Solar panel that is also known as photovoltaic panel is a device that absorbs sunlight and converts the solar energy into usable electricity. Solar panels are comprised of several individual solar cells (photovoltaic cells). Solar panel efficiency depends directly on the number of solar cells.
With the recent technological advancements, the efficiency of panels is expected to get better and research and development in this field aim at reducing the price of solar panels further making solar-powered equipment available and affordable to a wider number of people.
A photovoltaic module is made up of solar cells, glass, EVA, back sheet and frame. Modern solar light systems use either monocrystalline solar panels or polycrystalline solar panels. Monocrystalline solar cells are more efficient as they are manufactured from a single crystal of silicon and several silicon crystals are melted together to create polycrystalline cells. There are multiple procedures involved in manufacturing solar panels.
Refining raw materials
Most solar panels are made of silicon which is the second most abundant element on earth and is found in natural beach sand, rocks, plants and even some animals. Sand is converted into high-grade purified silicon by heating it at very high temperatures in order to form cylinder-shaped ingots.
In a procedure called doping, boron and phosphorous are added to give the silicone positive and negative electrical polarity respectively and attention is given to align all atoms perfectly in the desired structure. The ingots are sliced into thin wafers with the help of a wire saw. Pure silicon reflects sunlight as it is shiny and an anti-reflective coating such as titanium dioxide or silicon oxide is used on the silicon wafer to reduce the amount of sunlight lost and to improve absorption of sunlight.
Producing solar panels
There are mainly 6 components in a solar panel.
Solar cells
There are a lot of components that go into producing solar cells. The silicon wafers once converted into solar cells are capable of converting solar energy into electricity. Each solar cell has a positively (boron) and negatively (phosphorous) charged silicon wafer. A typical solar panel consists of 60 to 72 solar cells.
Glass
Toughened tempered glass is used to protect the PV cells and the glass is usually 3 to 4 mm thick. The front glass protects the cells from extreme temperatures and is designed to resist impact from airborne debris. Highly transmissive glasses that are known for their low iron content help enhance the efficiency of solar panels and have an anti-reflective coating to improve light transmission.
Aluminum frame
An extruded aluminum frame is used to protect the edge of the laminate that is housing the cells. This gives a solid structure to mount the solar panel in position. The aluminum frame is designed to be lightweight and able to withstand mechanical loads and rough climate. The frame is usually silver or anodized black and the corners are secured by pressing or with screws or clamps.
EVA film layers
Ethylene-vinyl acetate (EVA) layers are used to encapsulate the solar cells and hold them together during manufacturing. This is a highly transparent layer that is durable and tolerant of humidity and extreme climate changes. EVA layers play a critical role in preventing moisture and dirt ingress.
Both the sides of solar cells are laminated with EVA film layers in order to provide shock absorption and to protect the interconnecting wires and the cells from sudden impact and vibrations.
Back sheet
The back sheet is the rear most layer of a solar panel and is made of polymers or plastics to offer thermal stability and long-term UV resistance. This sheet acts as a moisture barrier and gives mechanical protection and electrical insulation. Some solar panels use dual glass panels for the rear side instead of a polymer back sheet. Dual glass panels are more durable than most back sheet materials and offer a longer lifespan.
Junction box - diodes and connectors
Junction box is used to securely attach the cables that interconnect the panels. This is a small weatherproof enclosure that also houses the bypass diodes. The junction box is located behind the panel and this is where all the cells interconnect and therefore, it is important to protect this central point from moisture and dirt.
Solar MC4 Connectors
Multi-contact 4 mm diameter connectors (MC4) are the standard connectors used for solar panels, these connectors with the help of weather-resistant plugs and sockets. The connectors are made UV resistant to withstand extreme weather conditions and standard 4 mm or 6 mm double insulated DC cable with tinned copper multi-strand core is used to maintain minimum resistance at both high and low voltages up to 1000V, there are various other types of connectors used with solar panels for solar street lights, which are smaller and more suitable for these lights.
Each of the wafers is coated with metal conductors to facilitate absorption of sunlight. Standard Test Conditions (STC) and Nominal Operating Cell Temperature (NOCT) are used as reference points to test the modules to ensure the cells perform as expected. Every panel displays the technical parameters to reveal the power output, voltage, efficiency, current and temperature tolerance.
With the help of automated robotic equipment and sensors, solar panels are assembled in manufacturing facilities in order to position the components precisely and care is taken to prevent any contamination during assembly. Cleaning and inspection of the panels are done throughout the manufacturing process using advanced optical/imaging sensors to ensure the components and wafers are positioned accurately and not damaged during the assembly process.
The energy used to extract the raw materials and to design and manufacture a product is called ‘embodied energy.’ The total amount of time it takes for a product to repay the embodied energy is known as the total energy payback time. A typical solar panel generates enough energy to repay the embodied energy within 2 to 3 years of installation.
A well made solar panel gives a life expectancy of about 25 to 30 years. Research and development in the solar energy industry is aiming at reducing the cost of solar panel and increasing efficiency. With increased panel efficiency, the payback time is expected to reduce further in the coming years.