The development of renewable energy technologies and solar energy, in particular, is revolutionizing the energy market. To reduce the impact of changing climate with the use of clean energy sources is the need of the hour. Solar energy is much developed renewable energy technology among others with large scale deployment in different parts of the world.
The intermittent generation of energy, either heat or electricity, is one hurdle that is usually substituted with energy storage technologies like batteries etc. Another hurdle in solar technology or solar photovoltaic (SPV) technology, in particular, is the efficiency of solar panels.
The electricity-generating solar panels are made up of metalloids like Silicon, Germanium, Tellurium and transition metals like Cadmium and Gallium etc. The metalloids and metals generate electricity when they are made impure or are doped with impurities like Boron and Phosphorous, etc. The main component of an SPV installation is the solar cell, which is connected in series and parallel to form a solar panel with a certain electricity generation output capacity.
It is the composition of the solar cell which defines the type of solar panel, in other words, what the solar cell is made up of defines the type of solar panel. These are monocrystalline silicon, polycrystalline silicon, amorphous silicon, thin-film silicon, Cadmium Telluride and many other types of solar panels . From these, monocrystalline and polycrystalline solar panels are most common.
Both these types of solar panels are made of silicon as the main component, but it is present in different crystalline forms. Monocrystalline solar cell is manufactured from single silicon crystal and polycrystalline from multiple silicon crystals. These solar panels differ in many aspects related to their manufacturing, efficiency, look and life, and we can review them one by one.
1. How Are They Manufactured?
The first step in manufacturing Mono and polycrystalline silicon solar cells is the same until the purification of silicon. Quartzite or Silica sand (SiO2) is used to extract out pure silicon. This is done by melting quartzite with carbon, distillation and zone refining. After getting pure silicon, the process of making mono and polycrystalline silicon differs.
For monocrystalline solar cells, the Czochralski process is used, in which a single silicon crystal seed rod is dipped in molten silicon and pulled up with heat and rotation to create an “ingot” of single-crystal silicon. This cylindrical ingot is sliced to 1 mm wafers and is doped with phosphorous or boron to form a p-n junction. These silicon wafers or cells are connected to form a panel.
For polycrystalline solar cells, the molten silicon is poured into square moulds to form cubic blocks. These cubic blocks are cut into wafers and doped with impurities to form solar cells. These polycrystalline solar cells are connected in series and parallel connections to form a solar panel.
2. How Do They Appear?
To a layman, all solar panels look the same, but there is a clear distinction between different types of solar panels. This difference is again because of the material used and their manufacturing process.
Monocrystalline solar panels have solar cells stacked to each other in the panel, with a diamond shape gap between each of them. These panels look black, as pure silicon cells reflect black colour after sunlight strikes them.
Polycrystalline solar panels have solar cells of square shape or rectangular shape with no gap between the cells. These panels give a blue hue in bright sunlight, with different shades of blue crystals when looked upon closely.
3. Which One Of The Two Is More Efficient?
Mono and polycrystalline solar panels are the most researched and developed of all the solar panels, and their efficiency is highest among other types of solar panels. Still, between the two of these solar panels, monocrystalline solar panels are more efficient because of the single silicon crystal structure.
The efficiency of monocrystalline solar panels is in the range of 15-20%, whereas the efficiency of polycrystalline solar panels is less and is in the range of 13-16% . For confined space scenarios, monocrystalline solar panels are chosen compared to polycrystalline solar panels.
4. Which One Of The Two Costs More?
The process to make a single silicon crystal cell with the Czochralski process is energy-intensive, time-consuming and silicon waste generating. This makes the mono-crystalline solar panel the costlier of the two, despite being more efficient.
The process of making polycrystalline solar cells and solar panels reduces 20% cost compared to making a monocrystalline solar panel. The use of less energy and generating less waste are the reasons for poly being much cheaper.
5. How Long Do They Last?
Monocrystalline solar panels degrade 0.3%-0.5% per year, and panel manufacturers give a warranty for 25 years. Still, these panels are seen working for more than 40 years with reduced output.
On the other hand, polycrystalline solar panels tend to degrade faster at 0.3%-1% with companies giving a 25-year warranty. These panels also tend to generate electricity for more than 25 years with reduced efficiency .
6. How Do They React To Heat?
Solar panels are meant to be out facing the sun, and they behave accordingly with temperature changes. In colder temperatures with good bright sunlight, solar panels are most efficient.
Of the two mono and polycrystalline solar panels, the latter is less efficient in higher temperatures and its efficiency of generating electricity is reduced. The temperature coefficient of monocrystalline solar panels is –0.3% to -0.4%, and that of polycrystalline is -0.5% per degree Celsius rise in temperature.
In the End
Both of these two types of solar panels are recyclable and around 90-95% of parts of these solar panels can be recycled. These Silicon solar panels are a choice of the masses where monocrystalline solar panels are more efficient, costly and with more lifespan. On the other hand, polycrystalline solar panels are less efficient but far cheaper and a common choice for large scale solar power plants. Each of these solar panels is used depending on the project specifications and economics designed for the same.