PV (photovoltaic) solar panels use rows of solar cells, made of a semiconductor material that reacts with sunlight to produce an 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.
A solar cell consists of two ultra-thin layers of semiconducting silicon that has 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 the intensity of sunlight the greater the flow of electricity. This process is called the photovoltaic effect.
The PV solar panel cell
1. The solar cell works using a covering of a thin layer of anti-reflective coating, which minimises light reflection.
2. The top semiconductor layer, or ‘n’ type layer, is doped with small amounts of phosphorus. A phosphorus atom replaces almost every thousandth silicon atom. This reaction 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 a boron atom replaces almost every millionth silicon atom. This reaction 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 neighbouring layer, they cross a boundary layer called the p-n junction. This movement of negatively and positively charged particles generate a strong electrical field across the p-n junction. When solar radiation strikes this area, it causes the electron particles and the aggregate 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 with the wiring circuitry that connects the cells.
PV solar cells made from some semiconductor materials, but by far the most commonly used and most efficient equipment 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 measured regarding its efficiency at turning the sun’s radiation into electricity.
A typical solar cell has an efficiency no more significant than 13-15%, as only a portion of the sunlight energy spectrum can convert 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 lost during the long-distance transmission to your home, which is why on-site micro-generation is good at reducing CO2 emissions.
The PV panel
As 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 are best, but southeastern and southwestern facing systems can also be installed, with only a 5% reduction inefficiency. When considering installation, it is essential that the PV solar panels, whether roof or grounds mounted, are free from shading during the daytime hours.
The PV System
PV solar outputs that measure in kW (kilo Watts peak), which is the rating of DC power produced by the panels at any one time during excellent lighting and temp conditions. The DC power is converted with an inverter, into AC power before appliances can use it or transferred to the National Grid.
A well-installed PV system should produce between 750kWh (Scotland) and 950kWh (South England) of power annually for every 1kW of a 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 homeowner, 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 standalone system, which generates and stores power independently from the National Grid. This type of systems is suitable for 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 stored in a bank of batteries. These rechargeable batteries contain specific parts and chemicals not found in disposable batteries and are, therefore, more extensive and more expensive to purchase and maintain.
You will NOT be able to apply for the feed-in tariffs with this type of installation.