Renewable energies The most important energy sources of our future Regenerative or renewable energy refers to the provision of energy from sustainable sources such as sun, wind, water, geothermal energy or biomass. They are available in almost inexhaustible quantities. In contrast, the supply of fossil fuels such as coal, oil, natural gas and conventional nuclear fuels is continuously decrea- sing as consumption continues. These fossil fuels belong to the non-renewable energy sources. Once they have been burned in a power or heating plant, they are no longer available. They do not regenerate, they are devalued. However, the growing world population and the advancing tech- nological development of mankind are leading to an enormous demand for energy, which is constantly increasing. It is also known that emissions of the greenhouse gas carbon dioxide (CO2 ) from the combustion of oil, natural gas and coal are very high and, ac- cording to current knowledge, are the cause of global warming. The transition from fossil and nuclear fuels to renewable energies is already in full swing. In addition to the increased expansion of renewable energies, reducing our energy consumption and in- creasing energy efficiency through technological progress are key issues and current challenges at the same time. In everyday life, we encounter the energy transition in electromobility in transport, when buying energy-efficient household appliances or when reno- vating buildings to make them more energy-efficient.