Solar Cell
Solar cells are semiconductor structures which convert solar radiation in into electrical energy. Solar cell is composed of a large number of diodes, p-n junctions. The process in the middle is Photovoltaic conversion. In this process electron-hole pair is generated due to the incident light. This amount of photon energy is sufficient to move electrons from the valence zone into conductive zone. When it comes to the ways how solar cells can be connected, serial, parallel, or combined connection is possible. However, it all depends on the projected power of the cells. The voltage that is obtained at the output depends on the cell type and can be in range of 600-700 mV, with a current density of about several tens of mA/cm2. These parameters strictly depend on the strength of solar radiation.
Materials for Solar Cell Production
In regards to the material which are made of, cell could be categorized as Si, GaAs, InP, CIS, CdTe, and organic. Number of p-n junctions may vary, even cells with four junctions are produced, obtaining significantly higher coefficient of efficiency (mainly are based on GaAs and Ge). In addition, there is another classification according to the type of materials used to build a junction, where n and p type of materials have different widths of forbidden zone Eg. These are the so-called hetero-structures, which is mostly the case with the cells with multiple p-n junction. In this way, better absorption of the incident light is provided.
Crystallographic Structure of Solar Cells
When price of the solar cells is concerned, there is a wide range of prices depending on the type of the cell exploited. The most common and commercially most acceptable are silicon solar cells. They are divided according to the crystallographic structure: monocrystalline, polycrystalline and amorphous. Monocrystalline solar cells are expensive due to their high coefficient of efficiency up to 18%. Polycrystalline solar cells cells have coefficient of efficiency up to 15%. Amorphous solar cells have the lowest efficiency of only 8%, however their are cheap alternative.
The Efficiency of Solar Panels
Cross-section of a typical solar cells, shows many different layers. The first layer is a protective glass (SiO2), which main purpose is protection of the cell from external influences. Below is anti-reflection layer, which reduces reflection of the light and ensures that the more energy reaches the semiconductor. Next layer is a system of transparent electrodes, after which n-type semiconductor and p-type semiconductor area are placed. On the bottom side is metallization contact.
As it was mentioned, maximum output voltage of individual solar cell is up to 0,7 V. Serial connection of the solar cells provides to obtain a desired voltage. The most commonly about 36 cells are serially connected providing a nominal voltage of 12 V. Given that output power of the individual solar cell is relatively small, in practice, more cells are grouped together forming a photovoltaic module. According to the projected power modules are connected regularly or in parallel, thereby forming a photovoltaic panel that produces much more electricity.
Solar Radiation
The energy of the solar radiation that reaches the Earth is 10,000 times greater than the energy required to meet the needs of humanity, for a period of one year. Only one square meter reaches 100 kWh of solar energy per year. This goes to the favor of promoting solar technology as a dominant form of the energy production in the distant future.
Nowadays, solar systems are utilized in homes, buildings, factories, shopping malls, etc.Trend in design of buildings is according to the highest possible exploitation of solar energy. It also should be noted that solar energy is converted into DC power, while some of home appliances requires AC power. Hence DC/AC converter must be provided.
Independent power source (off-grid)
Off-grid system is extremely convenient solution for where power distribution network doesn't exists. Here we have independent exploitation of electricity, eliminating financial burdens. Photovoltaic system is charging the battery bank during the day, and at night accumulated accumulated energy is used. By day it is possible to connect directly to consumers. Good practice is to provide additional supplies by the connected generator as an optional power source. This system is more expensive than on-grid system, mostly due to the battery bank. Price is higher at least 30% because battery bank is expensive and their service life is for five to fifteen years.
Source connected to the distribution network (on-grid)
"On-grid" system is a photovoltaic system connected to the distribution network. This systems works in a following way. When required strength cannot be produce, it uses power from the network. However, if system produced more power than needed, excess power is send to network. Main feature of this system is that it provides normal power supply regardless of time of day, season and weather conditions. Nevertheless, additional contracts with the agency for the power distribution has to be made. Selling excess power to the power distribution agency repayment period could be severely shorted.
Conclusion
Therefore, if we continue with the promotion of the solar technology and construction of solar power plants and investing in the deployment of solar energy systems in residential buildings, we can directly address the problem of environmental pollution, improve the quality of life, and more important, to reduce man's destruction of nature.
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