Photovoltaic systems can be used in a wide variety of locations, such as large cities, coastal regions, farms, rivers, forests, deserts or even in space. Each of these locations requires that the equipment used has special characteristics, ensuring its proper functioning throughout its operation.
This article will address studies related to the effects of salinity present in coastal regions on photovoltaic modules, in addition to presenting the test of salt spray, which is one of the evaluation procedures that can be carried out on photovoltaic modules to ensure their quality and durability.
Photovoltaic modules are developed to withstand the most diverse environmental conditions, whether wind, rain, snow, hail, sea air, ultraviolet radiation or even the ammonia present in the air.
Aiming at certification according to compliance standards, the IEC (International Electrotechnical Commission) proposes in the standard IEC 61215, a sequence of tests that determine the electrical, thermal and mechanical characteristics of a photovoltaic module.
As it is a standard that covers several qualification tests for photovoltaic modules, it has become a reference for INMETRO Ordinance 004/2011 (National Institute of Metrology, Quality and Technology), which regulates the certification of photovoltaic modules in our territory.
Although INMETRO's compulsory certification requires only a small part of the requirements of the IEC 61215 standard, manufacturers themselves request more specific tests from large testing laboratories, being able to acquire quality seals of different levels – such as, for example, the TÜV certification seal, which includes all the tests described in the IEC standard.
In Brazil, there are some initiatives to carry out tests in addition to those required by INMETRO. LESF (Energy and Photovoltaic Systems Laboratory) at UNICAMP (State University of Campinas), for example, should carry out from 2021 a large part of the procedures listed in the IEC 61215 and complementary standards, providing an additional quality reference for photovoltaic modules sold on the national market.
As it is a standard that contains the main tests that characterize a photovoltaic module, IEC 61215 is commonly cited in other standards that govern different operating conditions of photovoltaic modules.
As the scope of this article is focused on the effects of salinity on photovoltaic modules, discussions on the IEC 60068 2 52 (standard for environmental testing of photovoltaic modules, which defines tests under dry, humid and saline conditions), in addition to IEC 61701 (standard for testing corrosion of photovoltaic modules due to salt spray).
Since this article revolves around the effect of salinity on photovoltaic modules according to the aforementioned standards, the testing procedures will also be demonstrated. salt spray.
Motivation for testing salt spray
In photovoltaic installations near coastal regions, there is great concern regarding a phenomenon called salt spray, popularly known as sea spray. This effect occurs due to the fact that sea waves, when breaking on the coast, release a spray with saline content, causing the salt particles to become dispersed in the air.
The spread of sea spray in the air depends on several factors, such as:
- Concentration of sea salt in the oceans;
- Relative air humidity;
- Propagation of winds in the region;
- Room temperature;
- Civil constructions nearby.
Due to the various factors presented, the propagation of salt spray has a completely different pattern from one location to another. According to the ocean salinity map, the different concentrations of salt can be noted, demonstrating that the effect of salt spray can present itself with different levels of intensity in the most diverse locations in the world. The Brazilian coast, for example, is one of the regions with the highest levels of salinity in the world.
A study conducted in Rio de Janeiro analyzed the reach of sea spray from the sea that bathes Copacabana beach. The study found the presence of sea salts at a distance of 7 km from the coast, demonstrating that the effects of salinity must be considered, even if the installation is relatively far from the sea.
Given the inherent corrosive effect of sea spray on metallic elements, it remains to be seen how photovoltaic modules behave in the face of this natural phenomenon. The salt spray involves three different standards, namely: IEC 61701, IEC 61215 and IEC 60068-2-52. For its execution, two samples of the same model are required to carry out the test cycle.
Preparatory procedures
Given the fact that the test of salt spray be an activity that causes damage to the photovoltaic module, the IEC 61701 standard defines a series of tests that must be performed before and after the test. salt spray, in order to qualitatively elucidate the effects of the test.
Pre-test tests for the salt spray are as follows:
- Preconditioning with ultraviolet (UV) light, in which the module is exposed to ultraviolet radiation of at least 5 kWh/m2;
- Visual inspection to detect any imperfections or degradation in the module.;
- Flash test to determine the main electrical characteristics such as Isc (short circuit current), Voc (open circuit voltage), Pmp (maximum power);
- Insulation resistance test;
- Leakage current test with humidity.
camera of salt spray
Once the preliminary data collection from the samples has been completed, the modules are ready to perform the testing. salt spray. At this point, the IEC 60068-2-52 standard will be preponderant for defining the testing requirements for the samples in question. This standard regulates 8 different salt spray tests, based on 3 different processes. For this reason, it is necessary to explain the main mechanisms that make up the salt spray chamber. salt spray.
The chamber has a hydraulic connection to a deionized water source, so that its solution tank can be filled with a liquid free of minerals that could negatively affect the test. In this same tank, 100 liters of deionized water and 5 kg of high-purity sodium chloride are mixed, composing the saline solution specified in accordance with IEC 60068-2-52.
For this solution to effectively become a salt spray, it is necessary for the solution to through the saturation tower (internal component of the machine). In this tower, the solution is heated and pressurized through a compressor, reaching an ideal combination of temperature and pressure for transforming the water into spray.
The mist generated by the saturation tower is directed to the solution dispersion tower, allowing the saline spray to spread throughout the chamber. At the end of the tests involving the saline mist, the solution collection funnel captures the particles dispersed in the air, transporting the particles back to the solution tank.
The IEC 600682-52 standard mentions eight different tests, based on four different processes that can occur in the chamber, in addition to explaining the intensity levels of each. Learn more about each of the processes.
Salt spray process
In this process, the sample is exposed to a salt mist for 2 hours and a temperature of 35°C ± 2°C. The solution, when deposited on the surface of the sample, can create an electrolytic film, which can initiate the corrosion process;
Process under dry condition
In this process, the chamber operates at a temperature of 60°C ± 2°C and relative humidity of 30% for 4 hours. The heated air causes the evaporation of water on the surface of the sample, increasing the concentration of saline particles on the surface of the sample, thus accelerating the corrosion process;
Wet condition process preceded by salt spray
In this process, the chamber operates for 22 consecutive hours at a temperature of 40 °C ± 2 °C, in addition to a relative humidity of 93% ± 3%. This operation of the equipment maintains the existing humidity on the surface of the module at the end of the salt spray process;
Standard atmosphere process
In this last process, which can be performed by the chamber, the relative temperature and humidity are close to normal ambient conditions. This process allows the solution deposited on the sample to dry naturally, which can trigger different corrosive processes in the modules.
Based on these procedures, IEC60068-2-52 defines eight different tests for different scopes of analysis, namely:
- Tests 1 and 2: Tests aimed at elements that operate near the ocean, being of high interest for modules installed on naval vessels or near the coast, whose period varies between 3 and 28 days;
- Tests 3 to 6: Tests aimed at elements operating under intermittent salinity conditions, with test periods ranging from 7 to 56 days;
- Tests 7 and 8: Tests focused on the automotive sector, with a period ranging from 1 to 60 days.
Although these tests cannot perfectly portray a real salt spray situation, test 3 of IEC 60068-2-52 is the one that comes closest to the interaction of saline spray and photovoltaic module, in addition to having a satisfactory test period for it to be possible to carry out comparative analyzes of the effect on the samples.
IEC3-60068-2 Test Method 52
According to test 3 of IEC 60068-2-52, the modules are subjected to salt spray for 2 hours for four days and then subjected to humidity conditions for 22 hours. The relative humidity of the chamber must be between 90% and 96%, in addition to an internal temperature of 38°C to 42°C.
Finally, the modules are left in the chamber for another 3 days under usual ambient conditions of 21oC to 25oC and relative humidity between 45% and 50%. The flowchart of the chamber test is shown in Figure 4.
Final procedures
Once the test cycle is complete, the module is carefully removed from the chamber and immediately sanitized with demineralized water so that any saline residues are completely removed. The module is then subjected to a new series of tests in order to compare it with the results obtained prior to the test.
The first test to be performed is visual inspection. At this stage, the test element is checked for signs of degradation, such as corrosion of the metal surfaces, MC4 connectors, by diodes and internal welds.
As the modules undergo a thermal cycle, the internal welds end up being carefully evaluated, since the process of contraction and expansion of the welds occurs due to this thermal variation. In cases where the weld is of poor quality, sudden temperature variations can cause irreversible damage to the connections and bring undesirable consequences such as a greater propensity for hotspots [3].
Faults can be detected visually, simply by checking whether the welds connecting the busbars are deformed, or demonstrating electrical discontinuities. The flash test is then performed to analyze whether the electrical parameters were maintained or whether there was any significant degradation during the process.
After this test, the element undergoes a leakage current test under humid conditions, aiming to compare the module's insulation resistance before and after the test. Finally, the module undergoes an activation test of the by diodes. In this test, one of the cells is completely shaded with the aid of a dark screen and then the module goes through the flash test again to check the proper functioning of the diode.
Approval Requirements
After carrying out the sequence of tests in the chamber salt spray the following requirements must be observed for the approval or rejection of photovoltaic modules:
- Samples must undergo a rigorous visual inspection, described by the IEC 61730-2 standard, without showing mechanical deterioration or corrosion of the module components;
- The maximum power measured according to the flash test cannot be less than 5% of the value measured before the test;
- Insulation resistances under dry and humid conditions must remain intact;
- The module's by diodes must remain intact.
Conclusion
Photovoltaic modules must undergo rigorous laboratory testing before it can be said with certainty that they are capable of withstanding the most diverse operating conditions. The salt spray, which corresponds to the submission of the product to a salt spray environment, is an important qualification procedure for photovoltaic modules within the scope of analysis.
the test of salt spray It is not required in Brazil, but several global manufacturers submit their products for certification in international laboratories. If the consumer needs to know whether the module is certified to operate in regions of high salinity, it is recommended to consult the product data sheet or the distributor or the manufacturer itself.
