Renewable energy sources (RES) are the energy resources used to produce electricity or thermal energy. They are derived from nature, and their reserves are continuously or cyclically renewed. The very name “renewable” comes from the fact that energy is consumed in an amount not exceeding the speed at which they are reproduced in nature. This is in contrast to non-renewable resources whose reserves are estimated at tens or hundreds of years, while their creation took millions of years.
The main renewable resources in nature are: sunlight, waves, tides, rain, wind, biomass and geothermal heat. Renewable sources replace many conventional fuels in four areas: space / water heating, motor fuels, electricity generation and rural energy services.
Renewable energy sources can be divided according to their origin in the following categories:
- Solar energy
- Wind energy
- Geothermal energy
- Hydropower (water power)
- Marine energy (ocean energy)
Each of these renewable energy sources has unique characteristics and they require special technologies and power plants. In addition, it’s very actual production of energy from waste, so-called waste energy in recent years.
The sun is, directly or indirectly, the source of almost all available energy on Earth. Solar energy comes from nuclear reactions (fusion) at its center – connection of the hydrogen atoms leads to the formation of helium, with the release of large amounts of energy.
Basic principles of direct solar energy exploitation are:
- Solar panels or collectors (convert solar energy into thermal energy)
- The concentration of solar power (directing solar radiation to obtain heat)
- Solar cells (conversion of solar energy directly into electric energy)
Wind energy can be used directly or indirectly – for the production of electricity. It is actually a form of solar energy, created by circulation in the Earth’s atmosphere. Wind energy exploitation is the fastest growing segment of energy production from renewable energy sources.
This is the type of renewable energy sources that does not originate from the sun. The basic medium that transfers heat from the Earth’s interior to the surface is the water or water vapor.
Water from rain penetrates deeply through the cracks in the soil and arrives at the great depths where it is heated. Heated water is circulated back to the surface, where it appears in the form of hot springs or geysers.
Biofuels are fuels that are obtained by processing some form of biomass. There are various types of biofuels: ethanol, biodiesel, bioalcohols (methanol, butanol, etc.), green diesel, biofuel gasoline, vegetable oil, bioethers, biogas, syngas, and so on.
The term biomass means the biological material from living organisms. Biomass is used to generate heat that can be used to produce electricity. The most important form of biomass is dead trees (and wood shavings) that are very large potential of renewable energy source. In addition to wood biomass, there are residues and waste from agriculture, animal wastes / residues and biomass from waste (trash).
Water energy (hydropower) is the most important source of renewable energy sources, and also the only renewable energy that is economically competitive with fossil fuels and nuclear energy. Marine energy (ocean energy) is a form of hydropower. There are three main types of marine energy: wave energy, tidal energy and energy from the temperature difference between the warm and cold ocean water.