What are the advantages of half-cell batteries?
2022.Oct
20
The trend of half-cell cells compared to full-cell cells is already obvious. The most popular explanation is that the current of half-cell cells is only half of the original, so the power loss is lower.
However, the advantages of half-chip technology go far beyond power loss. This article will use the most popular explanation to tell you why half-cell technology will replace full-cell batteries in the future.
1. Introduction of half-chip technology
For half-chip technology, they're literally cutting a normal solar cell in half. Instead of having 60 or 72 cells like a common PV module, it becomes 120 or 144 half-cell cells, while maintaining the same design and size as conventional modules.
The half-cell technology generally adopts the laser cutting method. The standard-sized cells are cut into two identical half-cells along the direction perpendicular to the battery busbars, and then welded in series.
The half-cell package is also encapsulated with tempered glass, EVA, and a backplane, the same as conventional modules. A conventional solar panel typically contains 60 0.5-0.6V solar cells connected in series. The voltage is increased in series, so a 60-piece module operates at 30-35V. If half-cell cells are connected together as in a standard assembly, they will produce half the current and twice the voltage with the same resistance.
In order to ensure that the overall output voltage and current of conventional components are consistent, half-cell battery components are generally designed in a series-parallel structure in the panel design, which is equivalent to two small components connected in parallel.
As shown in the figure above, the open circuit voltage of a half-cell battery is the same as that of a full-cell battery, and the number of half-cell cells is doubled. After being divided into two parts, the number of cells in each part is the same as that of a full-cell module, and the voltage after the two parts are connected in parallel The same as each part individually, so the total output voltage does not change with respect to the full cell.
The half-cell battery is only half the size of the conventional battery, so the current of each battery is only half of the conventional battery.
The resistance of a half-cell cell is only half that of a full-cell cell, so each part connected in parallel has half the resistance of a full-cell module. By connecting the two parts with only half of the resistance in parallel, the total loop resistance is only 1/4 of the full chip resistance.
The change of the board design makes the connection design of the junction box different. Generally, a three-part junction box is used.
2. Advantages of Half-Chip Design
- Lower package loss
As mentioned above, due to the reduction of internal current and line resistance, the internal losses dissipated in the internal circuit are reduced, the power loss is proportional to the current, and half the current and one-quarter resistance allow the half-chip assembly to reduce the power loss 4 times, the corresponding output power and power generation will increase.
At the same time, due to the reduction in internal loss, the operating temperature of the module and the junction box also drops. When the module is working outdoors, the temperature of the half-piece module is about 1.6°C lower than that of the conventional whole-piece module, and the lower temperature allows the module to have higher photoelectricity. conversion efficiency.
Even if instead of using the two halves in parallel, all the half-cells were connected to work like a standard solar panel, the current would be half the current, but the resistance would be the same, and the power consumption would be 1/4 the power.
- Shadow tolerance reduces hot spot risk
Half-sheet panels resist the effects of shadows better than standard solar modules.
Half-cell modules do not have 3 panel strings like standard modules, but 6 strings, making it a 6-string panel. Although a small amount of shading on a module (leaves, bird droppings, etc.) can disable the entire string, the effect of shading is reduced due to the design of the bypass diodes (marked in red in the image below) that the string does not affect other strings .
6 independent strings with 3 bypass diodes provide better partial shading tolerance. Even if half of the component is obscured by shadows, the other half will still work.
- Low current reduces hot spot temperature
Half-cell cells distribute internal current in the system and improve its performance, longevity and shade tolerance.
When a cell of a cell string in a module is shaded, that cell forms a hot spot in the loop, and sustained high temperatures can damage the module. Since there are twice as many strings of half-cell modules, which means that there is only half the heat at the hot spot, and the lower heat causes less damage to the module, it can improve the resistance to hot spot damage and increase the use of the module life.
- Shadow tolerance reduces power loss
In a photovoltaic array, multiple modules are generally connected in series, and then connected in parallel with other sub-series. Current flows in and out of each series-connected component in turn in the same substring.
For the traditional module panel design, once a certain module loses power due to various reasons of shadowing, it will affect all the modules in the substring. Whereas in the half-chip module pictured above, the bypass diode limits the power loss in the shaded part rather than the whole module, it creates an alternate path for current to flow in the non-shaded part and avoids the current passing through the shaded part, reducing the shadowed part. affect and improve its performance.
3. The future of half-chip technology
The use of half-cell cells can provide great advantages and improved performance in shaded conditions, which is of great significance for building photovoltaics that are easily affected by other building obstacles.
Half-cell cells can increase power generation, but the system design is similar to full-cell modules, which does not increase installation costs and ensures lower LCOE. Improvements in laser cutting technology make the cutting defects of half-cell cells almost negligible.
With the popularization of large components and large silicon wafers, the trend of half wafers or even three wafers is becoming more and more obvious. According to industry-related institutions, the market share of half-cell modules is expected to exceed 50% in the next three years.
