What Are Polycrystalline Solar Panels Made Of?
Polycrystalline solar panels are made from silicon wafers; one panel contains 60-72 wafers. In these panels, efficiency is increased by 3%-5% by using anti-reflective coating. Efficiency generally ranges from 15%-17%, while durability is up to 25-30 years, with an annual degradation rate ranging from 0.5%-0.8%.
Silicon Wafers Blueish Panel Hue
The global price of silicon wafers in 2024 is about $0.25-$0.30 per wafer, while a typical standard polycrystalline solar panel usually contains 60-72 such wafers. The cost for the polycrystalline panels comes to approximately $0.20-$0.25/W, down about 15%-20% compared with the monocrystalline panel prices.
The anti-reflective coating increases photoelectric conversion efficiency by 3%-5%. A 10 kW system will generate approximately an additional 300-500 kWh of electricity per year.
Most polycrystalline silicon solar panels have efficiencies of 15%-17%, whereas more than 20% efficiency for the monocrystalline ones is achievable. If a residence uses a 10 kW polycrystalline system for 20 years, they might generate about 20,000-30,000 fewer kWh compared to using a monocrystalline system.
The temperature coefficient of the polycrystalline silicon panel is around -0.39%/°C. When the temperature surpasses 25°C, a certain rate of efficiency will be lost in the panel.
The installation cost per watt for projects with polycrystalline silicon solar panels in India was just $0.14. Compared to the average installation cost for polycrystalline systems at about $0.75/W in 2024, the installations for monocrystalline systems have reached a cost 10%-15% higher.
The normal service life for polycrystalline silicon panels is 25-30 years, while high-quality brands can be over 35 years. The average annual degradation rate of panel power generation efficiency is about 0.5%-0.8%. After 30 years, a polycrystalline panel may only have about 80% of its original output capacity.
Metal Frame Affordable Solar Option
The metal frame of a regular polycrystalline solar panel accounts for 15%-20% of the weight of the panel. The frame of a standard-sized polycrystalline panel, measuring about 1,650 mm × 992 mm, weighs in the range of 2.5-3.5 kg. If you mount a 100-panel photovoltaic system, the weight of the frames alone could easily reach over 300 kg.
It means that the transport cost per kilometer for an aluminum frame panel is 20% less than that of a steel frame panel.
The normal thickness of the frames ranges from 30 mm to 40 mm. For very bad weather regions, the polycrystalline panels need to resist snow pressure of up to 5,400 Pa and wind pressure of up to 2,400 Pa.
Aluminum alloy frames boast 200 times better thermal conductivity compared to their plastic counterparts. Therefore, for areas where summer temperatures range from 40°C to 50°C, aluminum frames are good options.
The average market price of an aluminum alloy frame is from $3-$5 per meter. Assuming a standard panel needs 6-7 m of frame length, the cost for a panel with a frame would be about $20-$35. Using plastic frames will reduce the cost by 30%-40% accordingly.
In the case of using panels made with an aluminum alloy frame, the whole installation can be done in 2-3 days. In the case of frameless or plastic-framed panels, installation may take 20%-30% longer.
Glass Layer Suitable for Large Projects
The thickness of the toughened glass lies in the range of 3.2 mm to 4 mm. In the last ten years, over 60% of the solar panels have been damaged due to extreme weather conditions. Panels with toughened glass can stay intact even when hailstones with a 25 mm diameter are traveling with a velocity of 23 m/s.
In contrast, using high-transparency glass layers for polycrystalline panels could potentially raise the photoelectric conversion efficiency by about 2%-3%. Every year, a 50 MW photovoltaic power station can produce an extra 2.5 million kWh of electricity; at the same price, it means extra revenue of $250,000 when selling it at $0.1/kWh.
It accounts for about 7%-10% of the entire system cost. Every square meter of tempered glass has a market price of approximately $4-$6. An ordinary polycrystalline panel is about 1.6 m², so the cost for the glass layer per panel is from $6.5-$10. For a 10 MW photovoltaic project, the total cost of the glass layer can be as high as $1 million.
The toughened glass with special processing is 4-5 times stronger compared to ordinary glass. The glass layer should be able to bear snow pressure of at least 5,400 Pa and wind pressure of 2,400 Pa.
In case a solar panel is not regularly cleaned, its power generation efficiency may be reduced by 3%-5% year after year. Self-cleaning glass layers on panels degrade less than 1% every year.
Weight for a regular polycrystalline panel is around 18-22 kg, with 30%-40% of the weight from the glass layer.
Encapsulation Layers
The thickness of EVA film can range from 0.3 mm to 0.5 mm. If there were no EVA encapsulation layers, the rate of breakage for solar panels could rise 3-fold. The light transmission rate for good quality EVA films in the market can be around 90%-95%. Yellowing can reduce efficiency by 5%-10%, and if it is really bad, that could result in system failure 5-8 years earlier than expected. A polycrystalline solar panel with high-quality EVA encapsulation can expect no more than a 20% drop in efficiency over 25 years. In panels with very inferior encapsulation layers, it is possible to lose over 30% efficiency within 10 years.
The encapsulation of POE has an edge over EVA in that it guarantees better resistance against moisture penetration. Since PID is currently affecting approximately 15% of photovoltaic systems worldwide, POE-encapsulated panels can evade all the troubles linked with that. The POE costs roughly 30%-40% higher per square meter than EVA.
Tedlar encapsulation film is suitable for photovoltaic systems on industrial roofs or projects within the vicinity of chemical plants. Panels with Tedlar encapsulation can extend the life of the system by 3-5 years.
In 2019, a large photovoltaic power station in Brazil experienced more than 30% power loss in just 5 years due to using inferior EVA encapsulation, with maintenance costs exceeding $1 million. A German project using high-quality POE encapsulation experienced less than 5% efficiency loss under the same conditions.
Backsheet
Materialwise, a qualified backsheet of solar panels normally consists of three layers. The most widely applied backsheet construction is PET + PVDF + fluorinated film. More than 85% of solar modules manufactured in the world adopt this structure. The ordinary thickness of the backsheet in solar panels should be about 0.3 mm to 0.35 mm, with a weight of approximately 1.5 kg.
The primary function of the backsheet is to electrically insulate and protect the solar panel. During operation, DC electricity is produced by the panel, and the voltage lies within the range of 30 V to 1,000 V, while the system voltage may be as high as 1,500 V. More than a third of all the failures happening in solar panels are due to damages to backsheets.
If PID occurs, the output power of the solar panel may be reduced by 10%-30%, and replacing damaged panels generally costs in the range of $200-$300 each.
In areas with high UV radiation, the quality of the backsheet can severely deteriorate in 5-8 years. Generally, high-quality PVDF backsheets serve for 20-25 years.
Types of Backsheet Materials Comparison
1. Fluorinated backsheets are made from materials such as PVF (polyvinyl fluoride) or PVDF (polyvinylidene fluoride), which can maintain stable insulation and protection performance for more than 30 years.
2. Non-fluorinated backsheets are made from materials such as PET (polyethylene terephthalate) or POE (polyolefin elastomer). Non-fluorinated backsheets cost about $4-$5/m², while fluorinated backsheets cost $7-$9/m². A high-quality fluorinated backsheet will raise the price by about 5%-10% per panel, while in a 25-year lifetime it may reduce cleaning/maintenance costs by 30%-50%. Lower-quality backsheets could require replacement of parts of the panels in 10-15 years.
3. In 2018, a large photovoltaic project in China, due to using inferior non-fluorinated backsheets, faced more than 20% panel aging in 7 years, which directly resulted in a generation decline of more than 15% and revenue losses of over $500,000. On the other hand, another similar-scale project that utilized DuPont Tedlar backsheets had almost no change in power generation efficiency, while the maintenance cost remained below $50,000.
Backsheet Color Choice and Its Impact
· White backsheets have higher reflectivity, reducing the temperature coefficient. Panels with white backsheets usually have temperatures 3°C-5°C lower than those with black backsheets. For every 1°C reduction in temperature, the efficiency of the panel increases by about 0.5%.
· Black backsheets are used more in residential roof systems but have poor temperature management.
Junction Box
This further extends to where the junction box will direct or focus this electrical output that comes from a solar panel onto an external inverter or possibly a battery bank. Its purpose is to reverse the DC power of the panel and send that onto the inverter for efficient dispatch.
Another important function of the junction box is the protection against electrical connections, which are usually equipped with reverse polarity protection and fuses. About 20% of the failures occurring in a photovoltaic system are due to malfunction or bad wiring inside the junction box.
It serves to automatically disconnect the circuit from overcurrents that exceed a set current limit to avoid panel damage or fire hazards. The reverse polarity protection ensures correct electrical connection, avoiding the inversion of positive and negative terminals of the solar panel.
Junction boxes made of plastic are lightweight and much cheaper, while their metal counterparts have better temperature, corrosion, and UV resistance.
It has to be able to withstand moisture, dust, and contaminants. If a box is not able to avoid water and dust entering it, that means the quality of electrical junctions is not good, and system failure could occur. Normally, a high-quality junction box would have an IP65 or higher protection rating, effectively blocking water and dust.
The design and quality of the junction box directly impact the power output and stability of the entire photovoltaic system. Poorly designed or low-quality junction boxes may cause current loss, heating, or even overheating, reducing system efficiency.
The efficiency of a quality junction box used on a solar panel can be around 1%-2% more efficient compared to those panels with standard junction boxes. Poor internal junction box connections might result in about 0.5%-1% power loss.
Conventional junction boxes are used for simple electrical interconnections and protection functions. Smart junction boxes provide features of monitoring and data collection to enable real-time monitoring of voltage, current, and temperature of the solar panel and wirelessly send the data to the monitoring platform for remote diagnostics and optimization of system operation.
Smart junction boxes provide more detailed performance data, enabling the user to predict and identify potential issues. The IQ series of smart junction boxes from Enphase improves efficiency and also provides real-time power output monitoring data for each panel.
The service life of the junction box is 25-30 years. The aging rate of the junction box mainly depends on external environmental factors. If installed in high-temperature or high-humidity environments, the aging of the junction box may be faster.
The price for junction boxes lies in the range of 5%-10% of the total installation cost of the solar panel system. Poor quality junction boxes increase maintenance costs and reduce the system's uptime. High-quality junction boxes will go a long way in enhancing the long-term benefit and return on investment for the system. Quality junction boxes can reduce the failure rate of photovoltaic systems by about 40%.
Conductive Metals
Conductive metals play a significant role in directing the current that is generated inside the solar panel, sending it from the photovoltaic cells to the outside electrical system, where it would be converted into energy and stored.
Commonly used conductive metals include silver, copper, and aluminum. Silver remains the most popular conductive material mainly due to electrode production. Each standard solar panel has about 0.1-0.3 g of silver used.
It is the best electrically conductive material, and its use is very extensive in the photovoltaic industry. Silver's conductivity is 1.6 times that of copper, and it has strong chemical stability. In the field of solar cells, it is used to make electrodes and conduction grids.
Copper is used inside solar cells for backside wiring and current conduction. It is about 60% as conductive as silver, but in PERC technology applications, copper can be used as part of the electrode material to help reduce manufacturing costs.
Aluminum is mainly used in the solar panel's frame structure. It not only provides structural support but also has good conductivity. Aluminum frames can effectively protect the solar panel and reduce transportation and installation costs.
The high conductivity of silver makes it the most ideal conductive material for solar cells, which can reduce the energy loss in current transmission effectively. The photoelectric conversion efficiency of solar panels with silver electrodes generally ranges from 18%-22%, while that of panels with copper or aluminum electrodes is a little lower.
Silver’s efficient conductivity ensures that the current inside the solar cell is transmitted quickly and without loss to the external circuit. In high-end photovoltaic projects, using more silver electrodes to optimize panel performance can effectively increase the overall system's generation capacity, improving the return on investment.
Silver prices are at about $0.7/g, while the prices of copper and aluminum are only about a fifth to a tenth of the price of silver. In this respect, the use of copper or aluminum instead of silver electrodes in solar panels would be far more economical for a homeowner or low-budget projects.