Usually photovoltaic system is divided according to following:
1) Functional requirements
2) Component Configuration
3) Type of Load
By keeping in mind these things we can classified it into two main systems .i.e.
a) Stand Alone System
b) Grid Connected System
This blog is about renewable energy sources. I am trying to cover the different types of renewable energy sources that can help in the generation of electricity.
Saturday, April 23, 2011
Wednesday, April 13, 2011
A PhotoVoltaic System
A photovoltaic system consists of number of arrays (combination of modules called an array).
A PV generator with mechanical support and sun tracking system.
Batteries or other storage devices.
A charge controller that not only prevents of overcharging of batteries but also prevents the discharging of batteries in night to arrays.
A rechargeable battery is used to store the direct current generated by the solar modules during day and discharging of battery at night if needed.
An inverter is used to to convert the direct current to alternating current in order to supply it to homes and businesses. This inverter consists of a circuit breaker for over discharging.
Above figure shows a typical PV system.
A PV generator with mechanical support and sun tracking system.
Batteries or other storage devices.
A charge controller that not only prevents of overcharging of batteries but also prevents the discharging of batteries in night to arrays.
A rechargeable battery is used to store the direct current generated by the solar modules during day and discharging of battery at night if needed.
An inverter is used to to convert the direct current to alternating current in order to supply it to homes and businesses. This inverter consists of a circuit breaker for over discharging.
Above figure shows a typical PV system.
Equivalent Model of a PV cell
An equivalent circuit of a PV cell is shown below
A diode shunt connected across the current source representing the diffusion current through the p-n junction.
Internal series and parallel resistances are represented by Rs and Rsh respectively.
This equivalent circuit of a pv cell can be connected in series or parallel to form a PV module as it is explain earlier.
A diode shunt connected across the current source representing the diffusion current through the p-n junction.
Internal series and parallel resistances are represented by Rs and Rsh respectively.
This equivalent circuit of a pv cell can be connected in series or parallel to form a PV module as it is explain earlier.
Answers
1) Well, actually that never happens. You can plot the i-v curve of a resistor on the same plot as the photovoltaic cell. It will be a straight line through the origin, with positive slope -- in accordance with Ohm's Law.
Where the two curves intersect will be the operating point for that particular load resistance. This happens in the "+v,+i" quadrant, so it will have voltage less than the open-circuit voltage and current less than the short-circuit current.
2) That's a general property of all power supplies. Open circuit means just that, i.e. the load resistance becomes (for all practical purposes) infinite. i=v/R=v/∞=0
Incidently, the i-v curve of a photovoltaic cell is related to that of a diode. Take a diode's i-v curve and flip it about the v-axis (equivalent to defining the current's polarity in the opposite sense). Then shift the curve upward by an amount equal to the short-circuit current. Works for photodiodes as well as photovoltaic cells, as they are the same thing but with different applications.
Where the two curves intersect will be the operating point for that particular load resistance. This happens in the "+v,+i" quadrant, so it will have voltage less than the open-circuit voltage and current less than the short-circuit current.
2) That's a general property of all power supplies. Open circuit means just that, i.e. the load resistance becomes (for all practical purposes) infinite. i=v/R=v/∞=0
Incidently, the i-v curve of a photovoltaic cell is related to that of a diode. Take a diode's i-v curve and flip it about the v-axis (equivalent to defining the current's polarity in the opposite sense). Then shift the curve upward by an amount equal to the short-circuit current. Works for photodiodes as well as photovoltaic cells, as they are the same thing but with different applications.
Questions
Here arises two questions
1) Whats happens when the resistance load of a circuit powered by a PV cell generates a higher voltage then that produced by the PV cell (does band gap get affected)?
2) Why does current drop near the Open Circuit Voltage? Surely the generation of current depends on the irradiance on the PV cell? So why does current stop at the Voc point?
1) Whats happens when the resistance load of a circuit powered by a PV cell generates a higher voltage then that produced by the PV cell (does band gap get affected)?
2) Why does current drop near the Open Circuit Voltage? Surely the generation of current depends on the irradiance on the PV cell? So why does current stop at the Voc point?
I-V Characteristics of a PV module
The current and voltage are the two main attributes of a photovoltaic module. The performance of a pv module can be determine by these descriptors. The I-V characteristics represents an infinite number of direct current and voltage operating points and varies with solar radiation and cell temperature.
As we know that power is the product of voltage and current,therefore, maximum power can be extracted at a point where voltage and current is maximum as shown in the above graph.
As we know that power is the product of voltage and current,therefore, maximum power can be extracted at a point where voltage and current is maximum as shown in the above graph.
Saturday, April 09, 2011
Module
When number of cells are connected together in series or parallel combination a module is form. If cells are connected in series it produces high voltage where as cells in parallel produces more electric current. The interconnected solar cells are usually embedded in transparent Ethyl-Vinyl-Acetate, fitted with an aluminum or stainless steel frame and covered with transparent glass on the front side.
The typical power ratings of such solar modules are between 10 Wpeak and 100 Wpeak. The characteristic data refer to the standard test conditions of 1000 W/m² solar radiation at a cell temperature of 25° Celsius. The manufacturer's standard warranty of ten or more years is quite long and shows the high quality standards and life expectancy of today's products.
The typical power ratings of such solar modules are between 10 Wpeak and 100 Wpeak. The characteristic data refer to the standard test conditions of 1000 W/m² solar radiation at a cell temperature of 25° Celsius. The manufacturer's standard warranty of ten or more years is quite long and shows the high quality standards and life expectancy of today's products.
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