Main problems found in photovoltaic modules

Photovoltaic solar energy is increasingly widespread as an excellent source of renewable energy, presenting solutions for both small-scale and large-scale applications. In Brazil, photovoltaic solar energy is growing rapidly, as can be seen in Figure 1. The dissemination of solar energy has accelerated the process of evolution of photovoltaic module technologies in search of better efficiency, return on investment and safety. With the number of installed photovoltaic modules increasing more and more, reports of problems encountered become more frequent.

Competitiveness and the search for cost reduction leads some designers and companies to make mistaken decisions based solely on short-term costs, evaluating only the cost per watt (USD/Wp) of photovoltaic modules, relegating quality to a lower level. This practice leaves the assessment of product quality in the background, putting the viability of the project in the medium and long term at risk. Problems are not always detected during the photovoltaic module manufacturing process, but they can become evident when the modules are already installed and in operation, and that is where the problem lies. Although the modules have guarantees, their replacement is not simple.

• How much does a photovoltaic system that is stopped, without producing energy for 1 month, cost the owner?
• How much does it cost for the installation company to send a team to evaluate and correct the problem in the field?
• Or even, how much does an unsatisfied customer cost by advocating against the installation company?

In this article, we will address the most common defects in photovoltaic modules and the effects on their operation.

Problems found in photovoltaic modules

Photovoltaic modules can present several problems during their useful life. Most of these problems occur due to the use of low-quality materials and manufacturing processes. Among the most common problems, the following stand out:

Fissures and cracks in cells

Photovoltaic modules are exposed to stress during the manufacturing, installation and maintenance processes. In operation, the modules are exposed to adverse weather conditions such as wind, rain and snow, which cause thermal stress and can cause damage to the cells.

Cracked cells can cause hot spots and non-generating areas, which reduce module efficiency and accelerate its degradation process.

Bubbles

The appearance of bubbles is a consequence of chemical reactions that produce gases.

In addition to the aesthetic problem that can cause strangeness on the part of the owner, bubbles can cause performance problems, especially in regions closer to the edges, as they can create a continuous path between the active part and the structure of the photovoltaic module, allowing the entry of moisture inside the module and reaching the photovoltaic cells.

Delamination

It is more likely to occur in conditions of high temperature and humidity. This problem is caused by the loss of adhesion between the encapsulant and the glass or the surface of the photovoltaic cells.

Delamination can cause greater reflection of light and the penetration of moisture inside the module, which contributes to the appearance of other types of degradation.

As in the case of bubbles, delaminations close to the structure are more serious, as they also create a continuous path between the active part and the structure of the photovoltaic module.

Discoloration of the encapsulant

It occurs due to the degradation of the encapsulating material (typically EVA) that covers the surface of the cells in the photovoltaic module, presenting a yellowish or brown appearance.

The aggravating factor for the occurrence of discoloration is the use of low quality materials, high temperatures and humidity.

Snail trail (snail trail)

The degradation of the paste used for the metallization of photovoltaic cells causes it to discolor, forming paths similar to that of a snail.

Although there is still no proof that this problem has an impact on the power generated, it can at least cause discomfort for the system owner, if he notices the irregularity in the color of the cells.

Cell misalignment

Manufacturing defect, which may cause contact between cells. In this case, an electrical contact is created between the cells, unpredictably modifying the IxV characteristic curve (current and voltage) of the photovoltaic module.

Welding and metallization failures

They cause a decrease in module efficiency due to an increase in ohmic contact resistance. This phenomenon occurs due to errors in printing the metal grid on the photovoltaic cell and inadequate or absent welding.

Hotspot (hot spot)

It is the increase in temperature in a certain area of the photovoltaic module, caused by various reasons such as shading, dirt, cells with different performances and cracked cells.

The increase in temperature at a point occurs due to the inversion of the cell's voltage, making it take on the characteristic of an electrical receiver. Microcracks in cells are the most common causes of hotspots after shadows and dirt.

Junction box and MC4 connector faults

Cracks or lack of continuous sealing allow moisture to enter components, which can cause corrosion and short circuits between metal contacts.

PID

The effect of potential-induced degradation (potential induced degradation) is more likely to occur in systems that work with high voltage, when there are strings with a large number of modules.

When the active part of the photovoltaic module does not have adequate insulation, the potential difference to earth forms a leakage current. This topic was explored in the article The PID effect and its action on solar modules. LID The effect of light-induced degradation (Light Induced Degradation) refers to efficiency losses that occur in the first hours of exposure of the photovoltaic module to sunlight. This problem is inherent to the manufacturing process of P-type (boron-doped) cells. This occurs due to the formation of the boron-oxygen complex inside the module. When associating with oxygen, this boron molecule ceases to be a charge carrier, which reduces the efficiency of the cell and consequently the module. Typically, losses are in the order of 2% to 3%, and occur in the first 5 kWh of energy generated by the module.

Evaluation of photovoltaic modules

During the period of operation, photovoltaic modules are subjected to climatic conditions that can cause the degradation of their characteristics, such as optical, electrical and thermal degradation. These conditions interfere with the performance of photovoltaic modules, therefore it is important that photovoltaic modules are subjected to tests that expose them to extreme conditions, so that the quality and safety of the product can be verified before being commercialized. In Brazil, photovoltaic modules can only be sold after the model has undergone certification tests in accordance with INMETRO ordinance 004/2011, through accredited laboratories. However, the tests required for certification in Brazil are not sufficient to verify the necessary safety and quality standards. Therefore, it is advisable to opt for photovoltaic modules that also have international certifications that subject photovoltaic modules to tests with more rigorous standards, in accordance with the IEC 61215 standard.

Conclusion

With the heating of the photovoltaic solar energy market, a large demand for photovoltaic modules emerged. As a result, there has been an increase in the number of manufacturers of this product, often without due preparation, who do not invest in quality assurance processes. To mitigate future problems such as those discussed previously, simplistic analysis based solely on price can lead to high future costs. Promises to deliver power and efficiency at low prices should be viewed with caution. Quality seals, despite being a good indicator, should also be looked at more closely, as certifications are made on a few samples and are worthless if the manufacturer does not have effective quality control over time. Therefore, it is essential to carefully check the different brands and models of photovoltaic modules available on the market.