What Are Solar Cells Designed For?

What are solar cells?

Solar cells, also known as photovoltaic cells, are devices that convert sunlight directly into electricity. They are made of semiconductor materials, most commonly silicon, that absorb photons from sunlight and convert them into an electric current through the photovoltaic effect.

The basic components of a solar cell include the semiconductor material, a negative electrode, a positive electrode, an antireflective coating and metal contacts. When sunlight hits the solar cell, photons with enough energy are absorbed by the semiconductor, knocking electrons loose. This generates electron-hole pairs that get swept into the electric field and create a flow of electricity. The metal contacts collect the current and transmit it to wires for powering electrical devices or charging batteries.

In summary, solar cells are a renewable energy technology that harness solar energy and convert it directly and efficiently into electrical energy through the photovoltaic effect. Their simple and modular design allows them to be integrated into a wide variety of applications.

History of Solar Cells

The history of solar cells dates back to the 19th century when the photovoltaic effect was first observed. In 1839, French physicist Edmund Becquerel discovered that certain materials would produce small amounts of electric current when exposed to light. However, early solar 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 a thin layer of gold to increase conductivity. This primitive solar cell had less than 1% efficiency in converting light to electricity.

In 1954, scientists at Bell Labs developed the first modern solar cell made from silicon. This solar cell had around 6% efficiency and was mainly used to provide power for space satellites. Through the 1950s and 1960s, space programs helped drive advances in solar technology.

In the 1970s, Exxon and ARCO helped develop more efficient silicon solar cells for commercial and residential applications. Solar cell efficiencies rose into the double digits. Federal tax credits in the late 1970s further propelled the growth of the solar PV industry.

Since 2000, solar cell technology has continued to advance. Manufacturing costs have declined dramatically while efficiency levels have increased. Today’s best silicon solar panels convert over 20% of sunlight into electricity.

How Solar Cells Work

Solar cells are designed to convert sunlight into electricity through a phenomenon called the photovoltaic effect. The photovoltaic effect refers to photons from sunlight knocking electrons loose in a solar cell’s semiconductor material, creating an electric current. Solar cells are made of semiconductors such as silicon that have electrical properties between those of a conductor and an insulator. When sunlight hits the solar cell, the energy from the photons causes electrons in the semiconductor material to break free from their atomic bonds and flow freely. This generates electricity in the form of direct current (DC).

The photovoltaic effect occurs at the atomic level as photons interact with the semiconductor material’s electrons. Solar cells have an electric field that acts to sweep the freed electrons in one direction, allowing us to harness the electrons as electric current. The electric field develops across the solar cell due to the special composition of the semiconducting material, which has both positively charged silicon atoms and negatively charged phosphorus atoms. This separation of charge creates an internal electric field at the atomic scale, causing freed electrons to flow in a single direction.

In summary, solar cells are designed to absorb photons from sunlight and convert them into an electric current via the photovoltaic effect. The semiconducting material, electric field, and photovoltaic effect work together to enable solar cells to produce electricity from sunlight.

Types of Solar Cells

There are several different types of solar cells, each with their own unique properties and best use cases. The main categories of solar cells are:

Crystalline Silicon Solar Cells

Crystalline silicon solar cells are the most common type of solar cells in the world, making up over 90% of the solar panel market. They are made from silicon wafers and come in two main types: monocrystalline and polycrystalline. Monocrystalline solar cells are more efficient but also more expensive to manufacture.

Thin Film Solar Cells

Thin film solar cells are made by depositing one or more thin layers of photovoltaic materials onto a substrate like glass or plastic. They are less efficient than crystalline silicon cells but can be cheaper to manufacture. Examples of thin film materials are cadmium telluride (CdTe) and copper indium gallium selenide (CIGS).

Organic Solar Cells

Organic solar cells, also known as organic photovoltaics (OPV), use organic electronics consisting of carbon-based materials like polymers and small molecules. They can be made using simple printing processes, making them potentially inexpensive, but they have lower efficiency levels.

Multi-Junction Solar Cells

Multi-junction solar cells contain multiple thin layers of semiconductor material, each tuned to absorb a different wavelength of light. This layered design allows them to achieve very high efficiency levels, making them ideal for applications like satellites, but they are complex and expensive to make.

Solar Cell Efficiency

Solar cell efficiency refers to the percentage of sunlight that hits the cell and gets converted into electricity. Research cells demonstrate the highest possible efficiencies, while commercial cells have lower efficiency for everyday applications.

Best Research Cell Efficiencies

The most efficient solar cells in lab settings are multi-junction concentrator solar cells. These have reached efficiencies over 47%, combining multiple semiconductor materials to absorb different wavelengths of light. Single-junction cells have achieved up to 29% efficiency in labs using gallium arsenide or silicon semiconductors.

Commercial Cell Efficiencies

The typical efficiency of commercial silicon solar panels is between 15-22%. Thin film solar panels using cadmium telluride (CdTe) tend to range from 11-13% efficiency. Higher performance monocrystalline silicon panels can reach up to 24% efficiency.

Factors Affecting Efficiency

The efficiency of a solar panel depends on the semiconductor materials, manufacturing quality, temperatures, and light exposure levels. Efficiency drops at higher temperatures and low-light conditions. Orientation and tilt also impact efficiency based on sun exposure. Overall system design, inverters and wiring also affect the conversion efficiency.

Applications of solar cells

Solar cells have a wide variety of practical uses. Some of the most common applications of solar cells include:

Solar panels

Solar panels are made up of many individual solar cells and are used to convert sunlight into electricity. Residential rooftop solar panels generate clean renewable energy for homes. Large-scale solar farms consist of thousands of solar panels and provide electricity to the utility grid.

Calculators

Small solar cells provide power for many handheld calculators. This allows calculators to operate without batteries.

Satellites

Satellites and spacecraft use high efficiency solar cells to convert sunlight into power. The solar arrays can reliably provide energy to satellites for many years as they orbit the Earth.

Spacecraft

Solar cells are vital for providing power aboard spacecraft. They provide electricity for systems while in space and are a clean renewable source of energy.

Solar cell manufacturers

Some of the largest solar cell manufacturers in the world include:

• JinkoSolar – Founded in China, JinkoSolar is currently the world’s largest solar panel manufacturer. They have manufacturing facilities located in China and Malaysia.

• JA Solar – Another Chinese company, JA Solar is one of the world’s largest producers of solar cells and modules. They have manufacturing bases in China, Malaysia, and Vietnam.

• Trina Solar – Founded in China, Trina Solar is a global provider of PV modules, solutions, and services. They have manufacturing facilities in China, Thailand, Malaysia, and Vietnam.

• LONGi Solar – This Chinese monocrystalline silicon solar producer has manufacturing facilities located in China, India, Malaysia and Vietnam.

• Canadian Solar – Founded in Canada, Canadian Solar now manufactures most of its solar products in China and Southeast Asia.

Other major manufacturers are based in the United States, Europe, South Korea, and beyond. Global solar cell production is centered in Asia, especially China, due to lower manufacturing costs and supportive government policies.

Cost of Solar Cells

The cost of manufacturing solar cells has dropped dramatically over the past few decades. In the 1970s, solar panels could cost over $70 per watt. Today, prices are below $0.50 per watt on average. This is due to improvements in solar cell technology and economies of scale as production has increased.

The most widely used solar panels on the market today use crystalline silicon cells. In the early 2000s, crystalline silicon solar modules cost over $4 per watt. By 2019, prices had fallen to around $0.37 per watt. In the last decade alone, crystalline silicon solar panel prices have dropped by around 80%.

Other solar cell technologies like thin-film have also seen price declines but remain slightly more expensive than crystalline silicon on average. Thin-film prices have dropped from around $1.50 per watt in 2009 to $0.36 per watt in 2019, about a 76% reduction.

Industry experts predict silicon solar panel prices to continue to fall by around 3-12% each year going forward. Developments in technology, manufacturing, scale, supply chains, and competition will facilitate further cost reductions.

Lower solar cell and module costs, combined with falling balance-of-system costs, make solar power increasingly cost competitive with conventional power sources.

Environmental Impact

The environmental impact of solar cells is complex. On one hand, solar cells provide clean, renewable energy without emissions. This helps reduce reliance on fossil fuels which produce greenhouse gases and air pollution. However, there are some environmental concerns around solar cells related to materials, manufacturing, and recycling.

Producing the materials for solar cells, like silicon and other semiconductors, can be energy intensive and result in some emissions. The manufacturing process also uses chemicals and water that need proper handling to prevent pollution. Most concerning is what happens at end of life when solar cells need to be disposed of or recycled.

Solar panels contain valuable materials like silicon, silver, and copper. But they also contain some toxic materials like lead. Proper solar panel recycling recovers about 80% of materials for reuse. This reduces the need for new raw materials. However, current recycling rates are low, with most old solar panels going into landfills. This wastes recoverable materials and risks leaking toxic substances.

Overall, solar power is far cleaner than fossil fuels. But the solar industry needs to prioritize more sustainable manufacturing, reusable components, and responsible recycling. This will help solar energy achieve its full potential as a green technology with minimal environmental impact.

Future of solar cell technology

The future looks bright for advances in solar cell technology. Here are some of the key innovations, growth projections, and challenges ahead:

Emerging innovations in solar cells aim to boost efficiency and lower costs. Companies are developing new materials like perovskites that have the potential to reach over 30% efficiency. Advances in manufacturing techniques like roll-to-roll processing could enable high-volume production of flexible, lightweight solar panels. And novel solar cell designs, like multi-junction cells with multiple layers, can optimize light absorption.

Market projections anticipate substantial growth for solar power, driven by increasing efficiency and dropping prices. One forecast predicts the solar industry will expand from under 1% of global electricity generation today to over 20% by 2050. Total solar capacity could reach over 8,500 gigawatts globally in the next few decades, more than 28 times what exists today.

However, the industry faces challenges to realize this potential. Installation costs remain high in some markets, and access to financing can be a barrier. Developing better storage technology to pair with solar would allow broader adoption. And recycling systems will need to improve to manage disposal of panels at end of life. But if these hurdles can be overcome, solar power is poised to become a major pillar of the global energy supply.