Shiza Charania, Pavi Dhiman, Anya Singh
Climate change and fossil fuel usage have been all the talk over the past few decades, but especially now, as we see the impacts overtake our personal human needs, overcoming climate change is our only option. One of the main contributors to climate change is the global usage of fossil fuels and energy sources releasing toxins into our atmosphere. So, we look towards renewable energy. From wind to geothermal, many hold promise, but solar energy has surged like none other. However, there have been limitations to the wide-scale implementation of solar, specifically due to its lack of efficiency.
Globally, the average efficiency of household solar panels is only 15-22% efficient due to their design configuration and lack of direct sun-ray acceptance.
Keep in mind, that with new advancements in the field such as photovoltaic cells and improved grid systems, the solar industry has reached an efficiency of 22%. This continues to be the overarching issue of global usage and the entrance of solar power into the residential market.
Solar panels are made up of photovoltaic cells, and it is these cells that convert solar energy in the form of sunlight into usable electricity.
Therefore, a panel’s efficiency is the percentage of energy hitting the panels that the photovoltaic cells actually convert into electricity. Not all solar panels are created equal, and the material and structure of a model determine its efficiency (and price).
The first, unbreakable, upper limit is the thermodynamic efficiency limit, which is 86%. This comes from the fact that every time you transform energy from one source to another (e.g. photons to electricity) you lose some in the process.
The second limit is called the Shockley-Queisser limit, and it is around 30%.
Solar panels are made of semiconductors (silicon, perovskites, gallium arsenide). All these materials have some “allowed” energies for the electrons inside.
The crucial property of semiconductors is that there is a “gap” between the occupied and unoccupied seats.
In order to excite an electron, it must be given enough energy to occupy a seat with higher energy. When this happens, the charge can be effectively collected and used. The problem is: the electron can’t be given energy less than the gap, which simply won’t be absorbed.
The light coming from the Sun comes with different frequencies, just like the colours you know. It goes from infrared (low energy) to red, green, blue, violet, and ultraviolet (high energy). The ensemble of frequencies is called the solar spectrum, which has a peak around the green and decays for lower and higher frequencies.
