There is a huge variety of manufacturers and models of photovoltaic modules on the market, which can make choosing the right solution a challenge. Finding the perfect photovoltaic panel that meets all your requirements can take time and careful analysis.
What should you look for when choosing solar modules?
There are several key factors to consider when purchasing solar modules.
- First, it is important to check the efficiency of the modules, that is, how much energy they are able to produce under real conditions.
- It is also important to pay attention to their durability and resistance to weather conditions, such as wind, hail or snow.
- It is very important to check the warranty offered by the manufacturer and any quality certificates.
- It is also worth comparing the prices of different solar modules and consulting a specialist to choose the best solution for your specific needs and installation conditions.
Product Warranty.
The product warranty covers physical defects in material and workmanship of the photovoltaic module that may occur within a certain period of time. Its length depends on the manufacturer and the product, ranging from 12 to 40 years. The product warranty is an indicator of the reliability and quality of the solar panel. A photovoltaic module with a longer product warranty also indicates that the manufacturer has confidence in the durability and strength of its product.
The product warranty is more important than the performance warranty because it covers the entire physical condition of the module and its functionality. A solar module that fails due to defects in materials or workmanship is worthless regardless of the performance warranty, since it does not generate electricity.
Performance guarantee.
A performance guarantee ensures that a solar panel will achieve a certain output for a certain period of time. It is possible to make claims if the actual performance of the panel is lower than the guaranteed performance. Most solar panel manufacturers offer a performance guarantee of at least 25 years, but some companies offer longer guarantees of up to 30 or 40 years.
The amount of guaranteed performance is quoted as a percentage and averages 85% of nominal capacity after 25 years. An annual decrease in efficiency, called degradation, of 0.5% is usually assumed. In practice, better results are often achieved, with annual performance degradation of only 0.15%.
However, it is worth remembering that the performance guarantee does not cover complete failure of the solar panel. Therefore, always consider the performance guarantee in cooperation with the product warranty.
TIER 1.
Tier 1 for photovoltaic panels is a ranking of photovoltaic panel manufacturers that meet certain financial and quality criteria. Companies on the Tier 1 list are considered reputable, offering high-quality products with a long service life, often exceeding 25 years. The Tier 1 ranking is compiled by Bloomberg New Energy Finance, among others, and helps identify trustworthy manufacturers in the photovoltaic market. The production of photovoltaic panels by companies on the Tier 1 list is seen as a guarantee of reliability and high-quality products, making it worth considering an investment in such panels.
Power tolerance.
The power tolerance of solar panels determines the possible deviation of the panel’s actual power from the manufacturer’s stated rated power. The values are given in percentages or watts.
Example:
A solar panel has a power rating of 300 Wp. Its power tolerance is +5/-5%. This means that its power can deviate by 5% up or down from the rated power. This means that a power output between 285 and 315 Wp is possible for this panel.
The power tolerance tells you how much you can rely on the power rating data in the manufacturer’s data sheet. A good photovoltaic installer should take this into account when planning a solar installation.
Solar panel efficiency and performance for maximum output.
Solar cell efficiency plays an important role in a solar panel. The best photovoltaic modules achieve efficiencies in the range of 21 to 22.9%. A good result is in the range of 19.5 to 20.5%.
It is important to distinguish between efficiency and rated power. Rated power depends not only on efficiency, but mainly on the size of the solar panel. The larger the PV module, the higher the power. Therefore, there are large PV panels of high power with lower efficiency. In this case, bigger does not always mean better, especially when the weight increases.
This is the case for many modules above 360 Wp. Bigger does not always mean better in this case.
Solar panels with efficiencies up to 20% tend to be cheaper, while PV modules with efficiencies above 21.5% can be much more expensive.
Instead of a few cheap PV modules, you can purchase a larger number with lower efficiencies – the result is the same, and the cost is often lower. The only limitation is the available roof area.
N-type vs. P-type solar panels.
N-type panels are gaining popularity because of their higher efficiency and better performance compared to P-type panels. They are particularly suitable for applications where performance and quality are priorities over initial cost. P-type panels, on the other hand, have been widely adopted for their cost-effectiveness, but the cost difference between the two types is narrowing.
Monocrystalline vs. polycrystalline.
These two types of solar panels differ in their manufacturing processes and efficiency. Monocrystalline panels are made from single-crystal silicon, offering higher efficiency and a sleeker look, while polycrystalline panels are made from multiple silicon fragments, providing a more cost-effective option.
Phase Change Materials (PCMs -Phase Change Materials) used for improved photovoltaic panels.
The use has brought success in improving the efficiency of photovoltaic (PV) panels. Nano-PCMs have proven particularly effective in cooling PV panels, improving their overall efficiency.
PERC technology.
PERC modules have an additional layer on the back of the solar cells. This layer has two main functions: it reflects photons back into the cell and reduces electron recombination. This increases the efficiency of the solar cells.
However, the degradation of PERC modules is more noticeable, resulting in a faster loss of efficiency. In addition, due to more complicated manufacturing processes, they are more expensive than solar wafers without PERC technology.
PERC modules are ideal for rooftop installations due to their higher energy yield per square meter. They are also optimal for east-west PV installations because they mainly use morning and evening light.
Shingled technology.
Shingled technology in the manufacture of PV modules is an innovative approach of laying thin silicon sheets in an overlapping fashion, similar to roof tiles. This technology reduces the distance between cells, increasing the power density per unit area of the module. Shingled photovoltaic panels are state-of-the-art and efficient, enabling greater efficiency compared to traditional photovoltaic modules. The technology achieves higher power density at lower or similar production costs, contributing to space and money savings for investors. In addition, Shingled technology allows for better space utilization through denser distribution of photovoltaic cells without the need for technological gaps between them.
HJT technology.
HJT stands for heterojunction technology (Heterojunction Technology) in photovoltaic modules. It is a combination of monocrystalline silicon and amorphous thin film silicon that enables high light absorption and efficient power generation.
- HJT modules have higher power generation efficiency compared to standard PERC modules, resulting in better utilization of solar energy.
- Double-sided operation (bifaciality): HJT-based photovoltaic panels are designed for bifacial operation, meaning they can effectively absorb light from both the front and back of the panel, which increases their efficiency.
- Higher durability: HJT modules are double-glazed, which makes them more resistant to damage and has a longer service life, estimated at more than 30 years.
- Lower risk of faults: Thanks to the HJT-based design, these panels have a lower probability of faults compared to PERC modules.
- Stable performance gains: HJT technology offers stable efficiency gains with the most stable power temperature coefficient of -0.24% and excellent resistance to PID (Potential Induced Degradation).
- High Efficiency: HJT solar cells achieve PV module efficiencies of up to over 21.5%, making them among the most efficient PV modules.
Thanks to these advantages, HJT technology is becoming increasingly popular in the production of photovoltaic panels, offering more efficient and durable solutions for producing electricity from solar radiation.
Glass modules (Glass-Glass) vs. glass-foil modules.
Glass modules consist of two glass plates with solar cells between them. Foil modules, on the other hand, use one glass plate on the front and an opaque film on the back.
Glass modules are favored for their durability and longer manufacturers’ warranties. However, glass solar panels are heavier and less convenient to install. In addition, they are also more expensive than film modules.
The choice between glass and foil modules depends on individual preference. If you want more security and are willing to invest more money, then it makes sense to choose glass PV modules. Otherwise, foil modules are also a good option.
Bifacial (double-sided) photovoltaic modules.
Bifacial PV modules can absorb sunlight on both the front and the back. This makes them more efficient than single-sided photovoltaic modules. However, the back side can only capture light reflected from the ground, roof or other surface. If roof mounting is not possible, it is better to forgo the extra cost. Double-sided modules, on the other hand, are a good alternative for flat roofs or installation in open spaces.
Full black module (Full black).
Full Black modules are photovoltaic modules in which both the cells and the frame and back of the module are black. They provide a more aesthetically pleasing appearance, especially on dark roof surfaces. However, solid black modules are more sensitive to high temperatures, which means their performance is usually slightly lower than that of regular solar modules. An additional disadvantage is the higher price – beauty comes at a price.
Frame color.
Yes, the color of the photovoltaic module frame is important from an aesthetic point of view. Photovoltaic modules can be mounted on the roofs of buildings, and their appearance and color can affect the aesthetics of the entire building. Available colors for photovoltaic module frames can include silver, black and other colors depending on manufacturer and customer preferences.
Half-cells versus full cells.
Full-cell modules typically consist of 60 or 72 solar cells connected in series, while half-cell modules consist of 120 or 144 cells divided in half. The efficiency of half-cells is about 3% higher. This is due to the fact that by dividing the cells, the current per cell is lower. Even in partial shade, half-cell modules can deliver up to 50% current.
Because of their advantages, most manufacturers opt for half-cell modules, so you can confidently use them.
Size and efficiency of photovoltaic panels.
Typical 400 Wp panels measure 1,722 x 1,134 mm and cover an area of 1.95 m². In contrast, 500 Wp panels have standard dimensions of 2,278 x 1,134 mm, which corresponds to an area of 2.58 m².
The results of our analysis of 72 current solar panels show that there are no uniform standards in the photovoltaic industry. Each photovoltaic panel manufacturer decides for itself the size of its solar panels.
The size of photovoltaic panels is crucial for obtaining solar energy. The rule is simple: the larger the photovoltaic panel, the higher its efficiency.
Large solar panels are also heavier and bulky during installation. It is also important to pay attention to the guidelines of the German Institute of Building Technology. According to their recommendations, photovoltaic modules larger than two square meters should not be installed on roofs with a slope of up to 75 degrees. This applies to virtually all single-family homes in Germany.
Power of the photovoltaic module.
A modern photovoltaic module has a power of between 350 and 670 Wp. Manufacturers are outdoing each other in the size and power of photovoltaic modules. Power output depends on the intensity of sunlight. In Poland, an average of 1,000 kilowatt-hours per 1,000 watts of solar power is achieved.
PVEL test.
PVEL (PV Evolution Labs) is an organization that specializes in evaluating the reliability of photovoltaic modules. It conducts independent tests and comparisons to assess the quality and durability of photovoltaic modules.
It works with a variety of manufacturers, conducting comprehensive laboratory tests, third-party testing and data analysis to identify key performance indicators and risk factors. Photovoltaic module manufacturers that score well receive the Top Performer award for a specific year of testing. Manufacturers themselves have no say in whether their modules are tested by PVEL. However, PVEL’s results are a good additional indicator for evaluating the reliability of photovoltaic modules.
Mechanical strength.
Mechanical robustness describes a photovoltaic module’s ability to withstand various weather conditions without losing performance or structure. A robust module reduces the risk of failure, protects against potential safety hazards from damage, and ensures consistent energy production throughout its lifetime.
Mechanical strength usually consists of two values, for example: 5400 Pa / 2400 Pa.
The first number indicates the permissible load on the front of the module in pascals (Pa), while the second value is the tension force on the back of the solar panel. The mechanical load on the front is due to rain, hail, snow and other external factors, while the load on the back is related to the force of the wind.
The value of 5400 / 2400 is sufficient for most photovoltaic installations.
Mechanical strength refers to the resistance of the entire solar module, and says little about how well it is protected from microcracks.
Fire ratings.
The fire ratings of photovoltaic panels determine their resistance to fire. In some cases, depending on the type of building, a specific fire resistance class is required. For example, buildings with fire resistance class A or B, and ZL III, ZL IV and ZL V buildings with usable attics for residential or office purposes, may require a specific fire resistance class for photovoltaic panels.
A Class A-certified photovoltaic panel is one that has passed a Class A fire test, meeting UL790 or IEC 61730-2 standards. Class A photovoltaic modules exhibit high fire resistance, ensuring safety in the event of an unexpected fire.
STC / NOCT performance comparison.
To compare the performance of photovoltaic modules, Standard Test Conditions (STC, Standard Test Conditions) have been introduced. STCs involve measuring power at 1,000 watts of sunlight, a cell temperature of 25 °C and an air mass of 1.5.
However, these conditions are laboratory conditions. In practice, the power obtained is usually slightly less. To find out how well a photovoltaic module performs and to make a realistic comparison, NOCT conditions were also introduced.
NOCT stands for Nominal Operating Cell Temperature, which is the temperature of the cells in normal operation, which is 45 °C. Additional NOCT conditions are:
Central European spring day temperature: 20°;
Insolation during a summer day in the south: 800 W/m²;
A low wind speed of 1 m/s.
Typically, all manufacturers provide NOCT values in their data sheets.
Summary of STC and NOCT conditions:
Standard Test Conditions (STC): 1,000 watts of sunlight, 25 °C cell temperature
Normal Operating Mode Cell Temperature (NOCT): 800 watts of insolation, 45 °C cell temperature
By now analyzing the ratio of NOCT to STC, one can get an idea of the actual performance of a solar panel on a sunny day. The following formula is used for this:
((STC [Wp] – NOCT [Wp]) / STC [Wp]) * 100The lower the percentage, the better. A good value is 25%.
Here is an example:
A photovoltaic module achieves 450 watts under STC conditions and 365 watts under NOCT conditions.
The difference between the power under STC and NOCT conditions is 19.51%.
If you still have questions or doubts about which photovoltaic panel to use, it is also worth comparing prices of different solar modules and consulting a specialist to choose the best solution for your specific needs and installation conditions.