Beatrice Lang
Solar cells, also known as photovoltaic (PV) cells, are non-mechanical devices that convert sunlight directly into electricity. This process, known as the photovoltaic effect, was first discovered by French physicist Edmond Becquerel in 1839. Today, solar cells are typically made from silicon, a semiconductor material that releases electrons and produces an electric charge when exposed to photons of sunlight. This electric charge is then captured by the wiring in solar panels and converted into usable electricity through the use of inverters. The efficiency of solar panels has improved significantly over time, with state-of-the-art modules approaching 25% efficiency and experimental PV cells achieving nearly 50% efficiency.
| Characteristics | Values |
|---|---|
| Basic building block | Photovoltaic (PV) cell |
| PV cell composition | Semiconductor material, usually silicon |
| Sunlight composition | Tiny packets of energy called photons |
| Photons | Reflect off the cell, pass through the cell, or are absorbed by the semiconductor material |
| Absorbed photons | Energize electrons within the silicon atoms, causing them to break free from their atomic bonds |
| PV cell design | Two layers of silicon – one positively charged (p-type) and one negatively charged (n-type) |
| Electric field | Directs the flow of freed electrons, generating an electric current |
| Electricity generated by solar panels | Direct current (DC) |
| Electricity used by most household appliances and power grids | Alternating current (AC) |
| Device to convert DC to AC | Inverter |
| PV cell efficiency in the mid-1980s | Less than 10% |
| PV cell efficiency by 2015 | Around 15% |
| Current state-of-the-art PV cell efficiency | Approaching 25% |
| PV cell efficiency for niche applications like space satellites | Nearly 50% |
| PV system electricity generation | Power devices directly, charge a battery for electricity when the sun is not shining, or supply electric power grids |
| PV system electricity supply | Possible in locations without electricity distribution systems (power lines) |
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What You'll Learn
Photons from sunlight knock electrons loose from atoms
Solar cells, also known as photovoltaic (PV) cells, are non-mechanical devices that directly convert sunlight into electricity. This process is called the photovoltaic effect. The photovoltaic effect occurs when photons from sunlight strike the surface of a silicon semiconductor material, liberating electrons from the material's atoms.
Silicon is the most common material used in solar cells, but other materials can be used as well. When photons from sunlight strike the surface of a solar cell, they will either reflect off the cell, pass through the cell, or be absorbed by the semiconductor material. Only the photons that are absorbed by the semiconductor material provide energy to generate electricity.
When photons are absorbed by the semiconductor material, they knock electrons loose from the material's atoms. This process is called excitation, where the electrons move to a higher valence level and are released from their parent atom. As there are billions of photons striking the cell every second, there are a lot of electrons knocked loose. The excited electron gets kicked out of the atom, allowing it to roam freely around the semiconductor material.
The front surface of the solar cell is specially treated during manufacturing to make it more receptive to these dislodged or free electrons, so the electrons naturally migrate to the surface of the cell. As one side of the PN junction has a "lack of electrons" (holes), while the other side of the junction has an "excess of electrons", these free electrons move through the junction, creating and filling in holes in the cell. This motion of electrons creates an electric current in the cell.
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The movement of electrons creates an electric current
Solar panels are made up of multiple solar cells, which are the key units responsible for converting sunlight into electricity. The solar cell, also known as a photovoltaic (PV) cell, is a non-mechanical device that converts sunlight directly into electricity. The PV cell is made of semiconductor material, typically silicon. When sunlight strikes a PV cell, it initiates a series of events:
Firstly, photon absorption occurs. Sunlight is composed of tiny packets of energy called photons. When these photons hit the PV cell, they are absorbed by the semiconductor material. The photons that are absorbed provide energy to generate electricity.
The absorbed photons then energize electrons within the silicon atoms, causing them to break free from their atomic bonds. This process is called electron excitation. The PV cell is designed with two layers of silicon—one positively charged (p-type) and one negatively charged (n-type). This creates an electric field that directs the flow of freed electrons, generating an electric current.
The movement of these electrons creates an electric current. This current is captured and directed through the panel's wiring and eventually becomes electricity. The electric field pushes the energized electrons, forcing them to move. This movement of electrons generates a direct electrical current (DC), which is the basis of electricity production.
The electricity generated by solar panels is DC, but most household appliances and the power grid use alternating current (AC). Devices called inverters are used to convert the DC electricity from the panels into AC electricity. AC electricity can then be used to power homes and businesses or fed back into the electrical grid.
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The electric current is captured by wiring in solar panels
Solar panels are made from silicon or another semiconductor material. When this material is exposed to sunlight, it releases electrons and produces an electric charge. This process creates an electric current, specifically direct current (DC), which is captured by the wiring in solar panels.
This DC electricity is then converted to alternating current (AC) by an inverter. AC is the type of electrical current used when plugging appliances into normal wall sockets. The inverter is, therefore, an essential component of the solar power system, as without it, the system would create electricity, but it wouldn't be able to power anything.
The wiring of solar panels is also known as "stringing", and it is a fundamental topic for any solar installer. There are two main ways to wire solar panels: in series or in parallel. Wiring solar panels in series involves connecting each panel to the next in a line, from the positive terminal of one panel to the negative terminal of the next. Wiring in series is generally less productive in terms of power production than wiring in parallel, which allows for more independent power production between panels. However, wiring in parallel also increases upfront costs for materials and installation.
To maximize electricity production without exceeding inverter voltage ratings, some solar energy systems use a combination of series and parallel wiring connections. The specific design of the system will determine the types and sizes of wires needed, and it is important to select an appropriate inverter for the array to ensure the system functions effectively.
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The direct current (DC) electricity is converted to alternating current (AC)
Solar cells, also known as photovoltaic (PV) cells, are non-mechanical devices that convert sunlight into electricity. They are usually made from silicon or another semiconductor material installed in a metal panel frame with a glass casing.
When the sun shines onto a solar panel, the PV cells absorb the sunlight's energy. This energy creates electrical charges that move in response to an internal electrical field in the cell, causing electricity to flow. This flow of electricity is known as a current, specifically, direct current or DC. This DC electricity is captured by the wiring in solar panels.
The direct current (DC) electricity is then converted to alternating current (AC) by an inverter. AC is the type of electrical current used when appliances are plugged into normal wall sockets. AC and DC are different in terms of the direction in which the electrons flow. In DC, the electrons flow steadily in a single direction, while in AC, the electrons switch directions periodically, going forward and then backward.
AC is also more easily transformed between voltage levels, making it more suitable for high-voltage transmission. This property of AC means it can be converted using a single component, a transformer, which is why it was chosen as the primary means to transmit electricity over long distances.
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Solar panels are made from silicon semiconductors
P-type semiconductors are often made from silicon wafers, while n-type semiconductors are created by adding impurities to a pure semiconducting material like silicon. Phosphorus, for example, has one more electron than the semiconductor material, and this additional electron becomes a positively charged ion, aiding in the creation of electric fields that generate power.
Silicon is a semiconductor, meaning it can conduct electricity better than an insulator but not as well as a good conductor like metal. When a silicon semiconductor is exposed to light, it absorbs the light's energy and transfers it to negatively charged particles called electrons. This extra energy allows the electrons to move through the material as an electrical current, which is then captured and converted into usable electricity.
The efficiency of a solar cell depends on the type of semiconductor material and technology used. Silicon solar cells offer high efficiency, low cost, and long lifetimes. They are expected to last for 25 years or more, still producing over 80% of their original power output.
Additionally, silicon solar cells have improved over time. In the mid-1980s, the efficiency of commercially available silicon solar panels averaged less than 10%, but today, state-of-the-art modules are approaching 25% efficiency. This continuous improvement in photovoltaic (PV) efficiency is a key focus of research, driving down costs and making solar energy more competitive with conventional energy sources.
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Frequently asked questions
Solar cells, also known as photovoltaic (PV) cells, are non-mechanical devices that convert sunlight directly into electricity. They are made from semiconductor materials, typically silicon, and are the basic building blocks of a solar panel.
When sunlight, composed of tiny particles called photons, hits the surface of a solar cell, these photons interact with the semiconductor material. This interaction excites the electrons in the material, knocking them loose from their atoms. The freed electrons then move, creating an electric current.
Solar PV panels generate electricity by converting the sun's energy into electrical charges through the photovoltaic effect. Solar thermal panels, on the other hand, generate heat by directly heating water or other fluids with sunlight.
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