Beatrice Lang
Solar power is an infinite and renewable energy source that plays a key role in the transition to 100% renewable energy. Solar cells, also known as photovoltaic (PV) cells, are electrically connected and packaged in a weather-tight solar panel. When sunlight shines on a solar panel, the PV cells absorb the light's energy, transferring it to electrons in the cell, which creates an electric current. This electricity can then be used to power homes and buildings, as well as feed into the electric power grid.
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What You'll Learn
Photovoltaic (PV) cells
When sunlight, composed of photons or particles of solar energy, strikes a PV cell, it can be reflected, absorbed, or pass through the cell. Only the photons that are absorbed by the semiconductor material provide energy to generate electricity. The semiconductor material absorbs the light's energy, transferring it to negatively charged particles called electrons, which are dislodged from the material's atoms. This extra energy allows the electrons to flow through the material as an electrical current. This current is then extracted through conductive metal contacts, the grid-like lines on solar cells, and can be used to power homes and the electric grid.
The amount of electricity produced by PV cells depends on the characteristics of the light, such as intensity and wavelength, as well as the performance attributes of the cell. The bandgap of the semiconductor is an important property, indicating which wavelengths of light the material can absorb and convert to electrical energy. If the bandgap matches the wavelengths of light shining on the PV cell, the cell can efficiently utilize all the available energy.
PV cells are electrically connected to form a PV panel or module, which is then packaged into a weather-tight unit. The number of cells in a panel and the surface area of the panel impact the amount of electricity it can produce. PV panels can be further grouped into arrays of different sizes to increase electricity generation. PV systems can be used to power devices, such as water pumps, individual homes, or supply electric power grids. They are also capable of charging batteries to provide electricity when sunlight is not available.
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PV modules and panels
Solar photovoltaic (PV) modules, also known as solar panels, are the fundamental components of a solar power system. They are composed of individual solar cells, typically made from crystalline silicon, that convert sunlight into electrical energy through the photovoltaic effect. This process involves the release of electrons when sunlight, composed of photons, strikes the semiconductor surface of the solar cells.
The PV cells within the modules are electrically connected in series to achieve the desired voltage, and then in parallel to increase the current. The number of cells and the surface area of the module determine its electricity-generating capacity. PV modules can be connected to form a PV array, which can consist of as few as two or up to hundreds of modules. The number of modules in an array determines the amount of electricity generated.
PV modules come in various sizes, power ratings, and configurations, allowing for customisation to meet the energy demands of residential, commercial, and utility-scale projects. They are typically installed on rooftops or in solar farms, supplying electricity to the grid. PV modules require minimal maintenance, such as periodic cleaning and checking for damage or cracks.
Smart modules are an advanced form of traditional solar panels, incorporating power electronics that offer enhanced functionality such as maximum power point tracking, monitoring, and improved safety. Additionally, concentrator modules use lenses or mirrors to focus light onto smaller cells, enabling the use of highly efficient materials like gallium arsenide while increasing overall efficiency to around 45%.
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PV arrays
Solar photovoltaic (PV) cells, PV modules (panels), and solar PV arrays are all used for electricity generation. PV cells are electrically connected in a packaged, weather-tight PV panel (sometimes called a module). PV panels can be connected in groups to form a PV array. A PV array can be composed of as few as two PV panels or hundreds of PV panels. The number of PV panels connected in a PV array determines the amount of electricity the array can generate.
PV cells and panels produce the most electricity when they are directly facing the sun. PV panels and arrays can use tracking systems to keep the panels facing the sun, but these systems are expensive. Most PV systems have panels in a fixed position that are usually facing south in the northern hemisphere and north in the southern hemisphere.
PV cells generate direct current (DC) electricity. DC electricity can be used to charge batteries that power devices that use DC electricity. Devices called inverters are used on PV panels or in PV arrays to convert the DC electricity to alternating current (AC) electricity. AC is the type of electrical current used when plugging appliances into normal wall sockets.
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PV semiconductors
The most common semiconductor material used in PV cells is silicon, which accounts for approximately 95% of the modules sold today. Silicon is a group IV element with excellent semiconducting properties. To create a silicon PV cell, polysilicon is first processed from mined quartz until it is very pure (semiconductor grade). Small amounts of boron, a group III element, are then added to create a p-type semiconductor with a higher number of electron holes. An n-type semiconducting surface is then created by depositing a very thin layer of phosphorus, a group V element.
Another important property of PV semiconductors is the bandgap, which indicates the wavelengths of light the material can absorb and convert into electrical energy. By matching the semiconductor's bandgap to the wavelengths of light shining on the PV cell, the cell can efficiently utilize all available energy. This matching of the bandgap to the solar spectrum is crucial for enhancing the electrical and optical properties of the PV cell.
There are two main types of thin-film PV semiconductors: cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). CdTe is the second most common PV material after silicon, known for its cost-effectiveness and ease of manufacturing. While CIGS cells have optimal PV material properties and high efficiencies in lab settings, transitioning from lab-sized cells to large-area modules remains challenging due to the complexity of combining four elements.
Organic PV (OPV) cells are another type of PV semiconductor composed of carbon-rich organic compounds. OPV cells are more affordable to manufacture in large volumes and can be applied to flexible materials like plastic. However, their efficiency is currently only about half that of crystalline silicon cells, and they have shorter operating lifetimes. Quantum dot solar cells are another emerging technology that uses tiny particles of different semiconductor materials to conduct electricity, but they are not yet very efficient due to challenges in creating electrical connections.
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PV efficiency
Solar photovoltaic (PV) cells are the fundamental units of solar panels, which are in turn made up of PV modules. PV cells are electrically connected within a PV panel, and the number of cells in a panel determines the amount of electricity the panel can generate. PV panels can be connected in groups to form a PV array, which can be composed of as few as two PV panels or hundreds of them.
PV systems can generate electricity to directly power devices or supply electric power grids. They can also charge a battery to provide electricity when the sun is not shining. PV systems can also supply electricity in locations where electricity distribution systems do not exist.
PV cell efficiency is the percentage of solar energy that is converted to electricity. The efficiency of the solar cells used in a photovoltaic system, in combination with latitude and climate, determines the annual energy output of the system. The average efficiency of solar panels available today is 21%, but some researchers have developed PV modules with efficiencies nearing 40%. The highest recorded lab efficiency is achieved by hybrid four-junction cells (40.6%). The world record for solar cell efficiency is 47.6%, set in May 2022 by Fraunhofer ISE, with a III-V four-junction concentrating photovoltaic (CPV) cell.
Another factor affecting PV efficiency is reflection. Minimizing the amount of light reflected away from the cell's surface can increase efficiency. Anti-reflection coatings and textured surfaces help reduce reflection. Bifacial PV modules, which can capture sunlight on both sides, offer increased energy production over single-sided modules. Tracking systems that follow the sun throughout the day can also enhance energy production, although they come with upfront cost premiums.
Improving PV efficiency is a key research goal, as it helps make PV technologies more cost-competitive with conventional energy sources. The average levelized cost of energy (LCOE) for utility-scale solar PV has dropped significantly in recent years, but global supply chain disruptions have recently caused a rise in LCOE.
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Frequently asked questions
A solar cell, also known as a photovoltaic (PV) cell, is a device that converts sunlight into electricity.
A solar cell creates electricity through the photovoltaic effect, where photons of sunlight are absorbed by a semiconductor material, typically silicon, and release electrons, creating an electric current.
PV cells directly convert sunlight into electricity, while solar thermal technology uses mirrors to concentrate sunlight and convert it into heat, which is then used to produce electricity or for direct heating applications.
Solar energy is an infinite and renewable source of energy that can help reduce electricity costs, provide backup power, create jobs, and reduce carbon emissions.
The efficiency of PV cells has improved over time and is now approaching 25% for commercially available panels, while experimental cells have achieved nearly 50% efficiency.
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