entertainment systems, and enhanced vehicle performance. Finally, car ownership and driving confer psychological benefits in terms of prestige and vehicle control; these will be greater for larger and more expensive vehicles.
In contrast to the claimed potential reductions from improved efficiency, the scope for energy reductions from social-psychological interventions has been seen as minor [35][36]. In a business-as-usual (b-a-u) world, the potential may indeed be small. Consider a major ‘TravelSmart’ trial conducted in the early 2000s in Perth, Western Australia, primarily aimed at providing personalised information about alternative modes to households. It was introduced into different local government areas (LGAs) at different times, allowing a natural experiment. Comparison of LGAs with TravelSmart intervention and matching LGAs in Perth yet to have the intervention showed no lasting significant effects on shifting motorists to alternative modes [37]. Overall, research suggests that in a b-a-u world, social psychological interventions of any type are of only minor value in affecting the large reductions in transport energy needed to combat further climate change [36].

3.2. Domestic Energy Efficiency Potential

The potential for domestic energy efficiency improvements differs from that for transport in several different ways. Whereas energy use in passenger transport is confined to devices, all of which provide a similar task, domestic energy use covers a multiplicity of tasks, including space heating and cooling, water heating, refrigeration, cleaning of clothes, dishes and rooms, lighting, and operating domestic appliances like TV sets and computers. Additional energy is needed to operate a variety of devices outside the home, such as lawn mowers.
Table 2, drawn from the 2014 IPCC report, gives estimates for the range of energy efficiency gains possible for various household and commercial buildings energy use functions. (For energy reductions from behavioural change for each end-use, the IPCC [35] found substantial but generally lower potential than was the case for energy efficiency improvement. Savings would come from actions such as lower thermostat settings in winter, shorter showers, full loads for clothes washing, etc.).
Table 2. Potential for efficiency improvements (%) for various building energy uses. Source: [35].
Pattanayak et al. [38] have claimed that ‘Three billion people rely on traditional stoves and solid fuels’. Given the very low efficiency of traditional stoves in low income countries (as low as 5%), there is clearly a great scope for energy efficiency (and indoor air quality) improvement. Improved efficiency could be achieved by redesign of traditional stoves, or by shifting to modern energy sources, electricity and gas. However, the authors showed that cost is not the only barrier to their introduction, stressing, among other factors, the importance of matching the technology to local needs.


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