The Anatomy of a Photovoltaic Cell
Now that we’ve talked about what solar energy is, what it’s not and photovoltaics, we’re going to discuss the anatomy of a solar cell. These solar cells individually form a much greater structure that powers homes, commercial buildings and even larger industrial buildings. Sometimes we forget about the little guy – the lone cell that makes the entire system work.
Before we get into the composition of a solar cell, there’re a few terms you should know first: photon, diode, current, voltage and semiconductor. A photon is a beam of light – pretty simple, right? There’s a much more complicated description, but this simple explanation is all that’s necessary to understand a photovoltaic cell. These photons travel through a material known as a semiconductor in a current of electricity. An electric field causes a voltage as the electric current acts as a diode that pushes electrons from one side of a surface to the other side, and voltages are how we get power. When we get an electrical charge called a direct current, it enters an inverter that converts it into an alternating current that is fed through a utility panel. This is how light becomes power.
Most photovoltaic cells are made from sheets of silicon. Silicon is used because it’s an incredible semiconductor material. Electrons can very easily travel through it in a current to generate power. The problem is that silicon is extremely shiny, and when used as-is for photovoltaic cells, the photons would bounce right off the cell. To remedy this problem, each cell is sprayed with an anti-reflective coating to reduce the reflection loss to below 5%. A firm glass plate covers photovoltaic cells to prevent them from the elements or other damage.
A long-standing problem has been the efficiency of the photovoltaic cell. Some can absorb sunlight at 25%, but most absorb sunlight at 18% or less, but recently there’s been advances to efficiency that has allowed cells to absorb sunlight at over 40%.
There are three types of solar cells: amorphous, monocrystalline and polycrystalline. Small cells such as calculators usually employ amorphous technology. It’s made by depositing a thin film of silicon onto a material like steel. The cells are not as visible but the efficiency is much lower. They require up to three times the number of cells to output the same amount of energy as one crystalline cell, so an amorphous solar panel takes up much more space. It also has a shorter life-cycle, which means you get less for your investment. Mono-crystalline cells are made with a single ingot of crystal silicon that is cut into a thin wafer and shaped into a square. With poly cells, molten silicon is poured into a square shell. A multifaceted surface results from the differing rates of the crystal silicon drying in various areas of the square shell.
Solar cells are a fascinating modern technology that gets smaller and more efficient with every passing year. This means that even lower income family can enjoy the energy benefits and financial incentives that go along with adopting solar technology.