How sunlight hits a solar cell, electrons

How do solar cells work?

Solar cells are built so the solar energy is converted directly into electric energy. Electricity which is produced in this way is called photoelectricity. The solar energy is absorbed into a semiconductor (usually of silicon) in the solar cell, and electrons are released by this energy. Solar cells are built so the electrons can not fall directly back into place, but they can be led through a separate cord (an electrical circuit) before they return to the solar cell. Because of this can the energy from the electrons be utilized as electrical energy.

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Most solar cells consist of two silicon plates. Silicon (Si) is a half-metal(semi-metal) and one of the most common constituents on Earth, but it is resource intensive to extract which makes it expensive. The silicon atom has four electrons in the outer shell. In pure silicon, the silicon atoms are bound together because they share electrons, so the atoms got eight electrons in the outer shell. The basic silicon is a semiconductor and has poor conductivity because the electrons are strongly bound to the atoms. Because of this, is it necessary to add other atoms between the silicon atoms in a solar cell so the solar energy can be able to release electrons.

The construction of a solar cell can be explained like this: The solar cells are very thin, approx. 0,3 mm, and the main body consisting of two silicon layers. In one of the silicon layers, very small amounts of boron (B) are added. A boron atom has three electrons, one electron less than a silicon atom, in the outer shell. We can say that the silicon is doped with boron, and (we can) call this p-doping (p=positive). The second silicon layer is doped with a few atoms of phosphorus (P). A phosphor atom has five electrons in the outer shell, one electron more than a silicon atom. This is called n-doping (n=negative).

When the phosphorus atoms and boron atoms bind together with the silicon atoms, will the n-side (phosphorous side) of the solar cell get a surplus and the p-side (boron side) a deficit of electrons. Electrons go from the n-side to the p-page. Eventually, it will fill up with electrons on the p-side, and it builds up a barrier between the two sides that make it virtually impossible for electrons to continue to go from the n-side to the p-page.

When sunlight hits a solar cell, electrons on both the n-side and the p-side will become loose. Electrons from the P-side can go to the n-side, while the barrier prevents electrons from moving in the opposite direction. By connecting a cord to the solar cell, we can direct the electrons from the n-side to the p-side through this cord. And because of this, we get electric energy that can be utilized.


Why is the sun such an important energy source?

Almost all the energy we use comes from the sun. It is the energy from the sun’s rays that makes water evaporate from the sea and lands. When the water vapor rises, it becomes colder. The water vapor becomes water drops that fall as rainfall. The precipitation on the hill accumulates in lakes, streams, and rivers that flow downwards towards the sea. In hydropower plants, the energy of the running water is transformed into electrical energy.                                                           In wind turbines, there is the moving energy in the wind that is transformed into electrical energy. Wind occurs when solar radiation in some places on the ground causes more warmth than elsewhere.                                                                                                                   Also, the energy from fossil fuels (oil, gas and coal) originates from the sun. It is solar energy that has been stored by plants and animals that lived many millions of years ago.

Even though most of our energy is originally from the sun, is it common to count/calculate solar energy as a separate category of renewable energy sources. It is when the solar energy is used directly for heating or to make electrical energy that we call it solar energy. Solar collectors and solar cells can transform energy from sunrays into energy forms that we can benefit from. Solar collectors convert the energy from the sun’s rays into heat. Solar cells convert the energy from the sun’s rays into electrical energy.

Because we do not have particularly strong sunlight here in Norway, solar energy will not be considered to be an equally large source of energy, such as bioenergy. Most countries in the world have far more sunshine than us. Worldwide, therefore, scientists believe that solar energy is the new source of renewable energy that has the greatest potential. By 2050, the world may get more energy from solar energy than from unrenewable sources such as coal, oil and gas.

The sun is a very important energy source. Because most of our energy sources originally come from the sun, and the sun is a renewable source. We get almost unlimited solar energy; solar energy reaching the earth in a year is 15,000 times greater than our energy consumption. Which mean that if we could find a way to unleash this energy, could it be our only energy source. Solar energy is great because it is renewable and does not send any toxic- or greenhouse gases into our atmosphere like the unrenewable sources do. A bad thing about using solar energy is that sunlight is necessary, almost at every moment, and that could be a problem in a country like Norway. Norway got neither much or strong sunlight, therefore is it hard for people in Norway to just get energy purely from solar energy, but it is a great alternative in countries who got more and stronger sunlight.


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