February 20, 2021
When it comes to solar panels, one of the most asked questions is which solar cell type is better: Monocrystalline or Polycrystalline?
Well, if you are looking for a detailed answer, then you came to just the right place.
In this article, we will do a full in-depth comparison between Monocrystalline and Polycrystalline solar panels including:
- How are they made?
- What do they look like?
- How efficient are they?
- How well do they react to heat?
- What is their expected lifespan?
- Are they recyclable?
- How expensive are they?
But first, let’s see how Solar PV works
Solar Photovoltaics (PV) is the direct conversion to electric current at the junction of two substances exposed to solar energy. It occurs through a process known as the Photovoltaic Effect which cause photons to be absorbed and electron discharge. Solar energy is composed of photons which are small packets of electromagnetic energy. Materials that exhibit this photovoltaic effect are known as PV or Solar cells.
Solar cells are composed of semiconductor materials, such as silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current — that is, electricity. This electricity can then be used to power a load, such as a light or a tool.
The first photovoltaic module was built by Bell Laboratories in 1954.
So, without further ado, let’s jump right into how solar panels are made.
- How are Monocrystalline Solar Panels Made
In 1918, the Polish scientist Jan Czochralski discovered a brilliant method for monocrystalline silicon production and called it the Czochralski Process, and later in 1941, the first cell was constructed.
The manufacture of monocrystalline solar cells contains 8 main steps and, in this section, we will quickly go through each one of them.
- Make Metallurgical Silicon
The main ingredient that makes monocrystalline solar panels is silicon also known as Silica sand, Quartzite, or SiO2.
The first step in manufacturing monocrystalline cells is to extract pure silicon from quartzite to make metallurgical silicon.
To make metallurgical silicon, special ovens are used to melt SiO2 and Carbon at temperatures of over 2,552 degrees Fahrenheit leaving behind 98% to 99% pure silicon.
Although the high purity of metallurgical silicon, it’s not pure enough to be used in PV panels.
Therefore, further purification needs to be done.
- Purify Metallurgical Silicon
The next step is to purify this metallurgical silicon using the Siemens process.
First, we expose the powder of metallurgical silicon Si in a reactor with HCl at elevated temperatures resulting in SiHCl3 gas.
The gas is then cooled and liquefied for distillation.
Distillation is the process of evaporating then condensing the liquid to get rid of unwanted impurities.
For instance, you can boil seawater (salted water), then condense the vapor to get pure water, as the salt will remain at the bottom of the pot.
Using the same concept, the liquified SiHCl3 is heated then cooled to remove impurities with higher and lower boiling points such as Calcium and Aluminum.
After distillation, the liquefied SiHCl3 is moved to a different insulated reactor with a hot rod, then mixed with Hydrogen gas and vaporized again at a temperature of up to 2732 degrees Fahrenheit.
Due to the heat and the presence of H2 gas, the Cl atoms will dissolve leaving around 99.9999% pure silicon behind.
- Creating Silicon Ingots
What differs monocrystalline cells from polycrystalline cells is that monocrystalline panels are made of a single pure silicon ingot.
Making a single pure silicon ingot was really hard until Czochralski discovered this brilliant way.
First, you dip a seed crystal, which is a small rod of pure single crystal silicon into the molten silicon.
After dipping the rod, now it’s time to slowly pull and rotate the seed crystal upward at the same time to minimize the effect of convection in the melt.
As the seed crystal is pulled up, the liquid silicon will slowly solidify over 4 days creating a big homogeneous cylindrical single crystal silicon also known as silicon ingot.
The size of the silicon ingot depends on 3 factors: temperature gradient, cooling rate, and rotation speed.
- Creating Silicon Wafers
So far you have a huge single crystal silicon ingot, but how can you make solar panels of it?
Well, the answer is very simple, wire saw.
The third step is to slice the silicon ingot into very thin slices using a very sharp wire saw creating 1 mm or 0.0393 inches silicon wafers.
After cutting the wafers, it’s about time to polish and wash the wafers to clean it from dust, dirt, and scratches.
- Improving the Wafers
Because the wafer surface is very flat, many light rays are reflected away, and obviously, you don’t want that, as it will decrease the efficiency of the solar panel.
For this reason, manufacturers roughen and etch the wafers’ surface, so the light can refract multiple times, which improves the panel’s efficiency and prevents light reflection as much as possible.
Silicon wafers are positively charged. In other words, they act as a p-type material.
To conduct electricity you need a p-n junction and in order to create a p-n junction, a negatively charged layer of phosphorus is added to each wafer, then wafers are moved to special 1652 degrees Fahrenheit ovens to inject the phosphorus with nitrogen.
The mixture of nitrogen and phosphorus creates a powerful n-type layer resulting in a very effective p-n junction wafer, which of course will increase the efficiency of the panel.
- Improve Conductivity
In order to decrease electricity loss, a highly-conductive silver alloy is pressed onto the wafer front, which ensures the power is perfectly transported and improves the monocrystalline cell conductivity even further.
Finally, the last step in building monocrystalline panels is assembling.
Each monocrystalline solar panel is made of 32 to 96 pure crystal wafers assembled in rows and columns.
The number of cells in each panel determines the total power output of the cell.
- How are Polycrystalline Solar Panels Made?
Polycrystalline also known as multi-crystalline or many-crystal solar panels are also made from pure silicon.
However, unlike monocrystalline, they are made from many different silicon fragments instead of a single pure ingot.
The difference between mono and poly solar cell production is that, after purifying the silicon, instead of pulling the ingot slowly to make a homogeneous cylindrical crystal (Czochralski Process), the molten silicon is left to cool and fragment.
These fragments are then melted in ovens and poured into cubic-shaped growth crucibles.
After the molten silicon solidifies, the ingots are cut into thin wafers, then polished, improved, diffused, and assembled just like monocrystalline panels.
B. Monocrystalline vs Polycrystalline Solar Panels Appearance
- What Do Monocrystalline Panels Look Like?
Because the pure silicon ingot is round, slicing them will result in square wafers with rounded edges, which creates small gaps between the cells once assembled.
And due to the fact that they are made of pure silicon, they appear with a uniform dark look because of how light interacts with pure silicon.
Therefore, you can easily recognize the monocrystalline solar cells by their uniform dark appearance and the rounded edges squares with small spaces between each cell.
ٍDon’t worry, although the monocrystalline solar cell is dark, there are plenty of colors and designs for the back sheets and frames that will meet your preferences.
- What Do Polycrystalline Solar Panels Look Like?
Unlike the uniform dark look the monocrystalline solar cells have, polycrystalline cells tend to have a blue hue because of how sunlight interacts with the multi-crystalline.
Moreover, because polycrystalline wafers aren’t cut from cylinders like the monocrystalline ones, they won’t have rounded edges.
Thus, you can easily recognize them by the bluish hue and the absence of rounded edges.
Polycrystalline cells also have plenty of colorful back sheets and frame designs that will definitely suit your roof.
C. Monocrystalline vs Polycrystalline Solar Panels Efficiency
The solar panel efficiency is an indicator of how good the cell is in converting sunlight into electricity.
For example, if we brought 2 different solar panels, one with an efficiency of 10% and the other with 20% and we shine the same amount of light for the same duration.
The latter will produce almost double the electricity generated by the first one.
- How Efficient are Monocrystalline Solar Panels?
Among different solar panel types, monocrystalline cells have the highest efficiency typically in the 15-20% range and it’s expected to get even higher.
Fun fact: In 2019, the National Renewable Energy Laboratory managed to develop a six-junction solar cell with an efficiency of 47.1% setting 2 new world records.
- How Efficient are Polycrystalline Solar Panels?
Because each polycrystalline cell is made of too many crystals, there is less room for electrons to move resulting in a lower electricity generation efficiency.
Although monocrystalline have higher efficiency rates, the difference between mono and polycrystalline cells isn’t that big.
Most polycrystalline PV cells have efficiencies between 13% to 16%, which is still a very good ratio and it’s expected to get only higher in the future.
D. Mono-Si vs Poly-Si Temperature Coefficient?
Another great factor that is greatly overlooked is the temperature coefficient.
The temperature coefficient is a measurement of how well the solar cell functions when the temperature rises.
In other words, it indicated the efficiency loss for every degree the temperature rises.
- How Temperature Affects Monocrystalline Solar Panels Efficiency?
Most monocrystalline solar cells have a temperature coefficient of around -0.3% / C to -0.5% / C.
So when the temperature rises 1 degree Celsius or 32 degrees Fahrenheit, the monocrystalline solar cell will temporarily lose 0.3% to 0.5% of its efficiency.
- How Temperature Affects Polycrystalline Solar Panels Efficiency?
Polycrystalline PV cells have a higher temperature coefficient than the monocrystalline ones.
This means that polycrystalline panels will lose more of their efficiency when the temperature rises making them not optimal to be used in hot areas.
E. Expected Lifespan
The lifespan of the solar cell is indicated by the degradation rate or the yearly energy production loss.
Most solar panels have a degradation rate of 0.3% to 1%.
Meaning that every year, the total power output of your system will decrease by 0.3% to 1%.
- How Long Do Monocrystalline Solar Panels Last?
Most monocrystalline PV panels have a yearly efficiency loss of 0.3% to 0.8%.
Let’s assume we have a monocrystalline solar panel with a degradation rate of 0.5%.
In 10 years, the system will operate at 95% efficiency, in 20 years, the system will operate at 90% efficiency, and so on till it loses a significant amount of its energy production capability that it becomes inefficient.
Most monocrystalline solar panels come with 25 or 30 years warranties. However, you can expect your system to last for up to 40 years or more.
- How Long Do Polycrystalline Solar Panels Last?
Polycrystalline PV cells have a slightly higher degradation rate than, which causes them to lose their efficiency a little faster than the monocrystalline ones.
Don’t get me wrong, they still have a lifespan of 20-35 years and sometimes even more.
- Are Monocrystalline Solar Panels Recyclable?
The short answer is yes, monocrystalline solar cells can be recycled.
Monocrystalline solar panels are made of 3 main components:
- Monocrystalline cells: Around 85% of the silicon wafers are recycled
- Glass: Almost 95% of the glass can be reused
- Metal: 100% of the metal parts are recyclable
2. Are Polycrystalline Solar Panels Recyclable?
Similar to monocrystalline, around 90% of all the material used to manufacture polycrystalline cells are recyclable.
And by the year 2030, it’s expected that almost 45 million new modules will be made using recycled materials, which is equivalent to 380 million USD.
- How Expensive are Mono-Si Solar Panels?
Monocrystalline solar panels have numerous advantages but one of their main disadvantages is the high initial cost.
Among all types of PV solar panels types, monocrystalline is definitely the most expensive one to produce.
This is due to the fact that the process of manufacturing monocrystalline solar cells is very energy-intensive and produces a big amount of silicon waste.
- How Expensive are Polycrystalline Solar Panels?
Compared to their efficiency, polycrystalline solar panels have less cost per watt making them cheaper than the monocrystalline type.
The reason for this is that the manufacturing process creates less waste and uses less energy resulting in less production costs.
Fun fact: Sometimes poly-Si panels are made from the left-over pieces of mono-Si production, which reduces the amount of silicon waste.
It’s important to mention that although poly-Si cells are cheaper, they occupy more space than monocrystalline to generate the same amount of energy making them less space-efficient.
Monocrystalline vs Polycrystalline Solar Panels
|Monocrystalline Solar Panels||Polycrystalline Solar Panels|
|Material:||Single Pure Silicon Crystal||Different Silicon Fragments Molten Together|
|Appearance:||Uniform dark squares with rounded edges||Blue squares with no rounded edge|
|Conversion Efficiency:||15% to 20%||13% to 16%|
|Space Efficiency:||Efficient||Less Efficient|
|Temperature Coefficient:||-0.3% / c to -0.5% / c||-0.3% / c to -1% / c|
|Lifespan:||Around 40 years||Around 35 years|
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