What are Solar Photovoltaic Cells?
Solar Photovoltaic as the name suggests uses energy from sunlight and converts it into electrical energy. A PV cell is the smallest semiconductor element module to perform the immediate conversion of light into electrical energy (direct current voltage and current)(source: Sunshot Initiative). A PV cell is made and there are 3 types of PV cells:
Module and Panel, although used interchangeably, are different terms. Module is the smallest assembly of PV cells, which is environmentally protected the essential elements (interconnections, terminals, diodes etc) and can produce a certain voltage and current. For e.g. a module of 36 cells would produce Panel is a collection of one or multiple modules depending on the voltage and current desired.
Here is a quick video that can guide you on Roof top Solar PV buying in India:
What are the voltages, curreand watts produced by Solar Panels?
If you had inquired about a solar panel, you would have encountered terms like maximum power (Pmax), Voc, Vmp, Imp and Isc. One thing that will worry work for my system”.
Now there are 2 ways in which you can use a solar panel:
The benefit of using batteries is that the energy can be stored and used whenever required. But if panels are used directly, then the energy can be used only produced (or during the day time).
Solar panels always produce DC current and can be used directly (as in 2nd way mentioned above) with a system that works on DC. But the biggest challenge the wattage, voltage and the current from a panel vary. It varies with the environmental temperature and also with the amount of light it gets. Lesser the current and wattage produced will be less. Higher the temperature, voltage it generates will reduce. A typical diagram is as shown below:
There are certain terms that you will encounter when you inquire about solar panels:
1. Max Power (Pmax): This is the maximum power (or Watts) that the panel can generate at standard test conditions. The standard test conditions are of 1000 W/m2 of solar irradiance and 25oC temperature .
2. Voc (or Voltage at Open Circuit): This is the maximum voltage a panel can produce at open circuit or when nothing is connected to it and when current system is 0. This is also at the standard test conditions.
3. Isc (or Short Circuit Current): This is the current that would flow through the solar panel if it were shorted at standard test conditions.
4. Vmp (or Voltage at Maximum Power): A solar cell has a characteristic of producing constant current up to a certain voltage at a given light level. If above graph, the current is constant till certain voltage and the panel produces maximum power at this voltage. This voltage is called Vmp and is at standard test conditions.
5. Imp (or Current at Maximum Power): The current that a panel produces at Maximum power at Vmp is the current at maximum power.
From all the details above, there is one myth that is broken: “A solar panel would produce maximum power on the hottest day in a year”. In fact higher temperature decreases the power output. A colder day (with about 30-35 degrees temperature) and good sunlight will result in better output from a solar panel.
What is a charge controller or solar regulator?
Now as it is established that a solar panel will not produce constant voltage or constant current, it cannot be used directly as a battery. One needs to put controller” or “solar regulator” to control the voltage and current that is generated from a solar panel. A MPPT (or Maximum Power Point Tracking) charge is used for Direct Coupled system (or a system where the load is connected to the panel directly) that regulates the output voltage from a solar panel.
Charge controller is also used when solar panel is used to charge a battery. A Solar Home Inverter system will have following components:
1. Panels mounted on a frame.
2. Charge Controller.
3. Wiring.
4. Batteries.
5. Inverter (not needed if the device connected can run on direct current)
Whereas if Solar Panel is used directly (direct coupled system) then it will have:
1. Panel mounted on a frame.
2. MPPT (Maximum Power Point Tracking) Charge Controller.
3. Wiring.
4. Inverter (not needed if the device connected can run on direct current)
How to size a solar panel?
We will analyze both the scenarios above to size a solar panel:
1. Solar Panel used directly with an appliance (direct coupled system): In this case it is important to know the voltage and current requirement appliance. Also it is important to make sure if the appliance runs on AC or DC. If the appliance runs on DC, it is better to choose a panel looking at Imp ratings of the panel and try to get one that is close to the voltage requirement of the appliance. A MPPT charge controller additionally will be control the voltage.
2. Energy from Solar Panel saved in batteries: In this case, it is important to look at the energy requirements of the system. Energy requirement can calculated by multiplying the wattage of appliances to be connected with the hours of usage. For e.g if a system with one 75 W fan and two 15 W be powered using solar panel for 10 hours each, then the total energy required is 75×10+2x15x10=1050 Wh. Now you will have to look at the Max Pmax) rating of the panel. If it is 525 W, then it will produce 1050 Wh in 2 hrs (=525×2).
As a thumb rule it is assumed that good sunlight will be available hours. So a 210 W Pmax system would be sufficient for the needs. You may take slightly bigger system to accommodate for lesser power generated conditions.
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Solar Photovoltaic as the name suggests uses energy from sunlight and converts it into electrical energy. A PV cell is the smallest semiconductor element module to perform the immediate conversion of light into electrical energy (direct current voltage and current)(source: Sunshot Initiative). A PV cell is made and there are 3 types of PV cells:
- Mono-crystalline Cell: Cells cut out of single crystal of silicon. In appearance they are smooth. They are most efficient types of cells (efficient in light to electricity) and also most expensive.
- Poly-crystalline Cell: A cell cut out of a block of silicon consisting large number of crystals. They are relatively inefficient as compared to mono cells and cheaper too.
- Thin Film or Amorphous Cell: These are made of non-crystalline (or amorphous) silicon placed as a thin film on a surface. They are least efficient expensive. They are also not rigid unlike mono and poly crystalline cells and thus can be folded into different shapes. Power of amorphous cells first few months of use and thus the quoted output of thin film should be that achieved after stabilization (source: solar-facts).
Module and Panel, although used interchangeably, are different terms. Module is the smallest assembly of PV cells, which is environmentally protected the essential elements (interconnections, terminals, diodes etc) and can produce a certain voltage and current. For e.g. a module of 36 cells would produce Panel is a collection of one or multiple modules depending on the voltage and current desired.
Here is a quick video that can guide you on Roof top Solar PV buying in India:
If you had inquired about a solar panel, you would have encountered terms like maximum power (Pmax), Voc, Vmp, Imp and Isc. One thing that will worry work for my system”.
Now there are 2 ways in which you can use a solar panel:
- Take the output of a panel and use it to charge a battery and then connect your system to the battery. In case you have multiple appliances to use will also need an inverter (inverter converts DC to AC) to control it.
- You can also use the panel directly just like you use a battery (producing DC output). Such a system is also called directly coupled system.
The benefit of using batteries is that the energy can be stored and used whenever required. But if panels are used directly, then the energy can be used only produced (or during the day time).
Solar panels always produce DC current and can be used directly (as in 2nd way mentioned above) with a system that works on DC. But the biggest challenge the wattage, voltage and the current from a panel vary. It varies with the environmental temperature and also with the amount of light it gets. Lesser the current and wattage produced will be less. Higher the temperature, voltage it generates will reduce. A typical diagram is as shown below:
1. Max Power (Pmax): This is the maximum power (or Watts) that the panel can generate at standard test conditions. The standard test conditions are of 1000 W/m2 of solar irradiance and 25oC temperature .
2. Voc (or Voltage at Open Circuit): This is the maximum voltage a panel can produce at open circuit or when nothing is connected to it and when current system is 0. This is also at the standard test conditions.
3. Isc (or Short Circuit Current): This is the current that would flow through the solar panel if it were shorted at standard test conditions.
4. Vmp (or Voltage at Maximum Power): A solar cell has a characteristic of producing constant current up to a certain voltage at a given light level. If above graph, the current is constant till certain voltage and the panel produces maximum power at this voltage. This voltage is called Vmp and is at standard test conditions.
5. Imp (or Current at Maximum Power): The current that a panel produces at Maximum power at Vmp is the current at maximum power.
From all the details above, there is one myth that is broken: “A solar panel would produce maximum power on the hottest day in a year”. In fact higher temperature decreases the power output. A colder day (with about 30-35 degrees temperature) and good sunlight will result in better output from a solar panel.
What is a charge controller or solar regulator?
Now as it is established that a solar panel will not produce constant voltage or constant current, it cannot be used directly as a battery. One needs to put controller” or “solar regulator” to control the voltage and current that is generated from a solar panel. A MPPT (or Maximum Power Point Tracking) charge is used for Direct Coupled system (or a system where the load is connected to the panel directly) that regulates the output voltage from a solar panel.
Charge controller is also used when solar panel is used to charge a battery. A Solar Home Inverter system will have following components:
1. Panels mounted on a frame.
2. Charge Controller.
3. Wiring.
4. Batteries.
5. Inverter (not needed if the device connected can run on direct current)
Whereas if Solar Panel is used directly (direct coupled system) then it will have:
1. Panel mounted on a frame.
2. MPPT (Maximum Power Point Tracking) Charge Controller.
3. Wiring.
4. Inverter (not needed if the device connected can run on direct current)
How to size a solar panel?
We will analyze both the scenarios above to size a solar panel:
1. Solar Panel used directly with an appliance (direct coupled system): In this case it is important to know the voltage and current requirement appliance. Also it is important to make sure if the appliance runs on AC or DC. If the appliance runs on DC, it is better to choose a panel looking at Imp ratings of the panel and try to get one that is close to the voltage requirement of the appliance. A MPPT charge controller additionally will be control the voltage.
2. Energy from Solar Panel saved in batteries: In this case, it is important to look at the energy requirements of the system. Energy requirement can calculated by multiplying the wattage of appliances to be connected with the hours of usage. For e.g if a system with one 75 W fan and two 15 W be powered using solar panel for 10 hours each, then the total energy required is 75×10+2x15x10=1050 Wh. Now you will have to look at the Max Pmax) rating of the panel. If it is 525 W, then it will produce 1050 Wh in 2 hrs (=525×2).
As a thumb rule it is assumed that good sunlight will be available hours. So a 210 W Pmax system would be sufficient for the needs. You may take slightly bigger system to accommodate for lesser power generated conditions.
Don't Forget to follow us !
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