Solar energy – is electromagnetic radiation of the sun . It is the result of the vibrations of the magnetic and electromagnetic fields. Solar energy obtained from the Sun is highly energetic and available all over the Earth. It can successfully replace conventional energy sources such as natural gas , crude oil , uranium or coal . It is very important from the point of view of environmental protection and obtaining clean energy.
- Why solar energy?
- The use of solar energy
- Solar panels
Why solar energy?
Nowadays, energy demand is mainly met from fossil fuels such as coal, oil and natural gas. However, these are non-renewable resources and one day their resources will be exhausted. In order to be prepared for this moment, we are already looking for alternative energy sources that will cover the demand for it in the future. The ideal solution seems to be energy coming from the sun. The use of this energy does not produce negative effects on the environment , as burning coal or biomass . According to estimates, the sun will continue to shine 4.5 billion years, which is much longer than human life span .
The sun generates energy through the fusion processes of the conversion of hydrogenin helium. These processes take place at a very high temperature , which is produced by the solar core. Energy in the form of solar radiation reaches the Earth, where:
20% is reflected
40% dispersed in the atmosphere – due to gases and dust suspended in the atmosphere,
40% of it finds its way to the earth’s surface and is used to produce electricity and heat .
Solar radiation does not reach every part of the earth with the same intensity and intensity, and this is due to, among other things, the elliptical shape of the planet, which makes the surface illumination uneven. Lighting also changes depending on latitude, season and day. Some of the rays fall directly to the ground, and some are reflected from various obstacles.
Solar panels. Fernando Tomás from Zaragoza, Spain [ CC BY 2.0 ], via Wikimedia Commons
The use of solar energy
Many technical solutions allow you to obtain solar energy. Systems that enable this can be divided into passive (passive) and active (active).
Passive systems use the phenomena of radiation , conduction and convection to convert solar radiation into heat . They are very simple and do not require a lot of money. An example of a simple passive system is a conservatory, where the sun simply heats the glass room. Currently, passive buildings are built that are shaped in such a way that they are able to use the energy from the sun to heat the building as much as possible. The elements that receive energy from the sun can be large windows facing the right side of the world, large glass surfaces, such as glass or concrete ceilings or brick walls .
Active systems convert solar energy into usable energy with the help of specially prepared devices. They are collectors solar and cells photovoltaic. Photothermal conversion takes place in solar collectors, i.e. the conversion of solar radiation into thermal energy. Photovoltaic cells, on the other hand, work on a different principle and the solar radiation is converted into electricity. This process is called photoelectric conversion.
Solar street lighting Jacek Halicki [ CC BY-SA 4.0 ], via Wikimedia Commons
Photons are quanta of radiation that are the energy of solar radiation. The frequency of the radiation determines the energy carried by the photon. The conversion of solar radiation into electricity in photovoltaic cells does not require the use of additional mechanical devices, as there is no indirect energy conversion, as is the case in collectors, where heat is converted into mechanical work to result in electricity.
Photovoltaic power plants use devices to control cells and voltage-current converters necessary to transmit the generated energy to the power grid. Photovoltaic cells produce low voltage direct current . The voltage is also largely dependent on the amount of radiation reaching the cell. The generated current is sent to the power grid after passing through inverters which convert direct current into alternating current .
The cells are made of silicon wafers. Siliconis a material that is widely used in electronics and is common on earth. It creates monocrystalline, polycrystalline and amorphous structures. Cells made of monocrystalline silicon are better than cells made of polycrystalline silicon, but the production price tends in favor of polycrystalline silicon, which is much cheaper.
In order to make the production of cells less expensive and to save valuable material, thin-film technology is used. It consists in placing a thin layer of a semiconductoron a base of other materials that are much cheaper. The advantage of this technology is that the cell can be given any shape that will allow the cells to be integrated into the facade of the building or create a cell on a base of flexible materials. Thin-film technology also made it possible to create multi-junction cells. Such a cell is composed of several layers of materials, each of which has different properties for absorbing the spectrum of solar radiation. Since each layer of such a cell is able to absorb a different wavelength , in the end the whole cell works better than one made of one type of material.
Photovoltaic systems, compared to other renewable energy sources, such as wind farms, do not produce the annoyingnoise . Erecting photovoltaic systems does not require transforming the natural environment and changing the land use, because no harmful substances are produced during the production of thermal energy. So there is no environmental pollution or production of greenhouse gases .
Solar power plant, photo pixabay.com
Solar collectors are used to obtain heat from solar energy. They work on a slightly different principle than photovoltaic cells. An important element of the collectors is the absorber , which absorbs solar energy and transfers it in the form of heat to the mechanical element. Solar collectors are divided into different mechanical elements, that is:
Liquid collectors are then classified into the following types:
- flat collectors,
- vacuum collectors,
- storage collectors,
- flexible collectors.
The most commonly used for heating water are flat collectors, which consist of a system of flow channels, a heat carrier, which in this case is a liquid , a solar radiation absorber, an outer casing and a thermal insulation layer. The task of thermal insulation is to separate the lower surface of the collector from the housing. From the top, the collector is covered with a transparent glass that allows it to collect sunlight.
Air collectors are divided into the following types:
- with a flat absorber,
- with an absorber with a developed surface,
- with a porous absorber.
The heat is taken in by the air that flows over or under the absorber. In order to increase the amount of heat that can be absorbed, the absorber surface is corrugated. Air collectors have some advantages over liquid collectors, namely the heat carrier does not change its state of aggregation (does not boil or freeze) and has a simple channel structure. The disadvantage is that, compared to liquid collectors, there are resistance to energy transfer from the absorber to the air , which ultimately increases the absorber temperature and leads to heat losses to the environment.