1.1 Types of RES and the Use of Renewable

Areas of use of renewable energy sources

Renewable resources are non-fossil fuel natural energy sources that have the ability to partially or completely renew themselves when gradually consumed. Such sources include energy from sunlight, water, wind or biomass, originating directly from the Sun or geothermal energy, which is the result of heat generated inside the Earth. The use of renewable energy sources has been on the rise recently. The reason for this is primarily the expiring stocks of fossil fuels and the negative impact of their combustion on climate change, as well as new technologies and constructional solutions that increase the efficiency and reduce the cost of installing these sources.

The benefit of renewable energy sources is particularly evident in three important areas: in electricity production, where their share has already exceeded the 25% boundary; in heating and cooling, where they provide more than 10% of the required energy and in transport, where, however, they only contribute to consumption by units of percent.

The main use of renewable energy lies in the production of ​​electricity, where it increasingly supplements or replaces fossil fuel-burning sources. A number of countries already achieve significant integration of various renewable sources into their electricity systems, but this trend of increasing the share of renewable sources in the energy portfolio is visible worldwide. There are even states that already cover all of their electricity production from renewable sources today and others that will follow them in the not too distant future. In recent years, more than 2/3 of newly installed energy sources have been renewable.

In the field of heating and water heating, the most widely used renewable resource is biomass when burned in ecological boilers of heating systems. A perspective way of obtaining heat for this area is the direct use of geothermal energy, of course only in areas where conditions are favourable for this. Heat pumps, which use the energy of the surrounding air or earth to heat the heating medium, have also recently seen a massive expansion. In addition to the methods presented, domestic hot water is being prepared using solar heating more often. Various types of solar collectors are used by tens of millions of households worldwide to cover at least part of their hot water needs.

The third area where renewable sources provide energy mostly in the form of biofuels is transport. The most common biofuel, at least in Europe, is biodiesel produced from vegetable oils. It is used as an additive to conventional diesel to reduce emissions of particles and hydrocarbons. Cellulosic biomass or carbohydrates produced in certain crops such as corn or sugar cane can be fermented to produce bioethanol. Similar to biodiesel, this technical alcohol is also added as an additive to petrol to reduce vehicle emissions. In the field of electromobility, renewable sources producing electricity are successfully used to charge electric cars and other electrically powered vehicles. 

The most important renewable energy sources

Distribution of RES and technologies for their use

Among the most well-known and also the most important types of carbon-neutral renewable sources suitable for electricity production are the use of water energy, wind energy and the direct or indirect use of solar energy. Biomass and geothermal energy are also used to produce electricity but they are more likely to be seen as sources of heat for heating needs. The technology enabling the use of individual resources is constantly being developed and improved, which in the long term leads to an increase in their efficiency, availability and competitiveness and reduces the cost of installing these sources. A greater number of installations of renewable sources subsequently means an increase in their share in the total energy produced.

The most significant renewable resource in terms of expansion and power capacity is water. Thanks to the natural cycle in nature, water constantly travels from higher areas to the seas and in hydroelectric power plants, that dam its flows, it transfers part of its potential and kinetic energy to the blades of water turbines. The use of hydropower for energy purposes is very scalable - sources can be from several kW to several GW, easily regulated - output can be changed by simply controlling the flow of water to the turbine and ecological - hydropower plants do not need fuel and do not produce any waste.

The energy of water masses can be used energetically in other ways than the classic power plant with a turbine. In marine areas, there are various wave and tidal power plants but some progress has also been made in the use of sea currents or in the use of the thermal potential of surface waters.

The second most widespread renewable resource is wind. Wind is created when air pressure differences in different parts of the atmosphere are equalized as a result of uneven heating of the Earth's surface. Today, the energy of flowing air masses can be reliably used for energy purposes. Modern, industrially produced wind turbines with a unit output of up to several MW are used for this. These mostly three-bladed windmills can stand completely alone in the landscape or they can group together in large wind farms in suitable locations with constant and strong winds. Free areas above the surface of the world's seas and oceans are becoming promising places for installing wind parks. Even though wind farms are noticeable in the landscape, they have virtually no negative impact on the surrounding environment.

The third most important renewable resource is the Sun. The use of solar energy, transmitted from the Sun to the Earth in the form of radiance, can be purely passive for energy purposes, for example by orienting buildings towards the Sun, or active, including solar technologies for heating and water heating, as well as technologies for converting solar energy into electricity. A simpler but still more expensive way is direct conversion using photovoltaics, the second option is indirect conversion using concentrated solar energy systems. Decentralized photovoltaic power plants are currently experiencing rapid growth and greater expansion. A large number of these micro-resources, as well as large solar power plants with an output of hundreds of MW must already be taken into account in modern energy strategies.

Another renewable source with interesting potential is geothermal energy. It is actually the use of the Earth's thermal energy created during its formation and recently, partially generated during the radioactive decay of elements in its core. Unfortunately, there are not many suitable places for the construction of geothermal power plants with a larger installed output which is why these ecological resources are rather local. To a much greater extent, geothermal energy is used in the form of thermal energy for heating or cooling.

The last significant non-fossil fuel renewable resource containing bound chemical energy is biomass. In addition to well-known plant and wood materials, biomass also consists of animal waste and organic components of municipal and industrial waste. For energy purposes, biomass is most often burned in biomass power plants or together with coal in classic thermal power plants. It also makes sense to burn it in cogeneration units. To produce heat for heating and water heating, biomass in various forms is burned in solid fuel boilers. Biomass also plays an important role in the production of alternative biofuels. Various thermal, chemical or biochemical processes are used to convert it into biofuels.