What is renewable energy?
Hydropower from large-scale dams is currently the No. 1 source of renewable energy
Energy is considered renewable when it is produced from a source that is constantly replenished by nature, as opposed to a finite resource. Although highly diverse, renewable energies all come from two main natural sources:
- The Sun, which emits rays of light that can be transformed into electricity or heat, causes the high and low temperatures and pressure areas that create wind, drives the water cycle and enables plant growth and biomass formation.
- The Earth, whose internal heat can be recovered at the surface.
Among the benefits of these energy sources are the fact that they are renewable and emit only small quantities of waste, pollutants and greenhouse gases. On the downside, they are relatively diffuse, meaning they have a much lower power density than their highly concentrated non-renewable counterparts. They can be "intermittent" – as is the case for solar and wind power – and difficult to store because they are instantly transformed into electricity, requiring occasional back-up from other energies. And they require substantial capital outlays, even if they are closing the competitiveness gap with fossil fuels over time.
What are the different types of renewable energies?
The largest wind turbines stand some 170 meters tall
- Hydropower from large-scale dams is currently the No. 1 source of renewable energy. Leading the industry are China, Brazil, Canada, the United States and, perhaps in the near future, Africa.
- Solar energy can be produced in two ways. Photovoltaic solar technology converts sunlight into electricity using panels made of semiconductor cells, whereas solar thermal technology captures the sun's heat and uses it directly or converts it into mechanical energy and, in turn, electricity.
- Wind power has made progress both offshore and onshore thanks to regular improvements to the technology.
- The various forms of ocean energy used today are generated by the force of waves, currents and tides, temperature differentials in the ocean and certain interactions between seawater and freshwater (osmotic energy). Ocean energy is still in the early stages of development.
- Biomass is made up of all matter derived from living organisms, be they plants (including microalgae), animals, bacteria or fungi (mushrooms). For centuries, wood was burned as the main source of energy, before being overtaken by coal, then oil and natural gas. But there are other ways to use biomass. Methanation produces biogas from municipal or agricultural waste, while plant-derived biomass can be refined to produce biofuels.
- Geothermal energy captures the heat of subsea aquifers, or even hot dry rocks, at varying depths and uses it to supply heating to urban districts, buildings and factories, or to produce electricity in power plants. Countries in favorable environments, such as the volcanically active islands of Iceland and the Philippines, harness the power of geothermal energy on a mass scale. Heat from other sources can also be captured and used in district heating networks and industrial processes.
Nuclear energy is not considered renewable because its feedstock, uranium, is only available in finite quantities – at least at economically viable costs. Nuclear fusion, however, could provide an inexhaustible source of energy if it were ever achieved on an industrial scale.
The largest wind turbines stand some 170 meters tall, with rotor diameters exceeding 150 meters.
How widespread are renewable energies?
Renewable energies across the board are currently being improved, but not all have reached the same level of maturity.
One of the most spectacular developments in the last decade has been the rapid increase in photovoltaic solar capacity worldwide, a trend made possible by the steep fall in production costs per kilowatt-hour. While Germany was the longtime leader in this area, China and the United States now boast the largest installed capacities.
Other renewables are still at the experimental or research stages, such as third‑generation biofuels made from microalgae and applications that use hydrogen as an energy carrier. The possibility of a "hydrogen revolution" has become the subject of recent debate, but this will only take place if scientists can find a way to produce large quantities of the resource without using fossil fuels.
At a symbolic level, the Solar Impulse 2 solar-powered plane continues to defy expectations year after year.
What is the place of renewables energies in the global energy mix?
With the exception of hydropower, which has a very long history and produces significant amounts of electricity, renewable energies currently represent only a very small portion of the world electricity mix, at less than 5%. Hydropower adds more than 16%, but over two-thirds of the total mix is still made up of fossil fuels.
While renewables are making fast progress, it will nevertheless be some time before they can compete in quantity with traditional energy sources, and fossil fuels in particular (see the infographic on changes to the energy mix over time).
What is the impact of renewables on society?
When combined with advances in digital technology, renewable energies have the potential to gradually usher in far-reaching changes to society as they enable more decentralized power production at every level, from regions to individual households. Energy is now an ever‑present feature of daily life, and a few simple habits can go a long way in reducing consumption.
Considerable challenges still must be overcome in the transition to cleaner mobility, both in terms of hybrid and electric vehicles (including hydrogen-based solutions) and new vehicle usage behaviors.
Lastly, the rapid spread of digital home automation and power grid technology opens the door to more effective decentralized production and distribution of electricity that is better tailored to consumers' needs.