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Solar Energy Technology : Basics
Solar energy technology basics is explained in this post:
Solar Power is the conversion of sunlight into electricity, either directly using photovoltaic’s (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaic’s convert light into an electric current using the Solar Cells by Photovoltaic Effect.
Here I am going to explain the solar power produced using Photovoltaic effect:
Power by Solar Photovoltaic’s:
Photovoltaic(PV) is a solid-state, semiconductor –based technology that converts light energy directly into electrical energy, without moving parts , without noise and without emissions.
“Photovoltaic” refers to the creation of Voltage from light and is often abbreviated as “PV”.A common more term of photovoltaic cells is “Solar Cells” although the cells work with any kind of light and not just sunlight.
Solar Cell is a converter. It changes light energy into electrical energy. A Solar cell does not store any energy. So when the source of light (typically sunlight) is removed, there is no electric current from the cell. The conversion process occurs instantly whenever there is a light falling on the surface of the Solar cell. The output of the cell is proportional to the incident light, the more light, the greater the electric output. The Sunlight acts as a fuel for the conversion process. This fuel is delivered free everywhere in the world.
Since the absence of Sun during night the solar cells cannot produce electricity, so some form of electrical storage like battery must be included in the system.
Principle of Generation of Electricity in Solar Cells:
When the light falls on the solar cell, the energy of the light penetrates into the solar cell and on random basis knocks the negatively charged electrons loose from their silicon atoms. To understand this, you can thick light as being made of billions of energy particles called Photons. The incoming photons acts much like a billiard balls, only difference is they are made of pure energy. When they collide with an atom, the whole atom is energized and electron is ejected or ionized from the atom.
Energy in the form of Photon from Solar radiation can transfer its energy to the electrons
The freed electron now has the extra potential energy and this is what we call “voltage” or “electrical pressure”. By creating an internal electrostatic field near the front surface of the cell during the manufacturing, free electron is brought out of Solar cell.The flow of free electrons or electrical charges with extra potential energy or voltage is called “Electric Current”.
Electric current in Solar cell:
The electrons freed by the incoming sunlight photons flow out of the cell and to the electrical load. They give up their extra potential energy (voltage) there and allow useful work to be done. The electrons then continue to flow back of the solar cell, where they become available once again to be knocked loose by photon and flow on to the load.
Commercial Solar Photovoltaic technologies:
There are a number of photovoltaic technologies today-in the commercial market, nearing commercial viability, or in some stage of pre-commercial research. These generally fall into two board categories: Flat plate and concentrator (a potential third category would be “other”, which would include organic solar cells and other novel or exotic technologies, which we will not cover here). First state technologies are the most common commercially. Concentrator systems, while using less of the expensive PV material and making up for by concentrating more light on the PV with inexpensive plastic lenses or reflectors
Flat plate technologies dominate the market today. These technologies are commonly subdivided into crystalline and thin films; through there can be a great deal of overlap. The Crystalline can be subdivided (in a simplistic way) into single crystal, which is relatively self-explanatory, and multi crystal, which is typically sliced from cast blocks of material, leaving it with many crystals in each cell. Another crystalline subcategory is sheet or ribbon technologies, where the PV material is drawn from a melt, which varies from nearly crystalline to highly multi crystalline.
Crystalline technologies have the advantage of relatively high conversion efficiencies and a large installed base of manufacturing equipment, while being burdened with the disadvantages of being labor-intensive, material intensive, and limited in physical form (made from fragile, rigid cells cut from larger pieces).
Thin-film technologies get their name from the fact the fact that they are typically deposited in very thin films on inexpensive substrates (e.g., glass, stainless steel, plastic, ceramic, etc). This category includes such technologies as amorphous silicon, copper-indium deselenide, and cadmium telluride. These have the advantage of being ideal for automated manufacture, they have low materials usage, and they can be deposited on a range of materials and in unique and unusual shapes. The disadvantages of these have included a lack of manufacturing experience and lower conversion efficiencies (until recently, when CIS-Copper Indium di-Selenide and Cdte-Cadmium Telluride technologies have begun to approach the conversion efficiencies of crystalline technologies.)
Types of Solar Cell:
There are two major types of Solar cells:
- Crystalline Cells
- Thin Layer (Thin Film) or Amorphous Cells
Research and development in this field is on-going as manufacturers are always looking for ways to make solar cell cheaper and more efficient. One such product is current on the market is Hybrid HIT cells which include both a mono-crystalline component and thin film component.
Types of Crystalline Cells:
- Mono-crystalline (Single)
- Poly-crystalline (multi-crystalline)
The Solar cells when joined physically and electrically they form a Solar or PV Module. It is a collection of cells interconnected by usually flat wire, and includes encapsulation to protect the cells and interconnecting wires from corrosion and impact. It usually includes a frame to allow easy mounting and a junction box to allow wiring to other modules or to the battery and loads. The number of cells connected in series determines the final voltage of the module.
Similarly a Solar Panel is the collection of modules physically and electrically grouped together on structure. This would be the building block for larger power systems. Usually, the modules are wired together on the panel to give the final system voltage (for example 12, 24, 48 volts and higher) and the panels are wired together through field junction boxes and then on to the system controls and batteries. Individual panels can be disassembled or maintained while other panels or operational.
An Array is the full collection of all solar modules. Sometimes an array is so large that it is grouped into SUB-ARRAYS, for easier installation and power management. An array can be as small as one module (for simple home lighting system) or as large as 100000 modules or more for very large utility connected systems.
Lab efficiencies of 25.0 percent for mono-Si cells are the highest in the commercial PV market, ahead of polysilicon with 20.4 percent and all established thin-film technologies namely, CIGS cells (19.8%), CdTe cells (19.6%), and a-Si cells (13.4%). These high efficiencies can be combined with other technologies, such as multi-layer solar cells in applications where space and weight become an issue such as powering satellites.
Solar module efficiencies—which are always lower than those of their corresponding cells—crossed the 20 percent mark for mono-Si in 2012; an improvement of 5.5 percent over a period of ten years. The thickness of a silicon wafer used to produce a solar cell also decreased significantly, requiring less raw material and therefore less energy for its manufacture. Increased efficiency combined with economic usage of resources and materials was the main driver for the price decline over the last decade.
Image sources : Concentrated Solar Technology
To be continued..