Tutorial Manthra

There are a lot of different types of solar panels are there in the market. Solar manufacturing has branched into a wide range of cell technologies. It can be confusing which type of solar panel you should buy for your solar project. Here in this article will list some of the major solar technologies and the differences between them.

The first set of terms describes how solar cells are formed out of raw materials.

Monocrystalline vs. Polycrystalline vs. Thin-Film Solar Panels

Traditional solar cells are made from silicon, a conductive material because they are widely available. The manufacturer shapes raw silicon wafers into uniformly-sized silicon cells.

Almost 90% of PV technology is based on Silicon which is mostly used in crystalline silicon solar panels. Solar cells can either be monocrystalline (cut from a single silicon source) or polycrystalline (from multiple sources). Let’s look at the differences between the two options

Monocrystalline Solar Panels

Monocrystalline solar panels also called as single crystalline silicon contain cells that are cut from a single crystalline silicon ingot. “Mono” as you know means “single”, as the name indicates, the monocrystalline solar panel cells are made of single pure silicon crystal and so the composition of these cells is purer and also it gives a uniform appearance across the PV Module.

Monocrystalline panels are slightly more efficient than polycrystalline panels. They also perform better in high heat and lower light environments, which means they will produce closer to their rated output in less than ideal conditions.

The main disadvantage is that they cost is higher. Mono panels are a bit more expensive than poly panels of the same wattage.

Mono panels are cut from square silicon wafers and the corners are shaved off to make the distinct cell shape. As a result the wastage in the process of production of monocrystalline panels are more.

Also monocrystalline panels have a uniform black look because the cells are made from a single piece of silicon.

Monocrystalline Solar panels are the most efficient solar panel available

Advantages

• The efficiency of Monocrystalline Solar panels are 15-20%, while the latest monocrystalline solar panels achieves 25% efficiency in the labs and 21% is the verified efficiency.
• Monocrystalline panels requires the least amount of space and so takes up a small area on the roof top.
• The average life of Monocrystalline solar panels are about 25 years while other PV panels manufacturers claims 25 to 30 year life expectancy.
• Its performance is better than polycrystalline at same rating light conditions. In addition, monocrystalline solar panels produce up to four times the amount of Electrical energy as compared to thin film solar panels.
• Monocrystalline panels have a black coloured uniform look which looks good.

Disadvantages

• The main disadvantages of Monocrystalline solar panels is its cost. The initial cost of monocrystalline PV panels is too high compared to thin film solar PV modules or Polycrystalline Solar panels.
• As it is made of single silicon crystal, partially covered area of solar panel with snow, dirt or shade may break the entire circuit of PV.
• The process of making monocrystalline solar cells (called as Czochralski process) ends up as waste of pure silicon. To make silicon wafers and arrays in large cylindrical shape (a process, which used to make monocrystalline Silicon called), the four ends of the PV cells are cut out of the ingots, which result in large amount of pure Silicon waste.
• It tends to be more efficient when the temperature goes up i.e., it works better in warm weather and full sunshine, but it is not a considerable fact for most homeowners.

Polycrystalline Solar Panels

Polycrystalline (also called polysilicon or multi-crystalline silicon) solar cells are blended together from multiple pieces of silicon. Smaller bits of silicon are moulded and treated to create the solar cell.

The shapes of these cells are rectangular.  To make Polycrystalline PV (photovoltaic) cells, pure raw silicon is melted and poured into a square mould which is cooled and cut into perfectly squared wafers and arrays.  So hardly any raw material is thrown out during manufacturing, so it needs less silicon as compared to monocrystalline solar panels and hence polycrystalline panels are less expensive.

The blended makeup of the cells gives poly panels their iconic blue colour. If you look at them up close, you’ll see the texture and colour is uneven due to the way the cells are made.

Poly solar panels are slightly less efficient than mono panels due to imperfections in the surface of the solar cells (approximately 13.5-17%). Of course, they’re cheaper to manufacture which means they cost less for the customer.

Advantages

• Polycrystalline solar panels have lower heat tolerance (which means their performance is lower in high temperature as compared to monocrystalline solar panels). Heat may disturb the solar panels and reduce their life.
• Less Expensive as the process to produce the polycrystalline silicon is less complicated and less wasteful method is used.
• It is commonly available and easy to use and replace.

Disadvantages

• The efficiency of polycrystalline solar panels is approximately 13.5-17%.It is slightly less efficient than monocrystalline solar panel.
• The same surface of polycrystalline PV modules (in size) would produce less power as compare to monocrystalline solar panel (but this is not always the case).
• Because it don’t have a uniform appearance and have a random and odd blue color the look and feel of the panels is not always great.

Thin Film Solar Panels

There is a third type of solar technology, called thin film solar panels (TFSC) or Thin Film Photovoltaic Cells (TFPV) or Amorphous PV Modules. These types of panels are usually deployed for large-scale utility projects and some specialty applications.

Thin film panels are created by depositing a thin layer of conductive material onto a backing plate made of glass or plastic. This is a second generation solar cell. The thickness of film varies from a few nanometers (nm) few micrometers (µm).

Since thin film solar panels are less efficient than monocrystalline or polycrystalline panels they are not widely seen in residential installs. Also since the roof space available to residential customers are less, they mostly use traditional crystalline silicon panels to maximize production from the less available space to them.

So majority of solar panels deployed today are made from either monocrystalline or polycrystalline solar cells.

However thin film solar technology is less expensive and so it becomes more cost-effective option at a larger scale. For commercial and industrial projects without any space restrictions, the lower efficiency of thin film technology doesn’t really matter. Thin film panels often end up being the most cost-effective option in these situations.

Thin film solar panels are very thin as the name suggest and flexible too. The thin film can be deposited onto plastic to create flexible solar panels. These panels are especially nice for RVs and mobile use where you might not have a flat surface to mount the panel.

Following are the subcategories (Types of Thin Film Solar panels) by which PV materials are integrated on a substrate.

• Amorphous Silicon (a-Si/TF-Si)
• Copper Indium Gallium Selenide (CIGS/ CIS)
• Cadmium Telluride (CdTe)

Below are the third generation thin film solar cells, which are not available commercially at all and researcher are hopeful to make the dream come true (very soon).

• Organic Photovoltaic Cells (OPC/OPC) … (It is available now)
• Dye-sensitized
• Polymer solar cells
• Quantum dot
• Copper Zinc Tin Sulfide,
• Nanocrystal
• Perovskite Solar Cells

Advantages

• They are cheap as compared to other monocrystalline and polycrystalline solar panels as the large scale production of thin film solar panels are less complicated.
• It comes in flexible form which may be used for many purposes and applications and can be used where weight of other panels becomes a problem.
• It has high temperature tolerance, i.e. high temperature and shading have less impact on thin film solar panels.
•  It is ideal for use where space is not an issue.
• The uniform appearance of thin film solar panels are more attractive and can be used for beautification purpose as well.

Disadvantages

• It requires a lot of space and hence are not useful for residential and homeowners.
• The additional support structure, cables, maintenance, etc. for thin film solar panel installation makes the system costly.
• The overall life expectancy of thin solar panels is lower than that of poly- and monocrystalline solar panels.

String Ribbon Solar Cells

A process in which multi crystalline silicon strips and foils are manufactured for Photovoltaic (PV) Technology. In this process, high temperature resistance wires are pulled through the molten silicon to form multi –crystalline thin ribbon of silicon crystals. These very thin ribbons then cut into different lengths to form PV and Solar cells. These have an efficiency is about 13-14%.

String Ribbon PV panels are also made out of polycrystalline silicon and hence Solar panels made with String Ribbon technology looks the same to traditional polycrystalline PV panels.

Advantages

• Lower cost production, simple and easy to use.
• String Ribbon Solar panels efficiency is about 13-14%

Disadvantages

• Manufacturing is more energy extensive
• Lowest space-efficiency

Amorphous silicon (a-Si or a-Si:H) Solar Cells

An amorphous silicon solar cell is a subcategory of Silicon thin film solar panels has recently become popular in the market.

To manufacture an amorphous silicon solar cell one or more layers of photovoltaic materials are sandwiched onto a substrate as a gas spray which is called “vapour deposition”.

They need very less Silicon (say 1%) to manufacture than crystalline solar cells. Also they have much less efficiency than poly or monocrystalline solar panels (approx 5-6%).

Cadmium Telluride (CdTe) Solar Cells

Cadmium Telluride thin film solar panels are based on Cadmium telluride. They are the only PV (Photovoltaic) technology, which is cost effective as compared to Silicon crystalline solar panels in a significant part of the market especially in the multi kilowatt system.

The efficiency of these solar panels tends to be in range between 9-11%.

Copper Indium Gallium Selenide (CIGS/ CIS) Solar Cells

The flexible Copper Indium Gallium Selenide PV cells are made of Copper, Indium, Gallium and Selenide by integrating on a substrate like plastic or glass, along with anode and cathode (electrodes) on the back and front side to collect electrical output power.

The efficiency rates for CIGS solar panels typically operate in the range 11-14 %. The commercial production of started in Germany in 2011.

CIGS or CIS solar panel cells have high temperature tolerance and work better in a warm climate, so they work even better when cells deposited on glass.

N-Type vs. P-Type Solar Cells

The previous section covers the process by which raw material is formed into silicon wafers.

This section has to do with the process by which those wafers are treated to turn them into a functioning solar cell that can generate an electrical current.

P-Type Solar Cells

P-type cells are usually built with a silicon wafer doped with boron. Since boron has one less electron than silicon, it produces a positively charged cell.

P-type cells are affected by light-induced degradation, which causes an initial drop in output due to light exposure. This has historically been the most common treatment method for solar cells.

N-Type Solar Cells?

N-type cells are doped with phosphorus, which has one electron more than silicon, making the cell negatively charged.

N-type cells are immune to boron-oxygen defects, and as a result, they are not affected by light-induced degradation (LID). As you might expect, these are positioned as a premium option because they degrade less over the life of the panel.

Difference between P-Type Solar Cells and N-Type Solar Cells?

P-Type solar cells are cheaper than N-Type solar cells but the life span of N-Type solar cells are more than P-Type solar cells. When you consider the lower cost of P-type cells, it typically pays to go with a cheaper module that degrades a little more, as opposed to a substantially more expensive panel with slightly less degradation. But that assessment may change as N-type technology advances and costs drop over time.

Other Different Solar Cell Technology

PERC Cells

PERC stands for Passivated Emitter and Rear Cell technology. PERC cells are distinguished by an extra layer of material on the backside of the solar panel, called the passivation layer.

The passivation layer acts like a mirror and it reflects the light that passes through the panel, giving it a second chance to get absorbed by the solar cell. Hence more solar radiation is absorbed by the cell, which results in a higher efficiency of the panel.

The inclusion of the passivation layer doesn’t add a huge manufacturing expenses or delays in production and hence the PERC cell technology is gaining traction. The efficiency boost more than justifies the extra step in the manufacturing process.

Half-Cut Cells

Half-cut cells are exactly what they sound like: solar cells cut in half. The smaller size of half-cut cells gives them some inherent advantages like improved efficiency over traditional cells.

Solar cells transport electrical current through ribbons that connect neighbouring cells in a panel. Some of this current is lost due to resistance during transport.

Because half-cut cells are half the size of a traditional cell, they generate half the electrical current. Lower current between cells means less resistance, which ultimately makes the cell more efficient.

In addition, half-cut cells can be more shade-tolerant. When shade falls on a solar cell, it not only reduces the production from that cell, but every other cell connected to it in series as well.

A traditional solar panel may have 60 solar cells, wired in series. If shade falls on one series of cells, you can lose one-third of that panel’s production.

In contrast, a panel made of half-cut cells would have 120 half-cut cells, wired in series/parallel with two strings of 60 cells. Shade that falls on one string would not affect the output of the other, which minimizes production loss caused by shading issues.

Bifacial Solar Panels

Bifacial solar panels are panels that are treated with conductive material on both sides. They’re designed to take advantage of reflected sunlight that hits the backside of the panel.

In theory, this sounds like a great idea because you are doubling the conductive surface area of the panel. But in practice, bifacial panels call for a much more expensive mounting setup to get any real benefits from the technology.

The system needs to be mounted in an elevated position so that there is clearance below the array. It also calls for the right reflective material beneath your array, like white rocks below a ground mount or a white roof.

Bifacial panels are significantly more expensive to install, and at this point, the minor efficiency gains don’t do enough to recoup the extra installation costs. Bifacial panels aren’t quite ready for the limelight, though that may change as the technology develops further.

Which Panels Should I Choose For My Home?

Now that you have understood the different solar technology it is up to you to choose which solar technology you should use for your projects. It all depends on lots of factors such as your available budget, load requirements, the available space for mounting solar panels, environment and region for peak sunshine hours and types of batteries used as backup power etc.

Monocrystalline solar panels are best than polycrystalline solar panels in efficiency but they are little bit costly.

As the majority of us haven’t large space on their roof, windows etc, forget about the thin film solar panel as it is not for you. Crystalline base solar panels in the best choice then.

monocrystalline solar panels are more space efficient and produce little more electrical power than polycrystalline but this is not always the case. For the same rating (say 100W) of mono and polycrystalline solar panels both would generate approximately the same electrical output power (with a few negligible difference) but polycrystalline would take up little more space as compared to mono-crystalline solar panel. And polycrystalline solar panels are slightly less expensive.

Also look at cost-per-watt of the solar panels. Divide the panel cost by its rated wattage. The result tells you how much it cost per each watt of power you get. Even though the panels have a warranty for 25-30 years their performance decreases over years. Also don’t go for the cheapest panels.