How solar cells work
Posted by Solar energy guru | Filed under Solar panels & photovoltaic cells
Solar cells are the heart of any solar energy system. They are the actual device that converts sunlight into electricity. The production of solar cells has been in constant expansion over the past 30 years, and continues to make up and ever-increasing percentage of the world’s energy supply. Solar cells have been in existence for over 150 years, and throughout that time, there have been billions of dollars spent on refining their process and construction to make them more effective in collecting energy. Solar cells power thousands of different appliances, and are not likely to see a decline in usage anytime soon.
The process that allows sunlight to be converted into electricity is called the photovoltaic effect, and this field of study is called photovoltaics – “photo” means light, while “voltaic” means electric. The word is fairly explanatory of the function of the systems – they convert photons into electricity.
Light contains a number of photons and electrons, and the purpose of solar cells is to absorb both. The photons and electrons are then separated, and the separation of these particles is what creates electricity. When the sunlight reaches the solar cells, the photons are absorbed into their material (more on this later) and filtered out of the cell. This process does not create any detectable waste; the light is simply extinguished.
This works because of the composition of solar atoms, which allows electrons to be directed into a usable current. Once the electrons are separated from their atoms, they are attracted to the connecting wire, and they begin to flow towards whatever application you are using. This flowing of electrons is electricity, and it is drawn in by the electrical application you are trying to power. The solar cells then convert this energy into electricity we can use (direct current, or DC power). DC power is the type of electricity we all use in our households so once the solar cell has produced this power, the process is completed.
In order for solar cells to absorb light correctly, they first have to have a layer of material that absorbs light effectively. This is the surface of the solar panels that we see at the surface of any solar power system. The most common of these materials (called semiconductors) is silicon, which is usually what is used for the solar cells in everyday use. Silicon has a number of unique properties which make it ideal for common solar panels. In its pure form it is actually useless as an electric conductor.
It’s the corruption, or doping of pure silicon that allows it to be used as a conductor of electricity. In order to make the silicon ready to conduct electricity, it has to be split into two layers – a “p type” layer and an “n type” layer. The “p type” layer is usually mixed with trace amounts of boron, while the “n type” layer is doped with phosphorous. When the doping happens correctly, these two layers interact – the “n type” field absorbs the sunlight atoms and separates the electrons, which are attracted into the “p type” layer. From the “p type” layer, the electrons flow into some type of wire that holds the electricity.
When solar cells were first invented, they were only able to convert about 1% of the energy they absorbed into electricity. Today, solar cells are able to convert anywhere in between 5% and 15% of that energy. This is somewhat less than in most of the types of energy we use, but not by much. That said, if we can find ways to use solar energy more efficiently, it will make up a much larger percentage of our total supply than it does now.