What Is A Typical Pv Cell?

Photovoltaic (PV) cells, also known as solar cells, are devices that convert light energy directly into electrical energy. PV cells are the fundamental building blocks of photovoltaic modules, otherwise known as solar panels.

PV cells are semiconductor devices that exhibit the photovoltaic effect – meaning that they absorb photons from sunlight and release electrons, generating an electric current. This electric current generated by PV cells can be captured and utilized as electricity.

PV cells and solar panels have become an increasingly important renewable energy technology worldwide. They are used to provide electricity in areas without access to an electrical grid, provide supplemental electricity from rooftop systems on homes and businesses, and operate massive utility-scale solar power plants.

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History of Photovoltaic Cells

The basic technology for photovoltaic (PV) cells dates back over a century. In 1839, the French physicist Edmond Becquerel first discovered the photovoltaic effect while experimenting with metal electrodes immersed in electrolyte solutions. He found that certain materials produced small amounts of electric current when exposed to light. However, early PV cells were very inefficient at converting sunlight into electricity.

In 1883, American inventor Charles Fritts created the first true solar cell by coating selenium with an ultra-thin layer of gold. This was the first solid state photovoltaic cell, but it was still only about 1% efficient in coverting light into electricity.

Over the next few decades, various scientists worked to improve solar cell materials and designs. In 1954, researchers at Bell Labs in the United States developed the first modern silicon solar cell, which was far more efficient than previous PV technologies. This pioneering work kickstarted the rapid growth of photovoltaics research and commercial development that continues today.

Some key milestones in PV history include the development of the first practical solar cell in 1958 (9% efficient), the first spacecraft to be powered by solar cells in 1958, and the production of solar panels for residential uses starting in the 1970s. Ongoing improvements in materials and manufacturing have steadily increased the efficiency and decreased the costs of PV cells over the past several decades.

How PV Cells Work

Photovoltaic (PV) cells, also known as solar cells, convert sunlight into electricity using the photoelectric effect. When sunlight hits the cell, photons are absorbed by the semiconductor material in the cell, such as silicon. This causes electrons to be knocked loose from their atoms, creating electron-hole pairs. An electric field across the material causes the electrons to flow in one direction, producing an electric current.

The photoelectric effect occurs when light is absorbed and electrons are emitted. Sunlight is composed of photons, or particles of light, that carry various amounts of energy corresponding to the different wavelengths of light. When a photon hits an atom in the cell, the photon’s energy can be transferred to an electron, giving it enough energy to break free from the atom. The wavelength of light determines how much energy each photon carries.

When an electron breaks free, it leaves behind an empty space known as a hole. Each photon absorbed creates one electron and one hole. The electrons want to reconnect with holes, but the electric field in the PV cell forces the electrons to flow in one direction, while the holes go the other way. This flow of electrons is an electric current that can be captured and utilized before the electrons reconnect with the holes again.

In summary, PV cells generate current through the photoelectric effect, where sunlight knocks electrons free to create mobile electron-hole pairs that can be induced to flow thanks to the built-in electric field in the PV cell structure.

Components

PV cells consist of several key components that enable them to convert sunlight into electricity. The main component is the semiconductor material, typically silicon, which forms a p-n junction. The p-n junction is created by adding impurities to the semiconductor in a process called doping. This creates an electric field between the positively charged side (p-type) and the negatively charged side (n-type). When sunlight hits the PV cell, photons with enough energy dislodge electrons on the n-type side, allowing them to flow through the circuit and generate electricity.

PV cells also contain electrodes on the front and back to collect the current generated by photon absorption. The front electrode is designed to be thin and transparent so that sunlight can pass through to the p-n junction. The back electrode is thicker and reflective to bounce unabsorbed sunlight back into the cell.

An antireflective coating is applied to the top surface of the PV cell to reduce reflection off the front glass surface. This allows more sunlight to enter and be absorbed in the cell. Antireflective coatings using materials like silicon nitride or titanium oxide minimize reflection off the cell’s surface from over 30% to less than 5%.

Types of Photovoltaic Cells

There are three main types of photovoltaic cells:

Crystalline Silicon Cells

Crystalline silicon PV cells are the most common type of solar cells used in solar panels. They are made from silicon wafers that act as semiconductors. Crystalline silicon cells are categorized as either monocrystalline or polycrystalline:

Monocrystalline silicon cells are made from a single continuous crystal of silicon. They tend to be more efficient but are more expensive to produce than polycrystalline cells.

Polycrystalline silicon cells are made from fragments of silicon crystals melted together. They are cheaper to produce but are less efficient than monocrystalline cells.

Thin Film Solar Cells

Thin film solar cells are made by depositing thin layers of photosensitive materials onto substrates like glass or plastic. They are lighter, flexible, and cheaper to manufacture than crystalline silicon cells, but less efficient. Types of thin film cells include:

Amorphous silicon

Cadmium telluride (CdTe)
Copper indium gallium selenide (CIGS)

Emerging Photovoltaic Technologies

Some emerging PV technologies that are still under development include:

Perovskites – cheap organic cells with high efficiencies
Dye-sensitized solar cells – use photosensitive dyes
Quantum dot solar cells – use quantum dots as semiconductors

Organic photovoltaic cells – use organic electronics/polymers

Efficiency

The efficiency of a PV cell refers to the percentage of sunlight that is converted into electricity. Typical efficiencies for commercial PV cells range from 10-22%. The most commonly used cells tend to fall on the lower end of that range, around 14-18% efficient.

There are several factors that affect the efficiency of a PV cell:

Cell material – Some semiconductor materials, like monocrystalline silicon, have higher efficiency potential than others.
Manufacturing quality – Higher quality manufacturing can produce cells with fewer defects and higher efficiencies.
Temperature – Solar cell efficiency decreases as temperature increases. Keeping panels cool improves efficiency.

Solar spectrum and intensity – The frequency and intensity of incoming sunlight impacts efficiency.
Surface area – Larger surface areas can collect more sunlight and improve efficiency.

Researchers continue working to push the limits of solar cell efficiency through advanced materials and novel device architectures. But in general, typical commercial PV cells operate in the 10-22% efficiency range, with key factors like cell material and operating temperature impacting performance.

## Costs

The cost of PV cells has fallen dramatically over the past few decades. In 1977, the cost per watt of PV modules was around $77. By 2020, prices had dropped to around $0.20 per watt. This represents a massive 97% reduction in costs over the past 40+ years.

There are a few key factors that have driven down PV module costs:

Economies of scale – Increased production and deployment has enabled manufacturers to achieve lower per unit costs through mass production.
Technology improvements – Newer solar cell designs and manufacturing techniques have increased efficiency and lowered materials/energy requirements.
Market competition – Many new entrants into the PV market has intensified competition and put downward pressure on prices.

In the future, costs are projected to continue falling, albeit at a slower pace than historically. Some estimates suggest PV module prices could drop to around $0.10 per watt by 2030. Further reductions in soft costs like installation labor and permitting/interconnection could also lower total system prices for consumers.

Applications

Photovoltaic cells have a wide variety of applications and can be implemented on both small and large scales. Here are some of the most common applications of PV cells:

Off-Grid

PV systems are commonly used for off-grid applications such as remote cabins, telecommunications equipment, boats, RVs, and more. Off-grid systems operate independently from the utility grid and include batteries for energy storage. They provide a cost-effective and reliable power source for locations where connecting to the grid is impractical.

Residential

Rooftop solar PV systems are becoming increasingly popular for homes. Residential systems are usually grid-tied, meaning they are connected to the utility grid. Excess power generated during the day feeds into the grid, while power from the grid supplements the PV system at night. This allows homeowners to reduce daytime electricity purchases from the utility.

Utility-Scale

Large solar “farms” with hundreds or thousands of PV panels are rapidly expanding worldwide. These utility-scale systems feed power directly into the transmission grid, providing clean, renewable electricity on a massive scale. Major solar power plants can now generate hundreds of megawatts, rivaling traditional power stations.

Advantages/Disadvantages

PV solar cells have several notable advantages compared to other energy sources:

Renewable – PV cells utilize the virtually limitless power of the sun and do not require any fuel source to operate.
Low maintenance – Unlike fossil fuel plants, PV systems have no moving parts and require very little maintenance over their lifetime.
Long lifetime – PV panels typically last 25-30 years before any significant degradation in performance occurs.

Scalable – PV systems can be installed in a wide range of sizes, from small residential to large utility-scale.
Quiet operation – PV panels produce electricity silently, without noise pollution.
Reduce air pollution – PV solar contributes to lowering toxic air emissions associated with burning fossil fuels.

Potential disadvantages include:

Higher upfront costs than fossil fuel plants.
Intermittent power supply depending on weather and daylight hours.

Large land area may be required for utility-scale PV farms.
Some toxic materials used in manufacturing process.

Overall PV solar energy has significant environmental and operational benefits compared to conventional power generation while costs continue to decrease rapidly.

Future Outlook

The future looks bright for photovoltaic technology as it continues to improve in efficiency and decline in costs. Some key trends shaping the future of PV include:

Emerging Technologies: Companies are investing heavily in next-generation PV technologies like perovskites, organic PV, quantum dot PV, and tandem/multi-junction cells. These innovations could enable higher efficiencies beyond traditional silicon cells. For example, perovskite-silicon tandem cells have achieved over 29% efficiency in lab tests.

Growth Projections: Solar PV capacity is expected to grow substantially in the coming decades. The International Energy Agency projects global PV capacity will reach over 5,500 gigawatts by 2040, a 10x increase from 2020 levels. This growth will be driven by improving economics, supportive policies, and the need for clean energy.

Cost Reductions: The cost of solar PV modules has dropped dramatically in the past decade, with an over 80% decline. Further cost decreases are expected as manufacturing efficiencies improve, supply chains mature, and technologies advance. This will make solar electricity cheaper than fossil fuels in more markets.

Energy Storage: Combining PV with energy storage technologies like batteries will enable broader deployment. Storage provides grid stability and allows solar power to be dispatched when needed. As storage costs fall, PV+storage systems will become increasingly commonplace.

New Applications: Solar PV has huge potential to expand into new applications like vehicle integrated PV, building integrated PV, floating PV on water bodies, and space-based solar power satellites. These creative deployments will open up new markets for adoption.