What is a Solar Cell?
A solar cell, also known as a photovoltaic cell, is the name given to an energy capturing device. A solar cell absorbs sunlight and transforms it into electricity by way of the photovoltaic effect. The solar cell has evolved dramatically since its creation, and in the past few years particularly large strides have been made in solar cell technology.
A solar cell works, most simply, by absorbing sunlight. The photons from the light run into the solar cell and are absorbed by some sort of semiconducting material. Most contemporary solar cells are made out of silicon, although other substances are being experimented with as semiconductors to make solar cells more cost effective and environmentally friendly. Electrons are then freed from their host atom, and they move freely as electricity. From the solar cell this electricity then passes through a larger array, where it is turned into direct current (DC) electricity, which may then later be converted to alternating current (AC).
The photovoltaic effect was first presented in the early-19th century. In the 1880s the idea was put to practical use in the creation of the first solar cell, made with selenium as the semiconductor. The first solar cell was around 1% efficient, meaning that it managed to capture 1% of the total solar energy that hit the solar cell.
In 1954 Bell Labs discovered that silicon could be modified slightly to make it incredibly photo-sensitive. This led to the modern revolution in solar cells, with the early silicon cells operating at around 6% efficiency. In 1958, a satellite, the Vanguard 1, was launched with solar cells as a source of energy. This allowed the satellite to remain in geosynchronous orbit indefinitely, since it didn’t rely on a finite amount of fuel.
Through the 1970s and 1980s solar cell technology continued to improve. By 1988 solar cells were being mass produced that were capable of 17% efficiency. By the end of the 1980s solar cells of both gallium arsenide and silicon had surpassed 20% efficiency. In the late 1980s a new type of solar cell technology also appeared, using lenses to concentrate sunlight on to a single solar cell. This high energy density allowed for efficiencies of up to 37% at the time.
There are three main classifications of solar cells, referred to as generations because of when the technologies first appeared. A first generation solar cell is what most people think of when they think of solar cells. They account for around 90% of the solar cells in the world, and have a theoretical maximum efficiency of around 33%.
A second generation solar cell is designed to be substantially cheaper and easier to produce than a first generation solar cell. Using technologies such as electroplating and vapor deposition, second generation solar cells can be mass produced relatively cheaply. Second generation solar cells are usually just a thin film of some sort of material, such as amorphous silicon or cadmium telluride, applied in a very thin sheet to something like ceramics or glass.
Third generation solar cells take the technology of second generation cells and try to greatly improve their efficiency. These are the cutting edge technologies, trying new concentration methods, using extra heat to increase the voltage generated, and other technologies to work towards target efficiencies in the 30% to 60% range.
Written by Brendan McGuigan
