| Photovoltaic (PV) systems convert sunlight into | | | | utility grid use batteries to store energy for use |
| electricity. The photovoltaic effect is the basic | | | | when the sun is not shining. |
| physical process through which this happens. | | | | A well-designed and properly installed PV system |
| Sunlight is composed of photons, or particles of | | | | with a consistent maintenance schedule will |
| solar energy. These photons contain various | | | | operate for more than 20 years. The PV module, |
| amounts of energy corresponding to the different | | | | which has no moving parts, has an expected |
| wavelengths of the solar spectrum. When | | | | lifetime of more than 30 years. |
| photons strike a PV cell, they may be reflected | | | | In the past 30 years, the photovoltaic industry |
| or absorbed, or they may pass right through. Only | | | | maintained a growth rate of 20 percent on the |
| the absorbed photons generate electricity. When | | | | average, while in the last five years, with an |
| this happens, the energy of the photon is | | | | average annual growth rate of as high as 35 |
| transferred to an electron in an atom of the cell | | | | percent. As of 2007, the global PV power installed |
| (which is actually a semiconductor). With its | | | | capacity is 9.1 million kilowatts, the growth rate go |
| newfound energy, the electron is able to escape | | | | up to 33 percent. in 2007, capacity of 2.2 million |
| from its normal position associated with that | | | | kilowatts is installed, and the growth rate is |
| atom to become part of the current in an | | | | 40%.on the optimistic view , in the next 30 years |
| electrical circuit. By leaving this position, the | | | | ,the photovoltaic industry will maintain a growth |
| electron causes a "hole" to form. Special electrical | | | | rate of more than 25 percent, while the |
| properties of the PV cell provide the voltage | | | | pessimistic view is that this opinion is not based |
| needed to drive the current through an external | | | | on reality. |
| load (such as a light bulb). | | | | Optimistic faction believes that as the technological |
| A PV system comprises several components. | | | | progress and industrial expansion, photovoltaic |
| The basic building block of a PV panel is the PV | | | | power generation costs will be quickly reduced, |
| cell, which is a solid state, or non-mechanical, | | | | thereby it bring a fundamental demand for the |
| device. A solar system uses a number of PV | | | | expansion, the process will run through the entire |
| panels, each made of silicon, plus boron and | | | | century. The latter part of the growth rate will |
| phosphorous. The output of a single cell under | | | | decline because the base PV will be huge. |
| direct sunlight is about one watt. To increase their | | | | Pessimistic view is base on the biggest obstacles |
| effectiveness, dozens of individual cells are | | | | for photovoltaic industry is the high cost. In the |
| interconnected together in a sealed, weatherproof | | | | Western developed countries, they mainly go |
| glass package called a module. Modules come in a | | | | through various kinds of financial subsidies to |
| range of wattages, and their nature allows for | | | | support the development of the industry, such as |
| great flexibility in designing systems that meet a | | | | United States allow advance photovoltaic project |
| variety of electrical needs. | | | | with the financial and tax incentives, and support |
| Since PV modules are only capable of producing | | | | the Internet price of photovoltaic for 21.29 cents |
| direct current (DC) electricity, an inverter is | | | | unit. |
| required to convert the direct current (DC) output | | | | According to our opinion, base on the cost of |
| produced by the PV array into alternating current | | | | photovoltaic, the next three to five years, in |
| (AC) power. AC electricity is needed to run | | | | some time and some areas, photovoltaic will have |
| computers, refrigerators and other appliances, and | | | | cost advantage. U.S. Environmental Co-op |
| lighting. | | | | non-profit organization says, the cost of solar |
| A utility PV system, such as those installed under | | | | power will be equal with the traditional fossil |
| the Sun4Schools project, generate electricity | | | | energy for power generation costs. With the |
| which is supplemented by the energy provided by | | | | decline of the cost for solar power, while coal, |
| the existing utility grid. A PV system requires | | | | natural gas and the rising cost of nuclear power, |
| neither battery storage nor an emergency | | | | United States will come to the intersection by |
| back-up system since it is connected directly to | | | | 2015.From Comprehensive opinion, the |
| the utility grid, which is used as the storage | | | | photovoltaic industry will have a high growth |
| medium. Systems that are not connected to the | | | | period. |