The latest technologies for the production of photovoltaic cells
The latest technologies of photovoltaic cells and panels offered by leading manufacturers are presented below. Some of the more popular and innovative panels on the market are also listed.
PANELS USING THE LATEST INNOVATIONS
Most panel manufacturers offer a range of models including mono and polycrystalline (also known as multicrystalline) with different power ratings and warranty conditions. The efficiency of solar panels has increased significantly in the last few years due to advances in photovoltaic cell technology. The most common technologies:
PERC – back cell emitter passivation
Bifacial – Double-sided panels and cells
Multi Busbar – busbars and wire
Split panels – cut cells
Dual Glass – frameless double glass
Shingled Cells – overlap cells (shingle technology)
IBC – Interdigitated Back Contact cells
HJT – heterojunction cells
These innovations are explained in detail below . They offer various performance improvements and increased reliability. Several manufacturers offer up to 30 years of performance guarantees.
SOLAR PANEL EFFICIENCY
Solar panel performance comparative table
MONO CELLS VERSUS POLYCRYSTALLINE
There has been a long debate as to which cell technology is better. Monocrystalline (mono) cells, which are cut from a single crystal cylinder , are more efficient but slightly more expensive to produce. Until recently, higher costs were the main rationale behind the choice of polycrystalline technology. However, in the last 2 years, the cost of mono wafers has dropped significantly. Most of the large producers have returned to monocrystalline cells or mono-cast cells , which are monocrystalline cells made using a polycrystalline manufacturing process.
The production process of polycrystalline solar cells is surprisingly simple. The first step is to crystallize the silicon in the crucible, allowing the silicon to solidify in the shape of a block. Melting at 1500 degrees C removes impurities from silicon to some extent. The lump is cooled and cut into thin slices.
During the production of monocrystalline cells, high-purity polycrystalline silicon is thrown into the crucible and melted there into one mass at a temperature of 1500 degrees.
A crystal seed is introduced into it, a single block of silicon from which the entire crystal will be formed. Slowly (the whole process takes 48 hours!) The embryo is pulled out, or rather what has grown out of it – a large, cylindrical single crystal of silicon. Like the polycrystalline block, the single crystal cylinder is cut into round slices. Previously used round cells caused a huge loss of the surface of the finished module, so they began to be cut to a shape close to a square.
Both types of cells are still widely produced and very reliable. Currently, monocrystalline cells are considered the best technology due to their higher efficiency.
Monocrystalline cells are generally dark black / blue with a diamond pattern, while poly or multicrystalline cells are square-edged, blue or navy blue in color, and lightly textured.
WHY ARE MONOCRYSTALLINE CELLS MORE EFFICIENT?
The advantages of monocrystalline silicon result from a uniform crystal structure free from grain boundaries and smaller impurities thanks to the unique Czochralski process. Mono cells also have a slightly better temperature coefficient. By comparison, poly or multicrystalline cells have very small but defined crystal boundaries that can act as fine barriers and reduce efficiency. Muticrystalline cells, while generally very reliable, can also be more prone to microcracking after several years of use.
PERFORMANCE AT HIGH TEMPERATURES
Monocrystalline cells have a slightly lower cell temperature coefficient. This results in a slightly higher performance at elevated temperature. The power temperature coefficient is the amount of power loss with increasing cell temperature, i.e. they slowly reduce the output power with increasing cell temperature. All solar cells and panels are assessed using the STC measurement method. During operation, the cell temperature is 20-30 ° C higher than the ambient temperature. The module’s output power loss is typically 8-14%. Monocrystalline cells have lower losses due to an average power factor of about -0.38% per ° C. Polycrystalline cells have an average power factor of -0.41% per ° C.
PERC – (FROM ANG. PASSIVATED EMITTER AND REAR CELL )
In the last two years, PERC technology has become the main technology for many manufacturers in both mono and polycrystalline cells. PERC stands for “Cell Rear Emitter Passivation Technology”. It is a more advanced cell structure that uses an extra layer of dielectric on the back of the cell to absorb more photons of light and increase “quantum efficiency”. In PERC cells, the efficiency is increased from the light reaching the bottom layer of the plate and after reflecting the returning photon back into the cell. Through this reflection, photons have a second chance to generate electricity.
PERC technology therefore allows the process of capturing solar radiation to be improved and the collection of electrons to be optimized.
Q Cells was the first manufacturer to introduce PERC technology into multicrystalline cells. The manufacturer used the trade name Q.ANTUM. Q.ANTUM technology is such an optimization turbocharger for conventional poly- and monocrystalline solar cells and solar modules. The Q.ANTUM module has been developed to ensure maximum performance in real conditions – even with low radiation during dusk and dawn and cloudy skies and on clear hot summer days, as well as in autumn and winter when the sun is low.
Jinko Solar recently broke the performance record with 22.04% of a standard size P-type multicrystalline silicon cell. PERC mono cells are currently the most popular and most efficient type of cells. Most manufacturers including Winaico, Trina Solar, Q Cells, Jinko Solar, Risen and JA Solar and many others use PERC architecture.
LETID – PERC PROBLEMS
Typical P-type PERC cells may degrade due to the so-called LeTID, also known as light and heat induced degradation. The LeTID phenomenon is similar to the well-known degradation of LID from light. In LID, a panel can lose 2-3% of its rated output power in the first year of UV exposure and 0.5% to 0.8% per year in subsequent years. Unfortunately, losses due to LeTID may be higher, as much as 6% in the first 2 years. The light-induced degradation is caused by the unstable oxygen compounds of the boron. They can be found in all p-type solar cells. If the loss is not fully taken into account by the manufacturer, it can lead to poor performance and potential warranty claims. Producers are taking steps to stabilize the boron oxygen compounds in order to minimize degradation. This makes PERC solar modules more efficient than modules not equipped with this technology.
Fortunately, N-type silicon cells used by leading manufacturers are resistant to LeTID. Also, several manufacturers that produce P-type PERC poly and mono cells have developed processes to reduce or eliminate LeTID, including Q Cells , which was the first to apply anti-LeTID technology to all panels.
Busbars are thin wires or ribbons that run along each link and carry electrons (current). As photovoltaic cells have become more efficient and generate more electricity, most manufacturers have changed the technology from 3 bars to 5 or 6 bars in recent years. Several manufacturers such as LG energy, REC, Trina and Canadian Solar have gone a step further and have developed multi-wire systems using up to 12 very thin round wires instead of flat busbars. The trade-off is that the rails obscure part of the cell, so they can slightly degrade its performance if they are too large. Therefore, they should be carefully designed. On the other hand, more busbars provide lower resistance and a shorter path for the electrons to travel, resulting in higher efficiency.
IF A CELL MICROCRUPT DUE TO AN IMPACT, HEAVY LOADS, OR PEOPLE WALKING ON PANELS , MORE COLLECTION Rails HELP REDUCE THE RISK OF HOT-SPOT (HOT ALTERNATIVE POINT).
In LG neon 2 modules, where the manufacturer first used 12 small round busbars, which LG called the “Cello” technology, which means “a combination of cells with low loss, low stress and absorption enhancement. The essentially multi-wire technology lowers electrical resistance and further increases efficiency.
Another recent technology is the use of half-size or half-size cells instead of full-size square cells and moving the junction box to the center of the module. This effectively splits the solar panel into 2 smaller panels, each of which works independently. This has many advantages. First of all, the increased efficiency due to the lower resistance losses of the busbars. Since each cell is half size, it produces half the current at the same voltage. This means that the width of the busbar can be halved, reducing cell shading and losses. The lower current also translates to lower cell temperatures. This in turn reduces the formation of hot spots due to local shading, dirt or damage to the cell.
In addition, a shorter cable distance from the top and bottom to the center of the panel reduces wastage and improves overall performance. It thus increases the output power of a similar sized panel by up to 20 W. Another advantage is that it allows partial shading of the top or bottom of the panel and does not affect the output of the panel.
Hanwha Q Cells Q.Peak Duo G5 panel use cut mono PERC cells with 6 round rails
BIFACIAL SOLAR MODULES
Double-sided technology has been available for several years. However, it is only now starting to become popular, as the production costs of very high-quality monocrystalline cells continue to decline. Double-sided cells absorb light from both sides of the panel and, in the right location, can generate up to 27% more energy than traditional single-sided panels. Double-sided solar panels usually use a glass front and a transparent polymer back sheet. This allows the reflected light to reach the back of the panel. Bifacial modules can also use a glass back side, which extends the life of the module and can greatly reduce the risk of failure. Some manufacturers offer a 30-year performance warranty on bifacial panels.
Double-sided panels have usually only been used in above-ground installations in places where sunlight is easily reflected from surrounding surfaces. Especially in more snow-covered regions. While proven to perform better when mounted on the ground in light sandy surfaces, they are also able to achieve up to 10% higher performance on light-colored roofs . In addition, glass provides better heat dissipation from the cell, improving efficiency.
BIFACIAL GLASS / GLASS
Many manufacturers nowadays produce glass panels, double or double glass / glass, not to be confused with bifacial technology. The rear glass replaces the traditional white electrical insulating film, which is considered better. Glass is very stable, non-reactive and does not age over time or deteriorate under the influence of UV radiation. Due to the longer lifetime of glass panels, some manufacturers, such as Trina Solar, now offer a 30-year performance guarantee.
Many double-sided glass panels are also frameless, meaning there is no aluminum frame. This can complicate the installation of the panels a bit as special fixing systems are required. However, frameless modules offer a number of advantages. The most important is the self-cleaning effect. Modules without a frame do not trap dirt and dust, especially when the angle of inclination is very small. They are much easier to clean only with wind and rain, which results in greater efficiency. However, without a strong aluminum frame, glass panels, while more durable, are not as stiff as frame panels and can bend, especially when installed horizontally.
OVERLAP CIRCUIT (SHINGLE TECHNOLOGY)
This new technology consists of overlapping narrow strips of links, much like a shingle on a roof. Standard cells are laser-cut into 5 or 6 strips and arranged in layers by gluing them together with a special conductive glue. The slight overlap of each link strip hides a single busbar that connects the link strips. This unique design makes optimal use of the panel surface. It does not require the use of busbars, which partially obscure the cell, thus increasing the efficiency of the panel.
Another benefit is that the long links are usually connected in parallel. This greatly reduces the shading effects. Each long cell works independently. Also, these cells are relatively cheap to manufacture, so they can be a very cost-effective, high-performance option, especially if partial shading is an issue.
Seraphim was one of the first manufacturers to release strip cell modules with the high-quality Eclipse series.
THE MOST EFFICIENT SOLAR PANELS – IBC N TYPE
The world’s most efficient and best performing solar panels are manufactured by SunPower and LG using IBC monocrystalline silicon cells and while they are the most expensive, they are without doubt the most reliable and highest quality panels available.
SunPower – Maxeon 3 – 22.6% efficiency
LG energy – Neon R – efficiency 21.7%
The higher cost of these high-end N-type solar panels ($ 1 or more per W) is offset by higher efficiency. The yield ranges from 20 to 22.6%. In addition, the panels exhibit better performance at higher temperatures and minimal light induced degradation (LID). This means significantly higher energy efficiency over the entire lifetime of the panels. Industry leading performance guarantee is offered for both SunPower Maxeon 2 panels up to 92%. In LG Neon R and Neon 2, the panels also come with a 25 year product warranty and a new minimum 90 to 90.8% performance warranty after 25 years.
LG Neon R solar modules with high efficiency N type IBC cells – up to 370 W (60 cells)
After early HJT development at UNSW and Sanyo, Panasonic has created an efficient range of “HIT” panels. For many years, Panasonic has been a leader in HJT cell technology. However, the REC group has just released new panels from the Alpha series, which use HJT cells with 16 micro-rails. An impressive 21.7% efficiency was achieved.
HJT solar cells use a base of common crystalline silicon with additional thin layers of amorphous silicon on both sides of the cell. The layers form a so-called heterojunction. Unlike conventional PN cells, multi-layer heterojunction cells significantly increase efficiency. In laboratory tests, they achieve efficiency of up to 26.5%.
Panasonic has developed a HIT cell using a high-performance N-type silicon base with an efficiency of up to 20.0%. High temperature performance has also been improved. N-type silicon cells are characterized by an extremely low power loss after 25 years of operation, reaching the efficiency of 90.76% of the initial power. This is the second largest result after SunPower.
HJT LEADING THE WORLD’S HIGH TEMPERATURE PERFORMANCE
The most impressive feature of HJT cells is the incredibly low temperature coefficient. It has been improved by 40% compared to regular poly and monocrystalline cells. The power output of the panels is rated at a cell temperature of 25 degrees Celsius under STC conditions. Any degree above this value slightly reduces the output power.
The temperature coefficient refers to the reduction in power with increasing cell temperature.
In typical poly and mono cells, the power temperature coefficient is 0.38% to 0.42% per degree C. Under real conditions, this can reduce the efficiency of modules by 20% or more on very hot and windless days. For comparison, Panasonic HIT cells have a very low temperature coefficient of 0.26% per degree Celsius. This is the lowest value among currently manufactured cells.
NOTE: PANEL AND CELL TEMPERATURE ALSO DEPENDS ON ROOF COLOR, TILT ANGLE AND WIND SPEED. INSTALLING THE PANELS ON A VERY DARK ROOF HAS USUALLY LOWER THE EFFICIENCY OF THE PANELS COMPARED TO ROOFS WITH LIGHTER COLORS.