SOLAR ENERGY

SOLAR ENERGY

Solar energy is the radiant light and heat from the Sun that has been exploiting by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available renewable energy on Earth. Only a little fraction of the available solar energy is used. Solar energy refers primarily to the use of solar radiation for practical ends. However, all renewable energies, other than geothermal and tidal, derive their energy from the sun. Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.

 Average Energy Over The Years

The Earth receives 174 pet watts (PW) of incoming solar radiation at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, ocean sand land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near- ultraviolet.

The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ  per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined.

  Solar Energy Is Used

1. Generate electricity using pv cells
2. Generate electricity using concentrated solar power
3. Generate electricity by heating trapped air which rotates turbine in a solar updraft tower
4. Generate hydrogen using photo electrochemical cells
5. Solar air conditioning
6.  Heat and cool air through use of solar chimneys

Solar cell

A  solar cell or photovoltaic cell is a device that converts light directly into electricity by

 the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, or photovoltaic arrays.

 Construction

Silicon solar cells have been available for a relatively long period of time. In order to increase the output from such solar cells it has been conventional to provide a single layer antireflection coating overlaying the solar cell. Typically these single layer anti- reflections coatings have been formed of silicon monoxide, a titanium oxide such as titanium dioxide or gas reacted titanium monoxide as well as tantalum pent oxide. Since the tantalum pent oxide and the titanium oxide have an index of refraction which is greater than that of silicon monoxide, they form a better anti-reflection coating between the silicon solar cell and the glass cover which conventionally covers such a solar cell.

The silicon solar cell construction consists of a body formed essentially of silicon and having a surface with a photovoltaic junction formed thereon. First and second layers are formed on the surface of the solar cell and serve to provide an anti-reflection coating which is effective within the spectral range of 400 to 1200 nanometers. A glass solar cell cover is provided which is secured to the body having the first and second layers thereon by cement. The first layer is, counting from the body, formed of material that has an index of refraction which is less than that of the body and which is greater than that of the glass cover. The second layer is formed of a material that has an index of refraction which is greater than that of the glass cover but which is less than that of the first layer.

1 Solar Cell                   

solar cells are in fact large area semiconductor diodes. Due to photovoltaic effect energy of light (energy of photons) converts into electrical current. At p-n junction, an electric field is built up which leads to the separation of the charge carriers (electrons and holes). At incidence of photon stream onto semiconductor material the electrons are released, if the energy of photons is sufficient. Contact to a solar cell is realized due to metal contacts. If the circuit is closed, meaning an electrical load is connected, then direct current flows.

2 Block Diagram Of Solar Pv                                                                   

 Solar Module and Array                                                                         

Regardless of size, a typical silicon PV cell produces about 0.5 – 0.6 volt DC under opencircuit, no-load conditions. The current (and power) output of a PV cell depends on its efficiency and size (surface area), and is proportional the intensity of sunlight striking the surface of the cell. For example, under peak sunlight conditions, a typical commercial PV cell with a surface area of 160 cm^2 (~25 in^2) will produce about 2 watts peak power. If the sunlight intensity were 40 percent of peak, this cell would produce about 0.8 watts. PV cells can be arranged in a series configuration to form a module, and modules can then be connected in parallel-series configurations to form arrays. When connecting cells or modules in series, they must have the same current rating to produce an additive voltage output, and similarly, modules must have the same voltage rating when connected in parallel to produce larger currents.

 3Solar Array

Solar cells are typically combined into modules that hold about 40 cells; about 10 of these modules are mounted in PV arrays (Array: A collection of photovoltaic modules electrically wired together in one structure to produce a specific amount of power) that can measure up to several meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. About 10 to 20 PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV syatem .




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