Table of Contents
Introduction
Transport moves people and goods, links economies, and shapes daily life. It also consumes a large share of the world’s energy, mostly in the form of fossil fuels. Because of this, transport is a major source of greenhouse gas emissions and air pollution. Bringing renewable energy into the transport sector is therefore central to any strategy for climate action, cleaner air, and long term energy security.
This chapter introduces how transport and energy are connected and explains why renewable energy in transport is both challenging and essential. Later chapters in this section will focus on specific solutions, such as electric vehicles, biofuels, aviation and shipping fuels, and new mobility systems. Here, the focus is on the big picture and the main ideas that link them together.
Energy Use And Emissions In Transport
Transport energy use is dominated by oil based fuels. Road vehicles, such as cars, trucks, buses, and motorcycles, typically burn gasoline or diesel. Aviation uses jet fuel, which is a type of kerosene. Ships use heavy fuel oil or marine diesel. Rail can be powered by diesel or by electricity, depending on the network.
When these fuels are burned, they release carbon dioxide, which is the main greenhouse gas, as well as other pollutants. These emissions contribute to climate change and also affect local air quality. In many cities, transport is one of the largest sources of urban air pollution, with health impacts such as respiratory and cardiovascular diseases.
Transport demand has grown rapidly with urbanization, rising incomes, and global trade. Freight transport has increased as supply chains have become more global, and passenger transport has expanded with larger vehicle fleets and more air travel. Without a change in how transport is powered and organized, energy use and emissions in this sector are expected to keep rising.
Why Decarbonizing Transport Is Difficult
Compared with sectors like electricity generation, transport is harder to decarbonize. Most vehicles carry their own fuel, which must have a high energy density. This means that the fuel needs to store a lot of energy in a small volume and mass. Oil based fuels are very energy dense and convenient to store and transport, which is one reason they became dominant.
Transport also uses long lived infrastructure and vehicles. Cars, trucks, and buses can stay in use for a decade or more, aircraft and ships for even longer. Roads, ports, and airports are also built to last many decades. This creates what is called lock in, where existing systems and investments slow down the switch to new technologies.
Some types of transport, particularly long distance aviation and shipping, have strict constraints on weight and space on board. For these modes, replacing fossil fuels is especially challenging. As a result, different transport segments will likely decarbonize at different speeds and with different technologies.
The Role Of Electrification
Electricity is a central pathway for bringing renewable energy into transport. Electricity itself is a secondary energy carrier, but it can be generated from renewable sources such as solar, wind, hydropower, and others. When vehicles run on electricity rather than on fuel burned by an engine, they can be powered indirectly by these renewable sources.
Electrification is already well established in some areas. Many urban rail systems, metros, and trams run on electricity delivered through overhead lines or rails. As the electricity grid becomes cleaner, these modes of transport become lower carbon.
For road transport, electric vehicles use electric motors instead of internal combustion engines. They store energy in batteries that are charged from the grid. If the electricity used for charging is produced from renewable energy, emissions from driving can be greatly reduced. Even with a grid that still includes fossil fuel generation, electric vehicles can be more efficient and less polluting than conventional vehicles, because electric motors convert a higher share of input energy into motion.
Heavy duty trucks, buses, and even some short range ships and aircraft are also being considered for electrification, either with batteries or with overhead charging systems and other infrastructure. However, energy storage capacity, charging times, and infrastructure needs remain important constraints for some applications.
Liquid And Gaseous Renewable Fuels
Electrification is not the only way to bring renewables into transport. Renewable liquid and gaseous fuels can be used in existing or adapted engines and can be transported and stored using much of the current fuel infrastructure.
Biofuels are produced from biomass, such as crops, residues, or waste materials. They can be used as blends with gasoline and diesel, or in some cases as nearly pure fuels. Their potential to reduce lifecycle emissions depends on how the biomass is grown, processed, and transported, and on how land is used.
Gaseous fuels can also be renewable. Biogas produced from organic waste can be upgraded to biomethane and used in vehicles that can run on natural gas. Hydrogen can be produced from renewable electricity through electrolysis and used in fuel cell vehicles or as a feedstock to create other synthetic fuels. These options allow renewable energy to be stored in chemical form and used where direct electrification is difficult.
Each type of renewable fuel has its own technical characteristics, costs, and sustainability considerations. Matching the right fuel to the right application is an important part of designing low carbon transport systems.
Matching Technologies To Transport Modes
Transport is diverse. Urban commuters, long haul truckers, shipping operators, and airline companies all have different needs. Therefore, there is no single universal solution. Instead, renewable options will likely be combined in different ways across modes and distances.
Short distance and urban transport is often most suitable for direct electrification. Passenger cars, urban buses, and local delivery vehicles can benefit from batteries and frequent access to charging points. Urban rail systems already depend on electricity.
Long distance road freight is more challenging, although battery technology and charging networks continue to improve. Other options such as hydrogen fuel cells or electric road systems, where trucks can connect to overhead lines, are also under exploration in some regions.
Aviation and shipping often require high energy density fuels for long journeys. Here, sustainable biofuels and synthetic fuels produced using renewable electricity are seen as promising avenues. For shorter routes, such as regional ferries or small aircraft, direct electrification or hybrid systems may be possible.
Planning which technology to use in which segment involves technical, economic, and policy considerations, as well as the availability of renewable energy resources.
Interaction With The Energy System
Transport does not operate in isolation. As vehicles and fuels change, their relationship with the wider energy system also shifts. Electric vehicles, for example, create new patterns of electricity demand. When many vehicles charge at the same time, they can create peaks in demand on the grid. Managed smart charging strategies can spread this demand and even help to integrate variable renewable energy into the grid.
Hydrogen production for transport can provide flexible demand for renewable electricity. When there is abundant solar or wind power available, it can be used to produce hydrogen, which can be stored for later use in vehicles or in other sectors.
Liquid biofuels and synthetic fuels can link agricultural and industrial systems with transport. They create demand for biomass and for renewable electricity and can affect land use and resource planning.
Because of these connections, integrating renewable energy into transport requires coordination between transport planners, energy system operators, fuel suppliers, cities, and national governments.
Co-Benefits And Trade-Offs
Shifting transport to renewable energy has several co-benefits beyond reducing greenhouse gas emissions. Electric vehicles and clean fuels can lower local air pollutants such as particulates and nitrogen oxides. This improves public health, especially in dense urban areas. Quiet electric motors can also reduce noise, which matters for quality of life in cities.
Reducing dependence on imported oil can strengthen energy security. Countries with strong renewable resources can rely more on their own energy for transport, which may improve balance of payments and resilience to price shocks.
There are also trade-offs to consider. Producing some types of biofuels may compete with food production or affect biodiversity. Building new charging or fueling infrastructure requires investment and space. Mining and processing materials for batteries and other technologies can create environmental and social impacts if not managed responsibly.
A sustainable transport transition therefore needs to consider full life cycles and broader sustainability goals, including social equity and environmental protection.
The Role Of Policy And Planning
Because transport and energy systems are large, long lived, and highly regulated, policy and planning play a key role in guiding the shift toward renewable powered transport. Governments can set targets for emissions reductions and renewable shares in transport, establish standards for vehicle efficiency and fuels, and support charging and refueling infrastructure.
Urban and regional planning influences how much travel is needed and which modes people can choose. Compact cities with good public transport, walking, and cycling infrastructure can reduce total energy demand for mobility, which makes it easier to supply that demand with renewable energy.
Economic instruments such as taxes, subsidies, and carbon pricing can change the relative costs of different vehicles and fuels. Information and awareness campaigns can help citizens and businesses understand the options available and the benefits of cleaner transport.
Looking Ahead
The transformation of transport is still in its early stages. Electric vehicle deployments are growing in many countries, new generations of biofuels and synthetic fuels are under development, and experiments with hydrogen and other technologies are underway in freight, shipping, and aviation. At the same time, transport demand continues to grow, particularly in emerging economies.
Moving toward renewable energy in transport will require both technological change and changes in behavior and planning. The following chapters in this section will explore in more detail how different renewable options work in practice, where they are most suitable, and how they can be combined to create cleaner, more sustainable systems for moving people and goods.