Energy Efficiency Potential in Transportation Sector
The main energy consumers in the transportation sector are light road vehicles (cars, buses, etc.). They represent half of the total energy consumption of the sector, and will correspond, according to the International Energy Agency (2012), to 40% of the total increase in energy consumption by 2035. Next comes air transportation. While the segment currently accounts for only 11% of total consumption, it will take a 40% share of the increase in energy consumption in the next 20 years, on par with light road vehicles. Consumption optimization in the sector will thus mainly be related to the optimization of energy use by light road vehicles and limiting the energy consumed by air transportation (Fig. 5.9).
Light Road Vehicles (Individual Transportation)
The most challenging issue concerns gasoline consumption by individual vehicles. There are today around 700 million vehicles in the world. Economic development could push the vehicle population to between two to three billion cars by 2050. Extensive research effort is being spent on reducing the environmental impact and gasoline consumption of individual vehicles.
Vehicle motorization has considerably evolved in the past decades. An engine is designed to operate at a nominal speed and power, so the main issue related to engine efficiency is related to its operation. The engine indeed runs at various speed
Fig. 5.9 Evolution of energy consumption in transportation (© OECD/IEA, Statistics 2015; © OECD/IEA, WEO 2012) and power, depending on the conditions of use. It is rarely used at its optimal ratio. The design of motors has therefore evolved in the past decades to optimize the gas consumption, favoring its efficiency with various levels of speed and power. The challenge lies in the compromises that are being made to optimize its efficiency. Modern engines are better designed and tuned to limit gas consumption. Direct injection has progressively replaced carburetors, and engines have been made smaller capacity-wise, with turbochargers compensating for the reduced horsepower. All these have helped reduce gasoline consumption.
A recent motorization innovation, hybrid engines, combine gasoline and electric motorization and can deliver up to 30% fuel saving. Electricity production is done using regenerative braking—the rotating energy of the wheels is transformed to electricity by the same process as the one used in power plants. The electricity is then stored into a battery that can then serve as a generator. While they are available in the market, fully electric vehicles have yet to take off. There are various reasons for this. First, current batteries limit the travel distance of such cars. In addition, the infrastructure for battery recharging is far less widespread that that for gasoline vehicles. And while electric vehicles emit no greenhouse gases, they are no greener than conventional vehicles if the electricity used to charge their batteries is produced by conventional thermal power plants. Hydrogen motorization is another technology that has the potential to serve as a substitute for gasoline. Hydrogen is mixed to oxygen in fuel cells to create a similar reaction as the one happening in a conventional electrochemical battery. Hydrogen motorization only produces vapor. However, the cost of this technology is extremely high and the lack of refueling infrastructure has so far limited its adoption.
Beyond motorization, some more recent technologies also help increase vehicles’ energy efficiency. The vast majority of transportation usages concerns small distances inside cities. In such travel, cars are often stopped. “Start/stop” technology automatically stops the engine when the car is forced to stay put for some time, and restarts it automatically when the driver depresses the accelerator. This leads to a sharp decrease of gas consumption in cities (around 7% on average). Another innovation further, valve rhythm adaptation, can also help improve the gas consumption of the engine by around 10%.
Transmission systems also play an important role in energy optimization. Maximum efficiency is reached with manual transmission systems. Automatic transmissions do not exceed 85% of yield, versus 97% of yield for fully manual transmissions. Now, as automatic transmission systems take a bigger market share, “manual automatic” systems have also been introduced, notably for small vehicles. They are essentially manual transmission systems which change the gears automatically, and give 90-95% of yield.
Aerodynamics also helps reduce gasoline consumption. Lightening vehicles by substituting traditional materials with aluminum and carbon leads to a gasoline consumption reduction of around 6% (for 10% weight reduction). The optimization of electricity consumption inside the vehicle can lead to 3% gasoline consumption reduction as well. Finally, tire manufacturing techniques also have an impact on gasoline consumption. New technologies reduce the friction on the road without compromising adherence, giving up to 5% reduction.
The final area in energy optimization in vehicles is the substitution of gasoline by biofuels. The two main biofuel producers in the world are the United States and Brazil. In most countries, gasoline can be blended with biofuels. Often 10% of the gasoline purchased is mixed with biofuels. In some countries like Brazil, this ratio is higher. There, most cars can run on only biofuels, and gasoline is generally blended with biofuels up to 25%. Biofuel production can be done using beans such as corn, sorghum and, like in Brazil, cane sugar. Cane sugar results in biofuels that are competitive against traditional gasoline. Other types of biofuels can be more expensive than gasoline. While biofuels help to reduce oil dependency, their use does not help to reduce greenhouse gas emissions—biofuel production does emit greenhouses gases. The agriculture of the crops that go into biofuels also generates greenhouse gases. According to Parmentier (2009), one ton of oil equivalent would be required to produce three tons of biofuels. Much current research focuses on reducing greenhouse gas emissions from the production of biofuels.
In summary, there are already a number of technologies which help to radically improve fuel efficiency. Obviously, vehicles that incorporate such technologies cost more. The extra cost can vary from a few thousand euros to 25,000 euros in the case of hydrogen or electrical motorization (© OECD/IEA, Transport 2009). The average lifetime of a car usually exceeds 15 years. There are today around 700 million cars in the world; 50 million are purchased new every year. This means that no more than 7% of the car total volume is renewed every year. In addition, this 7% combines both the replacement of old cars as well as the natural growth of the market. The actual replacement rate is therefore very low and market inertia is strong. Renewing entirely the world’s fleet of cars will probably take several decades.