“PV (photovoltaic) solar panels use rows of solar cells, made of a semiconductor material that reacts with sunlight to produce and electric current.”This electricity is then distributed around the property to power appliances and lighting, or if surplus to requirement, it is sold to the National Grid network.
The solar cells are the power stations of every PV system.
The PV solar panel cell
A solar cell consists of two ultra thin layers of semi-conducting silicon that has been specially treated with chemicals. These chemicals react to solar radiation when it is exposed to the cell, creating an electric field and produces electricity. The more intensity of sunlight the greater the flow of electricity. This process is called the photovoltaic effect. The scientific explanation is:
1.The solar cell works by means of a covering of a thin layer of anti-reflective coating, which minimizes light reflection.
2. The top semiconductor layer, or ‘n’ type layer, is doped with small amounts of phosphorus. Almost every thousandth silicon atom is replaced by a phosphorus atom. This creates free moving negative charges called electrons.
3. The base semiconductor layer, or ‘p’ type layer, is doped with minuscule amounts of boron, so that almost every millionth silicon atom is replaced by a boron atom. This creates free moving positive charges called holes.
4. When both the ‘n’ and ‘p’ type layers are placed close together, which they are, the positively charged holes and the negatively charged electrons are attracted to each other.
Moving into their respective neighboring layer, they cross a boundary layer called the p-n junction. This movement of negatively and positively charged particles generates a strong electrical field across the p-n junction. When solar radiation strikes this field it causes the electron particles and the whole particles to separate, which in turn creates a voltage of around 0.5V.
5. The voltage flow pushes electrons, or direct current, to contacts at the front and the back of the cell, where it is conducted away along the wiring circuitry that connects the cells together.
Solar cells can be made from a number of semiconductor materials, but by far the most commonly used and most efficient material is silicon, which is the main component of quartz sand and, after oxygen, is the second most common element in the Earth’s crust.
The performance of a solar cell is measured in terms of its efficiency at turning the sun’s radiation into electricity.
A typical solar cell has an efficiency no greater than 13-15%, as only a portion of the sunlight energy spectrum can be converted into electricity, and much of the sunlight is also reflected or absorbed by the materials that make up the cell. If this seems off putting, please bear in mind that a gas power station has an energy conversion efficiency of only 35% and that 70% of the electricity generated is lost during the long distance transmission to your home, which is why on-site micro generation is good at reducing CO2 emissions.
The PV panelAs an individual solar cell only generates a low voltage, a number of cells are connected together to form a solar panel that can generate anything between 80-165kWp. The solar panels are then connected together to form a PV array that will be fitted in homes and businesses at an angle of between 30 and 50 degrees to receive maximum light exposure.
South facing roofs is best, but south eastern and south western facing systems can also be installed, with only a 5% reduction in the efficiency. When considering an installation, it is extremely important that the solar panels, whether roof or grounds mounted, are free from shading during the daytime hours.
The PV System
PV solar outputs are measured in kW (kilo Watts peak), which is the rating of DC power produced by the panels at any one time during optimum lighting and temp conditions. The DC power is converted with an inverter, into AC power before it can be used by appliances or is transferred into the National Grid.
A well installed PV system should produce between 750kWh (Scotland) and 950kWh (South England) of power annually for every 1kW of PV system installed. System sizes range from 1kW -5kW for domestic installations. Larger systems can be installed in commercial applications too.
Grid connects or off-grid connected
On Grid systems
On-grid connected photovoltaic systems are the most common as it makes use of the existing mains electricity system. Simpler in design and easier for our MCS solar panels installers to fit than an off grid system. The electricity produced during daylight hours is either used by the home owner, or if surplus to requirements, is fed back into the grid via an export meter, or purchased from your utility company.
At night, or on dark days when the panels do not produce enough power, electricity will be supplied automatically from your existing import meter. You will be able to apply for the feed-in tariffs with this type of installation.
Off Grid systems
Less common is an off-grid or stand alone system, which generates and stores power independently from the National Grid. This type of systems is suitable in remote locations. Often the installation of an off grid PV system proves cheaper than extending the power lines to your home.
The power generated by the panels is stored in a bank of batteries. These rechargeable batteries contain specialised parts and chemicals not found in disposable batteries and are, therefore, larger and more expensive to purchase and maintain. You will NOT be able to apply for the feed-in tariffs with this type of installation.
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Stuart Lovatt on
Founder of Heat My Home.