In order to understand solar power and how it works, it’s important to first understand a few essential terms. These include:
This is the general term used when referring to any type of solar cell. The most common types of photovoltaic solar cells are:
- Solar Cells
- Silicon Cells
- Photo diodes
- Polycrystalline Cells
- Monocrystalline Cells
These are just a few examples of what are available. While there are many solar cells types, let’s take a look at their general functions.
These are the most common type of photovoltaic solar cells and are available in a variety of forms. However, they all work on the same basic principle. A silicon cell consists of a piece of silicon that has been processed to create electrical current when exposed to light. Although similar in function to other types of solar cells, the silicon in a silicon cell allows for more precise control of the electrical current produced. This makes it better suited for use in devices that require high levels of efficiency. Silicon cells are commonly used in situations where high levels of energy are needed but direct sunlight isn’t available, or when extra electrical current can be used for special purposes (like powering an appliance or a laser printer).
A photo diode is simply a device that conducts when exposed to light and becomes an insulator when exposed to darkness. This is in contrast to regular diodes, which only conduct when exposed to both positive and negative voltages. Just like regular diodes, photo diodes are commonly used in situations where regular diodes would not be practical (like in a flashlight). However, one of the best things about photo diodes is that they can be very efficient when used in photovoltaic solar cells (up to 80% according to some sources). This makes them ideal for use in situations where a small amount of power is needed, but the power output must be as high as possible.
These are fairly common in portable electronic devices (like cell phones and personal digital assistants) and small-scale applications (like home appliances and small solar arrays). They are also commonly used in situations where a very high level of efficiency is required (like satellites and some types of space equipment). However, the most common type of polycrystalline cell is the amorphous silicon cell (or “a-Si” cell for short). This is due to its ease of manufacturing and the fact that it has a very high efficiency rating (up to 19% according to some sources). Even though they are less efficient than monocrystalline or single-crystal cells, the amorphous silicon cell is still very efficient when compared to conventional technologies (like gasoline or coal-fired power plants). Furthermore, as the name suggests, it is very polycrystalline, making it ideal for use in situations where a large amount of power is required (like on a space station or in a dam). In terms of cost, polycrystalline cells are generally more affordable than other types of solar cells (especially when considering the high efficiency ratings that many of them have).
This is generally the most expensive type of photovoltaic cell, but it is also the most efficient. It is made of a single crystal of silicon (rather than polycrystalline or amorphous silicon) and as a result, it creates more precise electrical current. This makes it better suited for use in situations where a small amount of power is required (like in a flashlight or a wristwatch). It is also popularly used in situations where a high degree of efficiency is required (like in a data center or on a space station). Some sources even say that monocrystalline cells are essential for deep space exploration due to their high efficiency and reliability.
Basic Structure of Photovoltaic Cells
All of these different types of solar cells are based on the same general concept, but they are still fairly different in their internal structure. This is because each type has its unique advantages and disadvantages. The most basic structure of a photovoltaic cell is shown in the following figure (taken from Fundamentals of Solar Energy):
As you can see, the cell consists of a junction between two metal contacts. This junction is where the photovoltaic material comes in. When light hits the cell, it can either pass through the junction directly or be reflected off of it. In the latter case, the light is absorbed by the photovoltaic material and some of it converted to electrical energy. The metal contacts are then connected to the external circuit (like in a battery or a load) so that electricity can be generated or used as needed.
The type and amount of photovoltaic material used will determine the output of the cell. In general, the thicker the layer of material, the higher the efficiency will be (up to a point). However, too much of it and the cell will become less efficient. The general rule of thumb is that for every watt of power you need, put in half a watt of PV material (if your cell is efficient at all). For example, if you have a small flashlight that requires 300 milliwatts of power, you would need a cell that can handle 900 milliwatts. This is assuming that no extra energy is lost in the process due to heat (which is usually the case and can be very difficult to avoid completely). For more information on this, take a look at our primer on solar power.