A rise of global critical concern over environmental issues upon finding sustainable clean energy sources, the depletion of the ozone layer and global climate change. In order to address these problems, the use of renewable energy resources has been proposed decades ago. Photovoltaic (PV) is recognized as the cleanest and most viable form of renewable power generation that can be deployed throughout the world.
1. Why PV?
2. How does PV work?
PV technology converts solar energy directly into electricity through the Photovoltaic Effect.
The solar cells (electricity-producing devices) are the smallest basic element in a PV system. They are interconnected within PV modules, which are then connected together into arrays, for use in systems of varying power requirements.
In a PV cell, there are typically two or more thin layers of semi-conducting material like silicon solar power perth. When photons strike a cell, they may be reflected or absorbed (by the semi-conducting material). For photons absorbed, electrons will be freed from the semiconductor atoms and become part of an electric flow inside a circuit.
3. PV Cells
There have been many types of PV cells. The most common type (more than 90% of industrial PV) is the crystalline silicon cell. Crystalline silicon cells have always accounted for a large majority of the PV cells market. Over the years, PV cells have undergone substantial improvement.
The first generation PV cell consists of a single layer p-n junction diode that can generate electricity from sunlight. This generation includes monocrystalline and multicrystalline silicon cells, i.e., the traditional crystalline silicon cells.
Traditional Crystalline Silicon Cells
Silicon is the basis for most industrial PV devices. It is the second most abundant element on earth and usually exists in the form of silicon dioxide. After chemical conversion of the silicon oxide to metallic silicon, high-grade silicon is purified and further processed to produce monocrystalline or multicrystalline cells. These cells have been the most widely adopted PV cells in the market.
Monocrystalline cells are produced from very pure silicon ingots grown slowly from the molten metal. The ingots are then sawed into thin wafers which are used for solar cell production. Only absolutely pure silicon is utilized to ensure high efficiency.
For the production of polycrystalline cells, liquid silicon is poured into blocks and allowed to recrystallize before slicing into thin wafers. Crystal structures of different sizes are formed during the course of solidification of the material. While the multicrystalline cells are slightly less efficient, the casting process is more cost effective.
The second generation PV cell is often associated with multiple layers of p-n junction diodes. Each layer is designed to absorb specific wavelengths of light. As a result, more of the solar spectrum can be absorbed and hence a greater amount of electrical energy can be produced. Typical examples of the 2nd generation cells are amorphous silicon (a-Si), copper indium diselenide (CIS) and cadmium telluride (CdTe) cells. Many of these devices are produced via thin film deposition technologies.
4. PV Systems
PV systems generally fall into two categories, namely grid-connected and stand-alone.
Grid-connected systems refer to the PV systems that connect to the local electricity network. Electricity is produced both by the PV systems and electrical utility. It can be fed back into the utility grid in case the output from PV systems exceed its own usage demand. On the other hand, electricity from the grid can be utilized when the sunlight is insufficient or the home power demand is high. Additionally, grid-connected systems can be integrated into building facades or roofs, forming Building Integrated Photovoltaic (BIPV) systems.
Stand-alone PV systems are independent from the utility grid system. They can be used when grid-connection is too distant or unavailable. Generally, batteries and charge controllers are employed in stand-alone systems. Batteries are used to store energy temporarily inside the systems when it is not needed. Further, the PV system coupled with the use of wind turbines or other devices, can be used to form a hybrid power supply system in case greater amounts of electricity are required.