There are two types of grid connect systems, those without battery backup and those with battery backup.
Grid connected systems without a battery consist of two main components, a solar PV array and a grid-connect inverter. If the utility grid fails then the solar PV array has no way of providing power as the inverter will automatically disconnect itself from the utility grid.
Grid-tied systems with a battery backup also have an array and a grid-tied inverter, but include the addition of a battery bank and charge controller. Systems with a battery bank can provide power in the event of the electricity (utility) grid failure.
There are many advantages of using a grid connected system
a) Simple to install;
b) High efficiency;
c) reliable;
d) flexible;
If we examine a typical household installation, please refer to the diagram below a number of essential components comprise the solar photovoltaic system.
1. Solar panels - one or more modules wired together to generate a specific voltage and current
2. Combiner (junction) Box - allows termination of the solar panels
3. Grid tie inverter - device that converts DC (direct current) to AC (alternating current).
4. import / export meter - records energy generated and consumed
5. Grid connect point - distribution board connection
6. Electrical load - appliances that are powered by alternating current.
In a typical grid-tied solar system, the DC electricity produced by the solar array.
Ifs fed by cables into a combiner (junction) box where the solar panels are terminated and connected together. A cable from the combiner box feeds the DC electricity into a grid-tied inverter. The inverter converts the DC electricity into AC electricity which is used by the appliances or fed into the grid. The output from the inverter is fed via a fuse directly into the main distribution (fuse board).
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.
Friday, May 06, 2011
Difference between Stand Alone and Grid Connected Systems
A standalone system is the one which is not connected to the power grid. In contrast, the PV systems connected to the grid are called grid connected PV system. The primary difference between the standalone and grid connected systems comes from the storage feature, which is direct consequence of their connection with the grid. While the standalone PV systems usually have a provision of energy storage or deficit energy produce by the PV source in grid connected systems is supply or drawn from the grid.
b) Grid Connected Systems
The solar power systems which are connected directly to the grid (connected to an electricity transmission and distribution system) is known as grid connected systems.
Such system is shown in the above figure. In these types of systems electricity generated is used in homes or offices and excessive power is fed back to the grid. Grid connected systems are designed to replace all or a portion of the building’s total electricity needs. The energy generated by such a system is used first within the home, and surplus energy can then be sold back to the grid. The surplus energy “spins the electric meter backwards” when the energy produced by the solar PV system is greater than that being consumed by the home. In actual fact the utility company will normally install an export meters which measure the amount of electricity generated by the solar PV system.
Such system is shown in the above figure. In these types of systems electricity generated is used in homes or offices and excessive power is fed back to the grid. Grid connected systems are designed to replace all or a portion of the building’s total electricity needs. The energy generated by such a system is used first within the home, and surplus energy can then be sold back to the grid. The surplus energy “spins the electric meter backwards” when the energy produced by the solar PV system is greater than that being consumed by the home. In actual fact the utility company will normally install an export meters which measure the amount of electricity generated by the solar PV system.
a) Stand Alone System
A standalone system is the one which is not connected to the power grid. It usually have a provision of energy storage or deficit energy produce by the PV source in grid connected systems is supply or drawn from the grid. As standalone system is not connected to the grid, it must have battery support to supplement the load requirements during the night hours or otherwise. A standalone system can be divided into five categories which are given below:
i) DC Coupled PV System
It is the simplest possible standalone configuration where PV panels are directly connected to the load. The capacity of the PV panels is designed in such a way that it is sufficient to run the load during sunshine hours. As power available to the load varies according to the weather condition, this is called an unregulated system. There is no arrangement for the energy storage to have night time load operation. A figure below describes such system.
DC coupled PV System
ii) Standalone System with DC Load
The block diagram of the configuration is given below. It is similar to unregulated PV system except that the electronic control circuitry is inserted between load and PV panel. This circuitry can be a voltage or current regulator or a maximum power point tracker. In order to achieve the smooth operation of load this circuit is introduced.
Standalone system with DC load
iii) Standalone System with Battery and DC Load
This type of PV system configuration is used when night time operation of the load is required. It requires energy from the battery to operate. The block diagram of such system is given below.
Standalone System with Battery and DC Load
Batteries in a PV system contribute to the recurring cost as the life of the batteries is significantly shorter than the life of the PV modules. The battery life is affected by the manner it is used like overcharging or over discharging reduced the life of battery.
iv) Standalone with AC/DC Load
It is similar to the standalone system with battery and dc load, the only difference is that now AC load is connected with the system. The block diagram of such system is shown below.
Standalone with AC/DC Load
In this configuration an inverter is used in order to convert DC power to AC power which is coming from battery. This type is suitable for domestic and commercial applications.
v) Hybrid System with AC/DC Load
The block diagram of this type of configuration is given below. Whenever there is more than one type of power source connected in a system, the configuration is known as hybrid PV system.
Hybrid System with AC/DC Load
If the load is operated during the night time, when the sunlight is not available, large battery bank will be required to store enough energy. Supplying the load with wind or biomass will be much more economical because no energy storage is required.
i) DC Coupled PV System
It is the simplest possible standalone configuration where PV panels are directly connected to the load. The capacity of the PV panels is designed in such a way that it is sufficient to run the load during sunshine hours. As power available to the load varies according to the weather condition, this is called an unregulated system. There is no arrangement for the energy storage to have night time load operation. A figure below describes such system.
DC coupled PV System
ii) Standalone System with DC Load
The block diagram of the configuration is given below. It is similar to unregulated PV system except that the electronic control circuitry is inserted between load and PV panel. This circuitry can be a voltage or current regulator or a maximum power point tracker. In order to achieve the smooth operation of load this circuit is introduced.
Standalone system with DC load
iii) Standalone System with Battery and DC Load
This type of PV system configuration is used when night time operation of the load is required. It requires energy from the battery to operate. The block diagram of such system is given below.
Standalone System with Battery and DC Load
Batteries in a PV system contribute to the recurring cost as the life of the batteries is significantly shorter than the life of the PV modules. The battery life is affected by the manner it is used like overcharging or over discharging reduced the life of battery.
iv) Standalone with AC/DC Load
It is similar to the standalone system with battery and dc load, the only difference is that now AC load is connected with the system. The block diagram of such system is shown below.
Standalone with AC/DC Load
In this configuration an inverter is used in order to convert DC power to AC power which is coming from battery. This type is suitable for domestic and commercial applications.
v) Hybrid System with AC/DC Load
The block diagram of this type of configuration is given below. Whenever there is more than one type of power source connected in a system, the configuration is known as hybrid PV system.
Hybrid System with AC/DC Load
If the load is operated during the night time, when the sunlight is not available, large battery bank will be required to store enough energy. Supplying the load with wind or biomass will be much more economical because no energy storage is required.
Saturday, April 23, 2011
Types of PhotoVoltaic System
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
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
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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