Francisco CastroJune 4, 20191210
Last week, solar panel manufacturing company Canadian Solar announced it had set a world record of 22.28% conversion efficiency for its p-type multi-crystalline P5 cell. At the same time, another company, Trina Solar, announced they had also set 24.58% efficiency record for its n-type mono-crystalline silicon (c-Si) i-TOPCon solar cell.
Conversion efficiency has to do with the ability of the solar cells to convert the sunlight hitting them into energy. While both companies are reaching higher levels of efficiency, they are doing it using different types of solar cells. Canadian Solar is focusing its research on p-type cells; Trina Solar on n-type.
The knowledge about solar cells - the basic unit of a home solar energy system - has been around since 1839 when French physicist Alexandre-Edmond Becquerel noticed that small electric currents were produced when the metal electrodes were exposed to light. But it wasn’t until April 1954 researchers at Bell Laboratories demonstrated the first practical silicon solar cell.
That first working solar cell was n-type, but in the six decades since that discovery, technological advances within the solar industries also gave us p-type solar cells.
While the average consumer looking to use photovoltaic (PV) modules to power their home may not be thinking about the differences between these two types of solar cells, worried more likely about how much do solar panels cost, solar panel output and aesthetics, it’s something you should know about when making the switch to solar.
So let us explain.
First, a solar cell is a crystalline silicon wafer covered with various chemicals to allow electricity generation. What differentiates n-type and p-type solar cells is the number of electrons. A p-type cell uses boron, which has one less electron than silicon (making the cell positively charged). An n-type solar cell includes phosphorus, which carries one more electron than silicon (making it negatively charged).
While the first silicon solar cell discovered at Bell Laboratories was an n-type, p-type cells have dominated the solar industry market for the last four decades.
The reason for this was the space race.
Turns out p-type solar cells proved to be more resistant to space radiation and degradation. And since so much research went on space-related solar technology, it trickled down into the residential market. Standard equipment can make a p-type solar cell up to 19% efficient, meaning most solar modules are 15% to 17% efficient today.
Most major Chinese solar manufacturers produce a combination of polycrystalline and monocrystalline p-type solar cells.
Pros and cons
Still, manufacturers are now using n-type cells because of certain advantages. One of them is that they are immune to boron-oxygen defects, which leads to decreased efficiency and purity in p-type ones. Thus, n-type cells turn out to be more efficient and are not affected by light-induced degradation (LID). This is a loss of performance in the very first hours of exposition to the sun, in the order of 1%-3% (or even more). This may not seem as much, but when you consider that the solar panels are now responsible for delivering a big chunk (if not all) of your home energy needs, it's a significant loss of electricity generating capacity.
However, electricity output on both n-type and p-type solar cells can be similar.
Also, cell efficiency is calculated by what is known as the fill factor (FF) which is the optimum conversion efficiency of the cell at a specific temperature. The cell design also plays a big role in efficiency such as the number of busbars and finger layout. And there’s also the issue of monocrystalline vs polycrystalline.
Monocrystalline solar cells are made out of silicon ingots, which are cylindrical in shape. They are characterized by uniformity and their black color. They carry several advantages.
Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon. Monocrystalline solar panels live the longest.
As such, monocrystalline solar panels are the most expensive. And if the solar panel is partially covered with shade, dirt or snow, the entire circuit can break down
The manufacturing of polycrystalline solar cells involves raw silicon is melted and poured into a square mold, which is cooled and cut into perfectly square wafers. This gives them a blue-hue.
The process used to make polycrystalline silicon is simpler and cost less, which makes solar panels from this material more affordable. Also, polycrystalline solar panels tend to have slightly lower heat tolerance than monocrystalline solar panels.
If all of this sounds like a lot of mumbo jumbo, just know that while most solar panels are currently p-type cells, some high-end solar panels use n-type cells to give them an edge in efficiency. And higher efficiency means higher price. But it also means more power per square foot, less modules, less space, lower hardware costs, and less labor.
Much research and development is being conducted on both types of solar cells; looking for ways to improve the efficiency of p-type solar cells and bring down the cost of manufacturing n-type solar cells. And neither of these technologies is going away anytime soon.
The International Technology Roadmap for Photovoltaic (ITRPV) predicts that the market share of p-type mono-c-Si will hold around 30% through 2028, while n-type mono-c-Si will increase to about 28% from barely 5% in 2017. This in response to the industry demand for more high-efficiency modules, so solar buyers can expect more n-type designs entering the mainstream, according to Solar Power World magazine.
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