In this blog post, we’ll explore how solar energy can help address climate change, focusing on its principles, limitations, and the various ways we can put it into practice.
In Korea, spring and fall are getting shorter and shorter. Cherry blossoms are blooming earlier every year, and autumn foliage vanishes before we even have a chance to enjoy it. The Korea Meteorological Administration reports record-high and record-low temperatures every year. We are suffering from increasingly intense heatwaves and cold snaps. This is not merely a matter of being hot or cold. If this continues, South Korea will eventually transition into a subtropical climate. For future generations, “South Korea, a country with distinct four seasons,” will become a thing of the distant past. We must delay global warming—the primary culprit behind these abnormal weather patterns—as soon as possible.
One way to reduce carbon dioxide emissions—the primary cause of global warming—is through “photovoltaic energy.” We can generate electricity from the sun, that constant light source orbiting the Earth. So, how can we generate electricity from sunlight? First, let’s explore some basic concepts to understand photovoltaic energy.
The “Photo” in “Photovoltaic” comes from the Greek word for light, and “Volta” refers to the Italian inventor of the battery. We often use the terms “solar cell” and “solar energy” interchangeably. However, solar energy is a broader concept than solar cells. Simply put, solar energy means using sunlight to convert it into other forms of energy for use. A solar cell is one of the technologies that utilizes solar energy. In this case, the converted energy is electrical energy. The process by which electricity is generated in a solar cell is explained by the principles of semiconductors and the photoelectric effect. Let’s take a brief look at this below.
Among the elements that make up the Earth’s crust, oxygen is the most abundant, followed by silicon (Si). Silicon is the main component of soil, sand, and rocks, which are commonly found in our surroundings. Since there is no concern about silicon running out, it is widely used as the primary material for semiconductors due to its physical properties. All elements, including silicon, consist of an atomic nucleus made up of neutrons and protons, and electrons orbiting around it. The electrons build their own “apartments” around the atomic nucleus and live there. These “apartments” are called electron shells. The first floor of the apartment is very cramped, accommodating a maximum of two electrons, whereas the second floor and above can accommodate up to eight electrons. The electrons living on the top floor of the apartment are the valence electrons. With the exception of hydrogen and helium, all elements prefer a state where their outermost shell is filled with eight electrons. This is because electrons that have lost their “family” tend to easily break away. In the case of silicon, which has 14 electrons, two are in the first-level shell, eight in the second-level shell, and the remaining four form the outermost shell. Silicon, which is unstable due to a shortage of four electrons, forms bonds with neighboring silicon atoms to resolve this. They bond by sharing their four outermost electrons with one another. This type of bond is called a covalent bond, and the silicon atoms form a covalent crystal, behaving as if they each have eight outermost electrons.
What happens if we force phosphorus (P), which has 5 valence electrons, into the midst of these now-bonded silicon atoms? Phosphorus donates one of its valence electrons to form covalent bonds with the silicon atoms. Because of that single donated electron, the silicon crystal becomes an N-type (negative-type) semiconductor. Conversely, if boron (B), which has three valence electrons, is forcibly introduced, the boron behaves as if it has seven valence electrons within the silicon crystal. The silicon crystal, which is relatively one electron short, becomes a P-type (Positive Type) semiconductor. When these N-type and P-type semiconductors are joined, electricity is generated as electrons move across the junction. If we connect the two semiconductors with a metal that has high electrical conductivity and allow the electrons to move through that wire, we can generate a flow of electrons—that is, an electric current.
However, the single excess electron in the N-type semiconductor does not easily move to the P-type semiconductor. This is because a minimum amount of energy is required for the electron to jump out of the N-type semiconductor “apartment” and move to the P-type semiconductor. This minimum energy can be obtained from light energy with a threshold frequency. Light energy increases in proportion to frequency, and the minimum frequency of light capable of causing an electron to jump out of a metal is called the threshold frequency. Since sunlight provides the energy that allows electrons to move in a cell formed by joining an N-type semiconductor and a P-type semiconductor, it is called a solar cell. This phenomenon, in which electrons absorb energy and are ejected due to collisions with photons—particles of light containing energy—is known as the photoelectric effect. Photons act as “helpers” that enable electrons to “jump out” of their “apartments.” In a solar cell, these photons—the “helpers” in sunlight—transfer the energy needed for electrons in the N-type semiconductor to jump out of their “apartments.” However, sunlight consists of a mixture of various types of light, comprising the infrared, visible, and ultraviolet regions. Among these, the visible and ultraviolet regions—which contain photons with frequencies exceeding a specific threshold known as the cutoff frequency—are the components of light that trigger the photoelectric effect in solar cells.
To summarize the principle of solar cells mentioned above: when an N-type semiconductor is exposed to sunlight, photons from the portions of sunlight with frequencies above a certain threshold drive the excess electrons in the N-type semiconductor toward the P-type semiconductor, thereby generating an electric current. The efficiency of solar cells developed to date is around 10–20%. Yet, they are not cheap either. Even if only to delay global warming, it is worth further researching solar cell technology, which is often all hype and no substance. Global warming is a challenge we must all address.
However, in addition to solar energy, we can reduce carbon dioxide emissions through small changes in our daily lives. For example, small actions such as using public transportation, using energy-efficient appliances, and thoroughly recycling can add up to bring about significant change. Furthermore, it is crucial for the government and businesses to collaborate in actively promoting eco-friendly policies and increasing investment in renewable energy. I hope that our collective efforts will ensure we can pass on a beautiful Earth to future generations.
While global warming is a complex and multifaceted issue, the key to its solution lies in all of our hands. It is time to take action right now for a sustainable future.
