In our daily life we all need to consume energy. That consumption, however, has globally highlighted such conventional energy-related issues as global warming caused by the greenhouse effect due to exhaust gases including carbon dioxide, and the run out of fossil fuels. The clean energy approach has attracted particular attention as one viable method of solving these issues. Therefore, many countries around the world are discussing the adoption of the clean energy systems and promoting those systems by the feed-in-tariff, the RPS approach, or both. The clean energy systems have been employed in many countries. The photovoltaic system is considered to play a leading role among the clean energies.

The photovoltaic systems convert the solar energy from sunlight into electricity. The solar energy is inexhaustible and there is no fear that the energy could run out . In addition, photovoltaic systems are effective in reducing the greenhouse-gas emissions, since it produces no toxic materials such as exhaust gases from plant operation. While various types of photovoltaic systems are available, crystalline silicon photovolitaic systems occupy the major share.

Below is a cross-section view of the crystalline silicon photovoltaic system, which leads the market. The photovoltaic cell used in the system is composed of two thin plates of semiconductor, N-type and P-type. When the sunlight hits the surface of the cell, electrons are activated between these two different types of semiconductors, producing electric current.