Solar Photovoltaic: Future Energy Sources

In general, energy sources are categorized into two parts namely non-renewable energy and renewable energy. Fossil energy sources are among the first group that the bulk of activity in the world using these conventional energy.

It is no doubt that the solar photovoltaic is one source of environmentally friendly energy and is very promising in the future, because there is no pollution produced during the process of energy conversion, and more widely available source of energy in nature, namely the sun.

Fundamental issues in solar cell technology is a very low efficiency in turning solar energy into electrical energy, which to date the highest efficiency can be achieved no more than 20%, and even then in a laboratory scale.

For that in developed countries, research on solar cell is a very big concern, especially with the issue of environmental clean.

From light into electricity

In a simple solar photovoltaic consists of the p-type and n junction semiconductor material (pn junction semiconductor) that if by the sun there will be a flow of electrons, electron flow is well known as the electric current flow. While the structure of the solar cell is as shown in Figure 1.

Figure 1. Structure of a thin layer of solar photovoltaic in general

The main part of the energy changes of sunlight to electricity is the absorber, however, each layer is also very influential on the efficiency of the solar cell. Sunlight consists of various types of electromagnetic waves in a spectrum can be seen in figure 2. Therefore here absorber is expected to absorb as much solar radiation derived from sunlight.

Figure 2. The spectrum of solar radiation

More detail can be explained that the sun consists of a photon-photon, if it happen to solar cell surface material (absorber), will be absorbed, reflected or simply passed (see Figure 3), and only photons with certain energy level that will liberate electrons from atomic bonds, so that electrical current flows. Energy levels is called band-gap energy which is defined as the amount of energy required to discharge electrons out of its covalent bond so that there electric current flow. To free electron from its covalent bond, photon energy (hc/v) must be slightly larger or above than the band-gap energy. If the photon energy is too much of the energy band-gap, then the extra energy will be converted in the form of heat in a solar cell. Therefore it is important to the solar cell to regulate the materials used, namely by modifying the molecular structure of the semiconductor used.

Figure 3. Radiative transition of solar photovoltaic

Of course, that the efficiency of solar cell can be high if the photons from sunlight to be absorbed that as much, then reduce reflection and increase recombination and conductivity of the material.

To be able to make that a photon is absorbed can be as much, then the absorber must have an energy band-gap with a wide range, making it possible to absorb sunlight so energy has a variety of these. One of the many materials being studied are known CuInSe2 is one of the direct semiconductor.

So many advantages of solar photovoltaic as described above was not a polemic and not just stop, saying there was a solar photovoltaic is true when the energy change process there is no pollution produced, but have we calculated how much pollution has been generated in the process manufacturing, small compared to the resulting efficiency. Now the challenge here is indeed how to increase efficiency, which would affect its economic value.

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