How Does Solar Energy Convert to Electricity?

Solar panels convert light into electricity. It is a complex process involving physics, chemistry and electrical engineering. As solar panels play an increasingly important role in the fight against fossil fuels, it is essential to learn how solar panels convert sunlight into usable energy . Interestingly, the same concepts that allow solar panels to power our homes are also driving the technological revolution. 

 

Simply put, sunlight hits the panel and excites electrons in the silicon crystal. The silicon wafer is impregnated with impurities to create a natural electric field that directs the movement of electrons. The metal lines on the solar cell collect electrical energy and carry it to the inverter and then into your home.

 

What is Energy?

 

We need energy to work. Whether it's moving our bodies, growing food, or powering our homes, energy powers our world. Energy can take many forms, including light, motion, electricity, chemical reactions, and heat. The first law of thermodynamics states that energy cannot be created or destroyed, but only change form. This is an inherent problem of human needs, because energy itself is abundant but often does not exist in a directly applicable form. When we install solar panels for home, we harness the sun's light energy. When light hits the surface of a semiconductor material, a reaction occurs that converts light energy into electrical energy. But because solar panels are not 100% efficient, some of this light energy is converted into heat.

 

Once the energy is converted into electricity, metal lines on the panel carry electricity out of the panel and to your storage battery. The energy is then converted into chemical energy, where it is stored until ready to be converted back into electricity for household use. 

 

Photoelectric Effect

The photovoltaic effect captures sunlight and converts it into electrical energy. This phenomenon was discovered by French physicist Edmond Becquerel in 1839 while experimenting in his father's laboratory with platinum electrodes in an electrolytic solution. He noticed that when light shined into the solution, the electric current increased. The first solar panels on the roof were installed soon after.

 

Light is made up of photons that carry energy. The energy of a photon is proportional to the frequency of light. The photovoltaic effect is activated when photons hit the photovoltaic surface, which absorbs the energy of the photon and excites electrons present in the material. An electric current is generated when a sufficient number of electrons are excited. Depending on the material, the frequency required to trigger the effect may vary. In photovoltaic solar panels, semiconductors provide the photovoltaic medium used to convert sunlight into electricity. 

 

Semiconductors

Semiconductors are materials that conduct electricity better than insulators such as glass or wood but conduct electricity less than conductors such as copper or gold. The conductivity of semiconductors can be adjusted by doping or adding impurities to achieve a conductivity value suitable to the needs of a particular application. They are found in computers, cars, smartphones and home appliances. Silicon is the most common semiconductor, usually in the form of silicon wafers. The advent of crystalline silicon has been a key driver of the digital revolution of the past 50 years, hence the use of the term Silicon Valley to refer to the Bay Area, home to the world's largest technology companies. 

 

Semiconductor wafers can be positively (p-type) or negatively (n-type) doped. p-type and n-type can even exist in the same crystal, which is the case for photovoltaic panels. The p-type contains atoms lacking electrons, called electron holes, while the n-type contains atoms with an excess of electrons. Electrons and holes are collectively called charged particles. The two meet at a boundary layer inside the crystal, called the p-n junction. 

 

The crystal structure of silicon wafers is integral to their function. In the crystal lattice, electrons are fixed in place and cannot move freely. When an input source of energy excites electrons to a sufficient energy level, they can escape and move within the lattice structure. The electrons then diffuse across the pn junction, filling the electron holes and neutralizing both charge carriers. This creates a zone of neutral material called the depletion zone. Finally, the movement toward the p-n junction reaches a steady state and an electric field forms around the depletion region. The n-side boundary becomes positively charged and the p-side boundary becomes negatively charged, creating an opposing force that moves toward the p-n junction. This stops the flow of electrons across the p-n junction and the wafer remains in this state of equilibrium until the energy level in the system changes.

 

Semiconductors are limited by their band gap, an energy range in which electron movement will not occur. The light energy hitting the surface of the solar panel must be greater than the energy band of the semiconductor, otherwise electricity will not be generated. Just like in electronics, silicon is the most popular semiconductor for solar panels. Silicone sheets come in three types:

 

• Single crystal (MonoSi)

• Polycrystalline (PolySi)

• Amorphous silicon (a-Si)

 

Several other types of semiconductors are used in the photovoltaic industry, although they are less common. Some types are listed below.

 

• Cadmium Telluride (CdTe)

• Copper indium gallium selenide (CIGS)

• Gallium arsenide (GaAs)

 

Although this article focuses on the working mechanism of silicon solar panels, most semiconductors operate on the same principle.

 

From Sun to Electricity

Now that we've explored the different concepts and processes that allow your solar panels to produce electricity, let's take a closer look at what's actually happening inside your PV array.

 

You wake up in the morning and the sun rises above the horizon. As you start your morning routine, sunlight will illuminate your roof, bringing energy to your home. The Sun has a wide energy spectrum and emits photons with many energy values. Remember that photovoltaic semiconductors have a frequency range, and photons hitting the surface of your panel must be above the frequency range to increase the material's conductivity. 

 

These three things can happen when a photon interacts with your solar panel: 

 

• Photons can be reflected by the surface of the panel. 

• If the photon's energy level is below the band gap, it will pass through the panel. 

• If the photon's energy level is equal to or greater than the band gap, it will interact with the semiconductor. 

 

The structure of a solar cell plays an important role in the movement of electrons. The n-doped layer is very thin and is placed directly under the glass, above the much thicker p-doped layer. This means that sunlight penetrates the n side and reaches the p-n junction. The increased thickness of the P-face also creates a much larger depletion region than if both were equal in size. The energy from the photons is transferred to the electrons, giving them the energy to cross the depletion region and enter the p-side. Electrons recombine with electron holes on the p-side, while sunlight continuously excites new electron-hole pairs in the depletion region. This continuous movement is the source of electric current. The silicon remains in this charged state as long as the sun shines on the panel. When the sun sets, the silicon returns to equilibrium and the depletion region returns to its original width. 

 

While the depletion region prevented the generation of current, the solar power supply provided the charge carriers with enough energy to overcome the neutral layer. Since most photons interacting with silicon have an energy value above the band gap, the excess energy is dissipated as heat. 

 

Since electrons can freely move through the silicon, you just need to find a way for the electrical energy to exit the panel. Each solar cell has two sets of metal grids connected to its surface, called busbars and busbars. The electricity is collected in the fingers, which are a collection of very thin metal mesh that runs through the solar cell. The fingers transmit power to the bus bars perpendicular to the fingers. The busbar is much thicker than a finger, and most solar cells have two bus bars that span the entire length of the cell. 

Photovoltaic processes generate direct current, so an inverter is needed to convert direct current and alternating current. The electricity is then stored in the battery, where energy is stored in the form of chemical bonds until ready to discharge. 

 

Conclusion 

 

While humanity has been harnessing solar energy in the form of heat for centuries, photovoltaic solar energy has allowed us to directly utilize the sun's rays. Although technology developed slowly, the idea of ​​harnessing sunlight to produce energy has revolutionized the energy industry. The prospect of abandoning fossil fuels in favor of the sun's limitless energy has changed the way we view electricity. Photovoltaic panels exploit the unique properties of silicon semiconductors to convert light energy into electrical energy. The physical and chemical properties of crystalline silicon allow the material to react to light in a way that creates an electrical charge. Metal lines carry electrical energy out of the panel and into your home. It's a complex process that has the potential to energize sunny cities around the world.