‘PERC’ stands for ‘Passivated Emitter and Rear Contact’ – which is an indicator of how these solar panels work. Unless you work in the solar industry or take a keen interest in solar tech, those words don’t mean a great deal.
Basically, PERC Solar panels have greater efficiency than standard PV panels due to the design of the solar cells inside them.
Firstly let’s explore how standard solar panels work.
How do standard PV solar panels work?
Inside a PV Solar Panels are a number of cells made from silicon, wire and glass – this is where the magic happens.
Silicon is the second most abundant element on the planet and, when purified, it behaves in a very strange way if it is hit by light.
The particles of light that the sun bombards the earth with are called Photons.
When these photons hit a PV cell, they ‘excite’ the molecules within the silicon causing the negative electrons to move to a positive place.
This generates electricity which is then carried along the wires and to your home.
Solar panel efficiency
These are the standard panel types you find on homes, businesses and solar farms.
Monocrystalline: In which each silicon cell is a single crystal, giving an efficiency of 20 – 24%.
Polycrystalline: Where the silicon cell is made of a lot of crystals all squished together, giving an efficiency of 15 – 19%.
PERC panels: The clever design increases efficiency by around 1% which will generate 5% more electricity.
How do solar panels lose efficiency?
Modern solar panels have an efficiency rate of 20%.
This may sound like a small amount but other generation techniques like coal, gas and oil are hitting 42%, 52% and 45% respectively while spewing out pollutants.
Over the life time of a solar panel it will be subject to degradation rates of 0.3 – 0.5% with most older panels degrading at around 0.5%.
This means, at the end of 25 years, most panels will have dropped to 80% of their original efficiency.
There are 2 types of degradation that affect silicon PV cells.
Light-Induced Degradation (LID)
This is a bit technical.
LID, also known as UVID (UV light-induced degradation), is a chemical process within the PREC cells caused by the sunlight hitting the cells.
Heat from the light causes the free 02 radicals from the silicon lattice to form boron dioxide- which degrades the cell and lowers efficiency.
Told you it was a bit technical … and there’s more!
Potential – Induced Degradation (PID)
Like LID, PID degrades the cell.
This time it’s stray current between the solar cells and the capsule frame that causes the problem.
I won’t go into it as it involves things like ‘polarisation of the Al2O3 layer‘ and other techno jargon.
Suffice to say, manufacturers are working on mitigating these problems and they don’t really affect the panels in the first 25 years of their life.
How PERC panels are different?
PERC Solar panels are different as the boffins in the solar labs have added a few bits and bobs to the cell to make it more efficient.
In a ‘normal’ PV cell the back of the cell is covered will a layer of aluminium but in a PERC cell, that is replaced with a dielectric passivation layer, dielectrically displaced mirror and individual aluminium contacts.
Dielectric passivation layer
This is an outer layer of shield material that is applied as a micro-coating, created by a chemical reaction with the base material, or allowed to build by spontaneous oxidation in the air.
Dielectrically displaced mirror
A mirror made from multiple thin layers of dielectric material, typically deposited on a substrate of glass or some other optical material.
Individual aluminium contacts
These are individual aluminium contacts! They help ‘move’ the electricity.
A Dielectric is an insulating material or a very poor conductor of electricity.
How does this help PERC solar cell efficiency?
In 3, very clever, ways.
The Dielectric passivation layer keeps the electrons flowing instead of finding a handy atom to attach themselves to – this means the voltage remains higher for longer.
This layer also tends to absorb less heat than the backing of a ‘normal’ PV cell, keeping the cell cooler and giving the panel a higher efficiency.
The dielectrically displaced mirror surface reflects unabsorbed light back into the cell, creating more internal reactions and, therefore, more electricity.
Types of PERC solar modules
Don’t be fooled by the PERC title when it comes to the type of panel you are buying.
Although it says PERC on the box, it could be one of two different variations.
Polycrystalline PERC Solar Panels
Polycrystalline PV cells are made using silicon formed from many crystals all crushed together.
The fact that the crystals aren’t separate means the manufacturing process is much quicker and easier than that of mono panels.
While this means they are not as efficient as they could be, they are cheaper and are an excellent choice if you have plenty of room for an installation.
The PERC Technology increases the efficiency, and the cost, of polycrystalline panels, so they are not as popular as MONO-Perc panels.
Monocrystalline PERC Solar Panels.
As we mentioned earlier, the Monocrystalline PV cells are made from a single crystal of pure silicon, which gives the panels a cool black hue.
Monocrystalline panels are much more efficient than polycrystalline models, but they do cost more due to the way the single crystals are made.
Adding PREC technology to a monocrystalline panel increases its efficiency even more.
Although that increase is only 1 or 2 percent, it means a 5% increase in electricity generation.
Advantages of PERC Solar Panels
This is the main reason behind PERC tech, so it has to be the first advantage.
PERC panels are 1% more efficient than traditional panels.
As we said before that may not seem much, but when you consider that sun potentially generates 1380W per square meter, it’s a lot of power. 5% in fact.
You need fewer solar panels when using PERC
More efficiency means fewer panels per square meter to get the job done. That means they are perfect for domestic solar installations where the panels are mounted on the roof.
PERC Panels are good in extremes
Strangely, solar panels don’t usually work as well in extreme heat, as the hotter a panel gets the more resistant it becomes.
PERC panels reflect a lot of the light energy back into the solar cell instead of converting it to heat.
This keeps the panel cooler so it doesn’t lose efficiency as fast.
PERC panels also capture more of the light spectrum, so they work well in low light.
Disadvantages of PERC Solar Panels
The construction of a PERC cell is much more involved than that of a normal solar cell so this will, obviously, increase the cost of labour and materials.
That cost is absorbed by the savings made by generating more electricity, but it does make the initial outlay a bit more painful.
PREC panels are not the ‘norm’ yet, so they aren’t always available to the consumer.
That said, they are becoming much more popular, so prices will come down and availability will increase.
So, what do PERC Solar Panels cost?
You’ll be paying around 25% extra for your PERC panels.
We’ve seen PERC panels for as much as £250 for 400W, 20.1% efficiency and a similar size to standard roof mounted panels.
At the moment we’d say it’s worth getting PERC panels if you can afford it but the tech hasn’t quite caught up with the market, so standard monocrystalline panels are still your best bet.