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Why are we searching for new energy sources?

Nowadays more and more energy is needed. Population growth, the high rate of economic development and progress in developing and using new technologies – all these make the demand for electricity growing all the time. Current energy sources cause substantial environmental pollution, contribute to climate change and furthermore their resources are limited and found only in certain regions of the world. Besides the limited supply and high demand for fossil fuels make their prices higher. That is why, it is necessary nowadays to increase the amount of energy produced from renewable sources.

Water power

Water power has been used for centuries to irrigate fields, drive turbines or water‑wheels in mills, forges and industrial plants. For the first time water was used to generate electricity in the 19th century. Contemporary water‑power engineeringwater‑power engineeringwater‑power engineering is based on potential of rivers and open water reservoirs on which river hydro‑plants and dams are constructed or uses the potential of seas and oceans – energy generated by waves, tides and sea currents.

Wind power

Wind power production is the fastest growing branch of energy industry. Wind, that is a horizontal or nearly horizontal air movement in relation to earth’s structure, is caused by differences in the atmospheric pressure and temperature. Wind turbines are used to generate electricity using wind. Nowadays they are often found in the so‑called wind farmswind farmwind farms. In Poland there are favourable conditions for the construction of wind farms mainly in coastal areas and mountain passes. In Western Europe, this energy is used to the greatest extent in Germany and Spain.

Solar power

Sun is the greatest and most important source of energy on Earth. It has practically always been used by humanity. Nowadays, it is used to power calculators, watches, surveillance cameras, road signs. Solar energy can be processed into heat using solar collectors and use to produce electricity by means of photovoltaic cells constructed using silicon. The third solution involves conversion of solar energy into chemical energy. This process takes place in green plants and is called photosynthesis:

${\text{6CO}}_{\text{2}}\text{+}{\text{6H}}_{\text{2}}\text{O}\stackrel{\text{light}}{\to }{\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}\text{+}{\text{6O}}_{\text{2}}$

Solar energy can be used on a small scale at private homes or public institutions. Solar cell batteries are mounted on roofs of these buildings. Solar energy is used on a larger scale at solar power stations. Germany is the leader in using energy of this type.

Energy in the Earth

Geothermal energy is heat originating from radioactive decay of isotopes, such as uranium, thorium and potassium in the Earth’s mantle. Explosions of volcanoes, outflows of superheated steam (fumarole) or hot water (geysers) remind us of the huge potential of energy in the Earth. Hippocrates, the Greek physician, had already used geothermal energy to treat his patients. Water at a temperature of 40–90°C is used to generate heat, in balneology, agriculture and horticulture (for crops cultivated in greenhouses), fish farming and in the industry (for example to pasteurize milk or dry wood). On the other hand, water at a temperature of at least 150°C can be used to generate electricity. The US is the leader in using this type of energy.

Nuclear power

Nuclear power is generated as a result of fission of atomic nuclei of heavy elements such as: ${}_{\text{92}}{}^{\text{235}}\text{U,}$${}_{\text{92}}{}^{\text{238}}\text{U,}$${}_{\text{94}}{}^{\text{239}}\text{Pu,}$${}_{\text{90}}{}^{\text{232}}\text{Th}.$ In nuclear reactors, fission takes place as a result of collision of a neutron with a nuclei of: ${}_{\text{92}}{}^{\text{235}}\text{U}$ It is reflected by the following equation:

${}_{\text{92}}{}^{\text{235}}\text{U + }{}_{\text{0}}{}^{\text{1}}\text{n → }{}_{\text{36}}{}^{\text{92}}\text{Kr + }{}_{\text{56}}{}^{\text{141}}\text{Ba + 3}{}_{\text{0}}{}^{\text{1}}\text{n + γ}$

The resulting neutrons make more uranium nuclei disintegrate ${}_{92}{}^{235}U$, leading to a chain reaction accompanied by emission of approx. 80,000 MJ of energy from 1 g of uranium (compared with 30 MJ of heat generated during combustion of 1000 g of hard coal). There are 455 operating atomic energy reactors in the world (status as 1.01.2018). The share of nuclear power plants in global electricity production amounts to around 10.5%.

In the future nuclear power engineering will probably become the main source of energy in the world. Failure of reactors in Chernobyl (1986) and Fukushima (2011) raised new concerns and provoked discussions on the safety of this energy source. However, undoubtedly it is the lest failure‑prone source of energy, the best ally in the fight for clean environment and the cheapest way to produce electricity.

Biomass

Biomass consists of matter of plant and animal origin, mainly waste generated by agriculture, forestry, sludge, industrial and municipal waste. Biomass is the oldest and the most broadly used renewable energy source. It can be burned directly or processed into biofuels. Basket willow is a plant most commonly used in Poland for energy‑related purposes. Its yield from one hectare per year allows for getting on average so much energy as burning 10–13 tonnes of coal.

Liquid biofuels are used in cars. Potatoes or plant grains are fermented and this is how ethanol is obtained. Ethanol is more and more often used as a biofuel (bioethanol):

${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}\stackrel{\text{ enzyme}}{\to }{\text{2C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH + }{\text{2CO}}_{\text{2}}$

Its energy value is about 30 MJ/kg. This is why it can be added to petrol. A biofuel called biodiesel is obtained from rapeseed or sunflower oil, or from used cooking oil. It consists of fatty acid methyl esters, which are formed as a result of the esterification reaction of methanol and fats from oil plants:

${\text{CH}}_{\text{3}}\text{OH + vegetable oil}\stackrel{\text{ cat./temp.}}{\to }{\text{C}}_{\text{3}}{\text{H}}_{\text{5}}{\text{(OH)}}_{\text{3}}\text{ + biodiesel}$

This is how a natural biogas (called waste dump gas) is created in peat bogs and at waste dumps. It consists of methane, carbon dioxide, nitrogen and hydrogen sulphide. Combustion of biogas obtained in a controlled manner in biogas installations can be a source of energy that can be used to heat buildings, cook or power vehicles.

Other energy sources

Fuel cells are devices in which electricity and heat are generated as a result of the following chemical reaction:

${\text{2H}}_{\text{2}}\text{ + }{\text{O}}_{\text{2}}\text{ →}{\text{ 2H}}_{\text{2}}\text{O + electric current}$

A fuel cell needs a substance that is easily oxidized as a substrate, such as hydrogen. They can also be fed with other substances, such as methanol or ethanol. Such energy sources supply ships, ferries and space stations, at the same time providing drinking water. The availability of different types of fuel cells means that the list of their possible applications can be extremely long, starting from portable devices such as cameras, mobile phones, laptops, tablets, through cars and other vehicles, ending with home heating systems. This would eliminate losses arising during the transmission of energy from the power plant to the recipient. A single fuel cell has little power, which is why they are combined in modules, the so‑called fuel cell stacks.

${\text{2H}}_{\text{2}}\text{O →}{\text{ 2H}}_{\text{2}}\text{ +}{\text{ O}}_{\text{2}}$

The hydrogen burns explosively in presence of oxygen. The process taking place can be described with the following chemical equation:

${\text{2H}}_{\text{2}}\text{ + }{\text{O}}_{\text{2}}\text{ →}{\text{ 2H}}_{\text{2}}\text{O}$

A mixture of hydrogen and oxygen at voluminal ratio of 2:1 or of hydrogen and air at voluminal ratio of 2:5 is a detonating gas.

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Exercise 2

Wysłuchaj nagrania abstraktu, ułóż do niego pytania i zadaj je koledze.

Wysłuchaj nagrania abstraktu, ułóż do niego pytania i zadaj je koledze.

Select photographs below that show alternative sources of energy:

• Wind farms
• Solar panels
• Charcoal
• Wood
• Coal power plants
• Hay

Summary

• The main advantage of renewable energy sources (RES) is the protection of the natural environment against the emission of harmful chemicals. Furthermore, the use of RES allows for a significant reduction in the use of fossil fuels and oxygen consumption.

• The following alternative energy sources can be distinguished: water, wind, solar, geothermal, nuclear, biomass and hydrogen energy.

• Geothermal energy – is heat generated in the Earth which is accumulated in rocks and water filling rock pores and crevices.

• Nuclear energy – is released during nuclear transformation.

• Biomass -- is organic matter susceptible to biodegradation.

• It is possible to use alternative energy sources to a greater extent because new technological methods are being developed and the exiting ones are constantly being improved.

Keywords

wind farm, water‑power engineering, chain reaction, photothermal conversion

Glossary