Solar power could be the world’s answer to finding a sustainable energy source. Millions across the world already have solar cells mounted on their homes or use solar power to charge their devices. So, how do they work?
Solar cells are electronic devices that can take sunlight and turn it into energy. Hundreds or thousands of individual solar cells make up each solar panel, each cell being about the size of your palm. The individual solar cells in a solar panel can be thought of like cells of a battery. Each one is designed to generate power all on its own with the collective sum being output through the solar panel.
Battery cells use electrical energy from chemical reactions but solar cells generate electricity from sunlight. Sunlight contains photons, as does all light. Most solar cells today are made out of silicon, which is used as the catching and converting mechanism in the flow of photons to electrons. As the photons are received from the sun through sunlight, they blast electrons out of the silicon. These electrons then flow together to create a current – electricity.
This is a rather simple explanation of how solar cells work. To understand them further, we need to get deeper into the science behind them.
Silicon, as a material, functions as a semiconductor. This means that normally electricity could not flow through silicon but under certain circumstances, it does. In the manufacturing process of solar cells, engineers dope the silicon with electrons. This changes the way they allow electricity to flow through them, making it possible for current to flow through silicon sheets in a specific way.
Two silicon sheets are sandwiched together in solar cells after being doped. The lower layer is doped in a way that resulted in a net loss of electrons, meaning it has too few. The top layer of silicon is doped with too many electrons. The bottom layer is referred to as the positive layer because electrons are negative and it has too few – positive. Having too many electrons in the top layer makes it the negative layer. In more scientific terms, the bottom is called positive-type (p-type) silicon and the top is called negative-type (n-type) silicon.
Naturally, electrons from the negative layer want to flow to the positive (more to less), but a barrier in between makes that impossible under regular circumstances. It is only when light or solar energy is introduced that this becomes possible. The photons from the sunlight act as activation energy for the flow of electrons in the silicon sandwich (solar cell).
Between the two layers of silicon is something called the depletion zone, which keeps the normal transfer of electrons between the two layers from occurring. This is where electrons from the n-type side move to the p-type side to fill holes, or lack of electrons. The transfer of electrons in this depletion zone creates positively charged ions in the n-type layer and negatively charged ions in the p-type. The presence of these oppositely charged ions creates an electric field, which has enough power to keep electrons from the n-type from continuing to transfer to the p-type silicon.
When sunlight hits a solar cell, it knocks electrons out of the silicon through photon collisions. This leaves holes for other electrons to fill and an imbalance in the electrical field of the depletion zone. Electrons begin to move from the n-type layer to the p-type layer due to the imbalance. In solar cells, a metallic wire is embedded between these layers to capture the flow of electrons, creating a flow of electricity.
Just like that, with some interesting science, engineers have been able to create electricity from sunlight.