As was mentioned in the article “What is Solar Energy?”, photovoltaic technology is the process where semiconductive materials are used to absorb the sun’s radiant energy through a naturally occurring electronic process. I have spent some time doing the research and wanted to share my findings with you.
Before we get too deep into the photovoltaic technology, we should first start off with the sun and its light spectrum. As a kid, I used to love holding up prism crystals over pieces of paper to see the rainbow of colors as the sunlight passed through.
It seemed like the rainbow of colors were hidden in the sunlight. I found out later in high school that the light spectrum held so much more than just pretty colors.
Instead of going too far off track in the nerdy science of the light spectrum, remember that the sun’s light can be roughly broken down into three types of light:
- Visible Light – The light we all see and the main light used by photovoltaic technology.
- Infrared Light – This is the heat energy that you feel, but cannot see. This is the second most used by photovoltaic technology.
- Ultraviolet Light – This is most harmful to humans and the least used for photovoltaic technology.
Now that we have our SPF50 Sunscreen on, we are ready to head out into the bright, sunny day and create us some electricity.
What is a Semiconductor?
A semiconductor is a type of material that can absorb some energy and convert it to an electrical current, but not other types of energy. It is this ability of controlling the electricity that makes semiconductors useful in a wide variety of applications, including solar power.
In a way, humans could be considered as semiconductors because we take in an energy source (food) and our bodies absorb some of it while the rest simply passes right through and depending on what energy we take in, it is absorbed at different rates. We also produce electrical pulses throughout our bodies allowing us mobility….Oops, tangent over…
What Materials Are Commonly Used in a Photovoltaic Cell Semiconductor?
There are a variety of materials that are used as semiconductors for photovoltaic cells due to the type of energy it absorbs and the cost of the material. The most common type of semiconductor materials used are:
- Silicone (Si) – This is the most popular option in photovoltaic panels due in part to its abundance and lower cost of production. They have an efficiency between 14% – 20% depending on whether they are monocrystalline or polycrystalline in structure.
- Cadmium Telluride (CdTe) – This material has a high absorption rate, but has an issue related to the Cadmium which is a pollutant. They have an efficiency between 10% – 11%.
- Copper Indium Gallium Selenide (CIGS) – This material has an extremely high rate of absorption and while it contains some Cadmium, it is in small amounts. A disadvantage is the higher cost. They have an efficiency higher than 20% in laboratory testing.
- Gallium Arsenide (GaAs) – This material is costly to make due to the rarity of Gallium. It has a very high absorption rate and is not affected by heat making this material perfect for space applications. These solar panels are primarily used on satellites.
If you would like a more in-depth look at semiconductors, be sure to check out this article on What is a Semiconductor?
Monocrystalline vs. Polycrystalline
Since Silicone is the more widely used semiconductive material, here are the two main materials that make up the solar cells
Monocrystalline solar cells are the oldest of the semiconductive materials and tend to be a uniform color and nearly circular shape. This is due to the way the cells are created and they have been shown to be the more efficient of the materials. The main disadvantages of this type of solar cell is the higher cost than polycrystalline cells and the waste that occurs during the processing of the cells.
Polycrystalline solar cells have not been around as long and often have a blue hue to them due to the processing they go through during production. While polycrystalline solar cells are slightly less efficient than their monocrystalline counterparts, they are less expensive to produce and produce less waste during the process. As such, polycrystalline solar cells have become the predominant solar choice in the industry.
To learn more about the differences between monocrystalline and polycrystalline solar cells, check out this article on energysage.
How does Photovoltaic Technology Work?
As the sunlight hits the photovoltaic cell, the semiconductor material it is made of either reflects light, absorbs the light or it just lets the light pass through. The light that is absorbed ionizes the semiconductor material causing the electrons to become more energized and it is in this state that the electrons are freed and forced to move in a single direction through the semiconductive material as a current towards a positively charged junction. This is referred to as the photovoltaic effect.
You might think to yourself that this is fantastic that we can take one of these solar cells and capture the energy of the sun to power our homes forever, right? Unfortunately that is not how it will work. A single photovoltaic cell is not enough to even charge your phone because even though it captures sunlight and converts it into electricity, it is not 100% efficient at it or large enough to produce that amount of electricity.
For this reason you will find that photovoltaic cells are attached together to form a panel in order to push the power output of the solar panel higher. It is through this increased power of cells that we are able to generate any substantial electricity. If you take a look at some of the small solar powered phone chargers you will see that they typically have multiple photovoltaic cells just like their larger panel cousins.
For more information about photovoltaic cells, check out the article called “Photovoltaic Cell”
Series vs. Parallel Photovoltaic Panels
When it comes to the setup of the photovoltaic technology solar panels, you will find that they will typically be wired in either series or parallel. The question then becomes which one is the best to have? Let’s take a look at the advantages and disadvantages of each:
By connecting your panels in series, you increase the voltage output without increasing the amperage.
Advantage: You can transfer that voltage over long distances to the source of charging or storage.
Disadvantage: Shade from the sun really impacts the power output.
By connecting your panels in parallel, you are increasing the amperage while maintaining a steady voltage.
Advantage: You are able to maintain a steady volt charge on your system and shading does not impact the power output as drastically as series panels.
Disadvantage: High amperage cannot travel long distances without using very large wires so it needs to be close to the charging or storage device.
Which One is Right for You?
The answer is that it depends on a few factors that you need to take into consideration. Your decision on a solar system will come down to personal preferences, space, and financing.
- Personal Preferences – This could come down to something as simple as color preference since monocrystalline solar panels have a black tint and polycrystalline solar panels have a blue tint. This slight color variation changes how these look on your roof. Other preferences may center on where the solar panels were manufactured or the company who manufactured the panels.
- Space – Solar panels take up a lot of room when installed so the amount of free space you have is extremely important. Most solar systems are installed on the roof and with the finite space available, choosing higher efficiency solar panels would provide you the biggest bang for you buck.
- Financing – Solar is expensive and how you are planning to finance the system can be impacted. If you are looking at taking advantage of a Power Purchase Agreement (PPA) which has you paying per kilowatt-hour generated by your system then choosing a less expensive solar system is wise. If you are buying your system through other financing or in cash, then a high efficiency solar system will give you the best ROI.
Be sure to check out the other articles on this site and do thorough research on what you are looking for in a system before taking that leap.