General Overview
If you are thinking about a solar system for your home or business you will find the majority of the products available are crystalline silicon solar panels. Crystalline silicon solar panels are the most widely used photovoltaic (PV) technology. The panels convert sunlight into electricity through the photo-electric effect (fun fact: discovery of the photo-electric effect is what won Albert Einstein the Novel Prize in 1921) . When photons of sunlight hit the crystalline solar panels an electrical current is created. This is a direct current (DC) and only flows in one direction.
To install a solar system, multiple solar panels are connected together and then to a solar inverter. The DC electricity captured by the “string” of solar panels feeds the inverter that converts the electricity to Alternating Current (AC) that is used by everyday appliances and supplied by the power grid. In most cases the inverter also optimizes the DC power output of the solar panels using a technique known as maximum power point tracking (MPPT). Although in some off grid systems MPPT is performed by a separate charge controller.
Crystalline silicon solar panels are produced through a process that involves solar cell production, interconnections of solar cells with busbars and bypass diodes, and encapsulating the connected cells into a solar panel using a back sheet, aluminium frame, an encapsulant and antireflective glass.
How are solar cells connected in a solar panel?
A solar module, or solar panel, consists of multiple solar cells electrically connected in series and parallel configurations. The connections are established using conductive ribbons soldered to the busbars of adjacent cells. To enhance efficiency, modern panels use multiple busbars per cell, reducing resistive losses and improving current collection.
- Series Connection: Increases voltage while keeping current constant. The positive terminal of one cell connects to the negative terminal of the next.
- Parallel Connection: Increases current while maintaining voltage. Multiple series strings are wired together in parallel.
Each solar panel typically consists of 60, 72, or more cells, encapsulated within protective layers of glass and polymer materials including, the solar panel back sheet, the glass at the front of the solar panel, and the clear encapsulant material that sits in between and around the cells. These layers shield the cells from environmental damage while allowing sunlight to pass through efficiently.
How a crystalline silicon solar cells made?
To generate electricity from sunlight crystalline silicon solar cells rely on the photovoltaic properties of silicon, a semiconductor material that forms the core of the solar cells. Note that silicon atoms have 4 valence electrons, and pure silicon, in its intrinsic form, is not a good conductor of electricity. To enable it to generate and conduct electricity, the silicon undergoes a process known as doping, where small amounts of other elements are introduced to its crystalline structure to alter its electrical properties. Doped silicon can take the two basic forms.
- N-Type Silicon: Silicon is doped with phosphorus, which has five valence electrons. This results in extra free electrons in the material, making it negatively charged (n-type).
- P-Type Silicon: Silicon is doped with boron, which has only three valence electrons. This creates “holes” or missing electrons, resulting in a positively charged material (p-type).
The silicon used in solar panels is produced by allowing molten silicon to cool into crystals. In poly-crystalline solar cells, multiple crystals form together as a layer of silicon cools. In mono-crystalline solar cells a continuous crystalline structure is formed in a silicon ignot. The silicon is then cut up into thin silicon wafers.
To manufacture a solar cell, layers of P-Type and N-Type silicon are joined together. This creates what is known as a PN junction. The meeting of the two oppositely charged layers of silicon generates an electric field that acts as a kind of one way valve for electric current, and free electrons get swept up in. When photons of sunlight hit the valance electrons in silicon atoms in a solar cell the electrons get knocked free, and swept away in the electric field created by the PN Junction. As electrons leave their atoms and move they leave ‘holes’ in the crystal lattice. While the electrons carry a negative charge, the holes create moving positive charge. This creates a direct electric current which is fed through the circuits formed by the busbars and back contacts and out of the solar panel.
What is a P-type solar cell and what is an N-type solar cell?
Solar panels are classified based on the configuration of their active layer. The two primary classifications are:
- P-Type Solar Panels: These are the most commonly used panels in the industry, where the base layer of the solar cell is made of p-type silicon, with an n-type silicon layer on top. The majority of the charge carriers are holes, and they are generally more susceptible to light-induced degradation over time. Learn about how solar panel warranties account for degradation.
- N-Type Solar Panels: In these panels, the base layer is made of n-type silicon, with a p-type silicon layer on top. This design makes them more resistant to light-induced degradation, often leading to higher efficiency and better long-term performance.
Make up of a solar cell
A single crystalline silicon solar cell is typically around 156 mm (6 inches) in size and consists of several key layers:
- Anti-reflective Coating: Reduces sunlight reflection and increases absorption.
- Front Contact and Busbars: Conduct electricity from the cell’s surface.
- Silicon Wafer: The active layer where light-induced electron-hole pairs are generated.
- Back Contact: Helps collect and transport electrons.
What is the 'back contact' in a solar cell?
The back contact in a solar cell plays a crucial role in collecting electrons and facilitating the flow of electric current. It consists of:
- Full-Area Back Contact: Covers the entire back surface of the cell, providing excellent conductivity and reducing series resistance.
- Local Back Contact: Utilized in high-efficiency solar cells, where small contact points minimize electron recombination losses.
- Rear Passivation Layer: Some advanced solar cells include a passivation layer on the back to reduce recombination and enhance efficiency.
What is a solar panel bypass diode?
Solar modules incorporate bypass diodes to prevent power loss due to partial shading of cells or panels within a solar array. When a solar cell or section of a panel is shaded, it generates significantly less current than the rest of the module. This can create a bottleneck effect, reducing overall power output of the whole system. Bypass diodes provide an alternate path for current to flow around shaded strings of cells within a solar panel, preventing excessive resistance and overheating (hot spots) of solar cells.
Bypass diodes are housed within the junction box located on the back of the solar panel.
The role of solar panel junction box
In addition to housing the bypass diodes, the junction box also contains electrical terminals for connecting the panel to external wiring, ensuring a reliable and weatherproof connection to the solar array.
Wiring of solar panels in a solar system
Multiple solar modules are connected together to form a solar array. Similar to the wiring of individual cells, modules can be connected in:
- Series Configuration: Voltage adds up while current remains constant. For example, ten 40V panels in series will produce 400V while maintaining the same current as a single panel.
- Parallel Configuration: Current increases while voltage remains the same. Two parallel strings of ten 40V panels each will still provide 40V but double the available current.
Proper configuration depends on system voltage requirements and inverter specifications.
The role of solar inverters and Maximum Power Point Tracking (MPPT)
The electricity generated by solar panels is in direct current (DC) form. However, most electrical appliances and the power grid operate on alternating current (AC). An inverter is used to convert the DC electricity from the solar panels into usable AC electricity.
A critical function of modern inverters is Maximum Power Point Tracking (MPPT), which dynamically adjusts the operating voltage and current of the solar array to maximize power output under varying sunlight conditions.
- Tracking the Maximum Power Point (MPP): The voltage and current at which a solar panel produces maximum power fluctuate with changes in sunlight intensity and temperature. The MPPT algorithm continuously adjusts the load resistance to ensure that the panel operates at its optimal power point.
- Adjusting the Input Voltage: The inverter monitors the incoming DC voltage from the solar array and modulates it to keep the panels operating at its most efficient point. If the voltage is too high or too low, the inverter makes necessary adjustments to maximize power conversion efficiency.
- Ensuring Grid Compatibility: Once the DC electricity is converted to AC, the inverter synchronizes it with the local grid frequency and voltage, ensuring seamless integration with the electrical system.
Summary
Crystalline silicon solar panels function through a complex but well-optimized process. Silicon doping allows for the creation of PN junctions that generate electrical energy when exposed to sunlight. Solar cells, interconnected through busbars and assembled into modules, generate DC electricity. Panels are then wired together to form an array that feeds electricity into an inverter, which regulates solar panel power output through MPPT and converts electricity to usable AC.
These combined processes make crystalline silicon solar technology one of the most efficient and reliable means of harnessing renewable energy. If you are keen to understand how solar can reduce your electricity bills get in touch for a free quote and consultation today.
