Photovoltaic or Solar Cell
Definition: The Photovoltaic cell is the semiconductor device that converts the light into electrical energy. The voltage induces by the PV cell depends on the intensity of light incident on it. The name Photovoltaic is because of their voltage producing capability.
The electrons of the semiconductor material are joined together by the covalent bond. The electromagnetic radiations are made of small energy particles called photons. When the photons are incident on the semiconductor material, then the electrons become energised and starts emitting.
The energises electron is known as the Photoelectrons. And the phenomenon of emission of electrons is known as the photoelectric effect. The working of the Photovoltaic cell depends on the photoelectric effect.
Construction of Photovoltaic Cell
The semiconductor materials like arsenide, indium, cadmium, silicon, selenium and gallium are used for making the PV cells. Mostly silicon and selenium are used for making the cell.
Consider the figure below shows the constructions of the silicon photovoltaic cell. The upper surface of the cell is made of the thin layer of the p-type material so that the light can easily enter into the material. The metal rings are placed around p-type and n-type material which acts as their positive and negative output terminals respectively.
The multi-crystalline or monocrystalline semiconductor material make the single unit of the PV cell. The mono-crystal cell is cut from the volume of the semiconductor material. The multicell are obtained from the material which has many sides.
The output voltage and current obtained from the single unit of the cell is very less. The magnitude of the output voltage is 0.6v, and that of the current is 0.8v. The different combinations of cells are used for increasing the output efficiency. There are three possible ways of combining the PV cells.
Series Combination of PV Cells
If more than two cells are connected in series with each other, then the output current of the cell remains same, and their input voltage becomes doubles. The graph below shows the output characteristic of the PV cells when connected in series.
Parallel Combination of PV cells
In the parallel combination of the cells, the voltage remains same, and the magnitude of current becomes double. The characteristic curve of the parallel combination of cells is represented below.
Series-Parallel Combination of PV cells
In the series-parallel combination of cells the magnitude of both the voltage and current increases. Thereby, the solar panels are made by using the series-parallel combination of the cells.
The solar module is constructed by connecting the single solar cells. And the combination of the solar modules together is known as the solar panel.
Working of PV cell
The light incident on the semiconductor material may be pass or reflected through it. The PV cell is made of the semiconductor material which is neither a complete conductor nor an insulator. This property of semiconductor material makes it more efficient for converting the light energy into electric energy.
When the semiconductor material absorbs light, the electrons of the material starts emitting. This happens because the light consists small energise particles called photons. When the electrons absorb the photons, they become energised and starts moving into the material. Because of the effect of an electric field, the particles move only in the one direction and develops current. The semiconductor materials have the metallic electrodes through which the current goes out of it.
Consider the figure below shows the PV cell made of silicon and the resistive load is connected across it. The PV cell consists the P and N-type layer of semiconductor material. These layers are joined together to form the PN junction.
The junction is the interface between the p-type and n-type material. When the light fall on the junction the electrons starts moving from one region to another.
How Solar Cell Install on the Solar Power Plant?
Maximum power point tracker, inverter, charge controller and battery are the name of the apparatus used for converting the radiation into an electrical voltage.
Maximum Power Point Tracker – It’s a special kind of digital tracker that follows the location of the sun. The efficiency of the PV cell depends on the intensity of sunlight fall on it. The power of the sun varies with the time because of the movement of the earth. So for absorbing the maximum light, the panel needs to be moved along with the sun. Thereby the maximum power point tracker is used with the solar panel.
Charge Controller – The charge controller regulates the voltage drawn from the panel. It also protects the battery from the overcharging or overvoltage.
Inverter – The inverter converts the direct current into the alternating current and vice versa. The conversion is essential because some of the appliances require ac supply for their work.
Photovoltaic Cells (PVCs)
Photovoltaic or solar cell/panel converts sunlight directly into electricity which can be used to power light bulbs, household electrical appliances or recharge a battery. PV cells come in various sizes ranging from 10mm by 10mm to 100mm by 100mm, the most common size being 100mm by 100mm cells. A single PV cell produces about 1 to 2 watts of electricity; an amount that is quite insignificant compared to what is required by most electrical equipment.
Two or more PV Cells are built to produce a PV Module to provide higher wattages as required. For instance, a PV module producing 50 watts may comprise of at least 25 of 2 Watts output PV cells.
To meet the the electrical need of a home or an industrial setting, PV Modules are assembled together to form a PV Array that meets the total energy requirement.
A PVC system design begins with determining the total energy requirement for a facility to be powered. Next the number of solar panel units required and other components of the PVC (description below) are determined.
A basic Solar PV system comprises of the components shown in the drawing below and further explained in the notes that follow the drawing.
- Solar panels: Collect visible light from Sun and converts it to electricity. The type of electricity current solar panels is Direct Current (DC).
- Charge Controller (CC): Controls the amount of electricity deposited in the battery bank at any time. In other words, it f eeds electricity from the solar panel to the batteries in a manner that prevents the solar panel from overcharging the batteries. Solar PV system can operate without a CC but the solar panels may overcharge the battery.
- Batteries (rechargeable) Store solar energy up to provide electricity for sun-down periods (nights and cloudy days). They must be able to discharge and recharge. Rechargeable batteries are a little more expensive than the disposable batteries. Without batteries a PVC system can only provide electricity when it is sunny.
- Power Inverter converts the low-voltage direct currents (DC) from the battery to high-voltage alternating current (AC) required by most household appliances.
Solar panels generate low voltage Direct Current (DC) electricity. Some appliances (e.g. incandescent lights) may be powered directly by the energy from the panels as these appliances are DC compliant. However, most electrical appliances require Alternating Current (AC) electricity and usually at high voltages (110V in North America and 230V in most of Europe and developing world (e.g. Africa)) to function. Inverters are used to convert the low voltage DC to AC at required voltages.
In summary, the solar cells collect direct sunlight, converts sunlight into low-voltage DC. Where energy storage in a battery for future use is required, the DC is stored directly in batteries. A charge controller is installed between the Solar panels and the batteries to ensure he batteries are not overcharged. A Power Inverter is used to convert the DC from battery to AC to power the AC appliances.
Other PVC system components that may be required are: wires and cables (for connection of the components) and meters and monitors (for monitoring the voltage and reading the currents of the system.
PV system is a preferred approach for electricity supply because of its modular features, its ability to generate electricity at the actual point of use, its low maintenance requirements and its non-polluting technologies. It is an attractive option for electricity supply in developing countries where there is abundant sunlight and large rural population without the proper infrastructure to develop an electrical grid. In such countries, PV system can be used to provide electricity to homes, rural clinics and government/corporate offices.
PV systems are also useful in remote and isolated locations in developed Worlds (e.g. northern Canadian territories. Nunavut, Yukon and NWT, arctic Greenland and Iceland and various World Islands).
PV systems are not suitable for water heating or other heat related appliances. A solar heater can heat water more quickly and efficiently than an electric water heater powered by PV panels. Solar heaters convert up to 60 per cent of the sun’s energy into heat whereas PV cells are far less efficient and convert only 12 to 15 per cent of the sun’s energy into electricity.
The Size of a PV System
To size a PV system, follow these process:
Determine the amount of electricity required:
- Determine the number of devices to be supported,
- Multiply the power (in watts or KW) on each device by the number of hours in a day the device will be used to obtain the electrical energy required in KWh,
- Add all the KWhs together to get the current total energy requirement for the PV system;
- Allow for expansions to your system. Depending on your resources, you may want to consider a factor of safety of 1.3 (i.e. 30% above your current requirement) or 1.5 (i.e. 50% above your current requirement).
Size your PV Module and your battery capacities:
Keep in mind that a PV cell of say 100mm by 100mm cell produces about 1 to 2 watts of electricity. The battery should be sufficient to store electricity for use during sun-down hours (nights and cloudy days).
The Cost of PV System
A portable PV unit with a 50-watt solar panel, low-power inverter and battery, are about 700 and can operate three high-efficiency lights, a small TV and a water pump.
A more powerful PV system that produces 600 watts and operates several lights, a TV, stereo, microwave oven and water pump. but not at the same time. costs about 8,000.
New production techniques and applications combined with lowering for photovoltaic should increase the acceptance of this environmentally friendly technology.
What do you do with excess solar electricity
If you generate more electricity than you require to power your home, you can store the excess electricity in batteries or sell the excess electricity to the utility provider in your area under a feed-in-tariff scheme. To do the later, your home solar power electricity has to be connected to the regional or national grid in your area. You will need to find about the possibility of tying your grid to the regional/national grid in your area. Tying a solar (or other energy type) power to a national or regional grid is governed by some laws or regulations of the country in which you are. You will need to contact the responsible authority. obtain the permit to do grid tie and collect the specialized equipment that links your power source to the national grid. The equipment has to be installed by certified individuals. When you are under using power, the unused electricity is sent to the grid and used to provide power for other people, and you get a refund or credit from the regional or national body supplying you with electricity. The reverse is the case when your electricity usage is more that the electricity you are generating. Your excess electricity requirement is met from the regional or national grid in which case to pay the cost of the additional electricity you are getting from the grid to the national or regional authority supplying the electricity.
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Copyright © 2006 Environmental Business
A CLEAN AND GREEN ENERGY SOURCE
The most prominent advantage of PV cells is the clean and green energy it provides. There is no fear or worry about the panels generating any harmful greenhouse gases into the air like carbon dioxide.
FREE RAW MATERIALS
The second advantage is that you don’t have to pay for raw materials! PV cells depend on solar energy to produce electricity, which is freely available in abundance around you.
It’s a win-win solution for you.
While you will have to make an initial investment in the system, solar power is natural, free, and available in abundance for a long time. You end up saving in electricity costs once you start using the energy generated by PV cells.
VERSATILITY
Solar PV cells can generate electricity anywhere. All it requires is sunlight, making it a useful energy source while going on camping trips, traveling, and on long car trips.
SIGNIFICANT IMPACT ON Smart ENERGY NETWORKS
Solar PV has an integral role in Smart energy networks, which work on distributed power generation (DPG). DPGs are exceptionally environmentally friendly because it helps reduce the production of electricity at centralized power plants.
Besides, DPGs reduce the environmental impacts of a centralized generation system. It depends on, and uses the sun’s energy that otherwise ends up wasted, to generate electricity.
Lastly, DPG also helps reduce any possible loss of energy during the transmission and distribution of electricity in the power system.
REDUCED COSTS
About costs, while solar panels Mosolarapps were indeed once expensive, its rates are expected to reduce substantially within the next few years. So considering its economic viability and environmental sustainability, PV cells are indeed an investment worth making.
Besides, solar PV cell systems are also a renewable energy system promoted through government subsidy funding. The financial incentives offered makes solar energy panels an attractive investment alternative.
LOW IN MAINTENANCE
Solar PV cells are known for their low maintenance and operating costs compared with other renewable energy systems.
SILENT
Solar PV is perfect for urban areas and residential applications because it doesn’t produce any noise.
EASY TO INSTALL
Last but not least, you can easily install residential solar panels on rooftops or just on the ground without interfering with your lifestyle.
INTERMITTENCY ISSUES
Like all other renewable energy sources, solar energy and PV cells have intermittency problems. It means it’s not continuously available for converting into electricity like during night-time and during cloudy or rainy weather. So PV cells will probably be incapable of meeting an electric power system’s demand.
LESS RELIABLE POWER OPTION
It’s this intermittency and unpredictability that makes solar energy panels a less reliable power solution.
ADDITIONAL INVESTMENTS
PV cells require an additional investment in inverters and storage batteries. Inverters convert direct electricity to alternating electricity to use on your power network.
Storage batteries prove helpful in providing a continuous power of electric power in on-grid connections. This additional investment can, however, provide a solution for the PV cells’ intermittency issues.
USES A LARGE AREA
The large areas of land used for land-mounted PV panel installations remain committed to the purpose. That’s why it’s vital that you wisely select a spot for the solar energy system, and why many people install it upon their roofs.
EASILY DAMAGED
While solar PV needs no maintenance or operating costs, its fragility means it’s easily damaged. There’s a solution here in the form of additional insurance coverage to safeguard your investment.
Now that you know all about solar PV cells, it’s time to turn to one of the solar companies in Missouri for more information.
P.O. Box 1727Jefferson City, MO 65102
What Are Solar Cells Made of
A layer of p-type silicon is sandwiched between a layer of n-type silicon to form a solar cell. There are too many electrons in the n-type layer and too many positively charged holes in the p-type layer. The electrons on one side of the junction (n-type layer) migrate into the holes on the opposite side, which is close to the intersection of the two layers (p-type layer). As a result, a region known as the depletion zone is formed surrounding the connection, where the electrons fill the holes.
The p-type side of the depletion zone now contains negatively charged ions, and the n-type side of the depletion zone now includes positively charged ions when all the holes in the depletion zone have been filled with electrons. These ions’ opposite charges provide an internal electric field that inhibits the n-type layer’s electrons from filling the p-type layer’s holes.
- Purify the Silicon:Silicon dioxide is put in an electric arc furnace, where oxygen is released using a carbon arc. Carbon dioxide and molten silicon are left, but even this is not pure enough to be used in solar cells. This silicon will produce one with just 1% impurities.
- Create Single Crystal Silicon:The Czochralski Method, in which a seed silicon crystal is dipped into molten polycrystalline silicon, is the most used technique for producing single-crystal silicon.
- Cut the Wafers:A circular saw is used to slice the second-stage boule into silicon wafers. The best raw material for this task is diamond, which produces silicon slices that can then be further cut to create squares or hexagons that are simpler to slot together into the surface of a solar cell.
- Doping:This technique, also known as doping, often entails firing phosphorous ions into the ingot using a particle accelerator.
- Add Electrical Contacts:Electrical contacts serve as a conduit for the current generated by solar cells and connect them. These connections, made of metals like palladium or copper, are thin so as not to prevent sunlight from reaching the cell.
- Add Anti-Reflective Coating:To lessen the quantity of sunlight lost through reflection, an anti-reflective coating is put on the silicon.
- Encapsulate the Cell:To complete the process, the solar cells are sealed in silicon rubber or ethylene vinyl acetate and mounted in an aluminum frame with a glass or plastic cover for added protection and a back sheet.
Source: US Energy Information Administration
How Does A Solar Cell Work
The solar cell is a technological innovation that directly converts light energy into electricity through the photovoltaic effect, creating electrical charges free to travel through semiconductors. All solar cells share a similar fundamental design. An optical coating or antireflection layer that reduces the quantity of light lost through reflection allows light to enter the system. As a result, the light is trapped and is more likely to reach the layers below that do energy conversion. Spin-coating or vacuum deposition creates this top antireflection layer, commonly an oxide of silicon, tantalum, or titanium.
Below the top antireflection layer are three energy conversion layers. These are the top junction layer, the absorber layer, and the back junction layer. Two additional electrical contact layers carry the electric current to an external load and then back to the cell to complete the electric circuit. A solar cell is a sandwich of n-type silicon and p-type silicon. It generates electricity by using sunlight to make electrons hop across the junction between the different flavors of silicon:
- Photons (light particles) pelt the cell’s upper surface when sunlight shines.
- The photons (yellow blobs) transport energy through the cell at a downward angle.
- In the lower p-type layer, photons transfer their energy to electrons (green blobs).
- With the help of this energy, the electrons can penetrate the barrier into the top n-type layer and break out into the circuit.
- As the electrons move across the circuit, the lamp begins to glow.
Source: Advanced Renewable Energy Systems
The Types of Solar Cells
The three main categories of solar cells are crystalline silicon-based, thin-film solar cells, and a more recent innovation that combines the other two. P-type and n-type silicon are two types of semiconductors used to make solar cells. Atoms with one fewer electron in their outer energy level than silicon, like boron or gallium, are added to create p-type silicon.
Crystalline Silicon Cells
Crystalline silicon (c-Si) wafers, cut from massive ingots manufactured in laboratories, make about 90% of solar cells. These nuggets can develop into single or numerous crystals and can take up to a month to grow. Monocrystalline solar panels are made from a single crystal, whereas polycrystalline are made from multiple crystals.
Thin Film Solar Cells
While thin-film solar cells, also known as thin-film photovoltaics, are around 100 times thinner than crystalline silicon cells, they are still produced from wafers that are only a tiny fraction of a millimeter deep (about 200 micrometers, or 200m). Amorphous silicon (a-Si), in which the atoms are randomly organized rather than in an ordered crystalline structure, is the material used to create these thin film solar panels and cells. These films can also be produced using organic photovoltaic (PVPV) materials, copper indium gallium diselenide (CIGS), and cadmium-telluride (Cd-Te).
Third Generation of Solar Cells
The most recent solar cell technologies combine the best aspects of thin-film and crystalline silicon solar cells to deliver high efficiency and enhanced usability. They frequently have several junctions made up of various semiconducting materials’ layers. Also, they are typically made of amorphous silicon, organic polymers, or perovskite crystals.
Advantages of Using Photovoltaic Cells
The advantages of using photovoltaic cells are listed below −
- Photovoltaic cells do not cause pollution while producing electricity.
- The operating cost of photovoltaic cells is low as source of energy is natural light.
- The maintenance cost of PV cells is also minimum as they need little maintenance.
- Photovoltaic cells have long lifespan. They are highly reliable.
- PV cells are the best renewable energy sources.