This blog post explores how solar energy can address climate change, focusing on its principles, limitations, and various ways we can implement it.
In Korea, spring and autumn are becoming progressively shorter. Cherry blossom season arrives earlier each 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 annually. We suffer increasingly intense heatwaves and cold snaps. This isn’t merely a matter of cold and heat. If this continues, Korea will eventually transition into a subtropical climate. For future generations, the ‘Republic of Korea, a country with distinct four seasons’ will become a distant memory. We must delay global warming, the primary culprit behind these abnormal climates, as soon as possible.
One method to reduce carbon dioxide emissions, the cause of global warming, is ‘Photovoltaic Energy’. We can generate electricity from the sun, that ever-present light bulb orbiting our planet. So, how exactly can we create electricity from sunlight? First, let’s understand a few basic concepts to grasp photovoltaic energy.
‘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 ‘photovoltaic energy’ interchangeably. However, photovoltaic energy is a broader concept than just solar cells. Photovoltaic energy simply means using sunlight to convert it into other forms of energy for use. Solar cells are one technology that utilizes solar energy. The converted energy is essentially electrical energy. The process of generating electricity in a solar cell is explained by semiconductor principles and the photoelectric effect. Let’s briefly examine this below.
Among the elements composing our Earth’s crust, the most abundant is oxygen, followed by silicon (Si). Silicon is the primary component of soil, sand, and rocks commonly found around us. Silicon, which is unlikely to be depleted, is widely used as the main material for semiconductors due to its material properties. All elements, including silicon, consist of an atomic nucleus made of neutrons and protons, and electrons orbiting around it. The electrons build their own apartments around the nucleus and reside there. These apartments are called electron shells. The first floor of the apartment is very cramped, accommodating a maximum of two electrons, while the second floor and above can hold up to eight electrons. The electrons residing on the top floor of the apartment are the valence electrons. Except for hydrogen and helium, all elements prefer a state where their outermost shell is completely filled with eight electrons. The reason is that electrons that have lost their family tend to easily break away. Silicon, which has fourteen electrons, satisfies two in the first-floor shell and eight in the second-floor shell, leaving four outermost electrons. To resolve its instability from lacking four electrons, silicon bonds with neighboring silicon atoms. They share their four valence electrons to form a bond. This type of bond is called a covalent bond, and the silicon atoms form a covalent crystal, behaving as if they each had eight valence electrons.
What happens if phosphorus (P), which has five valence electrons, is forced into this stable silicon network? Phosphorus sacrifices one of its valence electrons to form covalent bonds with the silicon atoms. This single donated electron transforms the silicon crystal into a n-type (negative type) semiconductor. Conversely, forcing boron (B), which has three valence electrons, into the silicon crystal causes the boron to behave as if it has seven valence electrons. The silicon crystal, now relatively deficient by one electron, becomes a P-type (Positive Type) semiconductor. When these N-type and P-type semiconductors are joined, electricity is generated as electrons move at the junction. Connecting the electron movement between the two semiconductors with a highly conductive metal wire allows the electrons to flow through it, generating an electric current.
However, the single excess electron in the N-type semiconductor finds it difficult to move into the P-type semiconductor. This is because a minimum force is required for the electron to jump out of the N-type semiconductor “apartment” to reach the P-type semiconductor. This minimum force can be obtained from light energy possessing a threshold frequency. Light energy increases proportionally to frequency, and the minimum frequency of light capable of ejecting electrons from a metal is called the threshold frequency. In a cell formed by joining an N-type semiconductor and a P-type semiconductor, sunlight provides the force enabling electron movement, hence the term “solar cell.” This phenomenon, where electrons absorb energy and are ejected due to collision with light particles—photons—carrying light energy, is precisely the photoelectric effect. The photon acts as the helper enabling the electron to jump out of the apartment. In a solar cell, the photon, the helper within sunlight, delivers the force needed for the electron in the N-type semiconductor to jump out of the apartment. However, sunlight is a mixture of various types of light, composed of infrared, visible, and ultraviolet regions. Among these, the visible and ultraviolet regions—which have frequencies above a specific threshold called the cutoff frequency—are the light components that cause the photoelectric effect in solar cells.
To summarize the principle of solar cells mentioned above: when an N-type semiconductor receives sunlight, photons within the sunlight’s spectrum possessing frequencies above a specific threshold cause the excess electrons in the N-type semiconductor to move to the P-type semiconductor, generating an electric current. The efficiency of solar cells developed to date is around 10-20%. They are also not cheap. Even if only to delay global warming, solar cell technology—though currently a flash in the pan—is worth further research. Global warming is a challenge we all must tackle.
However, beyond solar energy, we can reduce carbon dioxide emissions through small daily changes. For instance, using public transportation, choosing energy-efficient appliances, and practicing thorough recycling—these small actions can collectively bring significant change. Furthermore, it is crucial for governments and businesses to collaborate in actively promoting eco-friendly policies and increasing investment in renewable energy. May our small efforts combine to leave a beautiful Earth for future generations.
The problem of global warming is complex and multidimensional, but the key to its solution lies in all of our hands. It is time to take action now for a sustainable future.
