Renewable energy flows involve natural phenomena such as sunlight, wind, tides, plant growth and geothermal heat, as explained by the International Energy Agency:  ^[19]

Renewable energy is derived from natural processes that are constantly renewed. In its various forms, it derives directly from the sun, or the heat generated in the deepest part of the earth. Included in the definition, electricity and heat generated by solar, wind, oceanic, hydroelectric, biomass, geothermal resources and biofuels and hydrogen derived from renewable resources.

Renewable energy resources and significant opportunities for energy efficiency exist over large geographic areas, unlike other energy sources that are concentrated in a limited number of countries. The rapid deployment of renewable energy and energy efficiency and the technological diversification of energy sources would result in energy security and significant economic benefits. ^[7] It would also reduce the environmental pollution such as air pollution caused by the burning of fossil fuels and improve public health, reduce premature mortality due to pollution and reduce associated health costs. several a year alone in the United States hundreds of billions of dollars. ^[20] Renewable energy sources, which derive their energy from the sun, whether directly or indirectly, such as hydroelectricity and wind energy, should be able to supply the energy of humanity for almost 1 billion years, how much of the expected increase in the sun’s heat The surface of the earth is expected to be too hot for liquid water to exist. ^[21]  [22]

Climate change and global warming concerns, coupled with high oil prices, peak oil and increased government support, are leading to increased legislation, incentives and the commercialization of renewable energy. ^[9]  New government spending, regulations and policies have helped the industry weather the global financial crisis better than many other sectors. ^[23] According to a 2011 projection by the International Energy Agency, solar power producers could produce most of the world’s electricity in 50 years, reducing greenhouse gas emissions. greenhouse that harm the environment. ^[24]

In 2011, small solar photovoltaic systems provide electricity to a few million homes, and micro-hydro configured in mini-grids for much more. More than 44 million households use biogas produced in domestic digesters for lighting and / or cooking, and more than 166 million households use a new generation of more efficient biomass cookers. ^[25] United Nations Secretary-General Ban Ki-moon said that renewable energy has the capacity to bring the poorest nations to new levels of prosperity. ^[13]At the national level, at least 30 countries around the world already have renewable energies contributing more than 20% of the energy supply. National renewable energy markets are expected to continue to grow strongly over the next decade and beyond, and 120 countries have various longer term renewable energy policy goals, including 20% ​​for the EU by 2020 Some countries have much higher long-term political goals, up to 100% renewable energy. Outside Europe, a diversified group of 20 or more countries are targeting renewable energy shares in the 2020-2030 period, ranging from 10% to 50%. ^[ten]

Renewable energies often replace conventional fuels in four areas: electricity generation, hot water heating / space heating, transport and rural (off-grid) energy services:  ^[3]

• Energy production

By 2040, renewable energy should equal coal and natural gas power generation. Several jurisdictions, including Denmark, Germany, the State of South Australia and some US states have achieved a strong integration of variable renewable energies. For example, in 2015, wind energy accounted for 42% of electricity demand in Denmark, 23.2% in Portugal and 15.5% in Uruguay. Interconnections enable countries to balance electricity systems by allowing the import and export of renewable energy. Innovative hybrid systems have emerged between countries and regions. ^[26]

• Heating

Solar water heating is an important contributor to renewable heat in many countries, including China, which now accounts for 70% of the global total (180 GWth). Most of these systems are installed in apartment buildings and meet a portion of the hot water needs of about 50 to 60 million households in China. Worldwide, solar water heating systems installed in total meet a portion of the water heating needs of more than 70 million homes. The use of biomass for heating also continues to grow. In Sweden, the national use of biomass energy has exceeded that of oil. Direct geothermal energy for heating is also growing rapidly. ^[27] The latest addition to heating comes from geothermal heat pumps that provide both heating and cooling, and also flatten the electrical demand curve and are therefore a growing national priority  ^[28]  [29]  (see also Renewable Thermal Energy) .

• Transport

Bioethanol is an alcohol made by fermentation, mainly from carbohydrates produced in sugar or starch cultures such as maize, sugar cane or sweet sorghum. Cellulosic biomass, derived from non-food sources such as trees and grasses, is also being developed as a feedstock for ethanol production. Ethanol can be used as a fuel for vehicles in its pure form, but it is generally used as a gasoline additive to increase the octane number and improve vehicle emissions. Bioethanol is widely used in the United States and Brazil. Biodiesel can be used as a fuel for vehicles in its pure form, but it is generally used as a diesel additive to reduce particulate levels, carbon monoxide and hydrocarbons from diesel powered vehicles. Biodiesel is produced from oils or fats using transesterification and is the most common biofuel in Europe.

A solar vehicle is an electric vehicle powered completely or significantly by direct solar energy. Usually, photovoltaic cells (PV) contained in solar panels directly convert the sun’s energy into electrical energy. The term “solar vehicle” generally implies that solar energy is used to power all or part of the propulsion of a vehicle. Solar energy can also be used to power communications or commands or other auxiliary functions. Currently, solar vehicles are not sold as a convenient means of transportation, but are primarily demonstration vehicles and engineering exercises, often funded by government agencies. However,