How Energy Generation Occurs in a Photovoltaic Panel? Understand the Process

Photovoltaic solar panels from AE Solar.

The solar panel is an essential equipment for generating photovoltaic energy. It consists of small cells formed by semiconductor materials, such as silicon, arranged in series and parallel. When photons (particles of sunlight) come into contact with the photovoltaic cells, some of the electrons surrounding the atoms move to the part of the cell that lacks electrons. This movement creates an electric current, generating photovoltaic solar energy. Check below the layers that make up the photovoltaic plate.

What is the Photovoltaic Effect?

The photovoltaic effect occurs when light is absorbed, causing the stimulation of an electron or another charge carrier to a higher energy state. In more detail, it is the potential difference created inside the cell, caused by the movement of electrons and atoms (raw material of the cell) upon encountering photons.

Composed of equal parts of semiconductor material, silicon cells mixed with other elements modify their structure. In this process, positive and negative electrons are separated, generating the lack (holes) of positive electrons.

When the junction of positive and negative electrons occurs, an electric field is formed, which does not allow the union of excess electrons (negative) to the missing ones (positive). When the cells absorb sunlight, the electrons receive energy from photons and detach from the attraction. With the accumulation of electrons in the negative part, a "web" is formed on one of the faces of the cells, along with holes, which captures free electrons and, thus, creates electric current.

Electricity generation in photovoltaic cells occurs in several stages, involving the collection and movement of charge carriers (electrons and holes) and voltage generation. Here is a summary of these stages:

• Collection of light-generating transporters: When sunlight falls on solar cells, photons from the light excite electrons present in the semiconductor material of the panel. These excited electrons (generated carriers) and the resulting holes (positive charges left by excited electrons) are then released and move through the semiconductor material.
• Generation of carriers (electrons and holes): The energy of photons absorbed by the solar cell is transferred to electrons in its semiconductor structure, allowing them to move and generate an electric current. These excited electrons are then collected by the metal contacts of the panel, while holes are captured by other adjacent contacts.
• Voltage generation through solar cells: As electrons are collected by metal contacts, they are forced to flow through an external circuit, creating an electric current. This current is induced by the potential difference between the region of the semiconductor material where electrons are excited and the region where they are collected. This potential difference is known as open-circuit voltage (Voc) and is responsible for generating voltage in solar cells.

Current generation involves two processes. The first part is the generation of electron-hole pairs by incident photons. However, stimulated electrons and holes are metastable and will only exist, on average, for a period equal to the minority carrier lifetime before recombining. If the carrier recombines, the electron-hole pair generated by light is lost and no current or energy can be generated. The second process is the separation of these carriers. This is done by connecting an external circuit to the solar cell. The stimulated electron crosses the external circuit and the generated hole crosses the junction barrier to recombine with the traversed electron.

Understanding the Photovoltaic Module

Illustration of a solar cell.

A photovoltaic module consists of individual solar cells connected electrically to increase their output power. It is composed of several interconnected solar cells encapsulated in a single panel/unit. There are many different types of photovoltaic modules, and the module structure usually differs for different types of solar cells. The most common modules have 60 cells or 72 cells with three bypass diodes. 60-cell modules were originally designed to facilitate handling in residential applications, while 72-cell modules, which are heavier, are for large utility-scale installations.

Solar Cell IV Characteristic Curves

Solar Cell I-V Curve.

Solar cell IV characteristic curves (current and voltage) show the performance of a specific cell, module, or photovoltaic (PV) array. The energy supplied by a single solar cell or panel is the product of its output current and voltage. Photovoltaic panels can be connected in series or parallel combinations, or both, to increase the panel's voltage or current capacity, respectively. When panels are connected in series, the total voltage in the array increases. When panels are connected in parallel, the total current output increases.

The IV curve contains three significant points: The Maximum Power Point (MPP), which represents the maximum power point of voltage and the maximum power point of current, Open-Circuit Voltage, and Short-Circuit Current. The solar cell IV curve depends on the module's temperature and irradiance.

Technological Advances and the Future of Solar Energy

AE Solar AURORA series of solar panels with nominal power from 485 W to 505 W.

Typical values for the parameters of a silicon solar cell are as follows: Short-circuit current = 35 mA/cm², open-circuit voltage up to 0.65 V, and Fill Factor (FF) in the range of 0.75 to 0.80. Efficiency generally varies around 15% - 20%. All these parameters are mentioned in the datasheet provided by manufacturers.

The photo above shows one of the various products offered by AE Solar. The AURORA series is a range of monocrystalline panels available from 485 W and has a maximum power of 505 W with efficiency varying from 19.88% to 21.4%. More features and information about the product can be found in the technical sheet.

AE Solar FV Modules.

Today, rapid technological advances have surpassed limits in terms of energy production and total efficiency of individual cells, as well as in manufacturing processes with innovative ideas. Solar cells can produce much higher efficiency and energy compared to the cells available 20 years ago. With more and more people opting to install photovoltaic systems, the solar technology industry is growing rapidly. As countries try to switch to green energy agilely, the future of solar energy seems brighter than ever.