How photovoltaic panels work
Electricity generation
Photovoltaic solar energy is a technology that converts thesun’s light energy into electrical energy using thephotovoltaic effect. This process relies on the use of photovoltaic cells, generally made from semiconductor materials such as crystalline silicon. Here’s a detailed overview of how photovoltaic solar energy works.
- Light absorption: When sunlight, made up of photons, strikes the surface of a photovoltaic cell, it interacts with the atoms of the semiconductor material. The photons transfer their energy to the electrons in the atoms’ valence layer, enabling them to cross the energy barrier known as the “band gap” and enter the conduction band, where the electrons are free to move.
- Creation of electron-hole pairs: Electrons that have gained enough energy to cross the band gap leave behind “holes” in the valence band. Conduction-band electrons and valence-band holes form electron-hole pairs.
- Charge separation : Photovoltaic cells are designed with doped materials, which have electron excesses or deficits. Semiconductor material is generally doped to form two layers: the N layer, negatively doped with an excess of electrons, and the P layer, positively doped with a deficit of electrons. When these two layers are brought into contact, a “PN junction” is formed, creating an electric field between the layers. This electric field separates the electron-hole pairs, with electrons attracted to the N layer and holes to the P layer.
- Current flow : When an external circuit is connected to the terminals of the photovoltaic cell, N-layer electrons are directed towards the load (e.g. an electrical device) and return to the P-layer to fill the holes. This flow of electrons constitutes the electric current generated by the cell.
- Conversion to alternating current : The current generated by photovoltaic cells is direct current (DC). However, most applications and power grids operate on alternating current (AC). An inverter is used to convert direct current into alternating current, which can then be used by electrical appliances or fed into the grid.
Using the electricity generated
Solar energy is intermittent, as it depends on weather conditions and the position of the sun in the sky. To guarantee a stable, continuous power supply, the energy produced by photovoltaic panels can be stored in batteries or other energy storage devices, then released when solar production is insufficient.
Integrating photovoltaic systems into the power grid requires careful coordination and regulation to maintain grid stability and reliability. This may include the use of energy storage technologies, demand-side management and the adaptation of grid infrastructure to accommodate variable renewable energy production.
Photovoltaic systems require regular monitoring and preventive maintenance to ensure optimal operation and longevity. This includes cleaning solar panels, checking electrical connections and monitoring energy production. Monitoring devices and management software can help identify potential problems and plan maintenance interventions.
Photovoltaic panel components
Photovoltaic panels are made up of several components:
- Wafers: Wafers are the basic element of photovoltaic panels: a thin slice of semiconductor material, usually silicon.
- Solar cells: Solar cells are made from silicon wafers, and convert sunlight into electricity using the photovoltaic effect. Cells are usually connected in series and parallel to form an electrical circuit.
- Encapsulation : Solar cells are encapsulated between layers of protective material, usually EVA (ethylene vinyl acetate) or similar, to protect them from moisture, debris and mechanical shock.
- Protective glass: A solar panel is coated with a layer of transparent, low-iron tempered glass to protect the solar cells and ensure optimum light transmission. The glass is also designed to withstand impacts and extreme weather conditions.
- Frame : An aluminum frame is generally used to reinforce the structure of the solar panel and facilitate installation. The aluminum frame is lightweight, corrosion-resistant and offers good mechanical strength.
- Backsheet: The backsheet is a protective layer located at the rear of the solar panel. It protects the solar cells and encapsulation materials from moisture and external aggression. Backsheets are generally made of polymer (such as Tedlar) or glass for bifacial panels.
- Junction box: The junction box is a box located at the back of the solar panel, which connects the electrical cables to the solar cells. It generally contains protection diodes to prevent reverse current problems and protect the solar cells in the event of a malfunction in one part of the panel.
- Cables and connectors: Cables and connectors connect solar panels to each other and to the electrical system. They are generally designed to withstand the elements and ultraviolet rays.
The most important elements are the solar cells and their main component: the wafers. The connection between the various cells can also be a technological challenge, with the development of new solar cells
Photovoltaic cell efficiency
There are several types of photovoltaic cells, each distinguished by the materials used and their efficiency. Here is an overview of the most common types of photovoltaic cells:
Monocrystalline silicon cells (c-Si)
These cells are made from pure crystalline silicon, which has a continuous, uniform crystalline structure. Monocrystalline silicon offers high efficiency, typically between 20% and 25%, thanks to its purity and ordered crystalline structure. Monocrystalline silicon cells are black or dark blue in color, and are often more expensive than other cell types due to manufacturing costs.
Multicrystalline silicon cells (mc-Si)
Also known as polycrystalline silicon cells, these are made from blocks of silicon composed of multiple crystals. The manufacturing process is less costly than that of monocrystalline silicon cells, but efficiency is generally lower, at between 15% and 20%. Multicrystalline silicon cells have a bluish color and a crystalline appearance.
Thin-film cells (TFPV)
These cells are manufactured by depositing thin layers of semiconductor material on a substrate. Thin-film cells are generally cheaper to produce and lighter than crystalline silicon cells, but their efficiency is generally lower, at between 10% and 12%. Materials commonly used for thin-film cells include:a. Cadmium telluride (CdTe): This material has low production costs and good light absorption, but environmental issues arise due to the use of cadmium, a toxic element.b. Copper indium gallium diselenide (CIGS): This material has a higher efficiency potential than CdTe, but is more complex and costly to manufacture.
Perovskite-based cells
Perovskite-based cells are a promising emerging technology, thanks to their high efficiency potential (up to 25%) and low manufacturing costs. However, they present challenges in terms of stability, durability and environmental impact that need to be resolved before widespread adoption.
The life cycle of photovoltaic panels
The life cycle of photovoltaic panels comprises several stages, from manufacture to installation, operation and end-of-life. Here’s an overview of the different stages in the life cycle of solar panels:
- Extraction of raw materials: The extraction of raw materials, such as silicon, indium, gallium, copper and other metals, is the first step in the process. These materials are extracted from the earth’s crust and then refined for use in the manufacture of photovoltaic cells.
- Manufacturing solar cells and panels: Photovoltaic cells are manufactured using a variety of processes, including silicon purification, crystallization, wafer cutting, p-n junction creation, metallization and encapsulation. The cells are then assembled to form photovoltaic modules, also known as solar panels.
- Transport and installation : Solar panels are transported to installation sites, where they are mounted on support structures, electrically connected and integrated with energy management and storage systems.
- Operation and maintenance : Solar panels generally have an operational life of 25 to 30 years, during which they generate electricity from solar energy. The performance of solar panels generally declines over time due to the degradation of materials and electrical contacts. Regular maintenance, such as panel cleaning and inspection of cables and supports, is necessary to ensure optimum energy production and maximum service life.
- End-of-life and recycling : When solar panels reach the end of their operational life, they are dismantled and recycled. Recycling solar panels is essential to recover valuable metals and materials, reduce electronic waste and minimize environmental impact. Recycling processes typically involve separating materials (such as glass, aluminum, plastics and metals), recovering precious and rare metals, and reusing recycled materials in the manufacture of new solar panels or other products.