Physics unit 3

SOLAR CELLSINTRODUCTION

This case study is about solar energy and how light is converted into electrical energy in solar cells. A solar cell is also known as photovoltaic (PV) cell, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), converts sunlight directly into DC electricity. This conversion of light energy into electricity works under the basic physical process of photovoltaic effect, which will be scrutinized under more detail subsequently after a brief history of this phenomenon.

HISTORY

The development of solar cell technology begins with the 1839 research of French physicist A. E. Becquerel. Becquerel observed the photovoltaic effect while experimenting with a solid electrode in an electrolyte solution when he saw a voltage generated when light fell upon the electrode.

According to Encyclopaedia Britannica the first genuine solar cell was built around 1883 by Charles Frits, who used junctions formed by coating selenium (a semiconductor) with an extremely thin layer of gold.

Early solar cells, however, had energy conversion efficiencies of less than 1%. In 1941, Russell Ohl invented the silicon solar cell.

In 1954, three American researchers, Gerald Pearson, Calvin Fuller and Daryl Chapin, designed a silicon solar cell capable of 6% energy conversion efficiency with direct sunlight becoming the first to successfully create a solar cell. Many breakthrough discoveries related to solar technology have arisen, improving efficiency of the cells, and until date more researches are on going across the world to take solar technology to the next level.

THEORY

Light’s particle is called photon and sunlight is made up of these packets of energy or photons. Every photon has an amount of energy, which is corresponding to its wavelength of light. When photons strike a solar or photovoltaic cell; those photons can either get reflected or be absorbed by the photovoltaic cell. When the latter takes place, the photon transfers energy to the electron and this knocks electrons loose, allowing them to flow freely. Electricity is generated through p-n junction semiconductor when the knocked electrons physically move across the p-n junction i.e. electrons leaving valence band to conduction band in the p-n junction and the positive charge carrying holes effectively move in the opposite direction, causes an electric potential difference. A current starts flowing through the material to cancel the potential difference and this electricity is captured.

Going into more detail, Assemblies of solar cells are used to make solar modules, which are used to capture energy from sunlight. When multiple modules are assembled together the resulting integrated group of modules all oriented in one plane is referred to in the solar industry as a solar panel.

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Physics unit 3

Structure of a Solar CellA typical solar cell is a multi-layered material. Let's review what the layers are:

Cover Glass - this is a clear glass layer that provides outer protection from the elements. Transparent Adhesive - this holds the glass to the rest of the solar cell. Anti-reflective Coating - this substance is designed to prevent the light that strikes the cell from

bouncing off so that the maximum energy is absorbed into the cell. Front Contact - transmits the electric current. N-Type Semiconductor Layer - This is a thin layer of silicon, which has been doped with phosphorous. P-Type Semiconductor Layer - This is a thin layer of silicon, which has been doped with boron Back Contact - transmits the electric current.

APPLICATIONS OF SOLAR TECHNOLOGY

In the contemporary world where the demand for energy is substantially hiking, with a relatively low supply and global warming increasingly becoming a great concern due to the lethal menace it’s posing to humanity and all inhabitants of earth, renewable energy sources are being explored as solutions to these problems. Solar energy as we all know is a renewable energy and is one of the less costly, safe and most productive sources of green energy, so it’s widely used in many energy dependant settings around the world.

Solar cells are popularly used in calculators to power batteries, it’s also used to power many other small electronic devices, and recently portable devices are starting to be integrated with solar cells and it is gradually expanding to other devices. Photovoltaic cells are as well used in many countries around the world to power road signs, traffic lights and streetlights. Most importantly, households to supply energy to their houses, which is less costly than grid electricity, use solar cells. New generation electric cars also have integrated solar cells to function and many more. The even most popular applications of solar cells are in satellites, which solely rely on their solar cells for electricity.

RELATIONSHIP WITH THE PRACTICALS

Unfortunately, not all of the solar energy converted to electrical energy inside the photovoltaic cells emerges at the terminals of the cells, as some energy is lost as a result overcoming the resistance against the flow of current inside the cells. However, this problem does not only occur in photovoltaic cells but also in chemical cells and other types of cells. With that being the case a lab experiment can be carried out to calculate internal resistance of chemical cells, which is essential in determining efficiency of cells. This experiment will help give a wider understanding of solar cell as its analogous to chemical cells based on how they function.

SOURCES OF INFORMATION INTERNET

http://inventors.about.com/od/sstartinventions/a/solar_cell.htm http://photovoltaics.sandia.gov/docs/PVFEffIntroduction.htm http://energybible.com/solar_energy/solar_cells.html http://science.howstuffworks.com/environmental/energy/solar-cell1.htm

BOOKS Benn, M and George, G- Edexcel physics for AS. Huddler education Oxford English dictionary and thesaurus

MAGAZINE JOURNAL Barras, C. (11/11/08) new scientist- optics letters (DOI: 10.1364/OL.33.002

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