Comparison of power of Half-Cut solar module and standard module under shading
Abstract：SUNRISE Energy Co., Ltd always focuses on manufacture of solar module with high efficiency and high reliability. Half-Cut technology is an effective way to reduce CTM loss and increase module power. This article studies the power increase of Half-Cut module and improvement under the shadow occlusion on the cells. In the experiment, modules with 144 half-cut cells and modules with 72 full-size cells are tested, and the electrical coefficients were compared. It demonstrated that the half-cut module could have 9w higher power, 1.16% higher Imax, 1.32% higher Isc than the standard full-size-cell module with the same efficiency cells. In addition, the effect of shading on the Half-Cut module was studied. With the same shading area on the module, Half-Cut module has a lower power loss than full-size-cell module, when the shading covers 90% of module with half-cut cells, the Vmax was still 2/3 of the module without shading.
These years photovoltaic technology has developed rapidly and has a wide range of application. The increasing demand of high-power module guides the module factories to look for methods to reduce the power loss during module manufacturing and increase the output power of module. Half-Cut technology is a method to increase the power of solar module by reducing the resistance of series circuit. By cutting a normal cell into two same half pieces, the current on the busbars can be reduced to 1/2, which causes the internal resistance loss to be 1/4 and makes efficiency of module higher.
The team of Schneider tested the mechanical properties of half-cut cell and full-size cell using a four-point bending method. The result shows that half-cut cell has better mechanical properties than full-size cell. In the experiment it was verified that the module with 144 pieces of half-cut cells has 5% higher power than the module with 72 pieces of full-size cells. Hanifi tested the performance of Half-Cut module with shading using simulation and experiment. It was verified that the performance of module with half-cut cells is better than the one with full-size cells. According to the research of Malik about the comparison of the difference in outdoor power generation, it was shown that the half-cut module power station has a monthly power generation of 1.9% to 3.9% higher than that of the Full-Size module, and the higher the irradiance is, the higher power generation gain is.
This article studies the power increase of Half-Cut module and the performance improvement under shading. The experiment compared the difference of electrical parameters between modules with 144 pieces of half-cut cells and 72 pieces of full-size cells. Considering design of series and parallel circuit of half-cut module, a further comparison was made between the electrical parameter differences between 144 half-cut modules and 72 full-size modules under different shading conditions .
Design of half-cut-cell module circuit:
The circuit design of Half-Cut cell module includes the structure of series type, series-parallel type and parallel-series type. Normally the standard full-size-cell module uses series type. If the half-cut-cell module also uses series circuit, the cost of solar system would increase due to that the doubled voltage, because half-cut cell has half current and constant voltage. Therefore, the combination circuit of parallel and series was chosen for the test, as shown in Figure 1.
Figure 1 Circuit of half-cut-cell module
EL-image and electrical parameters of 144 pieces half-cut-cell module and 72 pieces full-size-cell module were tested.
The appearance of two modules are in good condition. The EL-images of two types of modules are without micro-crack or cell-defect as shown in Figure2.
Figure 2 EL-image of different types of modules
The tested electrical parameters of the two modules are shown in Table1. As shown in Table 1, the power of half-cut-cell module was about 9W higher than of the full-size-cell module with the cells of the same efficiency. And the maximum current and short circuit current increased by 1.16% and 1.32% separately. The important indicator affecting the power of solar modules is CTM loss. The CTM loss mainly depends on the series resistance loss and optical loss of the packaging material of module. The series resistance of the ribbon is the main cause of power loss. Improvement of the reflection, absorption and the optical matching performance of the package material enables it to achieve power gain.
Laser cutting full-size cells into two half-cut cells of equal size reduces the current through each busbar to 1/2, and the internal loss is reduced to 1/4 of the full-size cell due to P=RI².
After lamination, the area of the gap between the cells increased. In the experiment, the one of the half-cut-cell module increased by 9.5 cm2 than of the full-size-cell module. It increased the amount of light received by cells and reduced optical loss.
Table 1:Electrical parameters of different modules
According to the initial stability test requirements of IEC61215 standard, the two module samples is subjected to an initial treatment of illumination of more than 20kW·h/m2 before shading test. A non-transparent material is chosen for the shading test. According to the number and position of the cells protected by different diodes, the shading diagram of the cells is shown in Figure 3. The full-size-cell module and half-cut-cell module are shaded according three types of A, B and C respectively. The total shading were 6 times.
Figure 3 diagrams of different shading on half-cut-cell module and full-size-cell module
The power of the half-cut-cell module and the full-size-cell module under the three occlusion conditions A, B and C were tested. The specific data are shown in Table 2. It can be found from the data that due to the feature of the parallel circuit structure of the half-cut-cell modules, when the same area of cells under the protection of a diode was shaded, the half-cut-cell module of the series circuit under three shading conditions is superior to the power of the full-size-cell module of the series circuit.
Table 2 Power paramters under different shading conditions for full cell moudle and halved cell module
In order to verify the electrical parameters of the half-cut-cell module when one cell of the half-cut-cell module has different shading areas, 50%, 60%, 70%, 80%, and 90% of the cell area, electrical parameter differences were tested. The shading diagram of the cell is shown in Figure 4.
Figure 4 Shading diagram of half-cut-cell module
The electrical parameters of the half-cut-cell module under different shading conditions of a single-cell were tested. The specific data are shown in Table 3. When the shading area of a cell reached about 90% of the half-cut cell, the voltage became about 2/3 of the voltage without shading. It could be judged that this shading area bypassed the parallel circuit.
In a real power station, the modules are mostly installed vertically. When there is shading in front of the array, the first row of cells is affected by the shadow. If it happens to the simplex series circuit of a full-size-cell module, it is likely to affect the entire row under the actual shadow process. It may cause three diodes to start, which affects the power generation of the entire module. But the design of the parallel circuit of the half-cut-cell modules makes the first four rows controlled by a diode, sothat the shadow only affected 1/3 of the module power, reducing the loss of power generation caused by shading.
Table 3 Power parameters under different shading areas for halved cell module
This article did studies about the CTM loss and the performance under shading condition, analyzing the effect of half-cut cell to the power of module. By analyzing the optical loss and electrical loss that affect the power of the module, it was found that the half-cut-cell is an important way to improve the power of the module. Experiments showed that the power of the half-cut-cell module was more than 9W higher than the full-size-cell module. And under the same shading condition, the special circuit design of the half-cut-cell module reduces the power loss of the module in the power station, and the performance is better than the full-size-cell module.