Technology

Currently the most popular and the fastest growing method for electricity generation is the use of photovoltaic cells. By using solar energy, these solar cells convert solar energy into electricity. When explaining the term photovoltaic effect, we come across a word known as photovoltaic effect. In simple terms, it refers to the energy packets (photons) of light striking electrons and ultimately moving them into a higher energy state. The energy which is released as a result of this effect is known as electricity. Solar cells produce a special type of current known as direct current which can have multiple purposes. For example, it can be used for DC applications and for AC applications also. This can be done by using an inverter that is used to convert DC into AC. Photovoltaic cells are used as modules i.e. they are a collection of single cells which are used for providing power to the regional grid. Applications like electric cars, emergency telephones and remote sensing are now using photovoltaic cells. Solar panels or photovoltaic modules are a collection of single photovoltaic cells which are connected together to form an array. AN array can be used to provide large amount of electricity for various applications like they are sufficient to provide electricity to houses. These photovoltaic cells are very important and their significance can be highlighted from the fact that approximately 1,864 GW of electricity can be generated globally by 2030 using these solar cells.

OLMEDILLA PHOTOVOLTAIC PARK
 Olmedilla photovoltaic Park is the Biggest Photovoltaic Array Park in the world. It is located in n Olmedilla de Alarcn, Spain and was completed in year 2008, September. This mammoth cell park utilizes 62,000 flat solar photovoltaic panels to generate a massive 60 MW of electricity on a sunny day. This output of electricity is sufficient to lighten up approximately 40,000 homes. Using unconventional silicon based solar panels, Olmedilla produce enormous amount of electricity on every sunny every day (worldofphotovoltaics.com).

SPECIFICATIONS
Most commonly used photovoltaic cells are mono-crystalline silicon cells, are either 83W or 180W panels. ZED is one of the producers of solar panels and the particular specifications of 180W panel are
Maximum power 180W180Wp Dimensions 1581x809x50mm                                        
Number of cells (Pcs) 72Maximum power voltage (V) 36.31                                            
Maximum power current (A) 4.98Open circuit voltage (V) 44.97                                                
Short circuit current (A) 5.23Maximum system voltage (V) 1000                                           Temperature range -40C to 80CTolerance Wattage (e.g. -3C) -5C                                      
Weight per piece (kg) 16.3Length of cables (mm) 900mm                                                    
Cell Efficiency 15.2Module Efficiency 15                                                                  
Output tolerance -5Frame (Materials, corners, etc) Aluminum                    
Test Conditions 1.5 AM 100mWcm 25C(BedZED)

INSOLATION
The amount of solar energy received on a given surface area at a particular time is known as Insolation. It is normally expressed as average irradiance, watts per square meter (Wm2) or kilowatt-hours per square meter per day (kWh(m2day)) (or hoursday). Insolation level for photovoltaic cells is measured as kWh(kWpy) (kilowatt hours per year per kilowatt peak rating). insolation level is the largest when the sun directly faces the surface of the panel. To increase insolation of a solar panel, the panel can be placed at a specific angle based on the latitude of its location. Insolation can also be increased by solar tracking which utilizes maximum sunlight thereby increasing the total power output (Deciding the Direction and Angle of Installation, 2008)

SOLAR CELL TECHNOLOGY
Most common material used in Solar Cells is Single crystal silicon, however the efficiency of single crystal silicon based solar cells is limited to about 25 only. Due to its limited efficiency, research is being done to find more efficient materials. Finally the latest concept is of Quantum Dot Solar Cell.

Quantum Dot (QD) Solar Cell.
Conversion efficiency of photovoltaic cells can be increased by using two or more p-n solar cell junctions. For this a new concept, namely the quantum dot (QD) solar cell is considered below. The model proposed is based on a p-i-n cell structure. Higher internal quantum efficiency for carrier collected photo excited electrons occurs as a result of channeling the electrons and holes through the coupling. This effect allows separation and injection of the generated electrons and holes in QDs into an adjacent p- and n-regions with high efficiency.

SCHEMATIC DIAGRAM OF A PHOTOVOLTAIC CELL TECHNOLOGY
A photovoltaic cell works by absorbing the incident photons carried by the radiation from the sun. The impact of Photons excites the silicon electrons of the solar panel moving them into higher energy state. Once they fall back into their original energy state they release the corresponding energy .in the form of DC (Direct current). Inverter connected to the panel inverts DC into AC as household applications and most electrical equipments run on AC (Alternating current).This AC current flows through PV generation meter as well as to the load providing normal electricity for household usage.

This single PV array can be employed on a large scale like Olmedilla Photovoltaic Park to Mega Watts of AC electricity which can sustain small towns and even cities fulfilling all there electrical applications

Standard Test Conditions
The DC output of solar modules is rated by manufacturers under Standard Test Conditions .STC conditions are
Solar Cell Temperature  25 Celsius
Solar Irradiance (intensity)  1000 Wm2
Solar spectrum as filtered by passing through 1.5 thickness of atmosphere

Overall System Efficiency
A solar cells efficiency is given as the percentage of power converted (from absorbed light to electrical energy) and collected. It is calculated using the ratio of the maximum power point, Pm, divided by the input light Irradiance irradiance (E, in Wm2   or kWh(m2da ) under standard test conditions (STC) and the surface area of the solar cell (Ac in m2).

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MERGEFORMAT

According to STC specification
Temperature (T) 25 C     Irradiance (E)  1000 Wm2      Air mass 1.5 (AM1.5)

Calculation
For example        
T25 C, E1000 Wm2, Surface Area0.05m2, Efficiency12
Maximum Power produced  (12) (1000)(0.05) 1.2W or 1.210-3 kWh(m2day) (According to the formula mentioned above)
Power produced per day  1.210-3 kWh(m2day)
Power produced over a year (1.210-3 kWh (m2day)) (365days) 0.438KWyear
From a single cell of the above mentioned efficiency. Using the above mentioned formula, these calculations can be performed using a simple calculator.

Power output of photovoltaic cell is dependent on the intensity and the ambient temperature. Variations in these conditions results in different power output levels. Similarly for photovoltaic cells of different efficiencies their respective power outputs can be calculated .Based on the power output and application the particular photovoltaic cell is selected.

Peak-power Output
Photovoltaic cell operates over a range of Currents and Voltages. To determine the peak power output, we increase the resistive load on an irradiated cell continuously from zero (a Short circuit short circuit) to a very high value.

The output produced by high quality, mono-crystalline silicon solar cell, at temperature of 25 C is 0.60 volts open-circuit (VOC). The Cell temperature will be around 45 C, at 25 C air temperature. This reduces the open-circuit voltage to 0.55 volts per cell. Maximum power (with 45 C cell temperature) is achieved with 75 to 80 of open-circuit voltage (0.43 volts in this case) and 90 of short-circuit current. Lower-quality cells rapidly drop voltage with increasing current and could produce only 12 VOC at 12 ISC. The usable power output decreases from 70 of the VOC x ISC product to 50 or even as little as 25. The maximum power point of a photovoltaic cell varies with incident illumination.

Watts Peak
Photovoltaic cell output power depends on various factors that include the. Incidence angle incidence angle of sun so to compare different cells and panels we use Watts Peak. This refers to the output power (under standard test conditions) at an of 1 kWm2, a solar reference spectrum AM (Airmass air mass) of 1.5 and a cell temperature 25 C.