A solar cell (photovoltaic), turns sunlight into electric energy. Other sources of light may be used, but for now sunlight is for free.
The total consumption of energy in our planet, based in the use of conventional energy sources such as petroleum, carbon, electricity and others, represents 1% of the total amount of solar energy coming to earth’s surface. This gives you an idea of its potential.
The first report on the photovoltaic effect comes from the French Scientist Henry Becquerel, in 1839, observed a voltage originated when illuminating platinum or gold electrodes submerged in an alkaline or acid solution. First inform of this phenomenon observed on a solid surfaces come from W. G. Adams and R.E. Day in 1877, the observed the effect of a small selenium bar that on the sides had the platinum electrodes. For the next 30 years the first useful application was the sunlight measurer for photographs and as a light sensor in optical devices.
It was Albert Einstein who, in 1905, wrote a scientific paper with the theory that explained that phenomenon, work that helped him to get the Nobel Pirze on Physic 1921. This is a quantum phenomenon, evidencing that energy contained in light, is delivered in energy packages or quantum.
This phenomenon and its theories are the base of Quantum Mechanics, science that studies phenomenons in an atomic scale (such as interaction of matter and light). It evidences dramatically the duality wave-light particle. Until then, theories considered light as a waving phenomenon while others considered it as a corpuscular phenomena. but this phenomenon shows the dual nature of light, sometimes wave, sometimes particle.
Incident radiation over the photo sensitive surface may be electromagnetic (infrared light, visible light, ultraviolet light, X rays, Gamma rays) or radiation of charged particles (electrons, protons, alfa or beta particles).
Incident light over the surface of certain materials (silicon ), gives place to a current of electrons (sometimes named photo electrons considering their origin). The flux of electrons is an unipolar current (one that does not change its direction), and has an intensity proportional to the frequency of the incident light. A solar cell is a “sandwich” of doped silicon (melted) with phosphore (negative pole) and Boron (positive pole)
Next figure shows the process described:
When a cell is exposed to the light (negative side), if the photons arriving to the surface have more energy than needed to liberate an electron from the network they belong, a photo electron current develops. Photons energy is bigger than the energy linking those electrons to the material, and it most occur ah semi conductive junction not allowing the recombination of positive and negative carriers and also that the average life of those carries enables a constant flux through a useful charge.
Silicon is the main component for silica (merge of silicon and oxygen, found in nature, forms quartz, stone crystal etc). After cleaning the silicon, blocks of mono crystal silicon are built (depending on fabrication techniques), from where they get the slices, added with boron and phosphorus. With proper electric contacts they got connected with other cells, making big solar panels or modules for commercial or industrial use.
Depending on the techniques and the quality of it (reflected on their costs), solar cells with an area of 12×12 cm may produce.5 volts and 1 ampere of electric current (a 100 watts bulb, function with 220 volts and almost .5 amperes of current). Panels are recovered with special glass to resist the impact of hail, and framed with an aluminum structure which gives in mechanical support, making easier its transportation an installation.
To assure its correct functioning, the surface must be clean to take advantage from the maximum amount of light possible. The performance of newer solar cells is more than 30%, compare to the 15% of most of electric generators. It is the relationship cost/benefits the one that maintains the use of solar panels as a solution considered only when it is cheaper than the use of other energy forms. However, those places with no access to other energies, have solar energy as an excellent alternative.
In Chile, Siemens, trough its Solar Energy division, implemented a project that allows the use of domestic electric artifacts away from normal distribution networks. It is also possible to use solar energy and a conventional electric network together. Besides the current of a solar cell is continuous ( as in batteries), it is possible to convert it into alternate current, it is possible to store the electric solar energy, to use it at night.
Solar cells have been used successfully since the start of the spacial era, as an energy source for satellites and spaceships . There are robots working with solar energy, and they show a Phototropic Behavior: they look for light and run away from shadows
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