Energy from the sun not only sustains life an earth but is also the source of almost all forms of energy used by man. Solar energy, experienced by us as heat and light, can be used in a number of ways and for many applications such as:
- Thermal route - using the heat for heating, cooling, drying, water purification and power generation.
- Photovoltaic route - converting the light energy into electric energy which can then be used for a variety of purposes such as lighting, pumping, communications and refrigeration etc.
Producing electricity from solar resource through:
- - Concentrating solar thermal
- - Solar photovoltaic
Concentrating solar thermal route uses the heat component of solar energy. Heat is used directly or through an intermediate fluid to generate steam which is expands in steam turbine to produce electricity.
Solar cells convert solar radiation (sunlight) directly into electricity by photoelectric/photovoltaic effect. Incident photons (light ray) strike on the photovoltaic cell, and knock off electrons. These free electrons start flowing through a circuit forming an electrical current.
Photovoltaic module contains a group of photovoltaic cells, connected mostly in series and encapsulated between a layer of front glass, EVA and back cover. The high transmissivity, toughened glass cover is used to ensure high light absorption and therefore enhance the performance of the cells. Solar radiation falls directly upon the photovoltaic cell and produce DC electricity.
Photovoltaic cells absorb both direct and diffuse solar radiation. Generally, flat plate photovoltaic modules/panels are mounted in a fixed position and tilted towards south (locations in northern hemisphere) to optimize energy production. However, flat plate PV panels with tracking mechanism (one/two axis) increase output of solar panels, particularly for high DNI.
The amount of power that a PV panel delivers is proportional to the amount of radiation that falls upon it. The advantages of PV system as compared to solar thermal are as follows:
- - It is modular in nature so that any size of system could be installed.
- - It is suitable for relatively colder climates
- - It is nearly maintenance free
- - Less water requirement
- - It does not make any noise
The various types of solar cells used for electricity generation are as follows:
The most common commercial crystalline solar cells are made up from silicon wafers. These account for about 85%[ ] of the world's solar PV industry. Silicon wafers either consists of one large singe crystal, called single crystalline wafers, or consist of crystallites in a single wafer, are known as polycrystalline (multi-crystalline) silicon wafers. The main advantages of cells produced from mono-crystalline (mono-Si) and polycrystalline (poly-Si) silicon wafers are: suit relatively small areas and have higher efficiency. The efficiency achieved by a crystalline solar cell depends on the processing technology used to make the solar cell. The most commonly used technology to make wafer-based silicon solar cells is screen-printed technology.
- Thin Film
Thin film solar cells are made up from a variety of materials, with the key features being that the thickness of the cells is a few microns. Thin film solar cells are made from amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium di-selenide (CIS). Thin film technology is comparatively cheaper, but produces less output per unit area due to its lower efficiency, so it requires large area per unit output.
The main advantages of cells produced from thin films are low cost of production and they can be made with requisite shape as per the requirement. But, unfortunately there are limitations of utility properties. However, it is possible to improve the utility properties of amorphous cells by means of changing the cross section of the window layer to improve sun light collection efficiency.
There are some other PV materials for solar cells like string ribbon silicon wafers (ribbon-hetero-junction with intrinsic thin layer hybrid silicon solar cell (HIT) and concentrator photovoltaic solar cell etc.