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Understanding inverters' role in the solar industry

Posted: 01 Sep 2011 ?? ?Print Version ?Bookmark and Share

Keywords:solar power? solar inverter? photovoltaic?

In the recent years, solar power has emerged as a major power source due to its numerous environmental and economic benefits and proven reliability. Since the solar power system does not consist of moving parts, virtually it does not need any kind of maintenance once installed.

In this paper, the overview of solar power industry will be discussed along with "Sun Farmer" solar inverter platform project designed by IMI Singapore D & D team.

Solar Power is produced by collecting sunlight on the solar panels and converting it into electrical energy. A solar cell (also called photovoltaic cell) is the smallest solid-state device that converts the energy of sunlight directly into electricity through the photovoltaic effect. A Photovoltaic (PV) module is an assembly of cells in series or parallel to augment voltage and/or current. A Panel is an assembly of modules on a structure. An Array is an assembly of panels at a site.

The performance of a solar cell is measured in terms of its efficiency at turning the sunlight into electricity. A typical commercial solar cell has an efficiency of 15 percent, i.e., about one-sixth of the sunlight striking the cell generates electricity. Improving solar cell efficiencies while holding down the cost per cell is an important goal of the PV industry.

Available PV technologies
Photovoltaic (PV) cells are generally made either from crystalline silicon sliced from ingots or castings, or from grown ribbons or thin film deposited in thin layers on a low-cost backing.

Crystalline silicon technology: This is the most common technology representing about 90 percent of the market today. Crystalline silicon cells are made from thin slices cut from a single crystal of silicon (monocrystalline) or from a block of silicon crystals (polycrystalline). Their efficiency ranges between 12 percent and 17 percent.

Three main types of crystalline cells can be distinguished:
? Monocrystalline (Mono c-Si)
? Polycrystalline (or Multicrystalline)(multi c-Si)
? Ribbon sheets (ribbon-sheet c-Si)

 Monocrystalline and Multicrystalline

Figure 1: (a) Mono c-Si, and (b) Multi c-Si.

Thin film technology: Thin film modules are constructed by depositing extremely thin layers of photosensitive materials onto a low-cost backing such as glass, stainless steel or plastic. Modern technologies use a printing process, far faster than conventional high-vacuum deposition, to create an efficient, durable solar cell. This method boosts the cost and capital efficiency of the solar panels.

Several other types of photovoltaic technologies developed today have begun to be commercialized or still at the research level. Some of these are:

Concentrated photovoltaic: Concentrated photovoltaic systems use lenses or mirrors to concentrate sunlight onto high-efficiency solar cells. These solar cells are typically more expensive than conventional cells used for flat-plate photovoltaic systems. However, the concentration decreases the required cell area while also increasing the cell efficiency. Efficiencies are in the range of 20C30 percent.

 Flexible PV cells

Figure 2: Flexible PV cells.

Flexible cells: Based on a production process similar to that of thin film cells, when the active material is deposited in a thin plastic, the cell can be flexible. Some of these are lightweight, bendable, easily interconnected, easily adjusted in size and capable of supporting up to 25 Amps of current per cell. These attributes open the range of applications, especially for building integration (roof tiles) and end-consumer applications.

Advantages of solar power
The use of solar power has many advantages. First, the energy from the sun is free and readily accessible in most parts of the world. Moreover, the sun will keep shining until the world's end. Also, silicon from which most photovoltaic cells are made is an abundant and nontoxic element (the second most abundant material in the earth's crust).

Second, the whole energy conversion process is environmentally friendly. It produces no noise, harmful emissions or polluting gases. The burning of natural resources for energy can create smoke, cause acid rain and pollute water and air. Carbon dioxide, CO2, a leading greenhouse gas, is also produced in the case of burning fuels. Solar power uses only the power of the sun as its fuel. It creates no harmful by-product and contributes actively to the reduction of global warming.

 Greenhouse gases

Figure 3: Greenhouse gases (grams per kilowatt-hour of CO2 equivalent).

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